found a chassis in my storage place :D

[talbany]

Thanks, Erwin. That’s exactly as I suggested above, basically a local star for the loop. I would not be concerned about relocating the speaker jack ground. Did you keep that in the usual location, at the speaker jacks?

Martin
So what was it that changed your mind with regard to preamp grounding? wondering

I like grounding the OT secondary directly to the speaker jacks... less chance of a poor connection taking the load off the power amp. A wire could be run from there to the main filter ground if the jacks are isolated from the chassis, but usually its fine to let the jacks take care of grounding the secondary to the chassis. They are usually located well away from the preamp ground(s).

https://ampgarage.com/forum/viewtopic.php?t=15147

Tony

[martin manning]

Thanks, Erwin. That’s exactly as I suggested above, basically a local star for the loop. I would not be concerned about relocating the speaker jack ground. Did you keep that in the usual location, at the speaker jacks?

Martin
So I guess you changed your mind on preamp grounding then

I like grounding the OT secondary directly to the speaker jacks... less chance of a poor connection taking the load off the power amp. A wire could be run from there to the main filter ground if the jacks are isolated from the chassis, but usually its fine to let the jacks take care of grounding the secondary to the chassis. They are usually located well away from the preamp ground(s).

https://ampgarage.com/forum/viewtopic.php?t=15147

No, I will stand by that statement. The speaker jacks are well away from the preamp grounds here.

[talbany]

Thanks, Erwin. That’s exactly as I suggested above, basically a local star for the loop. I would not be concerned about relocating the speaker jack ground. Did you keep that in the usual location, at the speaker jacks?

Martin
So I guess you changed your mind on preamp grounding then

I like grounding the OT secondary directly to the speaker jacks... less chance of a poor connection taking the load off the power amp. A wire could be run from there to the main filter ground if the jacks are isolated from the chassis, but usually its fine to let the jacks take care of grounding the secondary to the chassis. They are usually located well away from the preamp ground(s).

https://ampgarage.com/forum/viewtopic.php?t=15147

No, I will stand by that statement. The speaker jacks are well away from the preamp grounds here.

Really? Within a few inches is far enough apart. OK? Good Luck.

Tony

[10thTx]

Tony,

That's helpful! Really appreciate the information. I will try this out in the next few days to see how well it lowers the floor noise for me around the on board FX loop.

THANKS! With respect, 10thtx Jeff

[norburybrook]

Tony,

That's helpful! Really appreciate the information. I will try this out in the next few days to see how well it lowers the floor noise for me around the on board FX loop.

THANKS! With respect, 10thtx Jeff

be interested in your findings Jeff.

@Tony I thought the issue was the closeness of the loop grounding to the speaker jack/OT grounding and by isolating one of those you can ground them with some distance between them.

As i have a 2mm metal face plate over the rear chassis I'm struggling to find an isolated socket with enough thread to even try this. I might have to see how it goes and then improvise if I've got problems.


M

[martin manning]

I think you will be fine Marcus. If you bring the OT secondary common to the jack as usual, then there isn’t any heavy current flowing through the chassis. Erwin’s experience seems to prove that out.

[talbany]

Tony,

That's helpful! Really appreciate the information. I will try this out in the next few days to see how well it lowers the floor noise for me around the on board FX loop.

THANKS! With respect, 10thtx Jeff

be interested in your findings Jeff.

@Tony I thought the issue was the closeness of the loop grounding to the speaker jack/OT grounding and by isolating one of those you can ground them with some distance between them.

As i have a 2mm metal face plate over the rear chassis I'm struggling to find an isolated socket with enough thread to even try this. I might have to see how it goes and then improvise if I've got problems.


M

Marcus.. IT IS!
Here is what I recommend doing.
If this amp is just going to sit in your studio then see if you have any noise issues. If not good!..If this is an amp that is going out on the road and will see a bunch of different rooms then in your case I would isolate the output jack somehow (Plastic jacks are cheap) and run a wire back to the B+ node of the amp then call it an insurance policy when you run into a bad shed.
Look the return amp in the loop is going to have some noise! no way around it. Question is how much are you willing to put up with. Wiring all your grounds properly insures that you've done everything you can do (electrically) to keep the noise floor to a minimum,that's all I am saying.


Tony

[norburybrook]

still waiting for parts so made a start on the cab today. It's winter here but it didn't rain this afternoon so managed a couple of hours outside in the garden.

Tomorrow I'll fill the screw holes, sand it all smooth and the do the routing, paint it black inside and be ready for tolexing at the weekend.

IMG_20191106_172632-01.jpeg

IMG_20191104_155719.jpg

M

[10thTx]

That's helpful! Really appreciate the information. I will try this out in the next few days to see how well it lowers the floor noise for me around the on board FX loop.
THANKS! With respect, 10thtx Jeff

be interested in your findings Jeff

OK, I did change the grounding on the FX on my amp. Everything that's grounded that's part of the FX loop section is ALL grounded to the FX send/return jacks which are grounded by a wire to each other. FX pots, filter cap "D" on B+ rail, cathodes on FX loop tube, etc...… It's essentially a star ground for everything FX. I should say that the FX jacks are about 6 inches away from the speaker jack. And none of these jacks are isolated from the chassis. Node D on B+ for the FX is not shared by any other triodes.

Yes, it made a significant difference in the noise level for the clean channel. While I was not able to A/B this quickly (such as with a switch), I am aware that on the clean channel when I turn up the "Level" pot for the FX …………. I hear an increase ONLY in white/hiss noise. Previously when I turned up the FX Level pot, there would some buzz/hum introduced into the floor noise. So that buzz/hum is gone now & no longer present when I turn up the FX level pot (which is on the front of the amp) .

I could not tell for sure if it made a difference on the OD channel? My best guess is my amp design and layout has some intrinsic hum/noise in the OD channel?

It was not a difficult job in rewiring and rerouting the wire to make a star ground for the FX. And it was worth while changing this. I am appreciative of the advice on the
FX grounding.

PLEASE keep in mind that this is not a Dumble clone and doesn't use a Dumblish layout. I use a paralleled turret board similar to a HiWatt which is easier for me to experiment and
mod on. The amp is my Carolina Overdrive Special with 5879 in the OD channel. It's my favorite amp and the best sounding amp I've played or built. (I've never played a Dumble or D-clone)

With respect, 10thtx/Jeff

PS: For some months I've been experimenting changing silver micas to ceramics. And changing out plate resistors and some resistors in the signal path. I am finding over all that
these changes seem to open the amp up and make it more transparent & dimensional in the tone. It's like the changes are removing some artifacts that were hindering the amp from
having an open sound. I'm using 2w metal film resistors for the plate resistors and 2w carbon film for some of the resistor changes in the signal path.

[norburybrook]

cool.

I've ordered a cliff jack socket so I can Isolate the speaker and OT ground from the proximity of the Loop. I'm going to start ground all the loops stuff at the loop tube socket ground and then run the Speaker/OT across to the main filtercap/B+ ground point the other end of the chassis.

Still waiting for my Transformers, but the weather gods did smile on London today so i finished the cabinet. Tomorrow I will tolex and grill cloth


it will be nice to have a finished cabinet ready to put the amp in for once

IMG_20191107_124012.jpg

IMG_20191107_124026.jpg

IMG_20191107_123949.jpg

M

[martin manning]

Marcus, can you do an experiment when you power up? I’m curious to see if there is any difference in noise level grounding the speaker jack at the main B+ reservoir ground vs. to the chassis at the speaker jack location.

[talbany]

That's helpful! Really appreciate the information. I will try this out in the next few days to see how well it lowers the floor noise for me around the on board FX loop.
THANKS! With respect, 10thtx Jeff

be interested in your findings Jeff

OK, I did change the grounding on the FX on my amp. Everything that's grounded that's part of the FX loop section is ALL grounded to the FX send/return jacks which are grounded by a wire to each other. FX pots, filter cap "D" on B+ rail, cathodes on FX loop tube, etc...… It's essentially a star ground for everything FX. I should say that the FX jacks are about 6 inches away from the speaker jack. And none of these jacks are isolated from the chassis. Node D on B+ for the FX is not shared by any other triodes.

Yes, it made a significant difference in the noise level for the clean channel. While I was not able to A/B this quickly (such as with a switch), I am aware that on the clean channel when I turn up the "Level" pot for the FX …………. I hear an increase ONLY in white/hiss noise. Previously when I turned up the FX Level pot, there would some buzz/hum introduced into the floor noise. So that buzz/hum is gone now & no longer present when I turn up the FX level pot (which is on the front of the amp) .

I could not tell for sure if it made a difference on the OD channel? My best guess is my amp design and layout has some intrinsic hum/noise in the OD channel?

It was not a difficult job in rewiring and rerouting the wire to make a star ground for the FX. And it was worth while changing this. I am appreciative of the advice on the
FX grounding.

PLEASE keep in mind that this is not a Dumble clone and doesn't use a Dumblish layout. I use a paralleled turret board similar to a HiWatt which is easier for me to experiment and
mod on. The amp is my Carolina Overdrive Special with 5879 in the OD channel. It's my favorite amp and the best sounding amp I've played or built. (I've never played a Dumble or D-clone)

With respect, 10thtx/Jeff

PS: For some months I've been experimenting changing silver micas to ceramics. And changing out plate resistors and some resistors in the signal path. I am finding over all that
these changes seem to open the amp up and make it more transparent & dimensional in the tone. It's like the changes are removing some artifacts that were hindering the amp from
having an open sound. I'm using 2w metal film resistors for the plate resistors and 2w carbon film for some of the resistor changes in the signal path.

Jeff
Thanks for the shout back!. So it would seem that 6" downstream was sufficient as mine was about 3" away (on a Steel chassis) and hummed slightly. Also my amp was a 100W Twin style OPT. So it would appear that your hum issue was coming from your power supply gnds If you want to try and cut down on the white noise you can try to pick up an old square foil getter Beijing 80's 90's 12AX7. You can pick these up on ebay for pretty cheap as these tubes sound great in loops and have a dark background. I use these things quite a bit if I want to cut back on the hiss levels.
It's amazing how changing out resistor and treble cap types can transform the sound of an amp.
Welcome to the Mafia


Tony

[stelligan]

If you want to try and cut down on the white noise you can try to pick up an old square foil getter Beijing 80's 90's 12AX7. You can pick these up on ebay for pretty cheap as these tubes sound great in loops and have a dark background. I use these things quite a bit if I want to cut back on the hiss levels.

Tony

Are these the critters you are referring to? Mine are marked 6N4?? Turns out I have a small stash of them...

tube.jpg

P.S. Dig the snakeskin, Marcus

[talbany]

If you want to try and cut down on the white noise you can try to pick up an old square foil getter Beijing 80's 90's 12AX7. You can pick these up on ebay for pretty cheap as these tubes sound great in loops and have a dark background. I use these things quite a bit if I want to cut back on the hiss levels.

Tony

Are these the critters you are referring to? Mine are marked 6N4?? Turns out I have a small stash of them...
tube.jpg

P.S. Dig the snakeskin, Marcus

Yep! Looks like it. Triple mica square foil getter Military version . The noise floor might very tube to tube however overall they are very quiet. Another great spot would be return amp in a Fender reverb circuit
Tony

[norburybrook]

Marcus, can you do an experiment when you power up? I’m curious to see if there is any difference in noise level grounding the speaker jack at the main B+ reservoir ground vs. to the chassis at the speaker jack location.

Sure.

I hope that's all I've got to worry about when I power up... It's been a complex build for me this one after my last 2 amps, a traiwreck express and a princeton!



God knows what could have slipped by in this build with 3 relays etc and a loop


M


p.s. just returned from seeing Greg Koch.....WOW...... LOUD as hell, no pedals, just telecaster into his sig amp....Killer tone and playing...very inspiring