Hi All,
Looking for some help with a Dumble #183 build. The amp is together and working, but there is some unwanted noise coming from the relay circuit. I used the Hoffman relay boards and power supply. which runs off the heaters. The heaters are center tapped w/2 150r resistors per the schematic. The 5v+ supply runs to a pair spdt switches on the back of the amp for channel switch and preamp boost. It then comes out of the switches to a stereo jack for a 2 button footswitch, which has the same spdt switching configuration. It then runs to the corresponding relays, then the negative sides are connected and run back to the power supply. If I touch the chassis, the hum reduces. When I unplug the footswitch, the hum goes away almost completely. When I disconnect both sides of the power supply and ground out the negative terminals of the relays, the noise totally goes away.
This is the first time I've done a build that uses relays. Any help would be much appreciated. Thanks.
Dumble Channel Switching Relay Noise Help
Moderators: pompeiisneaks, Colossal
Re: Dumble Channel Switching Relay Noise Help
You have created multiple ground references for the filament suply. I would isolate the relay supply from the filament supply by using a dedicated 6.3V transformer.
TM
TM
Re: Dumble Channel Switching Relay Noise Help
Is you footswitch jack isolated from the chassis? I've had to use plastic 1/4" jacks for the footswitch in order to keep from forming ground loops.
Re: Dumble Channel Switching Relay Noise Help
Yes mhartman, the footswitch jack is isolated from the chassis w/a cliff jack. ToneMerc, I had thought of adding a dedicated trans, but talked myself out of it on the premise that the 5vdc relay power isn't connected to a chassis ground. I'll try that now. Thanks for your help guys.
Re: Dumble Channel Switching Relay Noise Help
Hey ToneMerc (or others with any insight)
Not to hijack but my question is related
I am in the middle of an SLO style build using a Marshall style pt that does not have extra 6.3v taps for the switching supply
I bought a small transformer but am unsure where to put it for least noise - it will fit in the chassis by the PT/power supply board or I could put it up top somewhere.
The current chassis layout has PT and OT at opposite ends and choke in the middle (which I have read is kind of a no no because the choke can add to any magnetic coupling that might happen) but for not it is what it is and I see many high gain builds with that layout.
I worry adding the small transformer for the switching supply will possibly add to any coupling or noise problems I might run into.
1st picture picture of inside of chassis is where I was thinking I would put it (between power supply board and main board near in upper center in photo) and other picture shows the topside layout if someone thinks it might be better up there.
How about orientation? Any suggestions
any insight would be greatly appreciated
Not to hijack but my question is related
I am in the middle of an SLO style build using a Marshall style pt that does not have extra 6.3v taps for the switching supply
I bought a small transformer but am unsure where to put it for least noise - it will fit in the chassis by the PT/power supply board or I could put it up top somewhere.
The current chassis layout has PT and OT at opposite ends and choke in the middle (which I have read is kind of a no no because the choke can add to any magnetic coupling that might happen) but for not it is what it is and I see many high gain builds with that layout.
I worry adding the small transformer for the switching supply will possibly add to any coupling or noise problems I might run into.
1st picture picture of inside of chassis is where I was thinking I would put it (between power supply board and main board near in upper center in photo) and other picture shows the topside layout if someone thinks it might be better up there.
How about orientation? Any suggestions
any insight would be greatly appreciated
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Re: Dumble Channel Switching Relay Noise Help
Lindz,
Put it right by the indicator light. Keep the diodes and ac wires away from the NFB and or the presence pot, grid wires from the master vol etc.
Put it right by the indicator light. Keep the diodes and ac wires away from the NFB and or the presence pot, grid wires from the master vol etc.
Re: Dumble Channel Switching Relay Noise Help
Thanks for the tips John
So you feel inside should be OK if I keep it away from sensitive areas?
Since you are not familiar with my layout it would not be apparent that where I have it laid out in the picture is further from the NFB than if I locate it by the pilot light (the pots closest to the pilot light are Resonance and Presence) and where I have it in the picture, the 6.3v out of the transformer only has to run for a couple inches to the switching circuit on the top left of the board in the picture - the four empty turrets in a square are where the switching supply rectifier goes and the filter cap etc for the switching supply are located.
By the pilot light would result in me having to run the 6.3v to that point on the board, a few more inches than as shown in the picture if I ran direct across the chassis to it, or several more inches if I snake around the chassis edge.
That said would there be any other reason you would see locating by the pilot light a potentially less noisy position? I know one would be speculating as this is a non standard layout but I assume many of you may have put switching or reverb tranformers in amps before and have experience keeping things quiet when using them
So you feel inside should be OK if I keep it away from sensitive areas?
Since you are not familiar with my layout it would not be apparent that where I have it laid out in the picture is further from the NFB than if I locate it by the pilot light (the pots closest to the pilot light are Resonance and Presence) and where I have it in the picture, the 6.3v out of the transformer only has to run for a couple inches to the switching circuit on the top left of the board in the picture - the four empty turrets in a square are where the switching supply rectifier goes and the filter cap etc for the switching supply are located.
By the pilot light would result in me having to run the 6.3v to that point on the board, a few more inches than as shown in the picture if I ran direct across the chassis to it, or several more inches if I snake around the chassis edge.
That said would there be any other reason you would see locating by the pilot light a potentially less noisy position? I know one would be speculating as this is a non standard layout but I assume many of you may have put switching or reverb tranformers in amps before and have experience keeping things quiet when using them