I have a valve integrated, audio innovations series 3 MK2. Uses 12AX7 and ECL86.
Lovely amp, great sound etc etc etc. I also have a chinese 6P1 amp, also ovely soudn but different flavour.
Both have a volume control that is a simple pot, 100K I think.
AFAIK, on the chinese amp this volume control is situated on the line in from the input RCAs, ie acts as a simple attenuator. Why is it when I turn the pot up all the way (ie defeated) I get hum/buzz etc etc (like full power)?
Next question, the AI300 is the same although I think that in this case the volume pot is after the preamp section and before the ECL86s. Turn it up more than halfway and you hear a significant amount of hum/buzz. Again, why is this?
I was under the impression that with the pot turned all the way up, you were basically having the amp running at full power (eg like a power amp). Reason I ask is that I've just built a passive pre and was going to use the attenuator on it to control volume rather than the one on the amp. (although even with the volume halfway up on either amp, befoer I hear buzz, I still have enough gain). A RLD should be started in the near future.
A bit rambling I know, but comments please!
Fran
Lovely amp, great sound etc etc etc. I also have a chinese 6P1 amp, also ovely soudn but different flavour.
Both have a volume control that is a simple pot, 100K I think.
AFAIK, on the chinese amp this volume control is situated on the line in from the input RCAs, ie acts as a simple attenuator. Why is it when I turn the pot up all the way (ie defeated) I get hum/buzz etc etc (like full power)?
Next question, the AI300 is the same although I think that in this case the volume pot is after the preamp section and before the ECL86s. Turn it up more than halfway and you hear a significant amount of hum/buzz. Again, why is this?
I was under the impression that with the pot turned all the way up, you were basically having the amp running at full power (eg like a power amp). Reason I ask is that I've just built a passive pre and was going to use the attenuator on it to control volume rather than the one on the amp. (although even with the volume halfway up on either amp, befoer I hear buzz, I still have enough gain). A RLD should be started in the near future.
A bit rambling I know, but comments please!
Fran
Fran,
I had similar problems with my new Aikido, although the hum was not all that bad. In the end, I elected to build a simple voltage (L-pad) inside my power-amp. My main amp is an AKSA 55N, solid-state (not tube). The input impedence is around 47K. On a previous post someone suggested that 47K would be less prone to noise than the 100K end. Anyway, it worked, I purchased a bunch of high precision resistors and found the combination that gave 47K and the attenuation I wanted.
You could also look for Ground Loops. Check that your pots are fully insulated from the chassis?
Also connecting my DVD player caused a loud hum, which I removed by disconnecting the signal GND on the preamp RCA's that connect to the DVD player.
I hope this helps.
BTW, where in Ireland are you? I have family near Clonakilty, Co. Cork. It is really beautiful down there.
Charlie
I had similar problems with my new Aikido, although the hum was not all that bad. In the end, I elected to build a simple voltage (L-pad) inside my power-amp. My main amp is an AKSA 55N, solid-state (not tube). The input impedence is around 47K. On a previous post someone suggested that 47K would be less prone to noise than the 100K end. Anyway, it worked, I purchased a bunch of high precision resistors and found the combination that gave 47K and the attenuation I wanted.
You could also look for Ground Loops. Check that your pots are fully insulated from the chassis?
Also connecting my DVD player caused a loud hum, which I removed by disconnecting the signal GND on the preamp RCA's that connect to the DVD player.
I hope this helps.
BTW, where in Ireland are you? I have family near Clonakilty, Co. Cork. It is really beautiful down there.
Charlie
all the pots I am using are just mounted directly to the chassis - so definitely the mounting part/body of the pot/attenuator (broskie stepped one in the case of the passive pre) are directly connected to the chassis. Actually now that I think about it, the darwin source selector uses 2 pots for input and output selection. These are essentialy voltage switches, switching ground on a 5VDC line to the relays on the boards. They are mounted close enough to the broskie attenuator and the body of the pots would also be directly connected to the chassis.
However, as I can see it, these pots are all meant to be connected like this to the chassis. Is there something I'm missing here?
Fran
However, as I can see it, these pots are all meant to be connected like this to the chassis. Is there something I'm missing here?
Fran
Sources are CDP/TT/Squeezebox/Tuner/Tape Deck.
I have asked around locally here to me to see if anyone would have a power amp I could borrow. That way I can see how much/what the preamp adds in terms of noise.
I also want to bypass the broskie stepped atten. to rule it out also. When I do that i will also isolate the pots to see if that makes any difference.
Keep the suggestions coming!
Fran
I have asked around locally here to me to see if anyone would have a power amp I could borrow. That way I can see how much/what the preamp adds in terms of noise.
I also want to bypass the broskie stepped atten. to rule it out also. When I do that i will also isolate the pots to see if that makes any difference.
Keep the suggestions coming!
Fran
Hi Fran,
Don't know if this will help but I had the same experience recently in one channel on my Baby Huey amp - when I turned up the vol, a strong hum got louder in one channel only. I traced it down to the DC increasing on this channel as I turned up the pot. The cause of this was a wrongly adjusted CCS on the differential pair feeding the output tubes.
As I said, don't know if this helps but maybe you can check out if there is any DC on the Vol pot.
John
Don't know if this will help but I had the same experience recently in one channel on my Baby Huey amp - when I turned up the vol, a strong hum got louder in one channel only. I traced it down to the DC increasing on this channel as I turned up the pot. The cause of this was a wrongly adjusted CCS on the differential pair feeding the output tubes.
As I said, don't know if this helps but maybe you can check out if there is any DC on the Vol pot.
John
OT: passive preamp
Hi all,
Finally got a chance to go and do some checking out on this. Turns out I do have some DC on the outputs. I did manage to reduce this somewhat by adding and extra ground from the PS back to the safety earth but its still there.
So I says to myself, if I add in a DC blocking cap on the outputs, lets see if that sorts out the problem. And lo and behold, it did. I just happened to have some 4.7uF 16V non-polar blackgates, so I soldered these in between signal ground and signal hot for each channel on one of the outputs, ie 1 cap per channel. Hum now completely gone.
However you shut one door and another opens! I obviously have set up some kind of filter because the broskie stepped attenuator now doesn't work! ie sound comes through when the attenuator is "off" but as soon as I switch it down to attenuate, the signal dissappears. So this must now be blocking the AC as well due to the set up between resistors in the attenuator and the caps on the outputs.
At this stage I cry HELP! Has anyone any solutions for me? To put it concisely: How can I eliminate the hum or alternatively how should I add in a blocking cap (should it be in series with the signal hot or paralleled from signal hot to ground?)
Fran
Fran
Hi all,
Finally got a chance to go and do some checking out on this. Turns out I do have some DC on the outputs. I did manage to reduce this somewhat by adding and extra ground from the PS back to the safety earth but its still there.
So I says to myself, if I add in a DC blocking cap on the outputs, lets see if that sorts out the problem. And lo and behold, it did. I just happened to have some 4.7uF 16V non-polar blackgates, so I soldered these in between signal ground and signal hot for each channel on one of the outputs, ie 1 cap per channel. Hum now completely gone.
However you shut one door and another opens! I obviously have set up some kind of filter because the broskie stepped attenuator now doesn't work! ie sound comes through when the attenuator is "off" but as soon as I switch it down to attenuate, the signal dissappears. So this must now be blocking the AC as well due to the set up between resistors in the attenuator and the caps on the outputs.
At this stage I cry HELP! Has anyone any solutions for me? To put it concisely: How can I eliminate the hum or alternatively how should I add in a blocking cap (should it be in series with the signal hot or paralleled from signal hot to ground?)
Fran
Fran
OK, a better description:
Its a passive preamp using a broskie stepped attenuator and a Darwin source selector from www.twistedpearaudio.com. This is a relay based selector. So in the pre, I have a simple 240V-12V transformer, which then goes through a cap 3300 uF - LM7805 - 3300uF cap to give a simple 5VDC supply for the relays. The idea of the relays is that the signal doesn't have to go through a switch in the normal way (and gives you 6 inputs and 2 outputs).
So going though the thing tonight, I find I have DC (2mV) on the broskie attenuator, but its also there before the attenuator. As I think now, I didn't check the CDP I was using, but its there on any source I've tried. Somehow the CD is getting into the signal on the relay board - I must open it up again and see if I can see any short anywhere. Problem lies within the preamp (tried out the power amp on its own and no hum/buzz).
However, I think now I put in the cap wrong: The non-polar should have been in series on the hot of each signal, not across the ground and hot. Could someone confirm that this is the way it should be...
Sorry I have no drawing or photos, I'll do some tomorrow.
Fran
Its a passive preamp using a broskie stepped attenuator and a Darwin source selector from www.twistedpearaudio.com. This is a relay based selector. So in the pre, I have a simple 240V-12V transformer, which then goes through a cap 3300 uF - LM7805 - 3300uF cap to give a simple 5VDC supply for the relays. The idea of the relays is that the signal doesn't have to go through a switch in the normal way (and gives you 6 inputs and 2 outputs).
So going though the thing tonight, I find I have DC (2mV) on the broskie attenuator, but its also there before the attenuator. As I think now, I didn't check the CDP I was using, but its there on any source I've tried. Somehow the CD is getting into the signal on the relay board - I must open it up again and see if I can see any short anywhere. Problem lies within the preamp (tried out the power amp on its own and no hum/buzz).
However, I think now I put in the cap wrong: The non-polar should have been in series on the hot of each signal, not across the ground and hot. Could someone confirm that this is the way it should be...
Sorry I have no drawing or photos, I'll do some tomorrow.
Fran
No, Fran, definitely in series, if I understand correctly.
Also it would seem that you are more or less solving your own problems. If further serious problems a diagram might help. Strange about the dc on the inputs - as said, it will need investigating.
I just saw a screen-flash that someone else has posted, so you may now get 2 replies.
Regards.
Also it would seem that you are more or less solving your own problems. If further serious problems a diagram might help. Strange about the dc on the inputs - as said, it will need investigating.
I just saw a screen-flash that someone else has posted, so you may now get 2 replies.
Regards.
OK,
I added the cap in series and it has cured the hum. Still a tiny bit there, so I will need to investigate this further. However, now when I turned the broskie attenuator, I get a good loud pop on each step (but only on the step of the centre control, not on the others). The lord giveth and the lord taketh away!!!!!!!!
So I now have to investigate a new issue!!!! Any ideas anyone???
This is now very off-topic and I'm sorry for that.....
Fran
I added the cap in series and it has cured the hum. Still a tiny bit there, so I will need to investigate this further. However, now when I turned the broskie attenuator, I get a good loud pop on each step (but only on the step of the centre control, not on the others). The lord giveth and the lord taketh away!!!!!!!!
So I now have to investigate a new issue!!!! Any ideas anyone???
This is now very off-topic and I'm sorry for that.....
Fran
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An externally hosted image should be here but it was not working when we last tested it.
Ideas? Yes. You are switching over a voltage step, however small. But I am surprised you have it after the capacitor was added and not before. Where one switches with caps in the circuit one needs to bring both sides of the switch on the same (dc) potential, as it were, mostly by bypassing switch contacts with a resistor value large enough not to influence the operation itself.
But to solve this a circuit of what you have is necessary. I will look up the Broskie (must run now) and come back later. Perhaps others are more "hands-on" than myself.
Regards,
But to solve this a circuit of what you have is necessary. I will look up the Broskie (must run now) and come back later. Perhaps others are more "hands-on" than myself.
Regards,
I'm guessing that something like a ground connection somewhere in the broskie is needed. I don't have a schematic here for the broskie but more info can be found here:
PDF of broskie stepped attenuator
tubecad page for stepped attenuator
Fran
PDF of broskie stepped attenuator
tubecad page for stepped attenuator
Fran
Hello Fran
There are two kinds of hum: electrostatic and magnetic.
You get electrostatic hum (pickup) in any high resistance circuit (like your 100K pots). For a quick sheck put your finger onm a signal wire (not the hi volts!). This is because all things have capacitance beteween them so your input "sees" the mains wires in your house.
Magnetic pickup is different. If ANYWHERE you have a closed loop of wire (any thing grounded more than once) then the magnetic fields in the air of your house (and from the supply transformer) thred this and it acts as a shorted turn - many anps can flow!. This causes voltage drops (resistance of wires) and your amplifier picks them up eand amplifies them - even in "ground" and "chassis"..
To test for electrostatic, enclose the whole thing in a grounded metal box. If the hum goes it is electrostatic.
Magnetic is harder. All you can do is disconnect earth and chassis wires one by one and see if the hum goes.
Good luck and have fum
John
There are two kinds of hum: electrostatic and magnetic.
You get electrostatic hum (pickup) in any high resistance circuit (like your 100K pots). For a quick sheck put your finger onm a signal wire (not the hi volts!). This is because all things have capacitance beteween them so your input "sees" the mains wires in your house.
Magnetic pickup is different. If ANYWHERE you have a closed loop of wire (any thing grounded more than once) then the magnetic fields in the air of your house (and from the supply transformer) thred this and it acts as a shorted turn - many anps can flow!. This causes voltage drops (resistance of wires) and your amplifier picks them up eand amplifies them - even in "ground" and "chassis"..
To test for electrostatic, enclose the whole thing in a grounded metal box. If the hum goes it is electrostatic.
Magnetic is harder. All you can do is disconnect earth and chassis wires one by one and see if the hum goes.
Good luck and have fum
John