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Thread: Sherwood AM-8500B MOSFET power amp

  1. #11
    Join Date: Mar 2015

    Location: Finland

    Posts: 237
    I'm Kai.

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    Well I had a bit more of a look around the circuit and upgrading some of the caps seems like a no brainer to me. For one thing right at the output of that buffer opamp there's a 4.7uF electrolytic cap which is not even bipolar(??) - then at the input of the following gain stage there is a 5uF bipolar electrolytic (actually two 10uF polar caps back to back). Replacing these with 4.7uF film should yield SQ benefits I think. Or perhaps this would be an opportunity to mess around with the Russian PIO caps I've been curious about, if they fit. Then at the output of the preamp stage there are 0.047uF ceramics, again probably better replaced with film I think. I'm not hell bent on replacing all the caps, but beyond the ones I mentioned I think it's probably a safe bet not all the electrolytics in the several hundred uF range are no longer up to spec. The smaller ones I guess might be fine, at least in my admittedly limited experience the small ones usually hold up better.

  2. #12
    Join Date: Jun 2015

    Location: Wuppertal

    Posts: 3
    I'm Axel.

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    Hello,
    I just read your report with great interest.
    You realize that you are writing here about one of the best kept secrets in the HiFi world?
    I myself own 2 of these amplifiers and thus operate very "critical" speakers in bi-amping. The impedance of these speakers goes up to 1ohm. The power amplifiers do it with pleasure.
    Have fun with your power amplifier, it's best to close this report quickly so that no one learns.
    greetings from Germany

  3. #13
    Join Date: Jun 2015

    Location: Wuppertal

    Posts: 3
    I'm Axel.

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    Good evening Kai,
    somebody in the USA did a nice new comment for the "powerhouse", please read:
    Alright....so it's 7 years later from the last post. No biggy. The amp is the biggy. I almost needed another can of spinach to help me carry the Sherwood to and from my car into my home. Then find a place/ shelf strong enough to support the weight and look good doing it. Success.
    After hooking it up to main out jacks of my Concept 4.5D (connected to a Dual 830c cassette deck and a Technics
    SL-1200mk2, later a CD player ). The Sherwood amp came with a adapter so it will fit in USA electrical sockets. The original plug prongs are round, Singapore perhaps? Defiantly not made for America to enjoy. Inkel has the whole matching set.....AVP8500 preamp, cassette deck, equalizer, compact disc player, and tuner. Speakers too. It's a beautiful set.
    Anyway this monster gold brick of an amp is mighty powerful and well built. Supposedly has many high end parts. This is my first amplifier. I'm still learning. Internet research on these turns up little results and information. That's makes this a rare treat to own. And a treat it is to listen to. I've owned it for over a year and also picked up some other brands amps which I've compared them all. The Sherwood wins! Clean power, wide frequency range, high damping factor, and A/B speaker selector. Sound transmission is straight. To me no colorization or brand traits come through, unlike Denon or Sony. Another nice thing is it doesn't run HOT! It's worked flawless since I got it.
    Overall I think this amp is great. I have nothing bad to say about it.


    The 8500 is nearly the same like the older AM-7040, the older one is slightly better. If you want i can demonstrat picutes here. Interesting is one of the last sentences about running hot.
    I owned 2 Krell KSA 150 - really "Monsters" and legends, but they did not do a better job at my speaker misfits..... But when the Krell's were running, it got very, very hot in my music room
    Greetings
    Axel

  4. #14
    Join Date: Mar 2015

    Location: Finland

    Posts: 237
    I'm Kai.

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    Quote Originally Posted by tallauscher_ View Post
    Hello,
    I just read your report with great interest.
    You realize that you are writing here about one of the best kept secrets in the HiFi world?
    I myself own 2 of these amplifiers and thus operate very "critical" speakers in bi-amping. The impedance of these speakers goes up to 1ohm. The power amplifiers do it with pleasure.
    Have fun with your power amplifier, it's best to close this report quickly so that no one learns.
    greetings from Germany
    Hi Axel,

    Yes I've been quite impressed with this beast. I didn't notice your posts earlier, but since I just made a little DIY passive "pre-amp" I was about to update this thread. Up until now I've been using the Sherwood with the cheap little chinese tube preamp, today was really the first time I got to hear the amp properly on its own without the Little Bear pre coloring the sound. It's a nice enough thing and better than you'd expect for the 20 or so euros they sell for, especially after changing the valves to something nicer, but it certainly imparts it's own sonic signature.

    Now the passive I just put together is nothing more than 20k volume pot fastened into a piece of wood, wired directly into some poor quality 80s interconnects - I salvaged the pot and the RCA-cables from a cheap and defective 80s Pioneer tape deck. Bass was just fine before, but certainly has even more oomph now at the very bottom and also a tad more control. Also dynamics seem better than before, one unfortunate side effect of that is playing vinyl some clicks and pops really pop out, which probably means the amp doesn't shy away from fast transients and voltage swings

    Also at higher volumes the sound stays better controlled, not that it was bad before but I think at higher volumes THD from the Little Bear was becoming noticeable before. Between the JBLs and the Sherwood there's a crazy amount of clean power on tap, the limit really is how much my room can take before windows and everything start to rattle.

    This was just a quick try to see if a passive might be a way to go and I think I'm gonna build a proper one using some nice (hopefully...) and cheap chinese stepped attenuators.

  5. #15
    Join Date: Mar 2015

    Location: Finland

    Posts: 237
    I'm Kai.

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    After my experience modding a cheap TC-750 phono pre and hearing the difference coupling caps make, I finally got around to changing the coupling caps in the Sherwood. So electrolytics out and Audyn Q4 PP film caps in. Pretty huge difference in clarity and detail. The amp sounds a bit less warm now but not at all in a bad way, no signs of stridency or coldness. It's just more like a blanket was lifted. In fact my cheap CD-player got more listenable for the change, despite the amp in general being more revealing of source material now. Spinning some discs, both vinyl and CD I first got concerned I made a bad solder joint or something because I was hearing some distortion I hadn't noticed before, but in all cases it ended up being about the source. One CD it seemed like on one track something on the right channel had been very slightly clipping during recording. In other cases it ended up being things like snare drum rattling in the background or similar fine details deep in the mix I hadn't noticed before. Part of it was also probably I was pretty neurotic in listening trying to spot distortions. Anyway, if anything the highs are smoother now. Mids are way more transparent. The only part where I'm not 100% sure all change was positive is the bass. While I feel like qualities of bass drum for example come through better now, sometimes I feel the bass got a bit overly round. But it also depends on the recording, since for the most part the change is not that noticeable with electronic music with really tight kick sounds etc. Anyway on the whole, the film caps certainly impose far less of a signature on the sound. Changing them was easy enough and didn't have to desolder anything apart from the replaced components. Couldn't fit the large Audyns directly on the PCB though, but that was no surprise and there was plenty of room to keep them close and avoid long runs of wire.

    I'm pretty stoked and so glad I bought this amp. Looking back it would've been bit of a bargain even at the original 200 euros asking price.

  6. #16
    Join Date: May 2010

    Location: Worcestershire, UK

    Posts: 1,101
    I'm Rob.

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    Nice update!
    Rob.
    Powered by crossed fingers and clenched buttocks

  7. #17
    Join Date: Apr 2016

    Location: Gravesend and France

    Posts: 1,498
    I'm paul.

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    Quote Originally Posted by helma View Post
    Yeah I think Sherwood was more famous (or not) for budget gear, this one seems a more serious effort though. I've been listening to it for a few hours now, it's a good sounding amp with very healthy power reserves and good dynamics.

    The thing with MOSFETs is ever since I got extensive experience with a MOSFET based guitar amp (there was a time in the 80s MOSFETs were all the rage for trying to get a valve like sound and distortion characteristics/behaviour from a transistor amp), there's a certain "MOSFET tinge" in the sound I seem to often hear. Not so much with this one as the Adcom though, actually I'm not 100% I'd notice it in this Sherwood if I didn't know it was a MOSFET design, where as with the Adcom it was very clear - I had no preconceived notions of how MOSFETs are supposed to sound when I fired that one up, but it instantly brought back memories of that Marshall Lead 20 or whatever it might've been called.

    Guitar amps really pronounce differences since things are often driven to distortion - even "clean" tones are often on the sweet spot right at the edge of break up. I used to think my experience with guitar amps was good for nothing regarding hifi, thinking they are completely separate worlds since one is about just producing what is there cleanly and other is about making the amplifier an instrument in itself. But I've come to find out the sound characteristics tend to be there in hifi as well (valves vs solid state, bjt vs fet etc.) just subtly in good kit at least.

    In any case I'd love to hear this one with a more competent preamp. Maybe I'll try putting together a little passive volume control from surplus parts (if I have some). Need to give this one some time (and time for my ears to adjust), might end up being a keeper.
    Early solid state guitar amps put me off solid state for many years, they just sounded dead, no sparkle.
    Bakoon 13r Denon DP80 Stax UA-70 Shure Ultra 500 in a Martin Bastin body with jico stylus, project ds2 digital Rullit aero 8 field coils in tqwt speakers

    Office system, DIY CSS fullrange speakers with aurum cantus G2 ribbons yulong dac Sony STR6055 receiver Jvc QL-A51 direct drive turntable, Leema sub. JVC Z4S cart is in the house

    Garage system another Sony receiver, cassette deck


    System components are subject to change without warning and at the discretion of the owner.

  8. #18
    Join Date: Mar 2015

    Location: Finland

    Posts: 237
    I'm Kai.

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    Quote Originally Posted by paulf-2007 View Post
    Early solid state guitar amps put me off solid state for many years, they just sounded dead, no sparkle.
    I was 14 when I got to play a tube amp for the first time. It was only some old 60s thing though, Vox AC30 I believe it was called It was amazing, how alive it not only sounded but felt, like a huffing beast at your finger tips. And that was some damn loud 30 watts. Not understanding anything about the technical side, power ratings or speaker sensitivity, it led to the obvious conclusion "tube watts" are way more powerful than "solid state watts" There was really no going back to solid state after that. For some odd reason I always thought valves make no sense whatsoever for hifi. Not sure where I got that idea from, but it didn't really occur to me to challenge that notion until quite recently.

    Anyway the Sherwood healed my Adcom reinforced MOSFET traumas of youth, apparently they can sound quite fine. Btw. I took a couple of photos of the insides while I was changing out the coupling caps, should post those later.

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