I do not want to disturb your discussion with Zen Mod...
But for heavens sake, I would put a cap before the pot only to see if the pops and clicks stop....to find the source of the DC.
But for heavens sake, I would put a cap before the pot only to see if the pops and clicks stop....to find the source of the DC.
I understood that ZUM placed caps between pot and Pumpkin input ...... and he aslo put 47K from Pumpkin input +cap node to gnd , to load that node more
pops are still there
if they are , then pops aren't DC issue on Pumpkin side , but on side of attenuator itself
ZUM - what's feeding attenuator ?
edit - I mean - is there any DC going in attenuator itself ?
pops are still there
if they are , then pops aren't DC issue on Pumpkin side , but on side of attenuator itself
ZUM - what's feeding attenuator ?
edit - I mean - is there any DC going in attenuator itself ?
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Thanks guys. I've tried 2 different sources both of which have negligible DC offset. I've also grounded the the inputs on the attenuator with same results.
Generg, sorry, I misunderstood you first suggesting the caps at the attenuator input.
Correct me if I'm wrong but if I ground the inputs without the source attached that should eliminate the source DC issue?
Generg, sorry, I misunderstood you first suggesting the caps at the attenuator input.
Correct me if I'm wrong but if I ground the inputs without the source attached that should eliminate the source DC issue?
The DC offset may not be negligible in that case..... Try a cap between source and attenuator to get it out.....
Generg, I get the symptoms with and without a source with caps installed before Pumpy. Also with inputs grounded, and caps installed at Pumpy input.
Murphy
must be something with physical arrangement ......... and you'll likely have the same , using it in front of any gain stage with same gain
must be something with physical arrangement ......... and you'll likely have the same , using it in front of any gain stage with same gain
I think you are right mighty ZM. I'll rip out the Twisted Pair and find another volume control more suitable. Any suggestions?
Thanks to you and Generg for helping.
Thanks to you and Generg for helping.
try to find something like this - dirt cheap ( say 20E) and hard to beat with anything up to 10x price
must be smd resistors , ladder if possible
one "stereo" per channel , or try to find balanced (then 4 decks , no ladder)
keep it in close proximity to inputs , extending shaft is way to go
either that , or AVC as next possible and worthy step , but they're mostly intended for SE arrangement and , frankly , I didn't tried them (yet) in floating balanced mode
must be smd resistors , ladder if possible
one "stereo" per channel , or try to find balanced (then 4 decks , no ladder)
keep it in close proximity to inputs , extending shaft is way to go
either that , or AVC as next possible and worthy step , but they're mostly intended for SE arrangement and , frankly , I didn't tried them (yet) in floating balanced mode
Attachments
Incredible....!
Of course it is now the time to say again the the sound comes from the attenuator.
Does the attenuator use a separate PSU?
Are the grounds of this PSU and Pumpkin connected?
Maybe you wrote this already.....
I just didn't want to answer with depressive silence ......🙂
Good idea, the attenuator power supply is floating so I've just grounded it with my star ground but no luck. I did measure the potential and it was less than a millivolt before grounding it.
try grounding attenuator audio gnd to some other point on P&S combo
did you ever tried it with any other gain stage , at preceding position ?
did you ever tried it with any other gain stage , at preceding position ?
You mean the attenuator? I have the same in the Aleph P. I exchanged the control boards to test since that was easy with same results. It's not worth it to me to continue trouble shooting this. I'll source another volume control. Thanks for your efforts in helping.
Cheers
Rick
Cheers
Rick
ZM,
While looking for a alternative volume control I had a go at my new to me oscilloscope. I think I'm finding oscillations in the Pumpy. I've attached photos showing a 1K square wave and then of the 1K up close and the last one is the Pumpy inputs grounded. What ever it is it is the same frequency so I don't know if it just noise or there is a problem. The scope is at the end of it's adjustments, .2uS and 5mV with x5 setting. I see the same results all up and down the volume control settings as well as grounded inputs.
Thanks
Rick
While looking for a alternative volume control I had a go at my new to me oscilloscope. I think I'm finding oscillations in the Pumpy. I've attached photos showing a 1K square wave and then of the 1K up close and the last one is the Pumpy inputs grounded. What ever it is it is the same frequency so I don't know if it just noise or there is a problem. The scope is at the end of it's adjustments, .2uS and 5mV with x5 setting. I see the same results all up and down the volume control settings as well as grounded inputs.
Thanks
Rick
Attachments
input wires to Pumpkin twisted ?
if that's no helping , tell me values (you're using ) of R5 and R6 , same as C1 and C2
you can try with disarming JP1 as first step , or increasing values of C1 and C2
you can go down to 45-50K (1/(2ΠRC)) without harm
if that's no helping , tell me values (you're using ) of R5 and R6 , same as C1 and C2
you can try with disarming JP1 as first step , or increasing values of C1 and C2
you can go down to 45-50K (1/(2ΠRC)) without harm
Thanks,
The R5 and R6 are 100k and C1 and 2 are 5pF as per Cookbook. When you say disarming JP1 you mean separate the ground planes? The input wires are not twisted but are short at about 50-60mm.
The R5 and R6 are 100k and C1 and 2 are 5pF as per Cookbook. When you say disarming JP1 you mean separate the ground planes? The input wires are not twisted but are short at about 50-60mm.
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You're getting something in the range of low MHz - generally I have found that poor wiring on the bench induced positive feedback around an amplifier produces oscillations in the few hundred kHz range. To get oscillations in MHz range I found it more likely to be quite localized to an unstable feedback loop on the circuit board itself, possibly via the power rails or the grounds. Are those heatsinks grounded ? You could try taking a board or two out of the chassis and separating them a bit to see if some local coupling is the problem.
Once I had similar very low level oscillations at the limit of my scope and it turned out not to be oscillations from my amplifier but from another source (another piece of test gear or a nearby appliance - there are lots of sources of 'environmental noise' around my house, including my CD player) that was getting picked up by the scope probe or grounding. The oscillations were still there when my amplifier was not powered!
Once I had similar very low level oscillations at the limit of my scope and it turned out not to be oscillations from my amplifier but from another source (another piece of test gear or a nearby appliance - there are lots of sources of 'environmental noise' around my house, including my CD player) that was getting picked up by the scope probe or grounding. The oscillations were still there when my amplifier was not powered!
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Hi Bigun,
Thanks for the help. No, the heatsinks are not grounded. I've actually probed them and see the same oscillations. It could be environmental noise. I've done what I could to eliminate as much as possible. Lights off, just the scope and Pumpy on. I'm in my garage and there is nothing else on the power circuit.
Thanks for the help. No, the heatsinks are not grounded. I've actually probed them and see the same oscillations. It could be environmental noise. I've done what I could to eliminate as much as possible. Lights off, just the scope and Pumpy on. I'm in my garage and there is nothing else on the power circuit.