Parallel effects loop for Marshall style amps

novosibir · Post by **novosibir** » Tue Jan 30, 2007 3:17 am

@ thinlizzy

You can easily use this loop for a volume boost, as it is - you haven't to change it to a 'serial only' loop and you even don't need a Boss GE-7 to obtain this!

With the Send Level and the Return Level dimed and the Send & Return jacks jumpered with a guitar cord produces a gain boost of about +12dB, much more than you'd ever need for a solo boost!

So simply put a on/off switch into the guitar cord from the Send to the Return jack, dime the Return Level and adjust the desired boost amount with the Send Level - that's all

Larry

thinlizzy · Post by **thinlizzy** » Tue Jan 30, 2007 4:56 am

Larry,

Thats one of the best idea's giving to me in a long time!
I'll go that route and see how it works!
So the origanel design it will be!

Thanks a lot, youre the best!

thinlizzy · Post by **thinlizzy** » Tue Jan 30, 2007 7:25 am

Larry,

If i want to put this loop in a 2204 amp, this loop comes after the master volume?

Marcel

novosibir · Post by **novosibir** » Tue Jan 30, 2007 8:03 am

Correct! In a MV desingn the loop section connects right after the Master's wiper, as it does connect right after the Treble's wiper in a NMV design!

Larry

thinlizzy · Post by **thinlizzy** » Tue Jan 30, 2007 8:57 am

Larry..

Is there a reason why I can't place it between the treble wiper and the master volume?
I've seen different tube loops and some say install before the master volume and some say after the master volume...

Marcel

novosibir · Post by **novosibir** » Tue Jan 30, 2007 9:16 am

thinlizzy wrote:Is there a reason why I can't place it between the treble wiper and the master volume?

In principle, no!

But I'll tell you (all) now the pros and cons:

When a Mastervolume control is placed directly before the PI stage and set to a low setting, the sound becomes pretty thin - therefore it's always a good mod, to place a 100K resistor between the wiper and the 22n PI's input cap, to avoid this phenomenon as much as possible. A higher value than 100K will cost you some highs and gain, because you create a voltage divider with the input impedance of the PI stage!

When you go from the loop's Return recovery stage directly into the PI, the upper phenomenon doesn't occur.

But when you place the Master after the loop, then you can boost the Return recovery stage from the preamp, to obtain more gain, as with the upper constellation. Although this would be sound colouring - you won't have your previous MV sound any longer.

Larry

thinlizzy · Post by **thinlizzy** » Wed Jan 31, 2007 5:19 am

Hi Larry,

I'm collecting part for the loop to build, some questions:

The pots are "log"?
Can I use 0,57uf instead of the 0,47uF (470nf)?
What voltage rate are the Caps?

Thanks
Marcel

(Am I the only one who wants to build this loop.....?)

antosimoni · Post by **antosimoni** » Wed Jan 31, 2007 5:24 am

thinlizzy wrote: ...
(Am I the only one who wants to build this loop.....?)

no

Freebird · Post by **Freebird** » Wed Jan 31, 2007 5:47 am

[quote=""thinlizzy"](Am I the only one who wants to build this loop.....?)[/quote]

Definitely no!

Daniel

novosibir · Post by **novosibir** » Wed Jan 31, 2007 5:52 am

thinlizzy wrote:The pots are "log"?

The pots are denoted 250KA and 1MA
A = audio taper = log.

thinlizzy wrote:Can I use 0,57uf instead of the 0,47uF (470nf)?

Shure! 470n is the lowest recommended value! You even can use a 1

thinlizzy · Post by **thinlizzy** » Wed Jan 31, 2007 8:56 am

Great i'm not alone!!

I'm gonne put the loop in a jmp 2204.

rockstah · Post by **rockstah** » Wed Jan 31, 2007 9:40 am

i have been waiting for this - Larry you rock@!

borbore · Post by **borbore** » Fri Feb 02, 2007 12:59 pm

hi,larry!thank's again for the loop schematic.one question:in MV amp ,the master volume becomes the send level or there is another 1meg pot after the mv whiper?

thinlizzy · Post by **thinlizzy** » Sat Feb 03, 2007 10:56 am

Building it right now!

novosibir · Post by **novosibir** » Sat Feb 03, 2007 11:16 am

borbore wrote:... in MV amp, the master volume becomes the send level or there is another 1meg pot after the mv whiper?

To include this loop into a MV layout there are two different ways.

The 1-st, which I'd recommend:

The Master stays at the tone stack and you go from the Master's wiper into the loop section. That keeps the origin. sound of the amp.

The 2-nd, as an additional gain stage:

You go from the Treble's wiper into the loop section (as with a NMV design) and place the Master right after the Return recovery stage (but don't forget an additional cap from the Master's wiper to the PI's input!).

Now you could patch in a guitar cord from Send to Return (instead of an effects device) and with the Send Level & Return Level dimed you'd get an additional boost of about +12dB. To practice with this, set the Send Level dimed and use the Return Level as a 'Post Gain Control'.

Now you couldt even put an on/off switch in this guitar cord to get an amp with two different gain settings

But that of course isn't the orig. MV sound anymore

Larry