Class A power amplifiers [Archive] - The Art of Sound Forum

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Reid Malenfant

11-12-2010, 20:05

This is a project that has literally been coming together for about 22 years :lolsign: Ever since i started working at a rather large electronics firm back in 1988 i have gradually been gathering components together to do just something like this ;)

I'm pretty sure that anyone who has experienced what a real class A amplifier can do with a decent set of speakers is never likely to be satisfied with anything less & i guess i'm one of those people. I have built a good few solid state class A power amplifiers of different design, only one pair were from a design other than my own which is here:-

Apologies as it doesn't give the component values, but it's a 60W RMS 8ohm class A amp (inverting).

http://i939.photobucket.com/albums/ad240/speakermark/Class%20A%20power%20amplifier/class-A-power-amplifier-with-60-watts-output.gif

This was actually the first one i built & it's quite a decent design with fairly low overall feedback due to the local feedback used to cut each stages gain. From what i remember there is 20Db (approximately) of global feedback. In contrast a class B amp may well have over 20Db @ 20Khz which will result in vastly more in the midrange & low frequencies. Class B amps need this to attempt to eliminate the distortion caused by the output stage due to the output transistors switching on & off ;)

In a class A amplifier the output transistors should never turn off & because they don't the distortion caused by the output stage is very much lower. The big problem though is that class A is so inefficient it's a joke. Theoretical maximum efficiency is 50% in a push pull output stage but with component losses 40% efficiency is nearer the mark or less. Here's the rub though, it's only 40% efficient at full output IE in the case of the above amplifier at 60W RMS output :eyebrows:

Taking the above example again to produce 60W RMS in a push pull output stage the output transistors need to have a bias (quiescent current) of 1.936 Amps assuming an 8 ohm load. In reality it's best to assume that the speaker (rather than an 8 ohm test resistor) is connected to the output & the impedance of these varies. So we'll assume the impedance drops to 6 ohms & set the bias current to 3 Amps. With a +/- 40V supply we are now dissipating 240W per channel without playing any music :eek: If i remember correctly the above amplifier was actually good for 75W RMS 8 ohms before clipping & this was probably the reason that it was suggested to set the bias current to 4 Amps. So how does a couple of 320W musical heaters sound?

The good thing about class A amps is that as you increase the volume level they actually cool down a bit as some of the power dissipated accross the output stage is actually fed to the speaker :lol:

There are ways of making things more efficient.

As i'm not the richest person in the world i'm going to make these amplifiers as efficient as possible. One reason is because they are going to be quite powerful & the second is because there are going to be 6 of them.

As long as the output transistors never turn off the amplifier will remain in class A operation. Only one manufacturer that i know of actually designed & built a much more efficient class A amplifier, but they made a hash of it :doh: In typical Japanese style they used a shed load of feedback on the thing & killed the sonics in the process, enter the Technics SE-A1 @ 350W RMS 8 ohm per channel. It cost a fortune & weighed a ton & probably sounded unremarkable. Here is the circuit diagram (as far as i know)..

http://i939.photobucket.com/albums/ad240/speakermark/Class%20A%20power%20amplifier/TechnicsSE-A1.jpg

What you have there is effectively two amplifiers, one class B & one class A. They are effectively in parallel & how it works is the class B amp output is connected to the ground of the class A amps power supply (which is floating). Because the class A amps PSU is only +/- 5V the dissipation is low. It's the class A amps output that is connected to the speaker though ;)

Here is a more simple block diagram:-

http://i939.photobucket.com/albums/ad240/speakermark/Class%20A%20power%20amplifier/ClassA.jpg

How the low voltage PSU tracks the output:-

http://i939.photobucket.com/albums/ad240/speakermark/Class%20A%20power%20amplifier/Waveforms.jpg

Finally a japlish explanaition :eyebrows:

http://i939.photobucket.com/albums/ad240/speakermark/Class%20A%20power%20amplifier/workingmethod.jpg

I'm not sure where or who designed these but here is a similar take on the very same thing with a few circuits :)

http://i939.photobucket.com/albums/ad240/speakermark/Class%20A%20power%20amplifier/audiotek69_supera_20SUPERA.jpg

http://i939.photobucket.com/albums/ad240/speakermark/Class%20A%20power%20amplifier/ClassABcleveramp.jpg

Here is a single ended ouput version :smoking:

http://i939.photobucket.com/albums/ad240/speakermark/Class%20A%20power%20amplifier/zu9.gif

Been there & done that.

Well i have also sucsessfully built a couple of these weird class A amps & like the Technics circuit i used two amplifiers per channel but unlike them i used a single ended output stage :) Only problem was that as i required each amp to have vastly different feedback (much lower in the class A section) there was a difference between the phase margins & phase shifts at high frequencies that i wasn't entirely happy with. Still i have a couple of 50W RMS 8 ohm single ended class A amps that sound rather good & are efficient. They'll also happily do 95W RMS 4 ohms again in class A. I just went to town on the things & built in stupid stuff like speaker sensing so it automatically selected the right bias current on power up & silly power meters etc :mental:

What i'm planning will just be as simple as possible with the exception of different bias settings for different loads. I have just about everything i need except for aluminium sheet & 6 dirty great big transformers for the class B amplifiers. I'm not going to list what i have here but I have all the output transistors for both amps (A & B) storage capacitors for the PSUs & all the small signal & medium power transistors as well as 36 x 0.5C Watt heatsinks (6 per amplifier).

These are drilled for 2 x TO3 transistors per heatsink:-

http://i939.photobucket.com/albums/ad240/speakermark/Class%20A%20power%20amplifier/Heatsink.jpg

I'll be using 6 x MJ15024 & 6 x MJ15025 per channel as the main dissipating elements in the class B section, these are 250W rating per device. In the class A section i'll be using 3 x MJ11032 & 3 x MJ11033 per channel. These are 50 Amp 300W darlingtons so well over rated :)

Improving efficiency further still.

As i'm not a goldmine i tend to use what i have kicking about. As i happen to have a couple of boxes of BHC 10,000uf 40V screw terminal capacitors i thought i'd use them in the class B PSU. The astute or knowing among you will know you can't generate 250W RMS 8 ohms with a +/- 40V supply (unless bridged).

So the class B amp won't be class B at all, it'll be class H or if you like rail switching. These are normally used in high power PA amps to increase efficiency & that's exactly what i intend to do. The problem is they tend to introduce spikes in the output of the amplifier when rail switching & even though i'll have a class A amp on the output which should sort it out i'm not that sure it'd be the best thing ;) So what i intend to do is use the MJ15024/5 as cascodes & the actual output transistors of the class B amp will be TIP35/6. The cascodes will not only seriously reduce the distortion from the class B amp but will shield the output transistors from the effects of rail switching & get rid of those glitches on the output :) Here is a simple block of what i intend to do. Notice that the class B (H) output & class A output stages have a gain of 1. I can use different amounts of feedback for each stage & only the class A output will have it's output fed back to the front end. This is an NDFL or nesting differential feedback loop & the same as what i used on my 50W single ended amps.

http://i939.photobucket.com/albums/ad240/speakermark/Class%20A%20power%20amplifier/LowDissipationClassA.jpg

Like my other stalled projects it'll be a little while before i get cracking on this. I need a room to work in & i reckon a few months will see me there with a clear room to get on in. Meanwhile i thought i'd dump this lot on here just in case i missed something. I can't think of everything & all this cobblers is floating around up here in my head so i guess it'd be easy to mess up.

I guess that gives a bit of time for any holes to be picked at & solutions thought through :eyebrows: Hope i haven't bored you all to death :lolsign:

Puffin

11-12-2010, 20:48

ZZzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz :lol:

Rare Bird

11-12-2010, 20:55

2 x 180,000uF! they would cost a fortune :eek:

anthonyTD

11-12-2010, 21:03

interesting stuff mark!
Early transistor circuits had quite a few similarities to valves, even down to using output transformers.
The first circuit you provided reminds me of that.
Anthony,TD...

Rare Bird

11-12-2010, 21:04

interesting stuff mark!
Early transistor circuits had quite a few similarities to valves, even down to using output transformers.
The first circuit you provided reminds me of that.
Anthony,TD...

Quad '50' used output transformers.

Reid Malenfant

11-12-2010, 21:06

ZZzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz :lol:
:eyebrows: Well you are still alive :)

2 x 180,000uF! they would cost a fortune :eek:
Got them already Andre, 12 x 120,000uf caps & a box load of 15,000uf caps ;) Don't forget they only need to be low voltage so not so expensive after all :)

The 120,000uf caps are 15V (well over rated & bloody huge i might add!) & the 15,000uf are just about the same at 10V ;) Supply will be between 4V & 5V per rail +/- so not a problem & all here already. The 120,000uf caps are each 3" diameter & just under 6" in height :eek: They'll fit in though - just..

I guess i have actually spent about £800 so far getting all this stuff together, like i say though it's taken many years :rolleyes: I have a feeling i'll be spending getting on for that again to complete this. Which is bugger all in reality :eyebrows:

For those that have posted after i started to reply to Andre there will be no output transformers, horrible things :ner:

Jonboy

11-12-2010, 21:12

there will be no output transformers, horrible things :ner:

My mate has just got a solid stater as above, it sounds very good indeed and very valve like, thus musical :eyebrows:

anthonyTD

11-12-2010, 21:13

:eyebrows: Well you are still alive :)

Got them already Andre, 12 x 120,000uf caps & a box load of 15,000uf caps ;) Don't forget they only need to be low voltage so not so expensive after all :)

The 120,000uf caps are 15V (well over rated) & the 15,000uf are just about the same at 10V ;) Supply will be between 4V & 5V per rail +/- so not a problem & all here already.

I guess i have actually spent about £800 so far getting all this stuff together, like i say though it's taken many years :rolleyes: I have a feeling i'll be spending getting on for that again to complete this. Which is bugger all in reality :eyebrows:

For those that have posted after i started to reply to Andre there will be no output transformers, horrible things :ner:
:lol:
I was refering to the circuit itself!
nothing wrong with output transformers when their designed correctly, also they provide excelent isolation for your expensive speakers when things go tits up further down the chain, unlike horrible directly coupled transistor output stages.:ner::lolsign:

Reid Malenfant

11-12-2010, 21:15

My mate has just got a solid stater as above, it sounds very good indeed and very valve like, thus musical :eyebrows:
Exactly ;) Low feedback & class A = happy bunny. Doesn't matter if it's valves or solid state if each are done right ;)

PS. pmsl at your avatar :lolsign:

Rare Bird

11-12-2010, 21:16

Got to admit i slightly prefer the sound of Quad '50's (Output Transformer) againt the '303' (Output Transistors)

Reid Malenfant

11-12-2010, 21:30

:lol:
I was refering to the circuit itself!
nothing wrong with output transformers when their designed correctly, also they provide excelent isolation for your expensive speakers when things go tits up further down the chain, unlike horrible directly coupled transistor output stages.:ner::lolsign:
:lol: Ok Anthony, yes i do agree that transformer isolation is a good thing ;) But an output capacitor will give the same protection in reality.. Not that i'll be using one :)

These will be over engineed. I have 4.5KW (dissipation) of transistors for each class B amp & 1.8KW on each class A section. They'll run at a cool temperature under normal conditions, i figure the heatsinks will be about 10C above ambient with a 4 ohm load & 11 Amp quiescent. Only 5.5 Amp for 250W 8 ohm allowing for a 6 ohm load..When driven though this will increase obviously, but this is a huge amount of heatsinking even for a 500W RMS class B amp. So going to H class with the rail switching will definately keep things cool :)

There will of course be some kind of protection for the loudspeaker if things go wrong :eyebrows:

Reid Malenfant

11-12-2010, 21:35

Got to admit i slightly prefer the sound of Quad '50's (Output Transformer) againt the '303' (Output Transistors)
Aye, the 303 is a class B amplifier though - the same as the 50 ;) With a transformer output it'll tend to filter out a good deal of the upper harmonics of any low level distortion. This might make it sound a little mellower as well as reducing the output damping factor & giving a very slightly fatter bass :scratch:

anthonyTD

11-12-2010, 21:39

:lol: Ok Anthony, yes i do agree that transformer isolation is a good thing ;)
But an output capacitor will give the same protection in reality.. Not that i'll be using one :)

These will be over engineed. I have 4.5KW (dissipation) of transistors for each class B amp & 1.8KW on each class A section. They'll run at a cool temperature under normal conditions, i figure the heatsinks will be about 10C above ambient with a 4 ohm load & 11 Amp quiescent. Only 5.5 Amp for 250W 8 ohm allowing for a 6 ohm load..When driven though this will increase obviously, but this is a huge amount of heatsinking even for a 500W RMS class B amp. So going to H class with the rail switching will definately keep things cool :)

There will of course be some kind of protection for the loudspeaker if things go wrong :eyebrows:
I'm not even going there!!!:eyebrows::lol:
but full respect on your design.
look forward to hearing about it when its finished.
Anthony,TD...

anthonyTD

11-12-2010, 21:43

Aye, the 303 is a class B amplifier though - the same as the 50 ;)
With a transformer output it'll tend to filter out a good deal of the upper harmonics of any low level distortion. This might make it sound a little mellower as well as reducing the output damping factor & giving a very slightly fatter bass :scratch:
I agree [partialy]
but if the amp has sufficient feedback then the damping factor should still be sufficiently low enough for the amp to produce a decent bass response.
Anthony,TD...

Reid Malenfant

11-12-2010, 21:45

anthonyTD

11-12-2010, 21:46

No arguement there Anthony :) That's why i said "very slightly" ;)
:)

DSJR

11-12-2010, 23:00

The only ss amp with transformer coupling I remember hearing was the old AR amp towards the end of its commercial life (1975 or so) and very lovely it was too. The few of these (and even more so the tuner) that come up tend to fetch good money I think.

Rare Bird

11-12-2010, 23:11

Reid Malenfant

12-12-2010, 17:19

I agree [partialy]
but if the amp has sufficient feedback then the damping factor should still be sufficiently low enough for the amp to produce a decent bass response.
Anthony,TD...
Actually having thought about this a little more carefully i doubt that many people would be able to detect the difference between an amp with a damping factor of 25 & one of 1000 :eyebrows: With a well designed speaker you might be looking at less than 1Db in difference near the speaker bass resonance. It's only when you start going much below about 25 that things might get a bit bouncy in the bass end :lol:

The only ss amp with transformer coupling I remember hearing was the old AR amp towards the end of its commercial life (1975 or so) and very lovely it was too. The few of these (and even more so the tuner) that come up tend to fetch good money I think.
Macintosh make some very nice looking (& performing as well apparently) transformer coupled solid state power amps. A little bit on the expensive side for most people though ;)

Reid Malenfant

12-11-2011, 19:35

Ok, time to resurrect the dead so to speak :eyebrows:

Some of you may recall that I bought a couple of class D amplifier modules a while back, which you can see here (http://theartofsound.net/forum/showthread.php?t=10415) :) I really should get back to that with my findings in actual fact, but for now lets just say that the heatsinking was totally inadequate & the amp would only stay alive with music signals. It certainly wouldn't last with a test tone due to the H bridge switching Mosfet having a totally insulated case & a maximum power dissipation of something like 18W. That'd be with a 25C heatsink to :mental: You don't need to do math to know that if the amp can output 200W RMS & is 90% efficient that 20W is being lost somewhere...

The whole idea of this is to make an efficient high power class A amp, a misnomer if ever there was one :eyebrows: My original intention was to build a class H rail switching amplifier to increase the efficiency of the class B amplifier, the class A section will be just about as efficient as possible due to it's low rail voltages.

Well time doesn't stand still & it was only a question of time before yours truly spotted something quite interesting ;) There have been a few more developments of that class D amplifier & the latest version uses two very fast standard packaged TO220 Mosfets. These are each capable of up to 100W of dissipation so a crazy idea crept into my head...

Enter the L25D Class D amp (http://www.ebay.co.uk/itm/L25D-250W-250W-8ohm-IRS2092-IRFB4020PBF-Class-D-LJM-/200664767403?pt=UK_AudioTVElectronics_HomeAudioHiF i_Amplifiers&hash=item2eb88d5bab)..

Like everyone on here I hate spending money unless I absolutely need to, so I sat down & had a good think about what exactly I have here that could make six class A amps a reality :) As it turns out I realised that I have over twelve 0 - 22, 24, 26V 500VA transformers & a couple of boxes of BHC ALS 10000uf 40V screw terminal capacitors. That'd be the class D amps sorted, as long as I go & run them in a bridge I'll get the kind of output power I'm looking for (200W RMS 8 ohm, 400W RMS 4 ohm). All the heatsinking I need for the class A amps, power transistors, transformers, capacitors etc.

So I make a couple of bridge amps with the class D amplifiers driving the zero volt rails of the class A amps & connect the speaker between the two class A amps... Sounds easy, not really :lol:

Though it shouldn't be impossible, there are is one problem that i'll need to overcome. As the frequency increases there will be a gradual phase shift of the output of the class D amps due to the output reconstruction filter. This appears to be centred at 45KHz. Now either I could put some kind of lead network on the class D amps (possibly the best idea), or I can put an all pass delay network onto the feed of the class A amps...

Anyway, I bought six lots of those kits which is twelve amplifiers in all to make six bridge amps. Looks like someone didn't read the application notes of the IRS2092, so it's a good job I realised I'd have to modify them to run at lower voltage & in a bridge ;) I found a few errors which could have compromised the amps, which will be rectified before they get soldered together.

Each of the class D amps will have a 0.8C/W heatsink to keep the power Mosfets cool & with an expected 20W of dissipation they should certainly stay cool. Each half bridge of class A amps will use 4 x 300W power transistors mounted on two 0.5C/W heatsinks. Current needed for 400W RMS class A 4ohm push pull is 7.07A, with +/- 4V rails these will run cool as well...

This is going to take some time, first of all I need to get these class D amps built & tested - all twelve of them :rolleyes: At least it'll give me something to do over the winter months....

Should be fun at any rate :cool: See you in another year :D

E2A:- I should say that unlike the L15D the PCBs of these kits come with the IRS2092 pre soldered to the PCB. It's not exactly fun soldering surface mount components without a tiny soldering iron bit. I managed it previously though with little difficulty, but I'm used to that kind of work.. Most are not ;)

Alex_UK

12-11-2011, 19:48

I wish I understood even 10% of what you've just written, Mark - reminds me of a post I made long, long ago...

http://t2.gstatic.com/images?q=tbn:ANd9GcSlmlgV7uTViSsrEBDB-9QEHYpfnRRyvYigr6Z9tkUC7oPki6WruKGyoaU0

;)

All the best with your project, and see you in 1985. ("Great Scot!") :lol:

Reid Malenfant

12-11-2011, 19:50

Yeah, I remember it well Alex :lol:

John

12-11-2011, 19:51

Yes fully agree but in my case its about 5%

Alex_UK

12-11-2011, 20:18

It should actually be written into the Ethos that a) you're not allowed to leave - ever - and b) that you will be immortal - refer to point a) ! Seriously, I do love reading your authoritative posts - even when I don't fully understand them! ;)

Reid Malenfant

12-11-2011, 20:44

Alex, I got into electronics simply because I wanted to make certain parts of my system that I could never afford to buy ;) That landed me a good few jobs by the way as well...

This is kind of a dream, but one that can be brought to fruition. No sensible person would ever run 3 x Krell KSA 250s or FPB 200s in an active system as they'd need serious air conditioning & a seriously deep wallet to pay for it & the electricity bills :eek:

Having done similar previously (the twin amp low dissipation class A thing) I know it's possible, now I'm just going to push it to it's (present technology) limits & given time I'll get there :cool:

A 400W RMS class A amp would probably dissipate 1000W of heat allowing for component losses. I aim to get that down to less than 150W at full power & about 115W idling. Still going to warm the room up in summer given six amps but not like 6KW would :mental:

As a brief explaination the errors that the class D amp generate should be taken care of by the low voltage class A output stage. The class A output stage is driven by a totally different voltage amplifier which would be similar to a standard class A amp of decent design. If the class D amp makes a mess of things, there is enough voltage & more than enough current in the A stage to correct for the mess.

I'm no good at explaining this in simple terms in all honesty :lol: It's more complicated than a standard amp by quite a bit so how do I expect otherwise :doh:

Watch the first one come together, it's all in my head :eyebrows:

jon1

12-11-2011, 20:57

macvisual

12-11-2011, 21:06

Anyone know how the XTZ AP100 power amp sounds running in class 'A' mode? Is this a good amp for relatively little money (£560)?

Love to hear any views/thoughts/experience please, thanks.

Reid Malenfant

12-11-2011, 21:11

Talk to Frank :lol: Seriously Frank (Effem) has an XTZ, apparently it sounds very nice indeed even if it is sliding bias class A ;)

E2A:- Frank might have the integrated, not a lot of difference though...

John

12-11-2011, 21:32

I imagine nice some nice reviews and heard a lot of their other stuff to suspect it be a good one

Reid Malenfant

12-11-2011, 21:39

Theory then mark?:eyebrows:

jon
:lol:

Just boring number crunching...

For a 400W RMS class A amp into 4 ohms...

4 ohm x 400W = 1600. Square root of 1600 = 40. That is the RMS voltage you need to swing. Now you need to calculate the current needed on a push pull output stage. 40 x 1.414 = 56.56, that incidentally is the peak voltage you need to swing into the speaker, pk - pk would be double that ;)

56.56/4 = 14.14 Amps, that is the peak current into a 4 ohm load when 56.56V is accross it. Now as you have a push pull output stage you can divide the current by 2 = 7.07 Amps.

7.07 Amps x 56.56 Volts x 2 as there are two rails = 800W. As I say, allowing for component losses somewhere near on 1000W will be dissipated for a 400W class A power amp (per channel)..

Reid Malenfant

14-11-2011, 20:36

Well this post is more for anyone that purchases an L25D IRS2012 powered class D amplifier PCB ;) For my own records as well if my PC goes t*ts up :eyebrows:

For some reason I can't fathom there are metal film resistors feeding the gates of the power Mosfets? :nono: Metal film resistors are inductive & shouldn't be in there at all. These will be replaced with carbon resistors (on the way now), also as the IRS2092 can supply up to 1Amp peak source & 1.2Amp peak sinking current I have dropped the gate resistor value to 15 ohms. Along with the IRFB4020 internal gate resistance of approximately 2.5 ohms with a 15V supply there will be no problems.

There are also two snubbers on the PCB, 10 ohms & 150pf, again the resistors are metal films :mental: Once again carbon resistors will be fitted.

Finally (for now) there is zero sign of a ground plane, or should I say three of them as per the IRS2092 application notes. What's even worse is that all the grounds are connected together at the ground/zero volt input. so this will need to be connected to the ground of a +/- supply & all the interference from output filtering, power supply decoupling etc will be superimposed on to the ground feeding the audio input :doh:

I have purchased a load of 0.1mm thick copper sheet & will make the required ground planes, cut tracks where needed & connect them back to the proper grounding point at the capacitor bank.

If a job is worth doing, it's worth doing right first time.

On another note the designer appears to have done something rather weird in yet another area. High side current limiting is done by measuring the voltage accross the high side Mosfet, in the application notes there is a resistor from the high side gate that forward biases a diode when the high side is on (thus enabling measurement of current minus the diode voltage). In this circuit the diode is biased on via the high side power supply :scratch: I can't think of any advantages to this as there is a 450nS delay from the high side switching on to measurement of current. I can't see any reason for this in all honesty. Might even cause problems. The diode was also as slow as hell in reverse recovery, as I'm using a lower voltage a very fast 1N4148 should be fine.

Anything else to pick to bits... Not right now :eyebrows:

Current limiting done right on the IRS2092 application notes. R1 is connected to the gate of Q1, on this PCB it is connected to the high side power supply or VB
http://i939.photobucket.com/albums/ad240/speakermark/Class%20A%20power%20amplifier/IRS2092currentlimiting.jpg

IRS2092 application note recommended ground planes... Makes sense as 500KHz + can make a lot of noise :rolleyes:
http://i939.photobucket.com/albums/ad240/speakermark/Class%20A%20power%20amplifier/IRS2092groundplanes.jpg

What no ground planes :eyebrows: Can anyone spot copper? :scratch: Oh you will given time... Stuff in red is new value resistors etc to do the job I want it to :cool: I'll need to keep a copy of this as most of that PCB & component selection is about to be covered with 0.1mm of copper foil glued on..
http://i939.photobucket.com/albums/ad240/speakermark/Class%20A%20power%20amplifier/L25DclassDampmods-1.jpg

Bye for now..

Reid Malenfant

27-11-2011, 18:35

Well I'd like to once again thank Steve (activexp) for this post (http://theartofsound.net/forum/showpost.php?p=269423&postcount=6) he made, I took a look over at DIYAudio & what was on there..

Loads of information on both the L15D, L20D & some on the L25D which these amp modules happen to be. It looks like these are some of the best implementations of the IRS2092 control chip out there :) It also looks like I fessed up the chip number in my previous post :eyebrows:

So in accordance with the old saying, "if it aint broke then don't fix it" I'm going to drop the ground plane idea & get on & build the things but with certain new components to increase the current limit etc.

As it happens the output inductors supplied as standard will be spot on for an 8 ohm load in a bridge amplifier as they are designed for 4 ohms single ended (in a bridge each amplifier sees half the actual load impedance). For a 4 ohm load I'll need to halve the inductance value, which got me looking on ebay as usual. Plenty to choose from but the most promising where on the other side of the pond. So I decided to look for similar iron powder toroids as used in those inductors... No problem winding my own & I can go ott...

I must be lucky as I stumbled accross a listing by an old work colleague who lives in the same city as me & who I'm still in touch with of the same type iron powder toroid but just a bit bigger :cool: So I get them at his BIN price & he'll drop them round at no extra cost... As an added extra he emailed me a list of components he has been put in charge of getting rid of in bulk from my old & now defunct employer, no reasonable offer refused :stalks:

It's good to keep in touch :eyebrows: