Dear specialists,
A local bass player has asked me to look at his Eden WT 550 Traveler. It is a bass amplifier, with solid-state output, and a hybrid preamp (tube and solid-state). I'm in Switzerland so the wall power is 50Hz (230V).
I think the amplifier has (at least) 3 issues :
I will detail the 2 remaining issues. All measures done without any signal on input and with speaker on output.
3. remaining hum
First, I disconnected the preamp, and I was left with only issue 3 (remaining hum, constant level). The DC level on the speaker output is about 3mV, which looks ok to me, I didn't bother to adjust anything.
The remaining hum frequency is difficult to identify, even on the scope. Maybe 50Hz, or 100/ or even 150Hz. Here is a scope shot connected to the output :
The P2P amplitude is about 30-40mV. What annoys me are the spike around the crossing. Maybe that's what I hear. At least it looks ugly. Looking at a spike detail :
I tried recording this noise with my smartphone, attached as file_3_output_sound.zip.
4. noise (is it white noise ?) with random "cracklings"
This issue is the most annoying, its level is too high to be ignored, and the bass player asked me to try to get rid of this. Looking at the crazy cascade of components of the preamp, I'm not surprised it's noisy, but still let's try to silent it. Here is an attempt to scope it :
I tried recording the noise and cracklings with my smartphone, attached as file_5_output_sound_noise_crackling.zip
The cracklings aren't the most disturbing and seem to be caused by the tube (removing the tube removes the cracklings). What is disturbing is the noise.
The schematics are attached as well. Do not ask me what version I have, there are notes all over the place and this amp has seen other hands before me.
Edit: reading this page made me wonder if this is worth the effort but let's try 🙂
It would be cool if you guys with decades of experience would be able to assist me.
Kind regards,
Charles
A local bass player has asked me to look at his Eden WT 550 Traveler. It is a bass amplifier, with solid-state output, and a hybrid preamp (tube and solid-state). I'm in Switzerland so the wall power is 50Hz (230V).
I think the amplifier has (at least) 3 issues :
- 100Hz hum
- very microphonic tube
- remaining hum, constant level
- noise (is it white noise ?) with random "cracklings"
I will detail the 2 remaining issues. All measures done without any signal on input and with speaker on output.
3. remaining hum
First, I disconnected the preamp, and I was left with only issue 3 (remaining hum, constant level). The DC level on the speaker output is about 3mV, which looks ok to me, I didn't bother to adjust anything.
The remaining hum frequency is difficult to identify, even on the scope. Maybe 50Hz, or 100/ or even 150Hz. Here is a scope shot connected to the output :
The P2P amplitude is about 30-40mV. What annoys me are the spike around the crossing. Maybe that's what I hear. At least it looks ugly. Looking at a spike detail :
I tried recording this noise with my smartphone, attached as file_3_output_sound.zip.
4. noise (is it white noise ?) with random "cracklings"
This issue is the most annoying, its level is too high to be ignored, and the bass player asked me to try to get rid of this. Looking at the crazy cascade of components of the preamp, I'm not surprised it's noisy, but still let's try to silent it. Here is an attempt to scope it :
I tried recording the noise and cracklings with my smartphone, attached as file_5_output_sound_noise_crackling.zip
The cracklings aren't the most disturbing and seem to be caused by the tube (removing the tube removes the cracklings). What is disturbing is the noise.
The schematics are attached as well. Do not ask me what version I have, there are notes all over the place and this amp has seen other hands before me.
Edit: reading this page made me wonder if this is worth the effort but let's try 🙂
It would be cool if you guys with decades of experience would be able to assist me.
Kind regards,
Charles
Last edited:
That is a BEAST of an amplifier, 500W RMS into 4 ohm, 620W RMS into 2 ohm, for chest thumping pants flapping power on stage, beside a LOUD drummer and loud Guitar players,and absolutely silent in that situation.
30-40mV peak to peak noise-hum-whatever is NOTHING.
Now, in a bedroom at night, or in a very silent studio, yes, you might hear it. No real problem.
I guess you are "chasing ghosts" 😉
Tell your customer to be realistic 😉
30-40mV peak to peak noise-hum-whatever is NOTHING.
Now, in a bedroom at night, or in a very silent studio, yes, you might hear it. No real problem.
I guess you are "chasing ghosts" 😉
Tell your customer to be realistic 😉
Yes.
Real 50Hz hum requires a solid 50Hz flat speaker, plus we don´t hear low level low frequencies very well.
Now, "buzzing" ... a mosquito putting out a picowatt energy doesn´t let you sleep 🙁
Some people put a .1uF ceramic cap acoss each rectifier diode , it often helps.
You may try that.
Real 50Hz hum requires a solid 50Hz flat speaker, plus we don´t hear low level low frequencies very well.
Now, "buzzing" ... a mosquito putting out a picowatt energy doesn´t let you sleep 🙁
Some people put a .1uF ceramic cap acoss each rectifier diode , it often helps.
You may try that.
Hello everyone,
first let me thank you for looking at my issue. Very qualified answers,I feel I'm standing on the shoulders of giants 🙂
I had the impression as well that this noise is to be expected from a preamp with so many stages of op-amps and circuits. I asked the customer to come to my place and indeed my lab is a very quite place so the noise was very disturbing, but the same on a scene would be ok... remembering the scene of Back to the Future when Marty tries the amp.
Still something I want to understand better are the spikes when zero-crossing the output. Are they related to the push-pull design of the output stage (say some "mis-alignement" of the driving), or to the PSU rectifier bridge ? Would it help to replace the PSU rectifier diodes with FRED ? Currently they look like standard silicium 400V/6A diodes. I'm somewhat reluctant to dis-assemble this board to replace them as it needs removal of a lot of connectors, the complete preamp board, and the regulators screwed to the bottom of the case. Desoldering them from the top is likely not a good idea as I won't be able to correctly resolder them for the under part of the pcb and they carry big currents.
first let me thank you for looking at my issue. Very qualified answers,I feel I'm standing on the shoulders of giants 🙂
I had the impression as well that this noise is to be expected from a preamp with so many stages of op-amps and circuits. I asked the customer to come to my place and indeed my lab is a very quite place so the noise was very disturbing, but the same on a scene would be ok... remembering the scene of Back to the Future when Marty tries the amp.
Still something I want to understand better are the spikes when zero-crossing the output. Are they related to the push-pull design of the output stage (say some "mis-alignement" of the driving), or to the PSU rectifier bridge ? Would it help to replace the PSU rectifier diodes with FRED ? Currently they look like standard silicium 400V/6A diodes. I'm somewhat reluctant to dis-assemble this board to replace them as it needs removal of a lot of connectors, the complete preamp board, and the regulators screwed to the bottom of the case. Desoldering them from the top is likely not a good idea as I won't be able to correctly resolder them for the under part of the pcb and they carry big currents.
You might try to solder a .1uF cap in parallel with each, from the top, either to exposed pad or simply diode leg, without disassembly.
It´s something very common, and worst case, it "does nothing", it will not damage or worsen anything.
Just try it.
Measure /scope noise before/after so as to rule out placebo effect 😉
It´s something very common, and worst case, it "does nothing", it will not damage or worsen anything.
Just try it.
Measure /scope noise before/after so as to rule out placebo effect 😉
I didn't want to make a component order for only 4 capacitors so I took what I had in the component box : Kemet X1 Capacitor, 22nF, 440VAC, 1kVDC, they are metallized polypropylene, not ceramic, but guess what, they did enhance the situation and got rid of the spikes. On the left the speaker output before snubbing the rectifier bridge, on the right after. Meaning the hum is reduced and the spikes are gone. That's a success I would say. Interesting how the waveform changes as well. Now at idle about 20mV P2P remains on the output and that's ok. The line "thickness" seems to be somewhat reduced as well, I suppose the spikes were exciting the preamp circuits.
The the second comparison, with gain and master volumes at 100%, the situation appears to be unchanged, but the amp is indeed somewhat more silent. I can't measure the diff but it's there on my ears.
So I would call it a done job, the bass player will likely be happy with the results. Thanks for all who contributed !
Charles
The the second comparison, with gain and master volumes at 100%, the situation appears to be unchanged, but the amp is indeed somewhat more silent. I can't measure the diff but it's there on my ears.
So I would call it a done job, the bass player will likely be happy with the results. Thanks for all who contributed !
Charles