Hello,
My new DIY amplifier is sounding terrific! Still I have a tiny issue with a sizzling sound.
When noting is connected to the input connectors, I can hear a normal breath sound in the headphone. I used this setup to play with all the input cables and the AC cables of the toroidal transformer and also turn it from it's center to minimize the noises. Here is the final result:
The input ground terminals and all the PCB HQG ground connectors are connected to one common HQG screw to the casing. (Not all connected yet in this picture).
If I connect the speakers to the output with nothing at the inputs, there is absolutely no sound in the speakers. No breath, no buzz, nothing! When I connect the RCA cables to the input, same status, no sound. My actual cables are RCA Van Del Hull M.C. Integration Hybrid, Halogen Free type. As soon as I connect the other end of the RCA cables to the output of my Technics SU-9070 pre-amplifier, I can hear a little tiny "gresil" sound. I tried others cables with the same result. The French-to-English translation of the "gresil" French expression is "sizzling". I am not sure if the translation is right. It's not a hum (60 or 120 Hz), it's a little background noise. If I raise the volume, I can cover it with the music, by mean the noise it's not amplified or louder.
I also tried to connect the amplifier AC cable to another outlet, with the same result. Then I tried to connect the RCA cable to another output source, my TASCAM 122 MKII cassette deck. The noise is a little lower but still present.
The weird thing is that this sound was present since day one, but so low that I could forget it. But this morning, is it because it is raining outside, I was listening the FM radio and was able to hear it more in the background.
What would be the cure for this? I saw some schematic with capacitors between the input ground terminals and the casing. Would this be a solution?
Any suggestion is welcome ;-)
My new DIY amplifier is sounding terrific! Still I have a tiny issue with a sizzling sound.
When noting is connected to the input connectors, I can hear a normal breath sound in the headphone. I used this setup to play with all the input cables and the AC cables of the toroidal transformer and also turn it from it's center to minimize the noises. Here is the final result:
The input ground terminals and all the PCB HQG ground connectors are connected to one common HQG screw to the casing. (Not all connected yet in this picture).
If I connect the speakers to the output with nothing at the inputs, there is absolutely no sound in the speakers. No breath, no buzz, nothing! When I connect the RCA cables to the input, same status, no sound. My actual cables are RCA Van Del Hull M.C. Integration Hybrid, Halogen Free type. As soon as I connect the other end of the RCA cables to the output of my Technics SU-9070 pre-amplifier, I can hear a little tiny "gresil" sound. I tried others cables with the same result. The French-to-English translation of the "gresil" French expression is "sizzling". I am not sure if the translation is right. It's not a hum (60 or 120 Hz), it's a little background noise. If I raise the volume, I can cover it with the music, by mean the noise it's not amplified or louder.
I also tried to connect the amplifier AC cable to another outlet, with the same result. Then I tried to connect the RCA cable to another output source, my TASCAM 122 MKII cassette deck. The noise is a little lower but still present.
The weird thing is that this sound was present since day one, but so low that I could forget it. But this morning, is it because it is raining outside, I was listening the FM radio and was able to hear it more in the background.
What would be the cure for this? I saw some schematic with capacitors between the input ground terminals and the casing. Would this be a solution?
Any suggestion is welcome ;-)
Yes. As mentioned I tried with my Tascam 122 MKII that have a volume output.
The noise is present as soon as I connect the RCA cables to the source Outputs.
My Technics SU-9070 has been totally recapped by me. The volume control also have been unsolded and cleaned with DeoxiT-D5 by it's bottom side. Then soldered back on the board.
I also have a Power Amplifier Rotel RB-1552MKII that when plugged into the setup replacing my DIY Amplifier doesn't make any noise.
I even tried to shield the two inputs on the Amplifier board as below, with the shields connected to the ground from the screw.
The noise is present as soon as I connect the RCA cables to the source Outputs.
My Technics SU-9070 has been totally recapped by me. The volume control also have been unsolded and cleaned with DeoxiT-D5 by it's bottom side. Then soldered back on the board.
I also have a Power Amplifier Rotel RB-1552MKII that when plugged into the setup replacing my DIY Amplifier doesn't make any noise.
I even tried to shield the two inputs on the Amplifier board as below, with the shields connected to the ground from the screw.
No! You misunderstood.
Still there.
- There is nothing plugged into the RCA inputs.
- The speakers are plugged to Outputs terminals.
- If I powered on the amplifier, there is absolutely NO sound. Total silence.
- Then I connect the two RCA cables into the RCA inputs. Others end of the RCA cable is floating. Still silence without any sound or noise. So nothing is grabbed there from any possible EMI waves.
- As soon as I plugged to others end of the RCA cables into an output source, the noise is present.
Both Amplifier and Power Supply schematics below...
Here are some screen captures from my scope. The probe was connected at the Right Output Speaker terminal with both speakers connected.
Amplifier OFF with one end of RCA cables connected to the inputs and the others end floating:
Amplifier ON with one end of RCA cables connected to the inputs and the others end floating:
Amplifier On with one end of RCA cables connected to the inputs and the others end connected to the pre-amplifier output. Technics SU-9070 Pre-Amplifier AC plug UNPLUGGED:
Amplifier On with one end of RCA cables connected to the inputs and the others connected to the pre-amplifier output. Technics SU-9070 Pre-Amplifier AC plug Plugged but Power OFF:
Amplifier On with one end of RCA cables connected to the inputs and the others end connected to the pre-amplifier output. Technics SU-9070 Pre-Amplifier AC plug Plugged but Power ON:
Conclusion : The source of noise seem to come from the Amplifier Power Supply as soon as the others end of the RCA cable is plugged into an Output Source. I even try to use my Revox B750 in Pre-amplifier mode to source the Amplifier and even if the tone of the noise is a bit different, it is present as soon as I connect the RCA cables.
Mechanically, in my original setup, the amplifier board was installed with the input at the rear of the case, in order to have them with the shorter cable as possible. Then I made the AC plug module hole in the middle of the RCA input connector and the PCB input terminal bloc. This setup result with a hum coming from the AC plug. That AC plug module contain the switch, the filters and the fuses. I fixed that hum by inverting the Amplifier board front to back. Now the AC Plug terminal is close to the rails filter capacitors. I tried to play with the cables and saw no change. On the contrary, playing with the shield microphone cable that connect the input RCA to the PCB input bloc terminal do make a difference. They are presently attached with Tie-wrap in the lowest noise possible into the headphone.
Amplifier OFF with one end of RCA cables connected to the inputs and the others end floating:
Amplifier ON with one end of RCA cables connected to the inputs and the others end floating:
Amplifier On with one end of RCA cables connected to the inputs and the others end connected to the pre-amplifier output. Technics SU-9070 Pre-Amplifier AC plug UNPLUGGED:
Amplifier On with one end of RCA cables connected to the inputs and the others connected to the pre-amplifier output. Technics SU-9070 Pre-Amplifier AC plug Plugged but Power OFF:
Amplifier On with one end of RCA cables connected to the inputs and the others end connected to the pre-amplifier output. Technics SU-9070 Pre-Amplifier AC plug Plugged but Power ON:
Conclusion : The source of noise seem to come from the Amplifier Power Supply as soon as the others end of the RCA cable is plugged into an Output Source. I even try to use my Revox B750 in Pre-amplifier mode to source the Amplifier and even if the tone of the noise is a bit different, it is present as soon as I connect the RCA cables.
Mechanically, in my original setup, the amplifier board was installed with the input at the rear of the case, in order to have them with the shorter cable as possible. Then I made the AC plug module hole in the middle of the RCA input connector and the PCB input terminal bloc. This setup result with a hum coming from the AC plug. That AC plug module contain the switch, the filters and the fuses. I fixed that hum by inverting the Amplifier board front to back. Now the AC Plug terminal is close to the rails filter capacitors. I tried to play with the cables and saw no change. On the contrary, playing with the shield microphone cable that connect the input RCA to the PCB input bloc terminal do make a difference. They are presently attached with Tie-wrap in the lowest noise possible into the headphone.
I had the same thought. Voltage gain would appear to be 27.6 V/V or about 28.8dB.
Have you tried with PA inputs shorted, no other equipment connected? In other words, noise of open inputs vs. shorted inputs?
The above is in post #4.
Guy's, please read the thread before asking already answered questions ;-)
Mark, no sound at all with the Rotel.
Yesterday night I was watching the TV that is connected to one AUX input. While the sizzling sound was very low, it suddenly raise in the middle of the program. I know that my TV is the worse gear for noise, in any case of any settings above.
So this mornings I will unplugged everything, AC power lines and RCA cables from all gear and reconnect them one by one while watching the scope...
Q1. Does this still happen if the item you plug the RCA into is entirely disconnected from the mains, and all other grounds?
Q2. Does a different power amplifier exhibit the same problem? (ETA: Ok I see previous post - A2 = No!)
TBH it sounds like a subtle grounding issue, and I would strive to see that the grounds returning the current to the power transistors, have their own current path back to the transformer, independent of the current return paths powering anything else.
Also i'd not ground the chassis to the signal ground directly, but via the regular trick of a shorted diode bridge, 120ohm and 220uF X2 in parallel - apologies if this is already seperate.
I actually had a similar effect from a computer ground, the monitor ground via the HDMI came into the small computer (on a wall wart) and up the USB ground, mixing with the chassic ground - both the monitor and the amp were powered from the same mains strip but just that tiny difference got in the way.
I also had another small loop - took the preamp ground from near the power amplifiers and picked up the hum from the current feeding the bias (and music, of course!), once solved, it was spookily quiet
This hum only appeared when the inputs were shorted by the supplying level control...
Hope you get it solved.
Those are Nichicon Gold Tune 6800 uF/63 V. I bought them from https://partsconnexion.com/ ! They are surely not Chinese fakes lol!
Let's reset from scratch... I just unplugged everything, I means EVERYTHING. AC Power plugs from all devices. Even the Internet hub and router from the wall. There is nothing in the AC circuit except the DIY Amplifier.
- If nothing is connected to the RCA Inputs connectors of the DIY Amplifier. Total silence
- If I connect one RCA terminated to ground Male connector into the right channel of the DIY Amplifier, although the sound is present, it is the most lower level I ever noticed.
- I try to record it from the video camera of my cellular phone. The sound is very low and you will have to raise the volume of your device to hear it, but at least you will be able to identify the kind of noise. Here is a Dropbox link where you can download the mp4 file.
The answer is probably "No". If you look in post #6, the schematics of both the Amplifier board (they are two in the DIY box, one for each channel) and the Power Supply board are attached. The MOSFETs Power Transistors don't have a return to ground. They have a return to the L1 inductor that goes to the load and a return to the feedback circuit.
Here is the Amplifier PCB layout with the Power Transistors return highlighted. Notice that they are joined together on the top side (Blue) and continue to the R11 and R12 resistors. From there, the path change side and rejoin the L1 on the solder side (Red) and goes back to the two protection diodes D502 and D602 and reach the feedback resistor R6: