ESP P3A component recommendations

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Hello everyone...

I'm interested in building a P3A to power a pair of Whatmough floorstanding loudspeakers in my lounge room.

I've built a few amplifiers kits, most recently the 41hz AMP6 which is powering my computer speakers. This is the first time I've had to source my own components. Note: I'll be ordering Rod's PCB.

After doing some reading here there seems to be a whole range of different suggestions for output transistors and passive components.

I'd really appreciate a "Bill of materials" consisting of good quality but not exotic components that will result in a great sounding amp. I'd prefer to buy everything from a single source such as Digikey or RS electronics since shipping to Australia is very expensive.
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When you buy Rod's PCB, you receive the circuit diagram and BOM etc. support documents with it. That's his product and details are discussed on his ESP forum.

There are many P3A cloning attempt threads here and people select what they think are good or better parts for the duty as it is an old, inexpensive, well known and understood design, as Rod indicates in his description. His current BOM is copyright, like the schematic and any site information. Posting that here is in violation.

However, plenty of people will make guesses and suggestions for you assuming the circuit diagram currently shown is actually the same as the one the current PCB is intended for! Read the notes re: the illustrative schematics shown on the site. What you see in the product descriptions may not be quite what you get. Many would just look at the pics and buy what they identify from catalogs or on-line. With a little practice, most guys here can identify common parts in seconds.
Instead of going in the vague territory, why not build a time tested and survived Leach low TIM amp. It gives very good mids and highs and if set for higher Iq of 150mA, will be good at bass also. Documentation and pcb files are available on the net.

Gajanan Phadte
Hello Ian, thanks for your reply. I recently stayed in Coffs on the way back to Brisbane during a drive down to the Hunter Valley. Lovely place.

I purchased Rod's P68 subwoofer amp board several years ago (never completed) and gained access to his secure website at the time. The construction notes for all his projects are listed there, and I've taken the liberty of looking up the P3A BOM, which details the component values, but not brand recommendations (e.g. I've seen references to Vishay resistors).
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It may sound like terse general advice but resistor brands are unimportant. Types such as metal film, metal oxide, wire wound, low inductance wire wound are. The same with capacitors. Just don't buy from suspect sources where substandard product or alleged unobtanium is offered at very cheap prices. You could purchase any type on sale at Mouser, Digi-key, E14, RS etc. and you will get good quality that meets specification.

Often capacitor types don't overlap with many different suppliers so quoting WIMA polypropylene is nothing other than to say it's MKP etc and box format. Panasonic make similar product but in powdercoated form like Sprague "orange drops".

The difficulty with capacitor types is size difference. You must check at least hole spacing against lead spacing for Radial types and this dictates choice. Near ideal caps like polypropylene film, are about 10 times the size of mylar metallised film caps which in turn, are more than 10 times the size of electrolytic caps, so interchanging types is seldom an option.
Can I suggest the following inexpensive cap types to begin with:
MKT: any, but use highest voltage option that will fit, MKP: use WIMA.
Electrolytics: Panasonic FC or FM in small sizes, THSA or similar for main power rail reserves. Frequency compensation caps can be NPO ceramic, Mica, Polypropylene film, or Polystyrene film according to availability, budget etc.
You can be sure others reading this won't find their favourite types here and will post them too.

Real improvements in sound quality by component choice are best targeted at certain areas of the amplifier rather than a shotgun approach. Follow Sakis's P3a comparison threads for some hints after you have built it in standard form. He does get it to "sing". Few that I know, even chock full of very expensive parts actually do, IMHO. The testimony to that is that their amplifiers languish in the cupboard - not in daily use.

Without proper comparison though, you'll only be guessing and hoping too.
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...but you will be surprized to know that the oldy is shown to be a winner when SIMed, by one diyer here......
I know the designs quite well and have seen and heard several but not built them myself. Yes, I agree that these are very good amplifiers but I would not suggest starting there.

They are a little too big, complex and expensive for newbs, In my view. If we consider larger, more ambitious designs like this we might also consider the forum "Honey badger" design by Ostripper. That is also a good design that performs and sounds very well and has the inexpensive support of the forum management for PCBs and documentation also covering protection boards, power supply etc.

As a step up from CMoy-like toys and minimalist class A designs, I think a simple 60W class AB design is appropriate. The problem is the choices and compromises designers and builders often make within that type description. Some of the worst audio I've ever heard came from this type of DIY design area too. A properly built P3A is in another world, though. It can deliver sublime audio for very little money and its high popularity is a fair testament to it. Just yesterday, I counted 4 P3 threads on this forum's first page.
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Good advice - ta. One last question: do you have any specific recommendations on the type and/or brand of transformer to use? I'm putting together a shopping list at Mouser and was thinking a 25-0-25V toroidal would be well suited?
The type and voltage is fine for 50-60W 8R and more into 4R. A 160-250VA size should be ok, depending on the speaker load. We don't know your Whatmough model so may be able to check if you post it.

Using FEDEX (compulsory with Mouser, Digi-key) for a heavy item like the transformer, from the US, may be more expensive than you anticipate. You can also buy these at Altronics outlets here and possibly keep freight down to $40 for the balance of items.
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I have the Performance P31 series, which according to Whatmough, have a nominal impedance of 4 ohms and 240 watts continous power handling. The speakers are fairly sensitive and I find myself setting the volume control on my Marantz AV receiver (100wrms per channel) at no more than 1/4, which produces the loudest tolerable levels.

I'm intending to use the suggested MJE15034/5 - sourced from Mouser - unless you have a better component recommendation. Despite using these higher power output transitions I planned to use a smaller 25-0-25V supply since that seems to be the recommended maximum for 4 ohm loads.

I would like the flexibility to use this amp with other loudspeakers with the more common 8 ohm nominal impedance.

Would you say a single 160VA toroidal would suffice, and if not, would 300VA or 500VA be more appropriate? Alternatively I am considering 2x 160VA units and a dual mono configuration.
sorry to say that i think that the question is pointless from the point that you don't have the ability to compare A to B

My thread and/or advice will be limited as a personal opinion only, probably other peoples opinion will be alike .

In 6 years of currently building P3A i have tried almost anything now days i am spooked to replace the drivers with tubes ( just a wild idea don't have a clue if even possible to do so ) ...

Here is a few things that i will think as a ""must "" given the original pcb .

--Do not use 150xx drivers ...eventhough pretty rugged sound very hard even BD139-140 will sound better i use often BD 829 -830 but the best are Toshiba's 2sA-2sc drivers

--match your ltp pick any you like from BC5XX series and you can pick also other models for lower voltage better noise etch etch, but match them closely

--- don't be afraid to run LTP transistors close or above operating voltage if it blows it should be fun but if it doesn't it will play a bit better than the standard transistors given in the original circuit .

---for the outputs you can use anything you like 3055-2955 will also play but will not sound that good i currently use 2SA1302 2SC3281 cause i have them available ( totally unobtainable ) but 1943-5200 will also do fine and sound different 21193 series i have never tested but i presume is a quality product and there is many many more .

--be aware of fakes get semis from trusted seller

--very critical parts are the miller caps in VAS stage and lower driver No way you use ceramics there ... Blue ones rated at >500V better than standard ceramics is the cheapest choice while i go with mika 2%

--very critical is the value of the miller capacitors and the lower possible value like 68 will alter the performance of the amp for the best but alter the safety margin for the worst ...To be able to play there you need to verify the changes with instruments after the choice of VAS and Drivers is all ready done . Suggestion for a NB : stay to the original value .

--- after you are done you may find out small changes depending on the input capacitor each and every one of them will add or remove something from you sound ...yet again don't forget that the original pcb will not accommodate exotic sizes

--For the input i use yellow Thomson MKT 2.2ufd times 2 parallel reversed polarity and i am very happy with them

There is other things that can change the performance of the amp for the best ( to my opinion ) but this will require other type of pcb .

Kind regards
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Hi and thanks Sakis, 'sounds good to me. That's an interesting idea about Thomson MKT caps. Is that an MKT type as in a Polyester/Mylar film cap? Why did you consider reverse paralleling them, if you can be certain which direction they are wound?

As I suggested, you can use even a single 160VA transformer but considering the 4R load, If 300VA is your only other option, it may be slightly better, even if it is overkill. Your idea of building as a dual mono amplifier is going to be better anyway and 160VA for each will be plenty of power. Don't even think of using 300 or 500VA transformers for a single channel amplifier - It's just more size and cost than you are ever likely to need.
well the Thomson capacitors probably are only marked as Thomson i think.
Found 500 pcs in one shop here in Athens try 10 of them and for some reason sounded better than wima or Philips that i had available to put next to .

2.2Ufd is not enough and reversed parallel also sounded better than standard parallel , you may ask why but i don't have the answer

Notice that the specific cap is 63 volt rated with 5mm pitch so you dont get size issues .I gave some to a friend to use in his preamplifier and amplifier and he come back to me also surprised from the sound of them I have no datasheet or other data to support my opinion i only talk about the things i listen .

kind regards
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Hello Ian

I have received my PCBs from Rod for the P3A, and P33 speaker protection circuit, which I intend to utilise for my project.

After perusing this forum the past week I have also purchased Peter Daniel's Universal PSU boards (

The Mouser order has been despatch, including:

  • Panasonic FC capacitors where electrolytics are specified
    Nichicon KG Super filter caps (2x 4700uF 63V per rail)
    C1 = WIMA MKS2 100V polyester
    C2 = WIMA FKP2 100V polypropylene cap
    C7,C+/- = WIMA MKS2 250V polyester

I took your advice and decided to source the heavy items elsewhere. Jaycar have 160VA toroidals in both 18V and 25V secondary windings? Which would you recommend? I've decided to use a single transformer to save space.

0.37C/Watt heatsink sourced from Conrad (see:

Do you have any suggestions for reasonably priced cases?

Many thanks.
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Case size is decided by the heatsink, which at 300mm is between a standard 2-unit high rack case size that you can buy locally, and one of those tidy little HK Ebay sizes. This guy has the widest range I've seen but, with freight charges they arent particularly cheap - no case is cheap unless it is poor quality. Times have moved on and rack case shapes just don't impress buyers any more so I look for cases around 350 wide and of course, everyone wants a slab of thick aluminium for the front panel so that the volume control or switches can be recessed and the skirt lie flush with the panel. You get no refinement with cheap rack cases and for similar money you can have a near pro. quality with the recessing and the matching controls if you wish. I need good appearance so this is the easiest suggestion and suits anyone without a workbench and good tools since virtually all holes are neatly precut, milled or drilled.

The recommended power rail voltage range is from 30-50 volts DC, IIRC, so the 25-0 + 25-0V type is fine, giving ~35VDC rails. That should give around 55W/8R which is quite enough to shake windows and get evil looks from neighbours. Work on your boards whilst waiting for a case, It may be worth the effort for a slick appearance if you plan to use this in the home.
Hope it goes well :)

Edit: Obviously, you now need a single 300VA transformer for 4R speakers and 35V rails.
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One warning concerning ESP boards. ESP boards do not have plated through holes so will not tolerate removal of components and soldering of the alternative components many times. If you are not very careful and have too powerful soldering iron pads can lift easily. My recommendation is to choose components carefully and what you solder first should stay there. Follow advices by Sakis!
Thanks for the tip. I've gone with the standard component values recommended by Rod (using the highest quality caps and other components I could find that will fit). That way I will have a baseline to compare against if I decide to buy another PCB and experiment with different values.
Hi again

I've drilled the heatsink, chassis plate and panels, and I'm nearly finished...

One problem I have is locating "quick disconnect" PCB terminals that will fit on the board. This is what Rod recommends but I can't find them anywhere (including Jaycar).

Any ideas?
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