Perhaps you mean the 3 x 1.0 ohm power resistors?
Elfa (Distrelec) will have what you need - you could even get quite exotic if you want and get some Isabellenhutte ones (Manganin power resistors)
If you are asking if there are any more pcb's available, probably not any more from the HK Audio group or 'Skylab' as I think I received the last one
However, if you get in contact with 'Prasi' (a member here - just look thru the GB listing for his contact) who has developed quite a few pcbs that are sent to a quite reasonable pcb manufacturer, perhaps he'd do an copy of the board and you could get some there - start a small GB
Elfa (Distrelec) will have what you need - you could even get quite exotic if you want and get some Isabellenhutte ones (Manganin power resistors)
If you are asking if there are any more pcb's available, probably not any more from the HK Audio group or 'Skylab' as I think I received the last one
However, if you get in contact with 'Prasi' (a member here - just look thru the GB listing for his contact) who has developed quite a few pcbs that are sent to a quite reasonable pcb manufacturer, perhaps he'd do an copy of the board and you could get some there - start a small GB
Multiple feedback loops (I see three). Not spending a lot of time looking at it, but it does look interesting. Busy doing a tube amp design right now, one that is also taking an unusual path and some SS hybridisation (SS current processing only, no voltage amplification at the front end) and a Triode output that halves Anode impedance, also uses high freq 55KHz bias. There will always be new ways to make amplifiers, even Gainclone types, so pleased to see you doing something different.
Cheers, Joe
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Multiple feedback loops (I see three). Not spending a lot of time looking at it, but it does look interesting. Busy doing a tube amp design right now, one that is also taking an unusual path and some SS hybridisation (SS current processing only, no voltage amplification at the front end) and a Triode output that halves Anode impedance, also uses high freq 55KHz bias. There will always be new ways to make amplifiers, even Gainclone types, so pleased to see you doing something different.
Cheers, Joe
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I am ways trying to look at different ways to get things better. Sometimes I like to visit different people with different setups just to listen and understand what they consider as good. I have been looking at current topology for a long time, but the MyRef with both current and voltage feedback caught my interest. After getting the kit and playing around, I did notice that increasing the current gain improved damping of the driver. I think your journey is also going to be interesting.
Thanks for the suggestions about the board.
About components: For those resitors I have seen a number of suggestions within this thread, but my question was regarding the rest of the components (resistors, caps etc).
Well I played around with different components (this same circuit) and each time the components made a substantial difference, some more noticeable than others -
For the first attempt (Verobrd) I used Zfoil Vishays for the input (a bit 'full of myself here!) some Takman and Phillips metal film resistors and the input cap was a Wima mkp10 and the 1n5 and 100nF were some Rifa pfe216 styrene - that 0R33 was a power Caddock met film - diodes were BYW29 (not the smoothest ones!) - power caps were Nichicon GoldTones - the sound was rather bright in my system and also in the AKG k701's but plenty of 'punch' and a but deficient in the bass - too much treble after awhile, annoying.
Number 2 went the other way - carbon resistors (mostly kawame, ABradley, etc) and the 0R33 was a handmade from Manganin resistance wire - input cap was an Audiophiler, the 1n5 & 100nF were Vishay PP, diodes MBR860 and Mundorf power caps - the sound was very 'laid back' in comparison - a bit dull actually - rather surprised.
I started assembling the pcb from the HK club using the Auricap, Takman, AB, and so on and unfortunately, the eBay amp chips weren't any good so put project aside to get some genuine ones and haven't got back to the project
A guy here used pretty standard Wima input, PP for the 1n5 and 100nF, Phillips power resistors in //, etc and same GoldTone power caps with MSR860 diodes and it sounded rather good indeed into both the AudioNirvana Classic 8" FR driver and the BetsyK in an OB (a very pleasant surprise with that one) - checked it out with the AKG k701 'phones and also rather impressive performance indeed so replaced the input 4k7 resistor with one of Uriah Daley's 'Resistor Replacer' LDR units and a much more open sound with better detail, etc and haven't any idea why this would be so effective but it seems to work the same with his 'ordinary' gain clone amp too - tricky little buggers, these chip amps!
So, some impressions of components and such fun - hope it'll be of some use in selecting your components
For the first attempt (Verobrd) I used Zfoil Vishays for the input (a bit 'full of myself here!) some Takman and Phillips metal film resistors and the input cap was a Wima mkp10 and the 1n5 and 100nF were some Rifa pfe216 styrene - that 0R33 was a power Caddock met film - diodes were BYW29 (not the smoothest ones!) - power caps were Nichicon GoldTones - the sound was rather bright in my system and also in the AKG k701's but plenty of 'punch' and a but deficient in the bass - too much treble after awhile, annoying.
Number 2 went the other way - carbon resistors (mostly kawame, ABradley, etc) and the 0R33 was a handmade from Manganin resistance wire - input cap was an Audiophiler, the 1n5 & 100nF were Vishay PP, diodes MBR860 and Mundorf power caps - the sound was very 'laid back' in comparison - a bit dull actually - rather surprised.
I started assembling the pcb from the HK club using the Auricap, Takman, AB, and so on and unfortunately, the eBay amp chips weren't any good so put project aside to get some genuine ones and haven't got back to the project
A guy here used pretty standard Wima input, PP for the 1n5 and 100nF, Phillips power resistors in //, etc and same GoldTone power caps with MSR860 diodes and it sounded rather good indeed into both the AudioNirvana Classic 8" FR driver and the BetsyK in an OB (a very pleasant surprise with that one) - checked it out with the AKG k701 'phones and also rather impressive performance indeed so replaced the input 4k7 resistor with one of Uriah Daley's 'Resistor Replacer' LDR units and a much more open sound with better detail, etc and haven't any idea why this would be so effective but it seems to work the same with his 'ordinary' gain clone amp too - tricky little buggers, these chip amps!
So, some impressions of components and such fun - hope it'll be of some use in selecting your components
Thanks Jameshillj, it helped. I will play around with som components. Maybe I will start with a mix of what I have and your different attempts.
BR
//H
It is a quite surprising little device/circuit - even tho it was developed to illustrate Joe's specific speaker design concept, it never-the-less is a rather good simple amp plus a 'current drive' into the bargain
If you've got some carbon resistors in the junk box, they could be worth a try - I don't think it's worth getting resistors like the expensive naked Vishays until you're got up and running (and Susumi's have a similar sound at a fraction of the cost) and it depends a bit on you other components and desired overall sound
I bought a First Watt F3 that is also a transconductance amp and it was a 'nice' sound but rather 'slow', if you'll excuse the terminology - there wasn't anything I tried that could make it better in this regard and this is now being converted into an First Watt F6 amp
However, there's nothing slow about the T40 and it isn't restricted to just high efficiency FR drivers either
All the best.
If you've got some carbon resistors in the junk box, they could be worth a try - I don't think it's worth getting resistors like the expensive naked Vishays until you're got up and running (and Susumi's have a similar sound at a fraction of the cost) and it depends a bit on you other components and desired overall sound
I bought a First Watt F3 that is also a transconductance amp and it was a 'nice' sound but rather 'slow', if you'll excuse the terminology - there wasn't anything I tried that could make it better in this regard and this is now being converted into an First Watt F6 amp
However, there's nothing slow about the T40 and it isn't restricted to just high efficiency FR drivers either
All the best.
I will - Tnx a bunch!!
I will probably start to see what they can do with my Elsinores (as an opposite to the current NCDX - Discrete mono blocks that are there now)
Arguably, the component value that makes the biggest difference is the 1n5 below, the input filter. You virtually have to ignore what it does to the frequency response and just adjust by ear. Perhaps other components makes it necessary to tweak that value to suit, but I will leave that up to them. But even a small change here is noticeable.
I have a selection of values of high quality 1% polypropylene non-inductive film, 100p to 10n @ 50V. Top drawer, made by Philips way back and picked up 10,000 in three boxes for $50. Johnny on the spot and didn't haggle the price. Maybe they didn't realise the value, but I sure did. Just paid and kept a straight face and said I would take them off their hands and that they would come in useful from time to time.
Deal done! 
But I would think Wima FKP would be good, but there should be others similarly.
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I wish you a happy new year for everyone. I have some doubts because I am a newbie in electronics. I address a few questions to Mr. Joe Rasmussen.
1 - The sink recommendation and direct current through 0R33 indicates being in front of an amplifier type class A? If this is true, would not the heat or overcurrent drive the SPiKe (SOA) protection chip?
2 - Its power indication is 35VDC but LM3575 runs from 10 to 42VDC. If you use 25 VDC for less power, is it possible?
3 - Apparently there is no negative feedback, how is your gain regulated? Is the 4K7 resistor in the input?
4 - Dual mono construction is expensive: can not even PSU with two outputs, two winding transformer, two bridge rectifiers and two electrolytic banks?
Thank you very much for the help. Augusto J. Hoffmann - Brazil
1 - The sink recommendation and direct current through 0R33 indicates being in front of an amplifier type class A? If this is true, would not the heat or overcurrent drive the SPiKe (SOA) protection chip?
2 - Its power indication is 35VDC but LM3575 runs from 10 to 42VDC. If you use 25 VDC for less power, is it possible?
3 - Apparently there is no negative feedback, how is your gain regulated? Is the 4K7 resistor in the input?
4 - Dual mono construction is expensive: can not even PSU with two outputs, two winding transformer, two bridge rectifiers and two electrolytic banks?
Thank you very much for the help. Augusto J. Hoffmann - Brazil
Hi Augusto
1. Not at all, and it is only slightly Class A.
2. Yes, should be possible with 25V, clearly somewhat lower power. But still needs a reasonable heatsink.
3. Yes, there is negative feedback. The gain is related to the value of the load. For that reason you will have twice the gain at 8 Ohm compared to 4 Ohm and 16 Ohm double the gain of 8 Ohm. That is because the output is current, so 1 Amp current will give 4V into 4 Ohm load, 8V into 8 Ohm and so on. Weird I know, but that is the nature of the beast.
4. As long as you have isolation, then separate windings should work, but you would need four secondary windings on the same transformer, not something you see often. Keeping everything separate and isolated reduces potential hum. The diagram in Post #1 will guarantee no hum, but I can't predict all other possible variables and they can be very hairy indeed.
Hope that helps, cheers, Joe.
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+/-25V DC for the rails is the sweet spot for the LM3875 if you want to driver 4Ω speakers.
dave
I have heard many speakers on both Daniel’s original TransAmp based on a rework on an amp he built to drive a CRT and the LM3875 one he reworked from the same boards as in mine. Bothe were very good… the 1st right up there with the best amps i have heard.
With the “TransAmp” dial you can set the output impedance to what best suits the speaker you are listening too.
dave
With the “TransAmp” dial you can set the output impedance to what best suits the speaker you are listening too.
dave