Parallel effects loop for Marshall style amps

[Evz]

Hello Larry, as noted before, the problem was infront of the amp, i just want to confirm my mistake and make sure i'm correcting it right - i have found i've switched Va with Vb on the schematic, BUT i've mixed my wires on pin's 6 and 1, so would this swithc accountfor a very highly compressed scooped mids and really overdriven sound i got? that almost seems to be independant of the send/ return levels and hihgly dependent on the master volume?

ps can you send me the schematic with the serial/ parallel switching if you have it?

Thank you!

edit: the effects of my mistake make sense to me since it seems the output of the loop came straight after a single gain stage from the amp with only the master volume and send level....

[novosibir]

Nice that you've found your bug!
But I can't send a schem in a PM, so you know, what still to do.

Larry

[hammeron]

Hello Larry,
I have put this loop in a Sovtek Tube Midget amp and it works, except for a slight hum so I must check everything again.
I have 370 Volt after the 4k7 resistor is that to high ? You mention 310 to 330 V in previous posts.
Is it necessary to shield the wire to the B+ (Uc)?

Niklas

[novosibir]

I have put this loop in a Sovtek Tube Midget amp and it works, except for a slight hum so I must check everything again.

Grounding! Shielded signal cables!

I have 370 Volt after the 4k7 resistor is that to high ? You mention 310 to 330 V in previous posts.

Woo-hoo! What voltage is at the PI? Over 400V?
So better try a 10K instead of the 4.7K, to at least come below 350V

Is it necessary to shield the wire to the B+ (Uc)?

No!

Larry

[hammeron]

Larry, I have gone through the loop and everything looks fine, all signal cables are grounded and I have increased the value of the 4K7 resistor and the voltage is now ok.
But I still have a very annoying hum in the amp and when I knock on the 22n coupling cap of V3b I hear the knocking sound in the speaker, all other components are quiet.
Is this normal ?
I have changed the cap and tried different tubes but no luck.
Any ideas ?

Niklas

[novosibir]

But I still have a very annoying hum in the amp and when I knock on the 22n coupling cap of V3b I hear the knocking sound in the speaker, all other components are quiet.
Is this normal ?

Yes, all signal caps are more or less microphonic, ceramic caps sometimes even terrible microphonic - but this is normal!

If your hum issue wasn't before the loop, then you've built in a ground loop in the loop circuit!
The loop related grounds have to meet all at the same spot! Grounds from the jacks & pots, from the additional filter cap, from the mixer area and from the tube's cathodes. Have you done it different?

Larry

[hammeron]

Yes everything is grounded at the same place, the only thing left is that I maybe built the loop too compact, Sovtek Midget 50H is a very tiny amp so maybe the wires are to close to each other, and I have to face the fact that it never get quieter than this.

Thanks Larry

[rjgtr]

I'm not sure which look you used, but you could try lifting the ground on the send jack by puting a 10ohm resistor from the ground tab of the jack to chassis ground. Of course for this to work the jack has to be a Cliff or other insulated jack.

I also don't know if this has been mentioned, but the shield of the FX cables should only be connected at one end.

[Just Mike]

Hi Larry. Is it too late to request a schematic?

Thanks!

[novosibir]

Hi Larry. Is it too late to request a schematic?

No, not too late.
But I can't send a pdf file in a PM

Larry

[russellw]

Larry
Can I get a copy? PM sent.

Russell

[novosibir]

Russel, hope the following will answer your request. It's written in the 1-st post of this topic.

Yes - it's for Metro board members only!

The only I'm expecting from you is:

- a Metroamp membership of at least 3 months
- a minimum post count of 10
- that you keep it for your personal use
- and that you don't forward the schematic to anybody else

Sorry, but too many have joined here in the past, just to request the schem - and after they got it, they never were seen again on the board.

Larry

[4el]

Larry, I was registered at a forum to receive the FX loop scheme which here so praise. I simply read before.

I from Russia. It is very difficult to me to communicate as I badly know English language. I know technical English language is even worse.

At a forum basically copies are discussed. And almost nobody tries to make something new. For example a theme from me http://forum.metroamp.com/viewtopic.php" onclick="window.open(this.href);return false;? f=7&t=29444 has not caused interest and discussions.


On asked by a question in a theme about a FX loop the scheme is almost clear.
The rest can be found out by means of personal messages. Asking a question: "Can it is necessary to increase the condenser to 2 µF?" And further questions of the same maintenance.

On the basis of answers of participants it is possible to restore the scheme completely. I think, it will be not fair in relation to you and your work. I do not wish to make a detour to try new realisation of a FX loop in the amplifiers.


Yours faithfully, Evgenie.

[GuitarManiac32]

Hi! I installed the Larry loop (using Rockstahs layout) to my JTM45 clone and it works perfectly! This is a really great loop! Now I tried to install it to my SLOclone as well but I´m having problems. I want to install the loop between tone stack and master volumes. Here´s a picture where and how I installed it: http://s51.photobucket.com/albums/f358/ ... ysloop.jpg" onclick="window.open(this.href);return false;

I tried the loop but I get a huge amount of hum when having treble pot at 1-9. At 0 and 10 there isn´t any hum and the loop works perfectly. Do I have a ground problem or something else?

Thanks for the help!

-Matti

[novosibir]

First you should remove the orig. Soldano loop entirely.
Then run from V3A's cathode directly into the tone stack - from beyond R25!
Remove C12 - go directly from the cathode into the tone stack.
And then you must run all grounds of the loop section to the ground connection of that filter, from which the loop's tube is fed - and your hum probably will disappear.

Larry