Monkeymatic ODS #183

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JazzGuitarGimp
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Re: Monkeymatic ODS #183

Post by JazzGuitarGimp »

xtian wrote: Wed Jun 14, 2017 4:02 pm I have a ground issue with my switching system. It's a bit noisy (hum) when OD is engaged, and much noisier when the footpedal is attached. Currently, the +5v/0v leads from the 5v PSU are connected to the relay boards and to the switching DIN jack, but I do not have the 0v return connected to the chassis anywhere. What's best practice here?

EDIT: The DC from the 5v PSU is currently reading 1.5v/-3.5v WRT chassis. I tried grounding the 0v lead to chassis, and that gets me a significant HUM in the output.

I just tried grounding the 0v lead from the switching PSU to chassis, and my jumper wire heated up quickly--so there's quite a bit of current flowing.

What did I do wrong?
Are you using a separate PT for the relay PS, or a winding on the main PT? Is this transfomer / winding used for anything else in the build (eg, heater string)? Can you post a schematic of at least the entire power supply?
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xtian
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Re: Monkeymatic ODS #183

Post by xtian »

Thanks, Dave!

Yes, the 6.3vAC supply has a CT that was grounded to chassis. I have lifted this now. Switching PSU still seems to be operating fine--it measures 4.99vDC at output, very steady. However, this 5vDC is floating, WRT chassis.

I still have the same noise issues. So, now that we've cleared the first hurdle, should I be referencing the 5vDC supply to chassis somewhere?
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Re: Monkeymatic ODS #183

Post by xtian »

Lou, I don't have an updated schematic. But...you know the main power board pretty well...
IMG_8093.jpg
IMG_8094.jpg
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Re: Monkeymatic ODS #183

Post by xtian »

In looking at the #124 layout, I see that A) the 7812 voltage regulator is bonded to the chassis, which is OK, I guess, because the body is ground, as is pin 2. B) the filter caps are grounded to the same spot on the chassis. C) a ground return wire runs from the switches on the rear panel all the way back to the same chassis ground point.

I went to the trouble to isolate the 7812 from the chassis with a mica insulator, so it's not grounded.

Now that I have lifted the AC center tap, I should be able to bond the output 0v to the chassis, right?
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Re: Monkeymatic ODS #183

Post by Colossal »

xtian wrote: Wed Jun 14, 2017 4:53 pm Thanks, Dave!

Yes, the 6.3vAC supply has a CT that was grounded to chassis. I have lifted this now. Switching PSU still seems to be operating fine--it measures 4.99vDC at output, very steady. However, this 5vDC is floating, WRT chassis.

I still have the same noise issues. So, now that we've cleared the first hurdle, should I be referencing the 5vDC supply to chassis somewhere?
Ok, that is good about the PS board.

The entire PS and any relay boards are grounded at ONE point downstream. Carry the 0V/ground pad from the PS down to the next relay, and the next. The ground returns from the footswitch all come back to the DIN jack and from there, everything grounds to ONE point on the chassis.

The 7805 regulator should have the (supplied) Thermosil insulator pad between the chassis and the regulator.
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Re: Monkeymatic ODS #183

Post by xtian »

OK, all good now.

I used an alligator clip to try grounding the switching system from the DIN plug to various points--they all sounded the same, except if I reached way back to the 5v PSU, then I got a lot of hum. Ended up grounding to the FX loop jacks, because convenient, and resulted in lowest noise.

Thanks!
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Re: Monkeymatic ODS #183

Post by norburybrook »

Colossal wrote: Wed Jun 14, 2017 5:42 pm
xtian wrote: Wed Jun 14, 2017 4:53 pm Thanks, Dave!

Yes, the 6.3vAC supply has a CT that was grounded to chassis. I have lifted this now. Switching PSU still seems to be operating fine--it measures 4.99vDC at output, very steady. However, this 5vDC is floating, WRT chassis.

I still have the same noise issues. So, now that we've cleared the first hurdle, should I be referencing the 5vDC supply to chassis somewhere?
Ok, that is good about the PS board.

The entire PS and any relay boards are grounded at ONE point downstream. Carry the 0V/ground pad from the PS down to the next relay, and the next. The ground returns from the footswitch all come back to the DIN jack and from there, everything grounds to ONE point on the chassis.

The 7805 regulator should have the (supplied) Thermosil insulator pad between the chassis and the regulator.
are these precision power supplies different in their grounding?

Only reason I'm asking is, the traditional power boards ground in 3 different places, don't know if that has a relevance here.

actually as I'm midway through a build the BM I'm building had a precision power supply on the layout and that shows the same three grounding points.
Bluesmaster Rev6.jpg



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Re: Monkeymatic ODS #183

Post by Colossal »

Sorry for any confusion Marcus. The power supply board I was referring to in my reply to Xtian is the little dedicated 5VDC board I supply with my relay boards.
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Re: Monkeymatic ODS #183

Post by norburybrook »

Colossal wrote: Wed Jun 14, 2017 6:40 pm Sorry for any confusion Marcus. The power supply board I was referring to in my reply to Xtian is the little dedicated 5VDC board I supply with my relay boards.
Doh!!!! you know what they say about a little knowledge.......


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Re: Monkeymatic ODS #183

Post by JazzGuitarGimp »

norburybrook wrote: Wed Jun 14, 2017 6:25 pm
Colossal wrote: Wed Jun 14, 2017 5:42 pm
xtian wrote: Wed Jun 14, 2017 4:53 pm Thanks, Dave!

Yes, the 6.3vAC supply has a CT that was grounded to chassis. I have lifted this now. Switching PSU still seems to be operating fine--it measures 4.99vDC at output, very steady. However, this 5vDC is floating, WRT chassis.

I still have the same noise issues. So, now that we've cleared the first hurdle, should I be referencing the 5vDC supply to chassis somewhere?
Ok, that is good about the PS board.

The entire PS and any relay boards are grounded at ONE point downstream. Carry the 0V/ground pad from the PS down to the next relay, and the next. The ground returns from the footswitch all come back to the DIN jack and from there, everything grounds to ONE point on the chassis.

The 7805 regulator should have the (supplied) Thermosil insulator pad between the chassis and the regulator.
are these precision power supplies different in their grounding?

Only reason I'm asking is, the traditional power boards ground in 3 different places, don't know if that has a relevance here.

actually as I'm midway through a build the BM I'm building had a precision power supply on the layout and that shows the same three grounding points.

Bluesmaster Rev6.jpg




Marcus
Hi Marcus,

Yes, there are a few differences. The board Aaron is using is my take on the PPS, but I have also added all the circuitry of the rectifier / bias board into the same PPS footprint and mounting hole locations. I have broken the PI node's ground off the Preamp node, to give the build a choice of grounding the PI at the preamp ground or the power amp ground. Some people (myself included) prefer to ground the PI at the power amp ground. Schematic is attached. I will be making these boards available for purchase in the near future.

Cheers,
Lou
Schematic, Luigi Retro-Custom PPS-1.pdf
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Re: Monkeymatic ODS #183

Post by xtian »

My other note for today on the #183 is about the two-position bright switch. Schematic calls for 100p and 220p bright caps. I am almost always allergic to bright caps, so often halve their value, or omit entirely. In my build, I have now gone from 47p/120p back to original 100p/220p values, and am much happier. There really is a stupid amount of tonal flexibility in this amp, and the original value bright caps are a good part of the tonal menu.
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Re: Monkeymatic ODS #183

Post by martin manning »

xtian wrote: Wed Jun 14, 2017 6:24 pmI used an alligator clip to try grounding the switching system from the DIN plug to various points--they all sounded the same, except if I reached way back to the 5v PSU, then I got a lot of hum. Ended up grounding to the FX loop jacks, because convenient, and resulted in lowest noise.
This doesn't seem to make sense. Keeping the relay PS ground return off the chassis except for a single point should be the best arrangement. Are there any other grounds?
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Re: Monkeymatic ODS #183

Post by Colossal »

martin manning wrote: Wed Jun 14, 2017 9:40 pm
xtian wrote: Wed Jun 14, 2017 6:24 pmI used an alligator clip to try grounding the switching system from the DIN plug to various points--they all sounded the same, except if I reached way back to the 5v PSU, then I got a lot of hum. Ended up grounding to the FX loop jacks, because convenient, and resulted in lowest noise.
This doesn't seem to make sense. Keeping the relay PS ground return off the chassis except for a single point should be the best arrangement. Are there any other grounds?
Yes, something seems amiss still. Looking at the photo showing the relay's power supply board, the 7805 regulator should be isolated from the chassis using the Thermosil pad.
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Re: Monkeymatic ODS #183

Post by martin manning »

I don't believe the regulator tab needs insulation if it is or is right next to the one ground point for the relay supply.
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Re: Monkeymatic ODS #183

Post by Colossal »

martin manning wrote: Wed Jun 14, 2017 10:18 pm I don't believe the regulator tab needs insulation if it is or is right next to the one ground point for the relay supply.
Yes, you're right. As a matter of practice though, I always recommend that the tab be insulated (and supplied the little Thermasil pad) since the single ground point for the whole system is usually more conveniently located over on the other side of the amp, usually by the DIN jack. Ultimately up to the builder however as switching applications will differ.
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