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PostPosted: August 26th, 2019, 9:41 am 
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Joined: March 12th, 2013, 11:12 am
Posts: 555
I heard Dave's newest hybrid amp (akido driver stage 6N1P/6n6, Pass First Watt VFET output) and it was really something special. That old cliche about amps that take the best of both SS and tube designs with none of weaknesses best describes this amp. It was free of grain, effortless sounding, well balanced and extended top to bottom, does sound stage and positioning really well, depth, height, detailed, got the tone right and just plain nice to listen to. I could not find much to critique. I suppose it did not have that extra, rich tonal goodness you can get from a SET amp but it was pretty close. I am not a fan of SS amps nor have I been very impressed with the hybrid designs I have heard over the years but I could live happily with this amp in my system. A monoblock version of this amp might be the ticket and since it puts out about 25wpc, it can be used with a fairly wide range of speakers.

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Last edited by TubeDriver on August 26th, 2019, 2:40 pm, edited 1 time in total.

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PostPosted: August 26th, 2019, 9:59 am 
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Joined: July 8th, 2016, 4:34 pm
Posts: 296
Speaking of amps has anyone tried the icepower modules now available at Parts Express?

https://www.parts-express.com/icepower


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PostPosted: August 26th, 2019, 11:05 am 
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Joined: February 28th, 2013, 1:19 pm
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Pete,

Thanks for the review, and the great pictures!

Just one thing to add, we did some tube rolling, and put in a pair of GE 6CG7s in the input position, which gave a bit more of a classic tube amp like character . The 6N1P presents a more neutral character. Both were good sounding.

David


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PostPosted: August 26th, 2019, 7:29 pm 
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Joined: March 12th, 2013, 11:45 am
Posts: 50
Location: Glen Burnie, MD
brombo wrote:
Speaking of amps has anyone tried the icepower modules now available at Parts Express?

https://www.parts-express.com/icepower


Those are not the most current models, I have an IceEdge 1200AS stereo Mivera amp which is their latest and it is a very good sounding amp. I'm currently comparing it to my Bryston 14B SST, both 600W @8 Ohms, 90lbs vs 20.


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PostPosted: August 27th, 2019, 8:20 am 
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Joined: February 28th, 2013, 1:19 pm
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Trying to reclaim the topic (I can't believe the discussion has diverted from a DIY low power Class A, no feedback tube/MOSFET hybrid amp intended for high-end reproduction to a commodity, Chinese made high power Class D amp board).

This is really a fairly simple and achievable project to accomplish, since it is highly modular. I believe I covered it a previous posting, but in summary, it consists of using the Pass Burning Amp complimentary source follower MOSFET output boards available at the DIYAudio.com Store, together with a Broskie (TubeCAD) Aikido front end, with the output configured as a White Cathode Follower. If you use the Broskie boards, there are provisions on the board to configure the output as such. The Aikido board is cap coupled to the MOSFET output board. The rest is power supply, and again, DIYAudio.com store has a nice bipolar universal power supply board, and Broskie has tube power supply boards of various configurations, regulated and non-regulated. Pick one that works for an Aikido preamp with LV heater supply. I did add some chokes instead of resistors so both the MOSFET supply and driver supply boards are CLC. Antek has decent toroidal transformers. I believe the biggest constraint on a project like this is the chassis, however I used a 4U Deluxe chassis from ModuShop 2000 (Italian made) sold through DIYAudio.com store that is shipped flat-pak in a few days. It is great working with this chassis, since the heatsinks are pre-drilled for the boards and MOSFETs, and the is a perforated steel base inside the enclosure for mounting standoffs and boards, etc., so minimal drilling is necessary.

If considering this, I would recommend reading through the BA3 build guide on the PASS forum on DIYAudio.com, keeping in mind that this hybrid version does not use the BA3 front end. However it provides documentation on how to build and setup the MOSFET output boards, as well as recommendations on power supply transformer selection. There is also a build guide for the DIYAudio.com universal power supply board, and the Deluxe 4U chassis should one choose this. Also, read the articles on TubeCAD.com on the Moskido, as well as https://www.madscientist-audio.com/mosk ... ifier.html. The Aikido boards have documentation (unfortunately, Broskie makes it hard to download without buying the boards first). This will provide guidance on tube selection and operating points. I did not use the Aikido board (too big for my layout), but the info is useful.

This is easily built up as individual, testable, modules that are assembled in the amplifier. I have to admit the 4U chassis ends up being tight for a stereo build, a 5U chassis would provide more space and allows the MOSFETS to be run with more current (no additional power output but better drive), or use a higher voltage on the MOSFETs for more power beyond 25W. If the latter, you will probably need to have more voltage gain in the front-end circuit, so perhaps a 12AX7, 12AY7, 12AT7, 5751 (6SL7 if running octal). You need to have a beefy tube for the White Follower, if noval, a 6N6P, ECC99, 6N30, or similar in the two standard basings, or a 5687 if building point-to-point. If you are building octal, then something like a 6BX7 should work well for a White follower, with a 6SN7 or 6SL7 at the front (depending on your voltage gain needs, a 6SN7 should work for a 25W version of the amp).

I hope this helps provide background. Pete, I suggest you read through the information I pointed to so you have a better idea of what is behind my amp.

David


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PostPosted: August 27th, 2019, 9:20 am 
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Joined: March 12th, 2013, 11:12 am
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Thanks for the details David. I think by design, a bit of luck (maybe both?) you have built up an amp where the driver and output stage combined are greater than the sum of their parts. I believe it is one of the very few SS amps I could live with.


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PostPosted: August 28th, 2019, 8:16 am 
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David,

Thank you for sharing the details of your build. I heard the amp at your house and was impressed, but we didn't compare the hybrid to another amp, and your system is not intimately familiar to me. So, thank you Pete for auditioning this in your house. The net result is very exciting and helpful.

A Moscode/Moskido type hybrid has long been on my bucket list. Like Tom P. and David B., I share their dislike of output transformers and their limitations. Eliminating them and maintaining decent power levels with excellent sonics means 1) extremely high impedance speakers (and a big nasty-ass coupling cap); 2) lots of parallel output tubes and reasonably (attainable) high impedance speakers; or 3) solid state output devices.

Obviously, option 1 is out of the question. Two and three are on that list of mine, with parts piles growing. David's success with this design has given me the impetus to push the hybrid ahead of the OTL. It'll be a fun time discovering whether a set of mosfets sounds better than a set of triodes as an output stage.

That's what this is all about.

Stuart


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PostPosted: August 28th, 2019, 10:00 am 
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Joined: February 28th, 2013, 1:19 pm
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There is a functional similarity between a MOSFET source follower output stage and a tube OTL amplifier (with the tubes connected as cathode followers). Think of the MOSFET as a pentode (which itself is typically makes a better follower than a triode). Easier to get low impedance on the MOSFET source follower and MUCH better reliability. The fact that you can adjust bias and DC offset easily on the MOSFET output which will not change or drift due to ageing is a real advantage. The main issue with MOSFETs is gate capacitance, which means you have to have a robust, high current driver and will limit the number of devices in parallel you can drive. To get more power (assuming you are looking for a 50W minimum), you need much higher voltage rails on the MOSFETs and BIG heatsinks (keeping in Class A) which will be the limiting factor. One is replacing expensive output transformers (for a classic tube amp) for expensive chassis + heatsinks. I don't think the higher gain requirements at the front end of the amp is a big issue, you can easily single gain stage, or a cascade if you need more. Doesn't have to be Aikido, a choke or CCS loaded input stage will get you full mu. I do not have a feel on what happens moving in the direction of a Class AB hybrid design, feedback may be needed (my amp uses NO feedback), so need to factor in higher gain front end so that feedback can be applied. Looking at the NYAL MOSCODE 300 and 600 schematics, you can see the global feedback loop back to the input stage. Worth studying on how that was applied.

I think it is a worthwhile exploration and there is a lot of room to play if you think about it. Keeping it modular, thinking about the output stage and its power/thermal management as one element, and the tube input/driver stage as another element. No phase splitter to worry about.

David


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PostPosted: August 28th, 2019, 4:38 pm 
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Joined: June 4th, 2013, 2:39 pm
Posts: 177
Thanks everyone for this thread. First time I've been interested in a SS project--and the first time I've thought I might actually be capable of doing it! I might just give this a whirl. I'm already familiar with the Aikido.


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PostPosted: August 28th, 2019, 8:20 pm 
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Joined: March 12th, 2013, 11:12 am
Posts: 555
About 5 seconds into the first track with David's amp, I nudged him on the shoulder and gave a thumbs up. It just IMMEDIATELY sounds good and right, a simple test that many amps fail IMHO.



Grover Gardner wrote:
Thanks everyone for this thread. First time I've been interested in a SS project--and the first time I've thought I might actually be capable of doing it! I might just give this a whirl. I'm already familiar with the Aikido.


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