Building a Rod Elliot ESP-P3A Amplifier

[mikte15]

After building a pair of speakers that sounded very good and having reasonably good success restoring vintage audio I was anxious to build my own amplifier from scratch. Rod Elliot’s Elliot Sound Products (ESP) offered an amplifier kit based on a single board. His site gives instructions on how to build the kit for a 60-70 WPC amp. Since I learned most of what I know about audio electronics by reading articles on his site I thought I would give it a try. I bought the board kit (P3A) and his speaker protection kit (P33), then it was up to me to design a case and power supply for it. After several different case ideas based on extruded aluminum and other materials laying around the shop I work at I settled on this design.

 

[mikte15]

I had some friends who ran the CNC machining centers to machine the case parts. I machined all the internal bits.

There are two because my buddy John wanted to build one as well.

 

[mikte15]

Power supply caps mounted on G10 board. This is where I varied from the original design because the original didn't provide a location for the speaker protection relays.

 

[ConradH]

Wow! Nice work.

 

[mikte15]

Building up the driver board.

 

[mikte15]

The P33 protection board - I had a bit of trouble with this and it wasn't the fault of the board. It didn't like the snubber caps around the rectifiers.

 

[mikte15]

In this picture the case has been fully anodized. The output transistors sit on copper bars for maximum heat extraction. The transformer is a Plitron 25-0-25 toroid.
Above and below the filter caps are industrial relay sockets that accommodate a pair of 24V relays.

 

[mikte15]

Here's the finished amp putting hours in on the test rig, driving a pair of Polk Monitor 10's quite loud!

 

[Artie]

Sweet. Nice job.

 

[drabina]

Very nice project. I like the case. How do you like the sound? I have parts for the P101 build but no enclosure yet. Unfortunately, I am not as skilled with design so I will have to fork over $$$ for an enclosure.

 

[rothwellaudio]

... I was anxious to build my own amplifier from scratch.

If you wish to make an amplifier from scratch, you must first invent the universe.
I'm paraphrasing, of course.

Anyway, very nicely done. What do you think of the sound?

 

[mikte15]

Thanks all for the nice responses!

The sound as far as I can tell rivals my main systems even though I have to account for the fact that the test setup I'm running it in is a very poor acoustical position in my house. Everything I've played in that location has a pronounced bass resonance.

But another pleasant surprise is the pre-amp I picked up for the amplifier. Last fall I got an Apt Holman pre-amp for an attractive price - it's wonderful!

It's a fairly full featured amp and I liked that it has the ability to reverse the phase. I've turned down the base control to compensate for the crazy resonance.

 

[HypnoToad]

Great work, the case you made looks fantastic, I wish I had such metal working skills. There is something really gratifying about making something yourself.

 

[mikte15]

Great work, the case you made looks fantastic, I wish I had such metal working skills. There is something really gratifying about making something yourself.

What's even better is when you're a design engineer. You get come up with cool designs and skilled machinists make the parts for you.

Here is a real big example of that: I'm the guy in the light grey shirt. The automation is my design but a whole bunch of very skilled technicians made it work.

https://www.linkedin.com/feed/update/urn:li:activity:6362256489930981376

 

[HypnoToad]

Here is a real big example of that: I'm the guy in the light grey shirt. The automation is my design but a whole bunch of very skilled technicians made it work.

Looks a bit better equipped than my garage/workshop.

 

[Scott75s1974]

This looks amazing. The case design is awesome.

I have a question about ground wiring-as I'm contemplating building one as well.
My understanding is that the center tap of the transformer, the chassis, the power line ground, the outside of the RCA jacks, and the ground side of the speaker jacks are all connected.

I just wanted to make sure of this, since getting this wrong would be very bad.

 

[avionic]

Nice work. Now go for the P-101..

 

[mikte15]

OK, where to start?

The transformer has two secondaries (4 leads total not including primaries). Each secondary pair is connected to the AC leads of a bridge rectifier. There are 2 rectifiers, one for each rail polarity (+ or -).
One rectifier output goes to either the positive or negative capacitor lead depending on which side the rectifier it's on. The other rectifier output lead goes to a copper strip ground between the two capacitor banks.
The - (minus or black) speaker lead comes back to the same capacitor grounding strip per Rod's instructions. The grounding strip is then connected directly to the grounding lug of the IEC socket. There is another chassis ground that can be seen in the lower left of the case back in the model image above. This is the 'star' ground, all the grounds from the circuit boards go there. It is also connected to the IEC socket ground. There is no daisy chaining and I hear no hum.

Hope this is clear.

This looks amazing. The case design is awesome.

I have a question about ground wiring-as I'm contemplating building one as well.
My understanding is that the center tap of the transformer, the chassis, the power line ground, the outside of the RCA jacks, and the ground side of the speaker jacks are all connected.

I just wanted to make sure of this, since getting this wrong would be very bad.

 

[avionic]

, the outside of the RCA jacks

If your going to build the same amplifier. Buy the boards from Rod.You will then have access to his build instructions. Almost idiot proof..The RCA input jacks will likely go to a signal ground point on the circuit board. This is isolated/ decoupled from the "star ground" . Or at least it is on my P-101. Which sounds awesome..

 

[avionic]

Very nice project. I like the case. How do you like the sound? I have parts for the P101 build but no enclosure yet. Unfortunately, I am not as skilled with design so I will have to fork over $$$ for an enclosure.

I went this route at the time..
http://www.par-metal.com/product-rmc-12series.phpV

http://www.par-metal.com/heatsink.php