Author Topic: Audi-O-Moron 40W amplifier  (Read 1067 times)

Offline Ufudu

Audi-O-Moron 40W amplifier
« on: April 28, 2019, 04:41:38 PM »
I have finally boxed my Raspberry Pi controlled P-P amplifier. It ended up rather monstrous!

All metal sheet was hand beaten into submission. No a single laser cut to be found in this construction.

Summary:

P-P output stage using toroidal OPT
Bias monitored & controlled by the RPi
Takes a range of power tubes (6550, KT88, 6L6, EL34 etc), the Rpi makes the bias adjustments as set from front panel (25-90mA)
B+ approx 400V
Driver is Pete Millet's P-P driver boards
Tone control is Braxandall. Can be switched off & out of the circuit via the front panel.

Pout = 40W RMS into 8 Ohm (visible distortion on scope)
Distortion at 2W is approx 0.1% (2nd & 3rd harmonic)







Offline Ufudu

Re: Audi-O-Moron 40W amplifier
« Reply #1 on: April 28, 2019, 04:52:47 PM »
The driver stage tubes can be set to triode or pentode mode, that gives the differing frequency response






Offline Skylark

Re: Audi-O-Moron 40W amplifier
« Reply #2 on: April 28, 2019, 05:21:46 PM »
Whoa, what an amazing build! 
:2thumbs:
Music is in the Mind

Offline El Sid

Re: Audi-O-Moron 40W amplifier
« Reply #3 on: April 28, 2019, 05:32:19 PM »
Wow!! Awesome!!

Online fredeb

Re: Audi-O-Moron 40W amplifier
« Reply #4 on: April 28, 2019, 08:14:14 PM »
« Last Edit: April 28, 2019, 08:18:34 PM by fredeb »
...evolution is the gradual development and stratification of progressive series of wholes, stretching from the inorganic beginnings to the highest level of spiritual creation.
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Online Family_Dog

Re: Audi-O-Moron 40W amplifier
« Reply #5 on: April 28, 2019, 08:55:38 PM »
Great job Ufudu! Please post an under-chassis view as well :)


-F_D



-Eric

That Guy in South Africa...
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Offline bushtech37

Re: Audi-O-Moron 40W amplifier
« Reply #6 on: April 28, 2019, 10:00:11 PM »
I just knew F_D was going to ask that :giggle:

Offline marantz123

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Re: Audi-O-Moron 40W amplifier
« Reply #7 on: April 28, 2019, 10:32:20 PM »
Wonderful!  Clever combination of metals there...with the brass strip separating the copper from the aluminuim. (The only regular metal that is galvanically compatible with copper ..is brass. Brass can be associated with most other regular metals without any risk of corrosion..like its been done here). Nice.  :)

Offline Mars

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Re: Audi-O-Moron 40W amplifier
« Reply #8 on: April 29, 2019, 06:30:36 AM »
Excellent job, Ufudu!
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Online Family_Dog

Re: Audi-O-Moron 40W amplifier
« Reply #9 on: April 29, 2019, 06:56:40 AM »
I just knew F_D was going to ask that :giggle:

Dirty-minded old sod, that F_D is!!

Just a fetish I have: Under-chassis wiring tells a lot about the love & care an amplifier gets during construction. It's not as easy these days as way back when tagboards were readily available, which makes neat wiring a lot more difficult but it can be done.


-F_D



-Eric

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Offline Ufudu

Re: Audi-O-Moron 40W amplifier
« Reply #10 on: April 29, 2019, 07:46:52 AM »
Not as tidy as it could be. This amplifier has remained an ongoing experiment and too tidy means you are reluctant to make changes!

Here are 2 inside photos, the first is the lower chassis with the auxiliary PSUs and RPi:

 5V for RPi with LiPo 3.7V charger & backup
 15V for the LT3751 capacitor charger demo board (that I had salvaged from a previous project) which generates the -110V for the control grid supply
+-15V for the grid voltage amplifiers
18V ac for the driver board, to generate the -Vneg needed
Filament rectifier & relay control

The 2nd photo shows the driver & power tube arrangement with the bias control. The 3 toroids are B+ PSUs and the centre for filament. The OPT are below the power tubes.







Offline Shonver

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Re: Audi-O-Moron 40W amplifier
« Reply #11 on: April 29, 2019, 07:53:08 AM »
Fantastic! Quite a lot of work going on there! Kudos for combining the old with the new technologies. Styling is exactly right.  :thumbs:
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Online Family_Dog

Re: Audi-O-Moron 40W amplifier
« Reply #12 on: April 29, 2019, 07:54:29 AM »
That is still most impressive! There is a lot of engineering, originality and thought gone into your amplifier and you have done an excellent job of it.

It must have been a thrill at first switch on and everything burst into life.  :thumbs:


-F_F



-Eric

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Offline Kent Kassler

Re: Audi-O-Moron 40W amplifier
« Reply #13 on: May 06, 2019, 07:48:55 AM »
Incredible! :notworthy:
Audiophile Sound Sommelier Extraordinaire....aka Manic Depressive Temporary Void Filler Deluxe.

Offline charles

Re: Audi-O-Moron 40W amplifier
« Reply #14 on: May 06, 2019, 09:28:26 AM »
Congratulations, well done.