100w plexi PT without center tap?

[abbey road d enfer]

So quick question, does this wiring seem legit to you?

Not really. What I see is the input signal is attenuated by about 35dB before reaching the grid, then the signal is picked up from teh cathode with a very low cathode resistor, for a cathode-follower where it's typically about 50-100k. Th eresulting Send signal is attenuated by about 40dB and more because of the pot. The Return circuit seems ok, but its gain may be too high in practice.

 

[eki1988]

I see no reason to use a pot ,it needlessly loads down everything .
If you show the schematic instead of the build diagram its easier to see at a glance whats happening.

I have no schematic for this, just something I picked up from google. But I found another, with schematic:

 

[eki1988]

I have no schematic for this, just something I picked up from google. But I found another, with schematic:

And it’s placed between master volume center leg and 22n capacitor

 

[eki1988]

View attachment 114037
So quick question, does this wiring seem legit to you?

Ok, so I built this. It kinda works, doesn’t suck gain, but instead sucks quite amount of distortion. Not too bad with ecc83, but with 82 the distortion just dies away.

 

[abbey road d enfer]

Ok, so I built this. It kinda works, doesn’t suck gain, but instead sucks quite amount of distortion. Not too bad with ecc83, but with 82 the distortion just dies away.

It "sucks" distortion because it sucks gain.
The Send section attenuates by about 40dB and the Return section has only about 30dB gain. The net result is about 10dB less gain.

 

[eki1988]

It "sucks" distortion because it sucks gain.
The Send section attenuates by about 40dB and the Return section has only about 30dB gain. The net result is about 10dB less gain.

But if it lowers gain, shouldn’t it lower also overall volume? Volume stays just about same, only less distortion.

And, made bit of a mistake. Pot should have been 10k, but I put 25k pot.

Also, if I put 100k resistor to cathode, and bypass that 1M grid resistor, shouldn’t it help? And put a 10k pot ofc.

 

[Tubetec]

The effects loop as shown in the partial Schem above is missing the link that bypasses the jacks when nothing plugged in , so there will be no sound unless theres something in the loop . nothing to stop you using a short patch cable though .

 

[eki1988]

The effects loop as shown in the partial Schem above is missing the link that bypasses the jacks when nothing plugged in , so there will be no sound unless theres something in the loop . nothing to stop you using a short patch cable though .

I’ll try to make that first loop built work first, added already a bypass switch.

I will also bypass that 1M grit resistor, wire input straight to pot and swap a 100k to cathode. See if it makes any difference.

But if I can’t get it working properly, I will have to try that other one. I also found a metaltronix loop schem. Might try that one, if these won’t work

 

[abbey road d enfer]

But if it lowers gain, shouldn’t it lower also overall volume? Volume stays just about same, only less distortion.

Distortion creates compression.

And, made bit of a mistake. Pot should have been 10k, but I put 25k pot.

That is trivial.

Also, if I put 100k resistor to cathode,

That would be somewhat better.

and bypass that 1M grid resistor, shouldn’t it help?

Those two resistors should be altered as to compensate the attenuation in the Send circuit. I would start with two identical resistors of 220k.

And put a 10k pot ofc.

Not necessary. Actually a 100k pot may be preferrable.

 

[eki1988]

Distortion creates compression.

That is trivial.

That would be somewhat better.

Those two resistors should be altered as to compensate the attenuation in the Send circuit. I would start with two identical resistors of 220k.

Not necessary. Actually a 100k pot may be preferrable.

Thanks a thousand times!. Will do those changes.

 

[eki1988]

View attachment 114037
So quick question, does this wiring seem legit to you?

Ok, so this was bad. Tried with multiple resistor values, and didin’t work properly.

Gonna try that ”marshall” loop schem. Looks bit simpler, hope it works.

 

[abbey road d enfer]

Ok, so this was bad. Tried with multiple resistor values, and didin’t work properly.

Define "didin’t work properly".

 

[eki1988]

Define "didin’t work properly".

It seemed to kinda choke up, whenever I added effects to loop. And with od in loop, it just squieled. No matter what pedal I used, even with od pot in zero. Swapping resistor values brought only little help.

I have cold clipping switch, with 2,2k and 10k amp could be played, but with 39k it started to squieal. And the longer I played, more quieter and compressed the amp got.

 

[abbey road d enfer]

It seemed to kinda choke up, whenever I added effects to loop. And with od in loop, it just squieled. No matter what pedal I used, even with od pot in zero. Swapping resistor values brought only little help.

I have cold clipping switch, with 2,2k and 10k amp could be played, but with 39k it started to squieal. And the longer I played, more quieter and compressed the amp got.

The big isseue is you haven't worked out the level diagram, i.e. how much you want the Send signal to be attenuated or amplified before sending to the outside world, and corollarily, how much gain or attenuation you need to apply to the Return signal.
In order to do that, you must assess the operating level at the point you want to insert the loop and the level you want the FX in the loop to operate. Some amps have fully adjustable Send and Return levels in order to accomodate guitar pedals (typically about -20dBu) as well as pro FX (+4dBu).
Only after that you can decide on the structure of circuits.

 

[eki1988]

The big isseue is you haven't worked out the level diagram, i.e. how much you want the Send signal to be attenuated or amplified before sending to the outside world, and corollarily, how much gain or attenuation you need to apply to the Return signal.
In order to do that, you must assess the operating level at the point you want to insert the loop and the level you want the FX in the loop to operate. Some amps have fully adjustable Send and Return levels in order to accomodate guitar pedals (typically about -20dBu) as well as pro FX (+4dBu).
Only after that you can decide on the structure of circuits.

I don’t want to do such things, all I want is to have fully working fx-loop .

One option is to use fxloop kit.

 

[abbey road d enfer]

I don’t want to do such things, all I want is to have fully working fx-loop .

Your choice, but you're losing an opportunity to learn something. Seeing you're not wiiling to do your homework, I think members will be reluctant to help you.

One option is to use fxloop kit.

Things don't work by accident; a working FX loop kit works because someone has done their job.
Even simpler, you could buy an amp with an FX loop built-in.

 

[eki1988]

Your choice, but you're losing an opportunity to learn something. Seeing you're not wiiling to do your homework, I think members will be reluctant to help you.

Things don't work by accident; a working FX loop kit works because someone has done their job.
Even simpler, you could buy an amp with an FX loop built-in.

Well this is true, at some part. My intrest lays in building amps, and then modding them. But I guess this falls into that gategory.

I have never needed an fx-loop, however this recent built has tons on gain, so I figured that silencer in fx-loop would be good.


But absolutely right, here is one area to learn from, and I should take it. Need to dig into it.

Anyway, it used to be lot cheaper building amps than buying them. And this was main reason for me to start this ”hobby”.