Elliot P3A question...

[JoeBob]

Well, I'm going to build a Rod Elliot P3A amp as soon as I match all my transistors but I've only got one question... In the P3A article he says that 300VA would be fine for a pair of amps. Does everyone agree with this? It seems rather low, and I'll be running it with a 4 ohm load and I'd obviously like as much power as possible.

Are there any other sudjestions on the VA of transformer I should use per channel?

 

[Jocko Homo]

Do I need to sell you a transformer too? [joke]

Jocko

 

[JoeBob]

LOL Actually I already have a PSU for it, 1500VA 120000uF +/- 35V, just wondering how many channels I could power with it...

 

[Jocko Homo]

Build it and find out. Best way to learn. Probably more than you would think is the answer.

Jocko

 

[JoeBob]

Hmmm... Actually, that's a really good answer. I think I'll do just that..

 

[tiroth]

JoeBob, my amp has 5 channels on a pair of 400VA xforms. This may be low by the standards of the forum, but it works well for me. I'm only shooting for 60W into 8 ohms though.

 

[Vivek]

I am using a 600VA transformer for the Project 3A amp.

 

[paulb]

I'd be more worried about the dissipation of the output transistors, especially into a 4-ohm load. Rod has some very specific recommendations about voltage maximum for 4-ohm loads. You can parallel more output transistors; I know he suggested this in the previous (project 3) version.
I'm very pleased with this amp, JoeBob, when you're done see if you can tell the difference with the LM3886 one you built. I can.

 

[NickC]

i built the 3a with 280va 28 0 28. and used it to power 4 ohm as the amp was bridged for 200 watts total. works fine. heed paulb advise though very important for 4 ohm even rod has said something about the transistors.

 

[JoeBob]

I do intend to parallel the output transistors, better safe then sory.

 

[NickC]

i want to increase power. Can I increase rail voltage for a 4 ohm
from 35v to a bigger value. What are the extra circuit should i add other than parrelling more transistors.

 

[kec]

I'm using 30-0-30 160 VA (Avel Lindberg Y236505) for monoblocks. I emailed Rod about this and he said this was fine.

-KC

 

[tiroth]

NickC, it is important to pay close attention to the SOA of your BJTs--you'll need to use MJ15003/MJ15004, 2SC3281/2SA1302, MJ21193/MJ21194, or other compatible transistors for rails>35V.

 

[trwh]

In my P3A amp, I'm using a single 500VA 30-0-30V transformer for both channels, aiming for about 100W into 4 ohms each side. I use two sets of output transistors in parallel as I have 4 ohm speakers. This amp comes highly recommended, btw.

 

[NickC]

tiroth, apart from soa of transistors do i need to add in any inductors in series of the output for stabillity. i plan to increase the voltage to maybe 42 volts

 

[tiroth]

Rod doesn't specify the need for an inductor at any rail voltage. My rails are actually at about 45V at idle, and I haven't run into any stability issues with the 0R47 output resistors and the specified zobel network.

I've put a page up that has some info on building the P3A, and the supply that I am currently (re)building.
http://www.anidian.com/audio/construct/p3a_1.shtml

 

[paulb]

Nice construction guide. I really admire people who take the time to pass on their experiences for others' benefit. Maybe when I retire I can do the same
Btw, the link for Page 3 seems to be missing.

 

[tiroth]

I'm going to throttle my ISP. They appear to have reverted to a backup from a few days ago, wiping out my updates.