P101 High power HiFi Amp

        I built an Elliott Sound Products P101 Amplifier a few years ago. I decided to build another using the high power version and bought boards last year. But I kept pushing it aside, now I have time and some budget to continue this project so on it goes.

        I bought heatsinks from HeatsinkUSA (10.080" profile) and used those to dictate the chassis size. Bought some more  aluminum plates and other materials, ordered some more quality parts online for the boards.

Work starts in the garage. Brought out the band saw and materials and started scattering aluminum dust all over.

Top plate is made from 2mm thick alu plate cut to 11" by 11"

The bottom, front and back plates also cut. Those are 3mm alu plate, Front plate is 16.5" by 4", rear plate is 11" by 4".

Panels mocked up.

All panels cut up so back to the workshop upstairs.

Several hours later of drilling and tapping and the chassis is finished.

I left a gap between the front and back plates and the heatsinks as ventilation holes for the internals. I didn't fancy drilling a lot of holes across the top and bottom plates.

Gnd return plate (1mm copper sheet) and acrylic plastic capacitor bracket.

Plastic bracket placed on top of caps.

Added threaded bushings under the 0V ground plate for bolting the return wires.

Ground plate positioned on top.

Several cuts made to prevent the copper from sucking all the heat off the soldering iron during soldering.

Caps soldered into place

The soft start board will be mounted on the back plate (but lower down) with tall standoffs so that the power inlet and outlet can be positioned behind the board.

Rectifier bridge on each side.

Mock up of amp layout. Still to add areP33 speaker protection circuit PCB, pre regulator board (for the P33 since it's not designed for 70V operation) and relay boards on each side near the P101 boards.

        More details to add as the project progresses.....

        15 Apr 2012

        Work resumed, drilling the front and rear panels to accommodate switches, boards, connectors etc.

Rear panel removed and planned for layout.

Holes to be drilled are marked.

After the holes have been drilled, the scroll saw is used to make the rectangular openings for the mains connectors.

One hole done...

Both openings done. A little cleaning with the file and it's good to go

A step drill is used for the bigger holes.

Connectors mounted

Thesoft start and speaker protector boards mounted.

There is just enough room behind the board to clear the mains connectors.

And there is just barely enough room between the soft start board and main reservoir caps.

Power switch with built in LED wired up.

Switch mounted on front panel. Still waiting for the stepped attenuator to arrive.

Back panel test fitted.

Once the mains switch and IEC connectors were wired up, a quick test to see if the soft start board works.

The wirings have been planned to be routed near the bottom of the rear panel so that it can fold down for easy servicing when necessary.

Another shot of the boards on the rear panel.

        23 Apr 2012

        More work... Support boards and wiring harness are made. Let's start with the amplifier feet.

I was thinking of where to look for decent looking feet and ended up in the cabinet supplies section in the hardware store. Found one cabinet handle style that looked like it will work.

Stuck on some felt discs and you get nice looking amplifier feet!

And it comes with M4 thread bolts. I had a bunch of shorter ones so I didn't have to cut the included long screws.

The height is just right too.

I also changed the front and top panel screws and countersunk them for a cleaner look.

What do you do if you can't get FR4 PCB in single sided? Get a double sided board and peel one side off. It costs more but I didn't have a choice.

My exposure bed made from a dead scanner/printer combo.

Used four 8W flouro tubes and added a switch and timer.

After developing and etching, I apply some solder paste and heat with the iron to coat the bare copper in solder.

Drilling the PCB...

Used a diamond cutting disc to separate the boards.

The pre-regulator board mounted beside the P33 board.

Populating the P101 boards.

The various boards temporarily mounted so that wiring can be done.

For connecting various control boards together, I used 22ga wire with connectors on all ends for easy removal/servicing of the modules.

For high current wiring, I used Russian Tchernov Audio Cuprum speaker wire.

Removed the outer jacket since it is too thick.

All done with properly crimped connectors.

Wiring harness for the control circuitry.

Connectors insulated with heatshrink tubing.

For the signal lines, a connector is soldered to a PCB edge cut off from a PC peripheral board.

Shielded wire used for input connections stripped and tinned.

..... And soldered to the connector.

Add a bit of hotmelt glue....

And some heatshrink and you get a nicely terminated cable end.

The connector is used for the RCA input lines.

P33 bodge circuit. This was done since the P33 relies on the main supply caps discharging to apply signal delay during turn on. Since I have a largish capacitor bank, it would take a while to discharge. This mod allows delayed muting at turn on even when the supply caps still haven't discharged.

The power switch has a red LED. I wanted to try another color....

And tried white, until it popped because of the way the SS board powers the LED. I need to do something about that.

P101 still waiting for the last few parts. Once those empty spots get populated, it should sing.

This is how it looks now.


        30 Apr 2012

        I could not wait for the last few parts so I bought temporary generic cheapo parts just to be able to test the amp modules.

The stepped attenuators from Ebay arrived so they go in first...

They look like an ordinary pot from the outside but are built with 1% MF SMD resistors and have 21steps. They seem to work pretty good.

Added an aluminum knob. Still deciding if I'll keep the black or change it to silver. Black matches the power switch though.

P101 boards populated and tested. I used cheapo electrolytics and 50V ceramic caps. The replacements will be Elna and Panasonic electrolytic caps and 630V C0G ceramic caps from TDK.

View of the generic caps.

First power up at full rail voltage. All worked first time!

Added a ground link to connect star ground to chassis.

Signal wire running along the bottom with cable anchors.

Same with the power switch line.

Signal wiring after the attenuator is routed close to the aluminum front plate for shielding.

All buttoned up.

A quick and dirty setup for a quick listening test in the workshop.

Even with the P101 boards right beside the transformer and wires running all over, the amp is very quiet with a slight hint of hum with my ear right at the midbass, and a very slight hiss coming from the tweeter (also with my ear against the tweeter) but it was in the wee hours in the morning so the environment is very quiet. Sound is already pretty good with a bit more bass than my previous P101 amp but with a stiffer chassis and no fan, this one is dead silent mechanically.


I then decided to test it with more demanding speakers. Dad's Mordaunt classics. I noticed the right channel distorts earlier than the left. It also runs much hotter than the other channel and after seeing smoke come off one of the source resistors, I suspected oscillation. I took out the scope and attached to the outputs. (yellow = left output, blue = right output) It is immediately apparent that the right channel clips much earlier. The amp has +/-70V rails so clipping at 5 volts is TOO early!

I took out the faulty channel out of the chassis and measured that there is only 0.7 ohms from the output connector to the heatsink. Took the PCB out of the heatsink and this is what happened. A metal shaving blew a hole through the Kapton tape and shorted the mosfet source to the heatsink.

I replaced the very thin Kapton insulator with more robust mica sheets and it's all good to go.

Here was my test rig. Trouble shooting in the bedroom.

The amp sounds much better after the fix and the hum and hiss is gone! The amp is totally silent now.

        01 May 2012

Had some more time today with the help of my uncles and we finished the outside of the amp.

Because everything could be disconnected without using a soldering iron, Removing the panels were easy with some basic tools.

We wet sanded the front, back and top panel with coarse grit paper then applied clear coat.

The rear panel had connectors and I used rub on transfer lettering after a light coat of clear. Then another coat after the letterings were applied.

The panels drying up ready to be re-installed.

Back panel connectors re-installed.

We added a rather thick coat of clear on the front to make it glossy.

Back side of the completed amp.

Front of the amp. I decided to keep it plain without letterings. Besides, there is only the power switch and volume control.

A couple shots of the front panel gloss.

A look around of the amp.

I also trimmed the 10mm square aluminum bar so that it's less visible from the sides and provides a little more vent area for heat to escape.

I wanted a uniqe colored power LED light. I found this LED from a scrap PCB. Here's a couple pics during testing in the bedroom.

With flash... The LED color looks closer to real life but the panel brushed finish looked worse.

        21 July 2012

Digikey goodies have arrived. (also has parts for other projects that's why there's a lot of bags)

Heatsinks removed to gain access to amp modules.

New parts coming in. Elna Tonerex, Panasonic FC, TDK FK series 630V C0G and Nichicon Muse for input coupling.

Jellybean parts taken out.

Amp boards cleaned and reinstalled in heatsink -ready to put back into chassis.

Putting the heatsinks back.

Last look before buttoning up.

        How does it sound? Now that I've been using it for a few weeks with the new parts, we tested it with various sources, Schiit DAC, Monitor Audio floorstanding speakers and Tchernov cables. Before the upgrades, the amp already sounds very clean and transparent. You know it has a lot of reserve due to the way it grips the speakers in the bass/midbass regions. It doesn't add any character to the sound. But after replacing the cheap parts with better quality ones, the sound now is no comparison to how it sounded before. There is very good clarity in the treble. Midrange is very smooth. Imaging of instruments separated and there is much greater depth to the stage. You can feel that there is a lot of headroom because it sounds very clean and no harshness even at high levels and the details are still there even at low volumes. I'm very pleased on how it turned out, much better than I hoped.

        For my own system, it is powering B&W 686s. Source will be a PC through a Schiit Bifrost DAC with USB option. Preamp is still undecided. Speaker cables and interconnects are Tchernov Audio.

Page updated and copyright R.Quan © 14 Apr 2012.