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PostPosted: 22 Oct 2010, 08:49 
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Location: Dartmouth, Nova Scotia
This is so GREAT Dinesh! :mrgreen: I mean the sound! :blush:

Your P3A turned out to look really good, at first sight of the final result the chassis setup reminded me of Audio Note's integrated amps, very clean and simple and the blue LED power indicator is a great added touch. :up:

Now this is where the sound comes in..... what you just described is what I just heard last night! The sound I heard matched your description so closely when I read it this morning stunned. :blush:

To be more exact I built a new P3A, much better than the first one I attempted, everything needed to run it is on one piece of proto board, all point to point and totally different types of semiconductors (All salvaged from many dead stereo's), the outputs are massive Sanken 2SA1169/2SC2773 150 watt packages. The input LTP are some odd ball 2SC3381, they are a matched pair of 80V NPN transistors all in one package. Drivers are 2SA968/2SC2238 and the input caps are 3.3MFD MKT.

And the best part is all I used to test the thing are two 9 volt batteries (really used 9 volt batteries but they still worked).... I was quite surprised by this since they only had about 7.5-8 volts left in them but I tried the amplifier on my MooseFET preamp and a pair of cheap headphones and it sounded amazing, finally I have fulfilled my P3A crave! :P

I owe it all to you Dinesh for your great project and your motivational posts in this thread. :thumbsup:

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PostPosted: 22 Oct 2010, 22:55 
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Hi Crazzy,

Very glad you like it. It is my reference amp now. I have gone again and again to A/B my other amps but they cannot come close. There is something special in the P3A's midrange. While I haven't built the Moosefet preamp, I can safely say that you have a spectacular match. The FETs used in Moosefet should provide a warmer tone, and that blends very well with P3A. In my case I have intentionally installed carbon films in the preamp module for that purpose.

Be very careful to ensure that the P3A is not oscillating. ( as you are using high speed Sankens)

When you are quite sure all is ok, connect them to your main speakers and do a little write up! :thumbsup:

Btw how does the P3A compare with your other valve amps ? (assuming that power requirements are not considered.)

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PostPosted: 23 Oct 2010, 10:07 
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How will I know if it is oscillating, will it be audible when listening to music?

It is interesting that you speak of the carbon film resistors, I uses a 2W 2.2K carbon comp at the input and a 22K 1W carbon comp for the feedback resistor, I made sure to mach them for each channel and also made sure to use the closest values, I think these are AB types because their values were well within 5%. The rest are a combination of metal film and carbon film types and I used a 100MFD 50V BG for the feedback cap that goes to ground.

I will have to post a picture to show you what is really there, the board is very organized and there is room to spare too. I am going to try the amp on a regulated 12+/- DC regulated power supply today and hook up some speakers to see how it holds up. ;)

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PostPosted: 23 Oct 2010, 11:27 
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Hi Crazzy,

Am not too sure as my amp never oscillated. I even put the preamp input wiring right next to my TV, but it survived the torture test.

If it does oscillate, the highs will be very harsh or heatsink gets hot.
Your bias adjustment may swing wildly instead of being linear.
I have it biased at 90mA (50mV on meter)

Some causes of oscillation in P3A -
1. Heatsink not grounded
2. PCB board layout sub optimal
3. Speaker return wire not taken from audio ground. (I actually have mine taken from the amp PCB's ground but it seems ok. No hum or weird behavior.)

+/- 12V ? :o
I wonder if it can even turn on :confused: ...

I am running a low voltage too as I have my Pass F5 project on hold (may even abandon it :bawling: ) so the 500VA, 18V tranny is being used for the P3A. I get +/- 25V DC powering the amp. It didnt show signs of strain when powering Sam's 87dB 3 way scanspeaks. His speakers were straining slightly, in fact.

Use some inefficient test speakers and crank it up first. I was confident after playing my 82dB/m 3.5'' very loud (85dB @ 3m) for long test periods. The heatsink did get very warm to the touch, even with the fan on. If you imagine me removing the test speakers, and connecting up the 8'' 2 ways without lowering the volume, the neighbours would be calling the cops on me :hot: .

As good as this amp is, I still treasure all my DIY amps, so once in a while I will have a listen. Special appreciation to the ZCA amplifier - lovely warm bass, very slightly bloated but very nice to listen to. Midrange light and musical - like a feather that floats from the skies but less detailed than P3A. Overall 7.5/10

Aussie amps - hard beast to tame. Needs special matching to preamp, of which I haven't found yet.
Best bass control of all amps. Most overdamped. The only amp which sounds too neutral, impossible to identify it's sonic identity. Weird...
Overall 7/10 - not a fair rating but I have not achived system synergy yet.

TDA 2050- superb soundstage forwardness for vocals. Good bass control but a little light.
Overall 7/10

*drum roll* - ........P3A rating - 9.2/10

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Dinesh

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PostPosted: 23 Oct 2010, 16:29 
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If only you could hear this thing Dinesh :o First off I was listening to the Eagles Hotel California, and was just stunned, 12 volts per rail really? and I get this? It sounded so smooth indeed, holy crap on the bass was killing my speaker when I listened to Tom Waits, it scared the crap out of me.

I have had it running for quite a few hours now in a test set up and don't want to take it down, it just sounds that good. Mids are so clear and undistorted, the highs are very detailed, every "ting" is there like it is right in front of you, yet it is smoother than a tube amp.

What about biasing? I have been setting the amplifier to have minimum DC output, but is that really the proper way to do it? I have had no noticeable oscillation problems and the outputs only get slightly warm (all depending on my bias setting too).

This thing sure is great, and you held your word to be true, this amplifier is no joke! :twisted:

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PostPosted: 24 Oct 2010, 00:19 
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Hmm, I tried a 20mA and 100mA bias but was not much difference. Since my heatsink is quite large, I decided to bias it higher. Here is the pic : I added a 2nd storey of heatsinks! :D

Yes, it is very smooth, extremely detailed in the mids/highs with solid bass. The bass is less pronounced when compared with my 1500W behringer amplifier, but the bass of P3A digs very deep, very layered bass. When the bass comes in, it doesn't force you to focus on it alone, thus giving chance to hear any instrument in the soundstage without distractions.

I had a guest come over to have a listen. She plays the violin and comes from a background of musicions. I played a violin track, but didn't tell her who it was. After a second or so ..." Wow, fantastic tone from the Stradivarious violin". There ya go, another strength of P3A - timbral accuracy.

CrazzyAbtTubes wrote:
yet it is smoother than a tube amp


LOL. :mrgreen: :cold: :up:

How did you find the soundstage of the amp? Layering of sounds etc?

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PostPosted: 05 Nov 2010, 19:23 
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Here are some pictures Dinesh, I have not done any real listening sessions with this amplifier to compare it with others, but I did have a couple of friends over who know nothing about audio what so ever and they hooked up their MP3 players to it and were blown away by the sound of what I would guess to be 10 watts or so. Their were things in their music that they said they had never heard before, but then again, I myself have heard allot of the music they have played on cheaper systems and it just sounds horrible, over contrasted, distorted and clipped off because the recording just was not that good it seemed..... well that wasn't the case with this simple setup I had, I was using some cheap found in trash speakers, they must be rated for about 100 watts, but the P3A running at about one tenth capacity had no problem driving them to the point that you were over whelmed by loud but clear undistorted highs, and a really powerful tight bass.

I will get into more description of the sound after I get the full amplifier built and running, it might be a while though because I have to save up money to buy a good quality 300-500VA Hammond toroid.

I built this amplifier with reused part that I did not even do any testing on, just measured and matched used resistors and checked for shorted transistors.

Now for some pictures......


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PostPosted: 05 Nov 2010, 23:43 
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Excellent work Crazzy. Takes a lot of skill to do it on a breadboard.
I like the transistors !! (Sankens)

Try and go for 2X 150W dual secondary transformers if possible. They will make quite a big difference.

I am thinking of doing up my 2nd P3A board with Sanken transistors and a more robust power supply.

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PostPosted: 08 Nov 2010, 18:40 
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You should try the same layout and components I used Dinesh, especially carbon comp resistors, the 1-2 watt ones are the best in signal path, but make sure you match them, as you know, they like to drift. ;)

I was thinking of two 160VA or 225VA Hammond toroids, but I don't think I can afford two at a time, they can get quite expensive but it would be so worth it.

Good luck with your second build, and BTW, I decided to sign the guest book on the ESP web site. I first found that web site when I was in Junior high school and always wanted to build the P3A amplifier for many years because of it's simplicity. :D

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PostPosted: 20 Nov 2010, 09:41 
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Hi Crazzy,

Did you manage to test the amp at a higher voltage? My P3A is sounding better and better everyday, and is really enjoyable to listen to. I have 2 more spare boards !!

I measured both channels and the bias is still rock solid . Meter shows 50mV on right, 51mV on left.

Rod also has the P101 which is mosfet based, but for now, I am all for transistors !!! :mrgreen:

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