New DIY amplifier completed

mondialfan

Well-Known Member
Thought I'd share some pictures of my newest toy. This afternoon I finished up my latest DIY Class A amplifier. I have named it the Frankenamp not only because it uses parts from other amplifiers, but also because its a massive slab of an amp at 65 lbs. I completed the chassis about a year ago at the same time I finished my Aleph Mono cases. The heatsinks and faceplate were anodized by Anodics in Ft Worth. The upper and lower panels I had professionally powdercoated in a fine textured black finish at Specialized Performance Coating in Arlington. In case you AK'ers didn't know it, Specialized Performance Coating is owned by Michael [a.k.a TOMLINMGT]. The handles are NOS for a Hafler XL600, I purchased them off of the bay many years ago.

Anyway, I wasn't sure a year ago what I wanted to build in this case. I finally decided to build up a Nelson Pass Class A push-pull amplifier and I wanted something different than the norm. This amp is based on an Adcom 5400, just a massively beefed up version of it. The 5400 is a Nelson Pass design from the early 90's. For this project I bought a defunct Adcom 5400 off of the bay and used the channel boards in my build up of this amplifier. The separate output driver boards I used were spares from a project I started over 10 years ago.

In this amplifier the 1KVA main transformer is shared by both channels, but each channel has its own dedicated output stage CRC power supply board with 66kuF per channel. The circuit front ends have dedicated L & R 25VA transformers and CRC supply boards. The output stage is running at about 35VDC and the front end has 55VDC being fed to it to allow the full +/- 35 volt swing at the output if needed. Currently I have it set up for 50 WPC Class A which I doubt I would ever exceed. My killawatt meter shows it drawing just under 300W from the wall at idle.

My initial impressions are extremely good. This amplifier is a lot more forward than the Aleph's which are extremely laid back. I have not had a chance to try it on the Vandersteen's yet, but I'm thinking it may be a better match for them than my Aleph's were. This is based on what I'm hearing now through my AR's.

I included one family picture showing the aleph mono's next to the new Frankenamp.
 

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That thing turned out nice! I really like the sculpted faceplate...great job with that. Looking forward to hearing it and yes, the Vandersteens will respond favorably to amplification that leans toward aggressive. You'll probably get some of those highs you've been lookin for.

And is that 50 @ 8?

Does it get much hotter than the Alephs?
 
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That thing turned out nice! I really like the sculpted faceplate...great job with that. Looking forward to hearing it and yes, the Vandersteens will respond favorably to amplification that leans toward aggressive. You'll probably get some of those highs you've been lookin for.

And is that 50 @ 8?

Does it get much hotter than the Alephs?

Thx, I spent a lot of time machining that faceplate. Machining is definitely not my forte, but I'm learning.

It is 50W@8 & 25W@4. I had hoped to be able to push it to 60W @ 8 or more, but the transformer is putting out about 3V more than planned and as a result I ran out of heat sink capacity sooner than planned.

It is about the same temp as the Alephs. HOT that is....
 
I'll tell you something else I like about that amp....the rounded corners on the cooling fins/heat sinks. :thmbsp: I'm constantly sustaining damage to the flesh from the the fins on my Thresholds and F5. :thumbsdn:
 
That is beautiful :thmbsp:

I like the separate PS for the front-end. Is the original 5400 like that?

What is the purpose of two heat sinks on the back side?
 
I'll tell you something else I like about that amp....the rounded corners on the cooling fins/heat sinks. :thmbsp: I'm constantly sustaining damage to the flesh from the the fins on my Thresholds and F5. :thumbsdn:

Yeah, my Aleph's tear me up as well.
 
That is beautiful :thmbsp:

I like the separate PS for the front-end. Is the original 5400 like that?

What is the purpose of two heat sinks on the back side?

Thanks!

Yes the 5400 has higher voltages for the front end of the circuit as well.

I have 4 output mosfets on each of the 3 sinks, 12 total. So all three side have an equal amount of power being dissipated on them. The rear heatsink has a good portion of it machined out to allow clearance for the speaker jacks, RCA's, XLR's, & AC pwr plug. This makes the rear sink less effective than the side heatsinks. I added the "booster" sink to help equalize the temperature of the rear sink with the side sinks. Without it I had a 5C higher temp on the rear panel than the sides. With the booster sink that difference has dropped to about 2 - 2.5 deg C.
 
That is beautiful :thmbsp:

I like the separate PS for the front-end. Is the original 5400 like that?

What is the purpose of two heat sinks on the back side?

Yes, that is friggin' sweet! :tresbon:

I have a 5400 and like it very much, but no, the separate PS is not how the 5400 is at all, alas.

OTOH, you can get working 5400s for $150-$200 all day long and IMHO they are a steal at that price. They're in a sweet spot: overshadowed by the 5500 but nearly as good as long as you don't need the extra 75wpc; and on the other hand really outclass the 5200 and 5300, which tend not to have the same build quality (or country of manufacture) as the 5400 and 5500.
 
Yes, that is friggin' sweet! :tresbon:

I have a 5400 and like it very much, but no, the separate PS is not how the 5400 is at all, alas.

.

Thank you!

Yes, the 5400 actually does have the higher front end voltages. Adcom does it with a custom wound transformer, separate windings for each channel and the higher voltage taps as well. Its a true dual mono all the way.
 
lot of thought went into that proj. and it shows.

How did you come about determining temps? Infrared meter? wonder if a factor of the heat is the internal box temp maybe a fan inside can knock off a couple more degrees.
 
restorer-john - I was torn on using green or blue for the LED. I have clear green LED's in the Alephs. I decided to go for the more modern look and use blue. Its still too bright for me though.

Binkman - I use a handheld IR meter for the temps. I also at times rely on the old touch method for Class A amps which works reasonably well. There is little doubt that the temps would drop with forced air, but my goal was to build it without a fan. The amp is well ventilated internally as even with the lid off it doesn't make a huge difference in the heat, maybe 2 deg.
 
restorer-john - I was torn on using green or blue for the LED. I have clear green LED's in the Alephs. I decided to go for the more modern look and use blue. Its still too bright for me though.

How 'bout using one of those tri-color leds that change color automatically? Then you'd really have the modern look. :D
 
How 'bout using one of those tri-color leds that change color automatically? Then you'd really have the modern look. :D

Red-Green-Blue-Red-Green-Blue-Red-Green-Blue-Red-Green-Blue..........

It already makes my head hurt!

I'd definitely need a beer before ever turning it on. :)
 
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