zero loss fx loop after master volume

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covil
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zero loss fx loop after master volume

Post by covil » Thu Oct 08, 2015 10:10 am

Hi, i installed metro's fx loop on krank revolution that had an passive fx loop.
So far, so good( well, not so good). It has a hiss that's loud, not very loud, but loud enough to upset me.
I known that metro's loop isn't supossed to be placed after a master volume, but in this case i had to (it's a two channel amp with some mods).
So i think my issue here is signal ratio problems, that 1M volume knocking down signal too much.
My question is: is there any way around this or just leave it alone?
Mod the loop for stronger send signal and reduce return gain? How?
Doesn't friedman and Cameron amps have the loop after mv, how did they solved this?
Sdm can you please say something?
Thank's, Jorge.
Last edited by covil on Thu Oct 08, 2015 5:27 pm, edited 1 time in total.

covil
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Re: zero loss fx loop after master volume

Post by covil » Thu Oct 08, 2015 5:26 pm

I'm also losing a litle bit of high frequency!

covil
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Re: zero loss fx loop after master volume

Post by covil » Fri Oct 09, 2015 9:45 am

This is not an issue with the loop! Let´s clear that out. The issue is trying to fit a circuit that´s not really meant to be used in this sittuation. However after some adapation ( no mod done to the fx loop needed) it´s working wonderfully, no hum, fx pedal are working with a clear signal, never heard a delay working so well!!!!
I´m sure there´s more people like me who wish to adapt a good fx loop to a 2channel amp! So i think i can help out!

SDM
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Re: zero loss fx loop after master volume

Post by SDM » Fri Oct 09, 2015 1:13 pm

Glad you got things working well Covil. Not familiar with the Krank circuit off hand, but yeah, post master installs are not usually ideal outright.

Are various ways to address that, one very simple way is to add a final/overall/global master after the loop. The regular masters then effectively become send controls, will be set high (for a pedal level loop) usually to optimize signal to noise ratios, but should be still able to get the balance of channel volumes desired, then just use the new global master to set amp volume overall.

Another option is to alter the loop as you were originally asking. Not too difficult to convert a pedal level loop to line level or such. Noise will completely disappear usually, but it's a compromise still though as the masters do still act as send controls. At moderate or lower settings the loop may see a pedal or lower signal, but at higher master/s settings it'll see the line level. So, depending on those settings, the effects used, loop level, may work very well, but may still have some issues at too low or too high master settings. Also a risk modding the loop board.

Any way, a bit late here I know, don't get to the forum here often these days. Are other possible ways to address, some depending on the particular amp. Again don't know this amp off hand, but glad you found a good solution and hope you enjoy your loop.

covil
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Re: zero loss fx loop after master volume

Post by covil » Sat Oct 10, 2015 6:36 am

The krank circuit is as modified jcm 800 but plate fed tonestack( although i modded mine 3rd and 4th stages are a dc coupled pair - cathode feeding tonestack). So tone stack to a 1M volume, then to fx loop. The only change i had to made was adding a volume pot after the fx loop. I tried a 1M pot but it didn´t work. It cut to much highs so i went to a smaller resistance pot. The only one had was a 25k and it works like a charm. Just use higher settings on normal volume and boost trim pot send!!
Hope this helps someone in the same situation because there isn´t many information on this situation.

I´ve seen somere on this forum, someone with an Orange, trying to install metro´s loop and couldn´t make it work. I had exactly the same issues as him ( loud buzz and hiss), and that added master really might have helped!

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Re: zero loss fx loop after master volume

Post by burialcloud » Tue May 08, 2018 8:32 am

I realize this is an old thread but I am having some major trouble with two separate amps of mine that I’m trying to use the zero loss loop in. Both are two channel amps and I need a post master loop. The loop works fine in both amps if I go “pre master” but as soon as I try to move it after the master, I get issues.

The first one is a Soldano slo clone I built and the other is a rather rare two channnel matamp GTV “Black”.

In both amps I am taking the signal directly after the channel switching device ( an ldr in the Soldano and a solid state switching device in the matamp) and right before it hits the PI.
My b+ voltages are great, my work is clean, and my tap runs are shielded.
On the slo it does work, but I get enough hum to be annoying that gets way worse as soon as I turn my delay on (strymon timeline and a vintage memory man) or when I’m looping (with the timeline). Basically there is a medium hum that gets real bad as soon as I turn a pedal on. Basically my delays are just amplifying the hum. ( my pedals are properly powered, isolated etc, and they work perfectly in my Rivera knucklehead loop, my sunn 300t loop, and my 5150 loop)

In the matamp it is literally unusable. Super loud buzz.
I currently have passive loops running instead in the same insertion points but the tone loss is horrendous. They are dead silent and work alright besides the loss in tone and about a 5-10db drop in volume.

I have tried everything I can think of but my skill set isn’t huge.

So you are saying I should try adding a 25k pot on the return? Before it goes back into the zero loss or after the ZL and before it hits the pi? Is this all you did?

Just curious if your fix might be able to help in my situation. Thanks for your time.

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