$1,599.95
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Starkrimson 25 Mono Premium
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Product Documents
Starkrimson Monoblock Amplifier is a state-of-the-art (SOTA) hi-fi audio power amplifier that was conceptualized to provide the listener with a truly life-like musical experience, presented with every significant detail intact, to convey an emotional connection to the music. Starkrimson Mono amps utilize gallium nitride (GaN) technology to achieve ultra-high performance in an easy-to-use small package that will easily blend into any décor.
What's in the Box?
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2 x Starkrimson® monoblock amp
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2 x Power supply w/ IEC power cable (country-specific)
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Instructions
Features of Starkrimson Monoblock Amplifier:
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Fully balanced from input to output
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Differential (XLR) and single-ended (RCA /w adapter) inputs
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Extremely low noise and distortion
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Power output 150W into 8/4Ω
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2-ohm capable
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Size: 5.5" (14cm) x 4.8" (12.2cm) x 1.9" (4.8cm) - w/o binding posts
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Ext. 250W Power Supply Size: 8" (20.4cm) x 3.7" (9.4cm) x 1.72" (4.35cm) - w/o cables
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Ext. 300W GaN Power Supply Size: 7.2" (18.3cm) x 3.35" (8.5cm) x 1.38" (3.5cm) - w/o cables
Standard one (1) year warranty included.
Customs Disclaimers (for non-U.S. customers):
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Any customs fees are the responsibility of the customer.
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We won't under-value merchandise or mark the item as a gift on customs forms. Doing that is against U.S. and international laws.
Shipping Information
| Weight | 10 lbs |
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| Dimensions | 10 × 10 × 6 in |






Afonso L. –
Outstanding performance without limits in any record we played! It is warm and delicate, the perception of a soundstage grew more vivid with these amps as well as the minutiae and rich details that now seem to enhance even more the quality of GAN and strengthen its future as a de facto audio technology fit for the XXI century!!! Leo and his team should be lauded as the real heroes in the audiophile universe and their entrepreneurship should serve as a model of absolute basis for the whole industry from here forward.
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Leo A. –
Wow! This review truly warms our hearts. We strive to create amps that disappear into the music, letting the details and emotion shine. Thank you for recognizing the potential of GaN technology – it’s an exciting future for audio!
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Tom C. –
The Orchard Audio Starkrimson monoblock amps deliver excellent spatial imaging with detail and a sense of depth and width I’ve not had in my home before. Bass is impactful, midrange believable, and highs with no edge to them. Hard to believe these little guys do so much. GaNFET technology, in my opinion is going to rock the HiFi high end market. I rate them a solid FIVE STARS.
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Leo A. –
We greatly appreciate your enthusiastic review! It’s fantastic to hear that the Starkrimson Mono amps have elevated your audio experience with exceptional spatial imaging, depth, and width. The impact in the bass, believable midrange, and smooth highs are all aspects we’ve worked hard to perfect. We share your excitement for GaNFET technology and are honored to be a part of the HiFi high-end market transformation. Your solid five-star rating means a lot to us, and we’re committed to continuing to provide you with top-tier audio quality. Thank you for your support!
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Jonathan K. –
I have the tiny little Starkrimson 150w into 4 ohms monoblocks (with the upgraded power supply). I did not need the power of the big boys because I run an active discrete all analog crossover (SPL Audio), so they only handle from 120 hz up.
I am also using studio monitors (Amphion Two18) which are ruthlessly revealing. In all my years I have never had a more truthful, revealing, yet easy on the ears amplifier. I can now listen all day long with pleasure, yet I am hearing more glorious detail (in well recorded or produced material). Ear fatigue be gone.
By the way, watching the movie DUNE on HBO is a revelation. Beautiful sound design! Orchard Audio is highly recommended!
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Leo A. –
We’re thrilled to hear about your positive experience with the Starkrimson 150w monoblocks and the upgraded power supply. It’s great to know they pair well with your setup and deliver a truthful, revealing, yet fatigue-free listening experience. We appreciate your kind words and recommendation for Orchard Audio. Enjoy your enhanced audio experience, whether it’s music or movies like DUNE, and thank you for choosing our products!
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Jerry S. –
High value audio…well worth the money.
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Leo A. –
Thank you for the review. I am glad you are enjoying your product.
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Jimmy S. –
,,,,,,, after countless years, of searching for the most neutral class, of amplifier circuitry, ,,,,, it’s now realized, by my audiophile ears, by the class D GaN FET Starkcrimson Monos, by Orchard Audio! bravo Leo! btw, Anyone want to buy my old class A, zero feedback, EL-34, 300B, 2A3, KT-88, or 845 tube power amplifiers? 😃👍
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Leo A. –
Thank you so much for sharing your experience with the GaN FET Starkrimson Monos. We’re thrilled to hear that you’ve finally found the amplifier circuitry that meets your discerning audiophile standards after years of searching.
It’s clear from your enthusiastic words that the Starkrimson Monos have left a lasting impression on your ears. We’re proud to have been able to provide you with a product that resonates so well with your audiophile preferences. I am delighted to have met your expectations.
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Reza E. –
I had some high end class D before, the Ncore NC400, back when they were brand new. Monoblocks. Was an astounding leap over anything that I had ever heard. Then i felt like as an audiophile who likes to try new gear, that I go all in on AB just to see if *great* AB would match what I heard. I went through 4 AB amps ending in a Parasound A21+. Incredible sounding amp, extremely engaging. I listened to it very hard the night before the Starkrimsons showed up. I said, this will be a very hard act to follow. Without going into all the flowery words: the speed of these amps is incredible. You may take that as having a masterful vice grip on the recording. Nothing gets past these. Gobs of power, gobs, of control, on my CSS 1TDX Superior. I’ll give you a hint: with the Parasound I used inline FMOD 100hz filters with 12dB rollout to reduce bass output to really get performance out of that monstrous amp. With these little boxes in use, the filters are removed and I now have thwacking, riotous bass that starts and stops on a dime. These amps are superlative in any sound quality metric you are concerned with. Are they good at this? YES, whatever that is, they are fantastic. The MUSIC comes through, pure and ultra high end sounding. Ultra high end. Forget class this versus class that. There are awful AB amps and there are great ones. Same as class D. These starkrimsons are world class, a stunning achievement, and a stunning value. Be careful you don’t order something else and regret it.
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Leo A. –
Thank you for your detailed review of the Starkrimson mono amplifiers. I’m so glad to hear that you’re enjoying it so much.
I agree with you that class D amplifiers have come a long way in recent years, especially when coupled with GaN technology, and we believe that the Starkrimson is one of the best examples of what this technology can offer. The Starkrimson is able to deliver a wide range of frequencies with excellent clarity and detail, and it has the power to drive even the most demanding speakers.
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Joe B. –
When shopping you choose both a product and a company to support . On both counts Leo is a joy to engage with . His Mono Block Starkrimson amps removed congestion from a soundstage compared with my Gilmore Audio Raptor amps , which were no slouch until they quit . It’s difficult to describe their sound , but precision comes to mind . Accurate, rich & warm in the natural way music instruments and voices sound LIVE . Great sound stage and speed . Leo was willing to accommodate my need for different terminals to work with the oversize spades on my Analysis Plus cables . Highest recommendation ! Dick Olsher was right .
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Leo A. –
Thank you for the feedback.
I’m happy to hear that you were so pleased with my customer service. I always try to be as responsive and helpful as possible, and it’s clear that you appreciated that.
I’m also excited to hear that you’re planning to upgrade to the PecanPi+ in the future. I’ve been working hard on the new model, and I think you’re really going to love it.
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Seok K. –
Clarity and nice focus.
This small amps rock.
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Paul W. –
These amps are as advertised and reviewed, extremely detailed, clean, quiet and very musical. They have me listening to a wider range of music as they sound great in all genres. I am very pleased already and wondering how great they will sound fully broken in. Great value as well, they sound better than amps costing 2 to 3 times as much. Highly recommended!
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Leo A. –
Thank you for the review/feedback.
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William S. –
I was unable to install these monoblocks in my system until January 16th, 2023, and wanted to live with them for a while before giving a review.
Once installed, there was an immediate perception of increased detail, clarity and soundstage depth without being edgy. The noise floor was noticeably blacker, which added to increased intelligibility of vocals. Bass also seemed more controlled, and overall, gave a very musical presentation.
I have been using a pair of very good Pascal module monoblocks for several years that sounded great to me, but these new Starkrimson monoblocks from Orchard Audio are amazing. I highly recommend giving them a try.
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Philippe G. –
Having already had positive experiences with Class D amps (XTZ Edge, based on ICE EDGE module, Purifi) I decided to buy the Starkrimson amps for two reasons :
– The GaN technology held the promise for a smoother, more refined presentation
– And more specifically the weakness of Class D amps is the output low pass filter, oftentimes Class D amps have a very robust and competent way of reproducing musical material but they lack that openness and refinement in the high frequencies that wide bandwith zero feedback amplifiers are capable off. Orchard’s approach of simplifying the filter design by virtue of much higher switching frequencies held the promise that this amplifier could indeed deliver a more open, free flowing sound.
From a listening perspective the amp seems absolutely capable to deliver on this promise at least it easily attains that treshold where you’re unable to say if you’re listening to a Class A, AB or Class D amplifier, those categories simply seem to evaporate. Due to its expert engineering and superlative measurements this amplifier will never be a bottleneck in your system, it will pretty much resolve anything that you throw at it. In case this amp does not pan out in your system it will most likely be an indicator that something’s not optimal either at source level or on the speaker side. What you’ll be hearing will be a reflection of your system, not the amp.
Concerning the GaN technology it seems noticeable in the highs (resolved and smooth) but most importantly in the Bass, this thing is capable of delivering current fast. The Bass slams and appears out of nowhere, fast. Very nice, very competent.
Now on to the other aspects of my ‘customer experience’
– I’d qualify the design of the boxes as a ‘missed opportunity’, their sole virtue being that they’re small and unobstrusive. But Orchard being a hardcore engineering brand one can’t blame them for that, what you get and pay for is performance, that’s it. I can live with that aspect although for the price one would expect a bit more ‘sugar’ so to speak.
– Another important point to consider (AND remember throughout ownership) is that these amps have ZERO protection, which is very different from the majority of Class D amps (mostly designed for professional applications) this amp :
– Will destroy itself when shorted
– Should not operate with the negative disconnected as it is a bridged design.
Personnaly I would suggest and recommend :
– To highlight that fact much more prominently, especially regarding shorting. Maybe a sticker on the amp, and a red box in the user manual. Especially in the speaker DIY community shorting can occur, just like in professional audio sometimes things can go awry. If you’re a speaker builder I might recommend going for a Purifi amplifier which has portections in place and delivers similar sonic qualities. I understand that an engineer might not understand such accidents to happen but not everyone in the audio community is an electronics engineer.
– I would definitely have integrated on/off switches directly on the amp, because the fact that you can ONLY switch it off by unplugging the power (on the power supply side only NOT on the amp side as the connector will spark) in combination with the amps extreme fragility opens the door to misshaps.
To sum it up I give the amp a 5 (or even 6) star performance but 4 stars for ergonomy considerations.
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Leo A. –
Thank you very much for your review and feedback.
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Daniel C. –
Outstanding clarity and openness are qualities that come to mind. Dead quiet background—perhaps the quietest amps I’ve owned. My only gripe is that the 5-way binding posts don’t accept all spade sizes, perhaps owing to a clear plastic protective cover over the spade lugs on the binding posts. I’m not sure if the clear plastic covers can be removed. But they don’t accept HAVE spade lugs.
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Leo A. –
Thank you for the feedback.
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Todd B. –
Dynamic with detailed top end, natural sounding mid-range and supreme bass control – all in a tiny package! This is what my system has been missing all along.
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Leo A. –
Thank you.
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Ken S. –
These amps sound great with my bi-amped JBL 4344Mk2 speakers driving the three drivers that cover 340Hz up. (I didn’t try them full range, but have no reason to question their performance with the lower frequencies; I simply already had that covered with another amp.) I compared the OA amps with my Berning Siegfried 10W SET (the 811 version). There was no clear-cut winner here. On the one hand, the AO was clearly better than the SET in some important ways—lower distortion and more power. I spent a lot of time comparing them with different music. I ran a pair of balanced interconnects to get the best quality and to make switching amps fast and easy. On balance, I preferred the sound of the SET on most music, as it seemed to express nuances of tremolo and vibrato in instruments and voices more clearly. This difference was immediately obvious and not subtle. I have to wonder if I like the second harmonic distortion of the tube amp, which as an SET without negative feedback has far more than the essentially immeasurable distortion in the OA. Another explanation is that the SET has a damping factor that works more to my taste with my speakers; it’s output impedance is much higher than the OA. Very generally speaking, the dynamics of individual voices are more distinct with the SET. By contrast, the OA is far better at reproducing the collective crescendo of a whole section or orchestra. Either one is satisfying, just in a different way. For such a small, lightweight, efficient package, the OA is amazing. And for the TWO monoblock amps, an incredible value for excellent performance.
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Leo A. –
Thanks for the review.
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David F. –
The Starkrimson amps throw a huge Soundstage with instruments well placed within the Soundstage.
From top end to bottom end these little amps excel with sparkling highs to deep tight bass. The Starkrimson amps replaced a pair of very expensive Class A amps in my system and are worthy competitors. AAA+++
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Leo A. –
Thanks for the feedback. I am glad you are enjoying them.
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Leonard K. –
I love the amps, but I got the wrong input gain.
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Leo A. –
Thank you for the review. Please contact me. We will find a solution. The gain can be increased or maybe the ultra will work better for your application.
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Jj –
Your mono blocks are superb!! Transparency and drive excellent, voices so natural!
Thank you so much also for the modifications to provide more gain and 100k input impedance.
I bet you would sell more if you made that standard!
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Leo A. –
Thank you for the feedback. I am now offering the higher gain as an option that customers can choose during checkout.
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Dave E. –
As a long time Magnepan owner, finding a powerful, resolving amp that didn’t cost over $4k and act like a space heater has been a challenge and long time search. After receiving and using the mono blocks for 72 hours, they are a home run. None of the issues I have had with past class AB and tube amp choices, just superb clarity and ease in handling demand in any part of the audio spectrum. I know earlier class D amps were criticized for treble but GaN behaves much better than the class AB amps I have owned for treble sweetness and clarity
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Leo A. –
Thank you. I am glad you are enjoying your amps.
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Steve L. –
I have ss, tube and D amps and this one is different. It was hard to get used to but in the end it is now my favorite. It is so musical that I can just enjoy the music and not concentrate on just the attributes. I’m running a shiit fraya + pre and teckton 2-10 set speakers.
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Leo A. –
Thank you. I am glad you are enjoying the amplifier.
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Renan J. –
I found the monoblocks good but not great. Reasons: They sounded “strident” on the high frequencies – massed strings sounded bright. Loud passages in classical music with full orchestra sounded stressed – not natural. I would like to return the mono blocks. Can I do that? I received them 2 weeks ago.
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Leo A. –
Thank you for the feedback. I have send you an email on how to make the return.
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Mike E. –
Amps sound great! Interactions with Leo were excellent. Highly recommended for the performance to cost ratio and prompt customer service.
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Leo A. –
Thank you.
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Urs T. –
I have had the Starkrimson mono amps in my home for four weeks now. They are my first class d amplifiers. I use a very fine, purely analogue German transistor preamplifier and I use speakers with one coaxial driver for treble and midrange and two drivers each as dipole for bass. And the reproduction of the bass has always been the problem. I no longer have this worry with the Starkrimsons! It is amazing, almost unbelievable and crazy, with what force and control the bass now sounds from my speakers. The bass is not boosted, not mulled, but dry, almost slim and yet very profound.
But the highs and mids are also amazingly good. Quite different from my transistor amps before. I asked myself what is different now. The answer: the absence of any kind of artefacts. I had to get used to that at first, it sounded somehow…. naked. But also very clear and clean.
I listen to rock and pop, but professionally I listen to a lot of classical music, with strings, brasses, woodwinds, percussion with lots of overtones, sopranos, tenors, choir, etc.
This is now a great pleasure!
Big compliments to Leo!
Best regards from Lüneburg/ Germany,
Urs-Michael Theus
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Leo A. –
Thank you. I am glad you like them.
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Dustin D. –
Really enjoying the amps. They sound great.
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Leo A. –
Thank you.
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Ted C. –
Very neutral. Seems to be particularly good at overcoming issues with existing long/high guage speaker wire and smallish drivers, as one encounters with in-wall systems. Because its physically small, and runs cool, its particularly well suited to be tucked away in a closet or cabinet, also something that happens with in-wall or in ceiling systems. IMO, its the ultimate solution for combining audiophile requirements with SAF (Spouse acceptance factor).
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Leo A. –
Thank you.
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Al G. –
Leo, you undersell your product. The Starkrimson mono blocks impress. They bring life back into the music I’m hearing. Brings back fond memories of systems I listened to back in the 90s with Naim stacks powering ProAc monitor speakers. These little mono blocks bring joy. Yes dynamics, imaging and PRAT are all there. They consume little power which works well with minimizing load (no Class A or tube amps) for my solar panels. I returned the Crown XLS amps which are great but not musical in comparison. I have Topping D90 and pre90 as front end. Makes me want to try the PecanPi. I’m not happy with the volume control of the pre90.
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Leo A. –
Thank you for the review. The PecanPi products will match very well with the monoblocks and no preamp needed.
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Mark H. –
I was able to test my new pair of Orchard Mono blocks against a $6000 150w tube amplifier VTL ST-150. Not only did my pair of Orchards hold its own against this massive amplifier but they performed superior in the higher frequency ranges. A tad less bass than the tube monster but just a tad and that may be due to the orchards accuracy. A great addition to my set up!
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Leo A. –
Thank you.
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Thanong B. –
This is the first day I started listening to Starkrimson monoblocks which just arrived. Matched with a tube pre-amp, jazz music just sound amazingly wonderful with my Klipsch Heresy speakers. Thanks for your innovation!
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Leo A. –
Thank you.
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Gagan A. –
Very impressed by the design.
Sounds great. There’s nothing more I can add another reviewers haven’t already said.
My personal experience beyond just fantastic sound has been with the in-line amp and external power supply design. Makes it easier to manage cables and hide the amp entirely.
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Leo A. –
Thank you.
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Victor W. –
paired this with a rogue integrated in preamp duty driving spatial m3 turbo, this was easily the crowd favorite over nuforce monos or just running the integrated. The added dynamics gave every instrument more expression/presence and they stood further apart into the room. My first time hearing the spatial articulate bass so far down.
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Leo A. –
Thank you for the feedback.
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Mark R. –
I bought two Starkrimson monoblock amps to use with a pair of Klipsch Cornwall 4 speakers. The speakers are very efficient and tend to make a feature of any noise in the electronics. The Starkrimsons are super-quiet and my music now plays against a silent background. Not only that, but the sound is wonderful. Separation and clarity are improved and the bass is noticeably tighter and more forceful. They are a clear step up from the power amp in the GoldNote IS1000 I previously used and also a little better than the Luxman MQ-88uC tube power amp that is sometimes in my system. Despite the Cornwall’s much trumpeted affinity for low powered tube amps, surprise surprise it turns out they also love high powered, ultra-low-distortion, ultra-low-noise amps like the Starkrimsons.
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Leo A. –
Thank you.
The Stakrimson Mono amps make a perfect pairing to high sensitivity speakers exactly for the reason you mention, the low noise and low gain.
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Ivar G. –
Incredible sound for such a small and power saving amp. No need for a power-button!
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Leo A. –
Thank you.
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Gregory L. –
The Starkrimson Mono Blocks are amazing. I am in love with my stereo system again. Every thing is better, bass, 3D imaging and control.
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Leo A. –
Thank you.
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Malcolm –
I’m really enjoying these monoblocks. They have a full-bodied sound with tight articulated bass and overall great integration from top to bottom. Very natural sounding amps. I’m not hearing any glare. And given the price and low power consumption, these are a real bargain. I leave them on all the time. A job well done Leo. Highly recommended.
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Leo A. –
Thank you.
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Ravi B. –
Used this in my biamped system for the low mids to high. Superb sound. More resolving than the 300b se amp that I was using earlier. Only difference is the slightly lower sensitivity
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Leo A. –
Thank you.
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Todd S. –
The Bosc/Starkrimson mono’s have been a wonderful addition to my system. A little soft sounding when starting up cold, within 20-30 minutes they just snapped into place, with a huge soundstage, detailed yet smooth sound, and an organic “you are there” type of realness. They are a delightful combination of the best of digital and analog sound I’d say, with little to none of the drawbacks!
Leo is also just great to deal with. Very responsive, helpful, and knowledgeable!
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Leo A. –
Thank you.
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David R. –
I have been impressed by the balance, clarity and rhythm of this amp, Bass is tight and controlled while highs are precise and detailed.
Performance matches amplifiers well above this price point. In short, great performance and fantastic value!
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Leo A. –
Thank you.
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Diego V. –
I’m not much for words but I’ll say this, small form factor, using XLR cables these amps are dead quiet , by that I mean no noise is heard. These amps are very detailed but not harsh. They make my Polk Audio LSiMs 703s sound good, and mate well with the Topping D90 to make a small compact system with hi end sound.
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Leo A. –
Thank you.
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Mandy T. –
is this full bridge design
What about using it with unregulated power supply?
I dont see any datasets for the amplifier?
Power supply voltage? Specifications?
Nothing mentioned about that.
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Leo A. –
Hello. I send you an email with the items you are looking for.
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David P. –
Leo is a great person to work with (knowledgeable, patient…) and the Bosc amplifiers sound very nice. I value quietness, detail and neutrality. Bosc provides everything that I want. Thanks Leo for designing a great product that is reasonably priced!
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Leo A. –
Thank you.
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Peter K. –
This is my second pair of BOSC Mono blocks. Clean crisp highs and mids, plenty of bass oomph for me and a low noise floor. Small form factor is a real bonus. I look forward to many years of listening enjoyment from these originals. Leo has been very quick in responding to any questions and his answers are always concise and to the point.
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Leo A. –
Thank you.
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Thomas S. –
I was looking to purchase 2 mono block amps when I came upon a review of the Bosc amp. Glad I did! Very impressive performance. Great soundstage which has opened up my listening experience dramatically. I have them attached to the back of my speaker stands with double sided tape, which allows for short speaker cable runs. Prior to purchasing I contacted Leo and he responded promptly to all of my questions. Great support. Highly Recommended. (I am using it with Qacoustics 3030i speakers and Anthem STR preamp)
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Leo A. –
Thank you for the feedback.
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Aleksandr G. –
Alright, after some careful listening I can say it sounds amazingly precise, clear and tight.
There is not a hint of distortions even if I push the volume to the limit.
However there is a slightly disappointing facet to this refresh – suddenly it turned out
too much of my recordings are of a poor quality. Which became immediately obvious
with the new amplifiers. I don’t need to pay any special attention to hear all imperfections
of the old and many newer recordings (doesn’t matter if they were remastered recently
and/or sold in hi-res formats). It is just there for me to easily tell what exactly is wrong
with this or that. Which by itself takes away some of the joy. And it makes me a bit sad
the beloved oldies will never sound as good as modern hi-res recordings. Speaking of which
recordings of true quality sound so good and exciting! Deep tight articulated … well everything,
all the spectrum of frequencies. Superb balance. All instruments are apart and simultaneously
play together. And the voices, oh my.
So you can already tell I am very pleased with the purchase.
Congratulations on a great product, Leo!
Here is what my listening setup was:
DAP Shanling M5S (double AK4490 DACs) -> BOSCx2 -> Usher V-601 monitors.
The amps replaced Peachtree Decco65 (night and day really).
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Leo A. –
Thank you very much for your feedback.
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Alex –
Small size, but powerful. Excellent quality!
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Leo A. –
Thank you for the feedback.
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Eric T. –
Fantastic sound in a small compact package.
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Leo A. –
Thank you.
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Ivars M. –
Some months ago, after ASR review, I purchased DAC Topping D50s, and that was a good purchase. After that I started to look for new Amp, and decided to test new technologies , the BOSC amp. My idea is to replace McIntosh MC275 MK4 tube amp in my home office. But this is not an easy task , that Amp is real classic piece, one of the best tube Amps for close to 60 years. I simply get tired to replace dysfunctional tubes, and wish to stay more green with less electricity consumption.
And I had suspicion, that maybe small Damping factor of MC275 (about 14) is some problem for my beloved acoustics (Triangle Magellan Concerto with sensitivity 93db, but with wide region with only 2 ohm resistance). What I liked from short specification of that BOSC project, is greater switching frequency (close to 1 mhz) and bigger Damping factor (more than 500), also smaller gain (for today output level 4-7V balanced , no need for gain 26, even 10 is enough).
So I preordered pair from Orchard Audio plus asked for individual measurements for extra 50 USD.
Couple days ago I received DHL package. Everything was in good shape, and I started installing in system. My system is bit unusual : my house is in forest area, and i have lot of short dropouts. Therefore my Home office is supplied with 5KVA Metasystem Megaline online UPS (with THD less than 1%). There are computers connected directly to that, but Audio system is connected through
heavily customized McIntosh isolation transformer (MPC1500). The essence is: Balanced power supply output plus 3-pole LP filter. And good grounding contour outside. That Balanced PS (2x115V, EU 230V) had profoundly impact on PS noise, especially limiting PC SMPS noise.
So MC275 was out, BOSC in.
There was no need to listen much.
Bass region was better controlled, perceptually even louder in lowest region.
Midrange I think the same, HF maybe better may be not. I am 62 , so what HF…
Hiss was close to hearing limit with ear directly in tweeter, remember speaker sensitivity 93db!
Resume, I don’t need to consume more electricity, take care to purchase extra tubes and with weaker bass. New BOSC amps stay in my system, I’m very satisfied with build and performance quality.
Anybody need MC275?…
Second compare I did with ReVox Exception E450 integral amp. Here hiss was for magnitude more
, but with better LF control than MC275. Somehow less clarity in HF. BOSC wins even more.
Some minor things. There is no delay to connect speakers when switching on, so we can hear some minor thump/clik. And when I connected from Bosc output to Velodyne Subwooffer Processor SMS-1 Power input (Parallel to speakers) input dividing resistor literally vaporised with characteristic smell. So after that I connected SMS-1 through linear input… Obviously switching on need some delay relays to speakers.
Overall, new elements and new technology clearly win.
Thank You Leo for excellent Amp!
Ivars M.
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Leo A. –
Thank you for sharing, great write-up.
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Andrew M. –
Thanks to Leo and the AOS forum I managed to borrow a pair for a few weeks and have a listen.
Below are my thoughts.
Had a few good days listening to the amps using my Myryad preamp and various front ends – Orbe through the Firebottle Phono amp, Technics CD player and also the Raspberry Pi, using stored FLAC files and the CD player up sampling the tunes to 176.4Khz on the Pi.
Start with the TT first. Started with some simple music, not over produced with generally just voice and simple arrangements (David Sylvian being one) and found the amps to allow the music to flow without appearing to not add or subtract anything.
Found it very easy to get lost in the music and before you know it the LP had finished. Wonderful.
Next up was music with more going on, more electronic and a bit faster paced (such as later recordings by A Certain Ratio) – midrange was very good (valve like) but the bass seemed a bit more muddled compared to the Burson and the Pure Sound valve amp – no real issues with the high frequencies, perhaps a bit forward but not in your face.
Next up, let’s go digital so step forward Mr Pi. Again, started with some simple (in structure and instrument wise) using FLAC files (such as Ludovico Einaudi) and absolutely no issues – the music appears to come across with nothing added or taken away and found it enjoyable. Used the same music through the CD players and very similar to the FLAC file (apart from the Technics CD player seemed to add extra sparkle to the highs – not the amps fault!!)
Tried it using more electronic (Nine Inch Nails) and faster paced (808 State) music on CD and FLAC format. Similar to what I heard using the TT, the bass a little muddled at times but nothing too detracting and on CD, the highs sometimes brighter than using FLAC or the TT so not a fault of the amps.
Very satisfied with how the amps were performing.
Next few days I took the Myryad preamp out of the equation and used a passive preamp (thanks BigBottle) and also the Pi direct to the amps.
The main difference with the PI now going direct was the bass seemed to be grasped better than when using the Myryad so perhaps the synergy with this and the BOSC amps wasn’t quite there (will look into this later).
Using the Passive Pre, I tried the TT and found that the simpler music worked very well, although less impact from the bass than before but the rest of the audio spectrum sounded great then moved to digital music. Much as before with the same issue with CD and the highs.
Went back to the Myryad and dug out some older (not sure who made them or where I got them from) interconnects and replaced the ones from between the preamp and the BOSC amps.
Noticed a slight improvement with more complex and electronic music in the bass registers – not a massive change but a little clearer in the lower registers.
Summary.
In general, I found the amps to be very good (a slight step up on the Burson but I need to do some opamp rolling) and on par with the valve amp – perhaps better grip when the volume is cranked up.
Liked the small form factor but found the PSU’s sizes to be on the large size.
Didn’t find the sound to be ‘digital’ at all but did prefer them with more simple music (as you could probably tell with from the text above), but paired with the correct preamp and cabling I am sure will work a lot better for more complex tracks – the more I tweaked the better they sounded.
Hope the above helps anyone interested in these.
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Leo A. –
Thank you for the great write-up.
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