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Elliot Sound Products - P3A 100W Amplifier
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Author:  dtsup1 [ 27 Sep 2010, 19:17 ]
Post subject:  Elliot Sound Products - P3A 100W Amplifier

Hi guys,

It's time for another ESP (elliot sound products) project !!
This Project 3A will deliver 100W into 4ohms, and 90W into 8 Ohms (35V and 42V PS respectively)!
Distortion is a low 0.04% and is -1dB @ 10Hz.
I decided on this amp because it is so simple, and am bored of that "Mosfet" sound !! :mrgreen:
This is a pure BJT power amp! Also, Sakis, from diyaudio forum has praised this amp and is the reference amp he uses. He has also repaired thousands of amps, and for the P3A to be his main amp speaks volumes about the sound and performance of the amp. After the P3A amp, I have one more SS amp to build(Carlos's DX Blame ES) before heading for SET VALVE AMPS :lildevil: :mrgreen: !!! :eek: :smoking:

I have ordered the circuit board, and they arrived today. Going to get the component parts soon.

CrazzyAbtTubes - Sorry to hear your P3A didn't work out. Hope that you will come back to it someday...

More to follow... :up:

Edit : PS will be the same 18VAC 500VA (25V DC) transformer I used for the TDA chip amp, so I expect power to fall by quit a bit. Maybe 50-60W for my 4Ohm speakers.

Author:  dtsup1 [ 30 Sep 2010, 09:34 ]
Post subject:  Re: Elliot Sound Products - P3A 100W Amplifier

The board is 3/4 installed with components. Waiting for the 2k multi turn trimmer and power transistos from Farnell. Will arrive in 2 days time.
The input cap will be a Mundorf M-Cap 2.2uF which is too large for the board, thus will be mounted outside the board.

Author:  dtsup1 [ 02 Oct 2010, 07:44 ]
Post subject:  Re: Elliot Sound Products - P3A 100W Amplifier

Adjusting the bias setting to 50mV for 75mA bias on the transistors.
Finished PCB worked the first time I powered on !! :lildevil:

More updates with attached speakers and inputs later.

Edit: One channel has 6mV DC offset, while the other has 23mV.
It remains that way regardless of bias setting.

Author:  dtsup1 [ 02 Oct 2010, 08:51 ]
Post subject:  Re: Elliot Sound Products - P3A 100W Amplifier

Ok, I still am in shock. I put on my test speakers to have a listen. Emi Fujita - The Rose brought tears to my eyes. Jeez! The realism of the guitar, the dynamic range of the vocals is stunning.
omg !!

Author:  Gio [ 02 Oct 2010, 10:40 ]
Post subject:  Re: Elliot Sound Products - P3A 100W Amplifier

Good stuff Dinesh. On the project page in the specs the DC offset is noted as <100mV. I would not start to worry about the DC offset unless is goes higher than about 50mV.

What have you planned for the enclosure?

Author:  dtsup1 [ 02 Oct 2010, 10:50 ]
Post subject:  Re: Elliot Sound Products - P3A 100W Amplifier

Amp testing in progress with Vifa 3.5'' test speakers. (hardly a "test" speaker since they cost $35 each) !. 82dB , 8Ohms.

Every amp I build gets tested by these speakers. The heatsink gets hot when the volume is pumped up so I added a fan to keep it cool during the abuse of testing. 90dB peaks recorded from 2m. Not a single touch of compression in midrange, though the bass is muddy. (enclosure issue + cone compression).

This may be the amp that can challenge the Aussie Amps head to head.
Right from listening to the test speakers, the bass is very fierce. Like a raging Mexican bull.
Midrange is a touch relaxed, but very clean. Highs are silky, great decay of cymbals.

Btw the PS is from my soon to be built Nelson Pass F5. I am using 60,000uF per channel for this low powered SS amp ! Not to mention a 500VA tranny LOL.

If everything goes well for the next 24hours, I will hook these up to my main speakers for a proper review !

Gio - I will try and fit it into a similar case that I built my TDA amp.
All my PS's will be remote, thus I can use smaller enclosures.

I am a little worried that the Class A power supply may be causing adverse effects to the sound but the PS Rod shows in his website is very small.

Author:  dtsup1 [ 02 Oct 2010, 12:26 ]
Post subject:  Re: Elliot Sound Products - P3A 100W Amplifier


I just couldn't wait as usual, and I was more confident than usual of this amp's performance, as well as my soldering skills. This amp blows my mind. Hooked up to my 94dB speakers, my jaw dropped and I was in a state of shock. Smooth is the word. Super deep soundstage, though not as wide. Vocals sound extremely natural and open. The most open sound I have heard. The top end beat all my other amps. Rich and detailed, not tizzy and transistor-like. Detail retrieval is insane, instrument layering is the finest. I don't know where the bass comes from, but my guts feel it !!

Why does it sound soooooo smooth !?!? :eek:

The passion it unleashes when each and every song is played is inspiring. I have heard Whitney Houston - I will always love you about a hundred times, but this is the only time my eyes started to water. A similar experience I had was when I heard Mark's valve amp with cheap bookshelf speakers.
This is incredible - SS amp with the passion of valve !! :shock:

Taylor Swift's - Tim McGraw didn't shed my ears. First time ever. Her voice was natural and lifelike.
Bass is perfect IMO. Not as well damped as Aussie Amps, but very rich and musical and digging below 20Hz with ease.

The only negative point is that the sonic image is not as acidly etched in space as Aussie Amps or my TDA chip amp. Guns n Roses's - Sweet child O mine was more thrilling on the Aussie Amps as the bite of each note on the guitar was more electrifying. Midbass performance loses to Aussie Amps as it was a tiny bit lean. For vocals and cymbals, nothing could touch the P3A. However, both amps are significantly different in presentation. While the Aussie Amps was more a "live" performance, with the presentation being more unfront and personal, the P3A threw the stage a few meters back, where I felt I was a a quiet bar listening to a small jazz quartet. I swear I am listening to a valve amp with the massive bass control of an SS amp.

So far so good. Am a big fan of Rod's stuff LOL. :smoking:

Author:  CrazzyAbtTubes [ 02 Oct 2010, 16:35 ]
Post subject:  Re: Elliot Sound Products - P3A 100W Amplifier

Hello dtsup1

Your story is motivating me now.... I have always wanted to build that P3A amplifier.... and allot of other stuff that Rod has designed, he even has a P3A class "A" version of the amplifier.

I can see the PCB layout, I bet I could copy it onto proto board or do it point to point, that would be a fun challenge, maybe it is time again for me to revisit this project, I have much more knowledge now of both tube and solid state circuits.

One thing I have always wanted to do is some how turn the input LTP on a P3A amplifier into a tube stage, like a hybrid. Probably more work than it is worth though, but I bet if it was done right it would sound even more amazing! :P

I am glad to hear it worked out for you dtsup1 :up: , I have heard many rumors of the P3A being very superior but have not seen many threads other than the one I made that did not work out.

BTW, what outputs are you using?

Author:  dtsup1 [ 02 Oct 2010, 22:24 ]
Post subject:  Re: Elliot Sound Products - P3A 100W Amplifier

Hi Crazzy,

Tube input stage would be insane ! :mrgreen:
Outputs as in output transistors ?

I used MJL21193G / MJL21194G
Hellava expensive chips. (US $8 EA), but all the other parts are just standard metal films. The 2nd most expensive component is the 1uF input WIMA MKT cap. Trimmers are also from Farnell, since none are available from local shops. (multi turn types)

I am using a 2.5A fuse on the primary side, and never had a problem of a blown fuse due to turn on inrush current. The 1.25A fuse that I used some time ago for the same PS used to blow. Thus, I did not use the thermistors since the fuse is ok.

I wish that you can get to build this...but you may need to use the PCB. His boards are expensive though IMO. Overall this is another highly recommended amp! I will evaluate more today, and I have a weird feeling that the Aussie Amps may lose. :bawling:

Author:  CrazzyAbtTubes [ 03 Oct 2010, 10:20 ]
Post subject:  Re: Elliot Sound Products - P3A 100W Amplifier

I would have built this amplifier by now if it weren't for the expensive PCB. I can easily see this amplifier beating just about any other, it is so simple there is nothing there to change the sound, I have craved so long to hear what it would sound like. :yumcoffee:

What is your total cost so far?

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