Non-Traditional 15 watt Liverpool with PCB
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Re: Non-Traditional 15 watt Liverpool with PCB
Here's my half-liv PCB:
[IMG:165:123]http://img11.hostingpics.net/thumbs/mini_225244liv1.jpg[/img]
It works but there is a big "hum" and a little hissss. Sounds like ground loop or something, however the ground points seem to be as good... any idea ?
[IMG:165:123]http://img11.hostingpics.net/thumbs/mini_225244liv1.jpg[/img]
It works but there is a big "hum" and a little hissss. Sounds like ground loop or something, however the ground points seem to be as good... any idea ?
Re: Non-Traditional 15 watt Liverpool with PCB
Make sure those stanchions in each corner are grounding to the chassis.
At least if I remember correctly that was the path to ground for that PCB board.
Also, filament supply center tap is grounded right? white/brown strip wire.
Mark
At least if I remember correctly that was the path to ground for that PCB board.
Also, filament supply center tap is grounded right? white/brown strip wire.
Mark
Re: Non-Traditional 15 watt Liverpool with PCB
RJ,
I would be curious IF the grounds in each corner could be contributing to the noise. It appears that there are separate (distributed filtering) stages but appears each stage does not go back to the respective cap ground?? I generally ground everything after the individual stage coupling caps to the previous filter stage ground (towards the rectifier). Are there ground traces underneath the board? From the top view it looks like there may be a series of ground loops??
1) I would try removing the screws (temporarily), put a piece of tape or paper under the corner ground points and use clip leads to imitate a star ground.
2) Try insulating the input jack, just remove from the chassis as a test.
3) Also curious IF the OT wires are picking up some buzz from the diodes?
I think I would focus on the ground points #1 the most.
Good luck, John
I would be curious IF the grounds in each corner could be contributing to the noise. It appears that there are separate (distributed filtering) stages but appears each stage does not go back to the respective cap ground?? I generally ground everything after the individual stage coupling caps to the previous filter stage ground (towards the rectifier). Are there ground traces underneath the board? From the top view it looks like there may be a series of ground loops??
1) I would try removing the screws (temporarily), put a piece of tape or paper under the corner ground points and use clip leads to imitate a star ground.
2) Try insulating the input jack, just remove from the chassis as a test.
3) Also curious IF the OT wires are picking up some buzz from the diodes?
I think I would focus on the ground points #1 the most.
Good luck, John
Re: Non-Traditional 15 watt Liverpool with PCB
I think I only used one aluminum standoff as ground and nylon or plastic on the other three standoffs.
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Re: Non-Traditional 15 watt Liverpool with PCB
Looks like all six of the board mounting screws are supposed to function as grounds. Is it possible that there is not a good contact between the the screw heads and/or stand-offs and the traces due to the thickness of the solder mask? Maybe an internal tooth star washer would help? I think I would connect the ground for the last three filters (upper right corner of the board) to the input jack only. The others may be ok as they are as long as good contact is made with the chassis.
Re: Non-Traditional 15 watt Liverpool with PCB
Yeah Martin I can't remember but all standoffs look like they are ground connectors. I used internal star washers to keep things tight.
rj can fill us in to be sure.
rj can fill us in to be sure.
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Re: Non-Traditional 15 watt Liverpool with PCB
Vincent,
thanks for posting this up. I love to see the build progress and I'm not sensitive about it if folks are having issues putting together a package I sent out... we all learn and benefit. I'll re-post my build photo for comparisons sake... this is pre-master volume but the amp was finished otherwise. I get the hiss but not the hum.
The grounds are at the corners of the PCB board and we've done about 12 of them now without issue so I am looking for other sources of hum... this is only the 2nd Liverpool so maybe some subtle differences. It's also the first one done in a Euro-voltage so maybe something to be learned there as well.
I'd like to send you out a 1K 25 watt power resistor, not sure that it is any issue but I meant to change out the traditional power resistor for the chassis mounts in the PCB packages... I'll be updating the parts list as we go.
Thanks again for sharing this.
rj
thanks for posting this up. I love to see the build progress and I'm not sensitive about it if folks are having issues putting together a package I sent out... we all learn and benefit. I'll re-post my build photo for comparisons sake... this is pre-master volume but the amp was finished otherwise. I get the hiss but not the hum.
The grounds are at the corners of the PCB board and we've done about 12 of them now without issue so I am looking for other sources of hum... this is only the 2nd Liverpool so maybe some subtle differences. It's also the first one done in a Euro-voltage so maybe something to be learned there as well.
I'd like to send you out a 1K 25 watt power resistor, not sure that it is any issue but I meant to change out the traditional power resistor for the chassis mounts in the PCB packages... I'll be updating the parts list as we go.
Thanks again for sharing this.
rj
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Re: Non-Traditional 15 watt Liverpool with PCB
Hi Rj,
I just see one thing on your build: just under the standby switch, did you ground the white/yellow wire ? I did not, could this be the issue's reason ?
Actually, I can identify 3 differences between our respective builds:
1. Euro voltage PT
2. I wired the presence pot according to the Liverpool layout (your is Express)
3. I attached the ceramic 1k 25w resistor onto the PCB, because there was enough room to do it, and I thought it was nice.
I just see one thing on your build: just under the standby switch, did you ground the white/yellow wire ? I did not, could this be the issue's reason ?
Actually, I can identify 3 differences between our respective builds:
1. Euro voltage PT
2. I wired the presence pot according to the Liverpool layout (your is Express)
3. I attached the ceramic 1k 25w resistor onto the PCB, because there was enough room to do it, and I thought it was nice.
Re: Non-Traditional 15 watt Liverpool with PCB
well, any thought regarding the yellow/white grouding ?
And the 3 others points above ?
And the 3 others points above ?
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Re: Non-Traditional 15 watt Liverpool with PCB
I'll attach a better photo of the wiring...
The yellow and white is a center tap for the 5V winding... what is important is that I don't use the 5V winding, the yellow wires are just bundled there but only the CT goes to ground. For those that might be tempted to ground the center tap on the 5V winding, don't do that if you are using it with a rectifier tube.
The yellow and white is a center tap for the 5V winding... what is important is that I don't use the 5V winding, the yellow wires are just bundled there but only the CT goes to ground. For those that might be tempted to ground the center tap on the 5V winding, don't do that if you are using it with a rectifier tube.
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Re: Non-Traditional 15 watt Liverpool with PCB
Ok... I doubt that will fix the hum, but I will try to ground it as you did...
And do you think the presence wiring or the 1k/25w resistor location would be the cause of the issue?
And do you think the presence wiring or the 1k/25w resistor location would be the cause of the issue?
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Re: Non-Traditional 15 watt Liverpool with PCB
It doesn't look to me like you have the 1k screen dropping resistor connected to the second filter cap ??? have you done that under the board?
The presence control is pretty sensitive and can cause issues ... I don't like the 'newer' style presence control like used in the Liverpool.
The presence control is pretty sensitive and can cause issues ... I don't like the 'newer' style presence control like used in the Liverpool.
Re: Non-Traditional 15 watt Liverpool with PCB
To check continuity of grounds, put one probe at the solder joint of the component nearest to ground and the other probe to the chassis. Resistance should measure less than one ohm between circuit and ground.
To test whether the tubes are generating the hum, swap tube positions and listen for changes in the quality of the hum.
To isolate sections creating the hum, pull tubes starting at V1, then V2, then PI.
Beyond that, it would be useful to measure voltages at each tube.
There's not much left. We'll get there soon.
Regards,
George
To test whether the tubes are generating the hum, swap tube positions and listen for changes in the quality of the hum.
To isolate sections creating the hum, pull tubes starting at V1, then V2, then PI.
Beyond that, it would be useful to measure voltages at each tube.
There's not much left. We'll get there soon.
Regards,
George
Re: Non-Traditional 15 watt Liverpool with PCB
Looks grand RJ- thanks for keeping us in the loop !!
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Re: Non-Traditional 15 watt Liverpool with PCB
Vincent,
Keep chugging away, you have access to the best 24/7 tech support on the planet here at TAG...
I'll try to look over the photos again. In the mean time I would be curious what your voltages look like.
thanks,
rj
Keep chugging away, you have access to the best 24/7 tech support on the planet here at TAG...
I'll try to look over the photos again. In the mean time I would be curious what your voltages look like.
thanks,
rj
Good, Fast, or Cheap -- Pick two...
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