Hello!
I'm a new member but a long time reader / follower here. Previously I have found many solutions to quite a few problems with DIY amps from these discussions.
I decided to try my luck with this OTL monoblock kit I assembled few years ago. I will attach the schematics so you can better inspect the amplifier.
My problem is that both of these monoblocks hum / buzz very loudly with my new 100+ dB speakers. I think the problem has always been present but became more (disturbingly) apparent with my new speakers. Previous speakers I had were about 92dB efficient.
Few observations I have made so far:
1. Noise is there with nothing but the monoblock connected to speaker. This means nothing else is on and input of the amp is shorted. I have also tried this with the input RCA connection taken apart so that the input has been shorted directly on the PCB.
2. If there is a ground loop problem it is inside the amplifier. I have checked the grounding and the solder joints and they seem to be OK. Meaning that PCB is connected as stated in the schematics and a ground loop blocker is used for PE connection (antiparallel diodes with resistor). PCB has it's own internal ground scheme which is connected from singular point to the mains / chassis ground.
3. Removing the input tube (ECC82) does not affect the noise but neither does removing the driver tubes (2 x 6V6).
4. Noise is not there instantly but takes time to come up. After tubes warm up and start conducting the noise is heard through speakers.
5. Noise is constant and independent of any volume control and noise is same with both individual monoblocks. This would mean that something about the design causes the noise rather than bad solder joint or intermittent problem (or I have made the exact same mistakes with both amps).
6. Tubes are indirectly heated and use AC heaters with CT for input (ECC82 )tube and driver (2 x 6V6) pair. Currently I'm wondering if the heaters / heater wiring (printed on the PCB not twisted point to point wiring) could be causing the noise. Designer decided to use AC and I know that he was a professional so I would hope that AC can be used. However if nothing else helps I'm willing to try DC...
I'm sure I forgot to mention something but I will provide more information if this thread gets some answers or sparks interest! 🙂
I'm sure these amps can be made a lot quieter. I used to chat with the designer of this kit. He was a very talented tube amp professional / guru from Estonia. Unfortunately he passed away in 2023 which is why this project was left a bit hanging.
Amps work and sound very good (except the noise) and that was enough for the dealer from whom I bought this kit.
They were satisfied with the monos working well enough and when I brought up noise problems with high sensitivity speakers they pretty much told me to "just live with it". This bums me out since I know that the actual designer build a lot of OTL amps which he used with high sensitivity speakers and had no noise problems.
I'm a new member but a long time reader / follower here. Previously I have found many solutions to quite a few problems with DIY amps from these discussions.
I decided to try my luck with this OTL monoblock kit I assembled few years ago. I will attach the schematics so you can better inspect the amplifier.
My problem is that both of these monoblocks hum / buzz very loudly with my new 100+ dB speakers. I think the problem has always been present but became more (disturbingly) apparent with my new speakers. Previous speakers I had were about 92dB efficient.
Few observations I have made so far:
1. Noise is there with nothing but the monoblock connected to speaker. This means nothing else is on and input of the amp is shorted. I have also tried this with the input RCA connection taken apart so that the input has been shorted directly on the PCB.
2. If there is a ground loop problem it is inside the amplifier. I have checked the grounding and the solder joints and they seem to be OK. Meaning that PCB is connected as stated in the schematics and a ground loop blocker is used for PE connection (antiparallel diodes with resistor). PCB has it's own internal ground scheme which is connected from singular point to the mains / chassis ground.
3. Removing the input tube (ECC82) does not affect the noise but neither does removing the driver tubes (2 x 6V6).
4. Noise is not there instantly but takes time to come up. After tubes warm up and start conducting the noise is heard through speakers.
5. Noise is constant and independent of any volume control and noise is same with both individual monoblocks. This would mean that something about the design causes the noise rather than bad solder joint or intermittent problem (or I have made the exact same mistakes with both amps).
6. Tubes are indirectly heated and use AC heaters with CT for input (ECC82 )tube and driver (2 x 6V6) pair. Currently I'm wondering if the heaters / heater wiring (printed on the PCB not twisted point to point wiring) could be causing the noise. Designer decided to use AC and I know that he was a professional so I would hope that AC can be used. However if nothing else helps I'm willing to try DC...
I'm sure I forgot to mention something but I will provide more information if this thread gets some answers or sparks interest! 🙂
I'm sure these amps can be made a lot quieter. I used to chat with the designer of this kit. He was a very talented tube amp professional / guru from Estonia. Unfortunately he passed away in 2023 which is why this project was left a bit hanging.
Amps work and sound very good (except the noise) and that was enough for the dealer from whom I bought this kit.
They were satisfied with the monos working well enough and when I brought up noise problems with high sensitivity speakers they pretty much told me to "just live with it". This bums me out since I know that the actual designer build a lot of OTL amps which he used with high sensitivity speakers and had no noise problems.