Hi Tomailatomaila,
(Your name is a mouthful to remember how to type btw 🙂 )
When using a single trafo for two amp boards, often a ground loop is formed.
Test this: disconnect the audio input rca from one channel. Is the other channel quieter?
Thanks for the photo. Nice build!
It would be helpful if you drew a sketch of the wiring connections. I would suggest analog ground be separated from dirty chassis ground through a central star chassis ground with an NTC or other ground loop breaker circa 10ohms.
Try not to form a loop consisting of the two RCA’s surrounding the power trafo. Send one side parallel alongside other channel together and go to one amp 1st then to second amp. One wire will be longer. Use coax cable for input leads. Move your trafo to vertical orientation with an L bracket.
Try these one by one and see if any help.
For the thump, all I can suggest is a speaker output protect with instant off and delay turn on to prevent thump and protect dc output to your speakers. I have some I can suggest if you PM me.
(Your name is a mouthful to remember how to type btw 🙂 )
When using a single trafo for two amp boards, often a ground loop is formed.
Test this: disconnect the audio input rca from one channel. Is the other channel quieter?
Thanks for the photo. Nice build!
It would be helpful if you drew a sketch of the wiring connections. I would suggest analog ground be separated from dirty chassis ground through a central star chassis ground with an NTC or other ground loop breaker circa 10ohms.
Try not to form a loop consisting of the two RCA’s surrounding the power trafo. Send one side parallel alongside other channel together and go to one amp 1st then to second amp. One wire will be longer. Use coax cable for input leads. Move your trafo to vertical orientation with an L bracket.
Try these one by one and see if any help.
For the thump, all I can suggest is a speaker output protect with instant off and delay turn on to prevent thump and protect dc output to your speakers. I have some I can suggest if you PM me.
Thanks XRK, i have change trafo position, disconnect mains ground from star ground and humm gone away. I have Arcam 9, NEC aua 8000 and Hk730 amplifiers. Alpha 20 have sweetest and warmest sound, very good bass authority and depth, 3d layering and stage maybe better in NEC, but i need more time for listening. Sorry for bad english, and thak you very much.
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You need the mains (IEC) ground connected or it’s not safe. Maybe use NTC between your star ground and mains ground. But mains needs to touch chassis directly.
Because it is too hard for me reading 179 pages with all of your posts( I have actually read the first ones) I would appreciate if someone can inform me about the trimpots settings ,adjustments or circuit upgrades before constructing and powering up the amp. Is there any pair of circuit boards left for purchasing? It is a very interesting design and I want to give it a try. Thank you very much in advance!!
There is nothing to trim. It’s an easy amp to startup. You need to swap out the trimpot with a fixed value. Someone can chime in what that is but I recall it is like 220R to 470R?
Post #1 has all the info you need in terms of BOM and recommended parts and components.
Let me see if I still have any boards left.
Post #1 has all the info you need in terms of BOM and recommended parts and components.
Let me see if I still have any boards left.
As I have built 5 class A solid state power amps , 8 tube preamps and 2 tube class A power amps, I am quite familiar in constructions. I would like to get the maximum quiescent current from that 20W amp because I have 1 pair of 48cm X 20cm X 5cm heat sinks which I think can bear a 2A QC. So what would be the resistors/trimpots values to supply the amp with 2A QC? Having 2A QC the o.33R must be 0.1R I think and the DC supply must be set to +/-28Vdc.Is that right?Thanks a lot. If there is no remaining boards, I woul be very grateful if you could send me the pcb gerber files. I am an expert in sprint layout 6.0 and I have designed a lot of pcbs.Thanks again!
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The circuit was originally designed to run at 2A bias current. I think I dropped it to reduce heatsink requirements.
Here was the as built circuit for 1.35A bias current.
I’ll let Hugh chime in for getting this to run at 2A but I suspect all you need to do is modify resistors to look like the initial LTSpice simulation:
You might look at the 52W variant which has +-37v rails and higher bias current of 3A. It’s the ABBB amp here:
https://www.diyaudio.com/community/...y-with-buttah-abbb-52w-class-a-amp-gb.339086/
I have lots of those PCBs available. That amp has built in PSU with active bridge and SSR speaker protection all built in.
However, I would highly recommend that you just build the latest variation of the Alpha, and that’s the Alpha Nirvana. It’s capable of 39w at +/-27v rails. Has better distortion figures and higher peak power. I also have plenty of PCBs available - that’s one reason I don’t have any Alpha 20 PCBs available - it’s not the latest design.
https://www.diyaudio.com/community/threads/alpha-nirvana-39w-8ohm-class-a-amp.344540/
It’s got about same parts count and higher performance. Fully supported and many many people have built it with great reports of superb sound quality.
Here was the as built circuit for 1.35A bias current.
I’ll let Hugh chime in for getting this to run at 2A but I suspect all you need to do is modify resistors to look like the initial LTSpice simulation:
You might look at the 52W variant which has +-37v rails and higher bias current of 3A. It’s the ABBB amp here:
https://www.diyaudio.com/community/...y-with-buttah-abbb-52w-class-a-amp-gb.339086/
I have lots of those PCBs available. That amp has built in PSU with active bridge and SSR speaker protection all built in.
However, I would highly recommend that you just build the latest variation of the Alpha, and that’s the Alpha Nirvana. It’s capable of 39w at +/-27v rails. Has better distortion figures and higher peak power. I also have plenty of PCBs available - that’s one reason I don’t have any Alpha 20 PCBs available - it’s not the latest design.
https://www.diyaudio.com/community/threads/alpha-nirvana-39w-8ohm-class-a-amp.344540/
It’s got about same parts count and higher performance. Fully supported and many many people have built it with great reports of superb sound quality.
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Thank you very much for your quick response. I would like to say that I have never used a psu and speaker protection all in the same pcb. I have designed my own capacitance pcbs in refference to diyaudio/firstwatt pcb with a total 60.000uF capacitance per rail (4 pcbs in dual mono). I could design a new pcb using my sprint layout 6.0 but it would be easier if I could purchase the boards from the original designer because it would spare me a lot of time and work. So what do you suggest. All I want is the amp pcbs without power supply and circuit protection.Is that possible? In my previous builts I have used separate power supplies using 2N6287/84 but there is a lot of heat although I use huge sinks. So what is your advice? Thanks in advance.The circuit was originally designed to run at 2A bias current. I think I dropped it to reduce heatsink requirements.
Here was the as built circuit for 1.35A bias current.
I’ll let Hugh chime in for getting this to run at 2A but I suspect all you need to do is modify resistors to look like the initial LTSpice simulation:
You might look at the 52W variant which has +-37v rails and higher bias current of 3A. It’s the ABBB amp here:
https://www.diyaudio.com/community/...y-with-buttah-abbb-52w-class-a-amp-gb.339086/
I have lots of those PCBs available. That amp has built in PSU with active bridge and SSR speaker protection all built in.
However, I would highly recommend that you just build the latest variation of the Alpha, and that’s the Alpha Nirvana. It’s capable of 39w at +/-27v rails. Has better distortion figures and higher peak power. I also have plenty of PCBs available - that’s one reason I don’t have any Alpha 20 PCBs available - it’s not the latest design.
https://www.diyaudio.com/community/threads/alpha-nirvana-39w-8ohm-class-a-amp.344540/
It’s got about same parts count and higher performance. Fully supported and many many people have built it with great reports of superb sound quality.
Hi X,
It’s got about same parts count and higher performance. Fully supported and many many people have built it with great reports of superb sound quality.
Why R171 ( NTC thermistor) has changed from 47R to 8R?
47R was wrong value for a ground loop breaker. Should be about 10ohms. I use 8D-20 because I have lots of them and 8ohms is close enough to 10ohms.
...yes and please use some isolation under the caps. yes i know that the caps have on its top a plastic cap , but if this cap is damaged you have a massive short cut between the housing of the cap (left side -V, ) and your heat sink...
kr
chris
Hi
For all these nice guys who made this nice amplifier with active fans, did you use filters at all to reduce electrical noise from fans?
BR Nikos
For all these nice guys who made this nice amplifier with active fans, did you use filters at all to reduce electrical noise from fans?
BR Nikos
Thanks XRK971.
Also i found these...
