found a chassis in my storage place :D

[norburybrook]

BTW what’s the voltage rating on those caps in the loop power supply branch? Since they are not stacked like the preamp filters they should be rated for the unloaded B+ voltage.

450V, . stacked as in parallel? hmm the unloaded B+ voltage is going to be higher than that sin't it?

Erwin told me 'I run my Hrm with built in dlator, at B+ on the power amp plates490-500v, with these values for over 10yrs without any problems' he was talking about the resistor values specifically but 10 years seems to be a good 'test'




M

[martin manning]

Stacked as in series, with balancing resistors, like the other filters. The danger is in powering up without tubes, especially the loop tube, in which case both of those caps will get charged up to the full screen node voltage. If none of the tubes are installed, that might get up to 500V. With a 450V rating, I think you might be ok, as there is always some margin. Just looking out for you ;^)

[talbany]

M
Looks good so far Just a heads-up I've built 2 of these amps with the loop built-in like the Normster and both were either noisy or hummed before I gave up and designed my own with isolated jacks and grounding scheme and dedicated filter can. The problem with the Normster design is (gnd loop #1)the signal ground for the loop (loop jacks) are on the same gnd plane (Yours are right next to it) as the output transformer sec which is a high current gnd point (2.5A. into 4 ohm load @ 50w) unless you isolate it.(loop #2) He is filtering the last preamp (most sensitive) with the Screens supply and tieing it with the PI/ Preamp/ ground points?? again in close proximity to the main filters when these should all be separated using the Dumble method. Ideally, the loop should have its own dedicated filter can(32uF+32uF @ 500) and preamp gnd point then your high current stages will be totally separate further downstream from low current (preamp) ones and the screens and PI back by the power tubes This is how I did mine and it is dead quiet!. Now this is not to say yours won't work? it might! just pointing some possible noise issues. If your amp/loop design or effects detects the slightest hint of noise or is not properly grounded that loop will buzz at you big time!
The other thing I don't like about the built-in loop is your master vol is now on the back. The return vol on the D-lator is really touchy which makes it even worse to have to reach behind an amp to adjust the (Backwards) volume during a show and try to find the sweet spot on a really touchy volume control. If it's just a small tweak I can sometimes use the output vol on my effect which sometimes works sometimes not. It's because of this I can not use my 2nd gen on my gigs anymore. I have to get to my master quickly, honestly, it's a giant pain in the ass!. Don't shoot the messenger. Just giving you a heads up!

BTW. You might be better served by putting the Mstr on the back and the loop return on the front.
Good Luck with your ground loops
Tony

[norburybrook]

M
Looks good so far Just a heads-up I've built 2 of these amps with the loop built-in like the Normster and both were either noisy or hummed before I gave up and designed my own with isolated jacks and grounding scheme and dedicated filter can. The problem with the Normster design is (gnd loop #1)the signal ground for the loop (loop jacks) are on the same gnd plane (Yours are right next to it) as the output transformer sec which is a high current gnd point (2.5A. into 4 ohm load @ 50w) unless you isolate it.(loop #2) He is filtering the last preamp (most sensitive) with the Screens supply and tieing it with the PI/ Preamp/ ground points?? again in close proximity to the main filters when these should all be separated using the Dumble method. Ideally, the loop should have its own dedicated filter can(32uF+32uF @ 500) and preamp gnd point then your high current stages will be totally separate further downstream from low current (preamp) ones and the screens and PI back by the power tubes This is how I did mine and it is dead quiet!. Now this is not to say yours won't work? it might! just pointing some possible noise issues. If your amp/loop design or effects detects the slightest hint of noise or is not properly grounded that loop will buzz at you big time!
The other thing I don't like about the built-in loop is your master vol is now on the back. The return vol on the D-lator is really touchy which makes it even worse to have to reach behind an amp to adjust the (Backwards) volume during a show and try to find the sweet spot on a really touchy volume control. If it's just a small tweak I can sometimes use the output vol on my effect which sometimes works sometimes not. It's because of this I can not use my 2nd gen on my gigs anymore. I have to get to my master quickly, honestly, it's a giant pain in the ass!. Don't shoot the messenger. Just giving you a heads up!

BTW. You might be better served by putting the Mstr on the back and the loop return on the front.
Good Luck with your ground loops
Tony

@Tony,

Thanks for the heads up, I went with this build as Erwin had recently built one and it sounded great and had no issues with hum etc so thought it was a tried and tested design. I presume if there's nothing in the loop then it wont hum. So , if I get hum then my first and probably only point of address then would be to isolate the loop jacks and give them a separate ground somewhere with all the other loop grounds. where is a good point on the chassis for this? the centre?

I've not use my dumbleator in a while as I've been wetr/dry so I'd forgotten about the way it all works, so with the loop engaged the master volume is redundant?

@Martin

thanks for the heads up, I don't think I ever power up without tubes in. I tend to power up tubes out on the limiter, then tubes in on the limiter, then if everything looks OK power up as per normal.

whatever happens to this build I've already learned a few things more and if I have to strip out the loop or make some kind of full board and grounding scheme then that will be a learning experience too so all is not lost whatever happens.

once again, I appreciate everyone's input here, it's all valuable advice.

I'm going to actually put bias test point in this amp today...first time for that too.......will stop the slip off spark show I've had the pleasure of in the past

M

[talbany]

What I would do is isolate the output jack. The best place to ground the output transformer center tap is back at the main filter ground. That frees up the back part of the amp for grounds for the loop.

I presume if there's nothing in the loop then it wont hum.

If the loop is in series with the preamp and power amp and is in circuit it's still a "voltage" amplifier and can amplify any noise generated either through the amps preamp section or the loops recovery stage.(the latter being the worst)If it's bypassed then yes no added noise.


Just so we are clear the Normster method worked it was IMO too noisy especially in Overdrive when I tried to record or cranked up the loops send or return vol too much noise for me.


.As far as the master redundancy thing goes IMO once I engage the loop I always use the return as the master volume and crank up the amps master. That way I am driving the cathode follower to get that nice even compression and 2nd order harmonics the CF gives me. I suppose you could control the overall volume still by the amps master it just doesn't have the same effect or feel. Try them both and see which way you prefer. For me if I dont use an effect I generally bypass the loop all together and just get the pure tone of the amp without the sound of the loop. This is all of course personal preference and one you can experiment with. I also used to run my pedals through my loop and use it on the front end of my old Tweed to give it a cleaner punchier sound . This was of course done with my external loop.

whatever happens to this build I've already learned a few things more and if I have to strip out the loop or make some kind of full board and grounding scheme then that will be a learning experience too so all is not lost whatever happens.

BTW. If the loop is too noisy it';s an easy mod to do and you don't have to strip anything. You already have a spot for a cap can The rest is just moving a few wires
Good Luck!

Tony

[erwin_ve]

Tony indeed grounding points are essential to keep the hum out.
I partly altered the Ps filter design(compared to the Normster layout)on the pcb I provided to Marcus to cover this.
I pm ed Marcus on potential grounding points.He can post them if he likes

My amps with build in dlators have no hum or hiss in the way you described.
My latest amp is on for 3 days a week @ my guitarschool and 1 band rehearsel every week for 3 hrs.
If of any of my students or bandmates would notice this I would have some complains by now.

Erwin

[talbany]

Tony indeed grounding points are essential to keep the hum out.
I partly altered the Ps filter design(compared to the Normster layout)on the pcb I provided to Marcus to cover this.
I pm ed Marcus on potential grounding points.He can post them if he likes

Nope thats OK sounds like you have it covered and tested. I just didn't want him to go through what I went through with that layout. Thanks for the reply.

Tony

[10thTx]

I've been following this thread with interest. Especially this information about the effects loop. I'm wanting to confirm that I am understanding this correctly:

1) isolate the speaker jack and ground it on the ground side of B+ 1st filter cap.

2) ground all FX pots to the FX send & return jacks which also have a ground wire connecting those send & return jacks grounding lugs.

3) ground all FX grounds (such as cathodes) to the ground of the FX send/return jacks

4) the FX tube plates needs it's own B+ filter cap (not shared with any other gain stages in the amp)

5) Even if the FX level pot is on the front of the amp, it still has a wire running to the ground of the FX send/return jacks

Am I understanding this correctly? Any changes or additions to this approach?

With respect, 10thtx

[erwin_ve]

Below is the Ps filter board Marcus is using. The grounding points are identical to the usual Overdrive Special fe. #102 or #124.
Gnd2b is the the one for the fx loop.

Gnd1: Main ground between filter and Ps board
Gnd2: At the powertube cathode ground points at chassis.
Gnd3: At input below buss bar.

Gnd2b: At loop jacks or at Dlator tube attached to a lug at screw noval socket.
In my latest amp I used the lug attached to the noval socket of the fx loop tube as ground. On this spot are also the grounding points of the recovery and cathode follwer triodes.

Ps+.JPG

[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?

[norburybrook]

Erwin, where did you ground the NFB because normally that gets grounded at the loop jacks.


M

[erwin_ve]

Erwin, where did you ground the NFB because normally that gets grounded at the loop jacks.


M

Marcus, The NFB and phase inverter cathode are grounded at the loop jacks.

I would not be concerned about relocating the speaker jack ground. Did you keep that in the usual location, at the speaker jacks?

Martin, I kept it at the speaker jacks, no problems.

[norburybrook]

thanks fellas .


Put the bias test jack in, PIA...fine plastic screw thread and a metal nut.....recipe for stripped thread.

still waiting for a few resistors and caps but most importantly the transformers.

I've followed the LED pilot light wiring from the second gen hybrid layout. This doesn't use the filament supply but takes it from the relay/footswitch boards. I thought it used less wire runs and looked tidier. Is it correct though? I've got the voltage coming from the board after the 1k current resitor going to the anode of the LED and the cathode of the LED is going to ground? yes?

IMG_20191105_171113-01.jpeg

IMG_20191105_171134-01.jpeg

it's starting to look like an amp.


M

[martin manning]

Pilot LED wiring sounds correct, positive voltage to anode, cathode to ground.., Just like tubes, eh? I agree using the relay supply makes a tidy solution.

[talbany]

Hey Jeff
Here is how I did mine.

1) isolate the speaker jack and ground it on the ground side of B+ 1st filter cap.

You can isolate either the output speaker jack or the loop jacks.(I've used the plastic ones) again you want to separate the high current gnd points to the low current ones.

2) ground all FX pots to the FX send & return jacks which also have a ground wire connecting those send & return jacks grounding lugs.

Correct!

3) ground all FX grounds (such as cathodes) to the ground of the FX send/return jacks

Correct!.

4) the FX tube plates needs it's own B+ filter cap (not shared with any other gain stages in the amp)

Correct this way you can gnd the filters further downstream.

5) Even if the FX level pot is on the front of the amp, it still has a wire running to the ground of the FX send/return jacks

Yes if you put the level pot on the front it can still be grounded at the pre-amp's main (low current) ground point

Am I understanding this correctly? Any changes or additions to this approach?

The theory is to keep your "low current" (preamp gnd) further downstream from your "high current" ones. High current ones generally being down by the power transformer and back center of the amplifier and the preamps down by the input jack.(opposite end front)
IMO the best way to do this is a separate PCB board mounted on the back that has it's own separate gnd plane

Here is a quick and easy test to do to check for noise levels.

Jump out the loop with a patch cable and with the amp on and master (on the amp) turned down crank up return pot and listen for when the noise starts to increase to where you can just start to here it. then bring up the amps master and send and see if this adds any noise (it probably will) then go to the OD side with the gain set about where you use it.Then hit the PAB all the while checking your noise levels on the way up.This is a great test to check each level in every stage of the amp on out to the loop
If it's dead quiet congratulations! successful test.


Tony