Parallel effects loop for Marshall style amps

jerrydyer · Post by **jerrydyer** » Mon Feb 19, 2007 7:44 pm

Hey Larry. My send level is more like a blend. hhhhmmmm. its a great loop thought. What pro 's and con's of only using a 2.2k on the receiving end instead of the 1.5k and a 22uf? thanx

thinlizzy · Post by **thinlizzy** » Tue Feb 20, 2007 3:35 am

Jerrydyer

You mean there is no volume boost when you turn up the send level?

And what do you think about the levels of the amp when you don't use the loop? I think mine 2204 is extremly loud with the master on 2....

Larry, when the loop is not in use the signal is not amplified is it??

Regards Marcel

novosibir · Post by **novosibir** » Tue Feb 20, 2007 4:20 am

jerrydyer wrote:Hey Larry. My send level is more like a blend.

Be more concrete! What happens, when...

jerrydyer wrote:What pro 's and con's of only using a 2.2k on the receiving end instead of the 1.5k and a 22uf?

The amplification factor of the recovery stage is going from 59.0 down to 24.3 - or in other terms from 35.4dB down to 27.7dB

Larry

novosibir · Post by **novosibir** » Tue Feb 20, 2007 4:36 am

thinlizzy wrote:Larry, when the loop is not in use the signal is not amplified is it??

The dry path of the loop has an attenuation of -33.0dB with the Return Level on zero or dimed and an attenuation of -32.5dB with the Return Level on about 6...7, when nothing is plugged in.

The recovery stage has an amplification of +35.4dB, that means, that the signal with the loop will be slightly amplified by about +3dB - theoretical.

That's based on average tube datas, but when you have a pretty strong tube for the loop, then it might be a tad more, kinda +5dB...+6dB.

In this case you can fine tweak the attenuation by swapping the 68K with a 56K, a 47K or even a 39K for more attenuation, to get to exactly that point, where it would be w/o the loop section.

Larry

thinlizzy · Post by **thinlizzy** » Tue Feb 20, 2007 5:43 am

Oke I will try that!

Larry, will a simple a/b box work if I want to make/break the loop for boost purpose?? Or will I get pop/noise sound when switching?

Thanks

marcel

novosibir · Post by **novosibir** » Tue Feb 20, 2007 5:51 am

Any A/B-box used as a on/off switch works fine w/o pop.

Larry

antosimoni · Post by **antosimoni** » Tue Feb 20, 2007 8:50 am

novosibir wrote:
thinlizzy wrote:Larry, when the loop is not in use the signal is not amplified is it??
The dry path of the loop has an attenuation of -33.0dB with the Return Level on zero or dimed and an attenuation of -32.5dB with the Return Level on about 6...7, when nothing is plugged in.

The recovery stage has an amplification of +35.4dB, that means, that the signal with the loop will be slightly amplified by about +3dB - theoretical.

That's based on average tube datas, but when you have a pretty strong tube for the loop, then it might be a tad more, kinda +5dB...+6dB.

In this case you can fine tweak the attenuation by swapping the 68K with a 56K, a 47K or even a 39K for more attenuation, to get to exactly that point, where it would be w/o the loop section.

Larry

as I'm tryin' to have the least influence of the loop on the head sound can I use a switch to make the entire loop switchable on/off?? if yes how I've to do it??
thanks for your help

thinlizzy · Post by **thinlizzy** » Tue Feb 20, 2007 11:08 am

novosibir wrote:
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.

Larry

So if you place the loop after the master volume, it is still a good mod to place a 100k at the wiper of the master volume?

Marcel

jerrydyer · Post by **jerrydyer** » Tue Feb 20, 2007 2:30 pm

when i have something in the loop, my send level acts more like a blend not boost. I happen to like it but I figure I have something wired incorrectly. It actually gets a little louder towards dry (counterclockwise) also i am using a 1meg instead of a 250k so. With the master still in place my sound was mushy. I removed the master and now I have a more traditional sound (non master tone) I like the loop a lot. Also my recovery cathode is just a 2.2k (no 22ufcap ) Still teaking.

novosibir · Post by **novosibir** » Tue Feb 20, 2007 2:41 pm

jerrydyer wrote:when i have something in the loop, my send level acts more like a blend not boost.

Seems, that you haven't read my concerning post correctly?

When you want to use the loop as a booster, then you have to loop in just a cable, not an effects device. The looped in cable of course should have an on/off switch, to that you can switch the booster on and off

Once again - either effects loop, or booster. Both at the same time isn't possible, except you build two of this loop in series into the amp.

Larry

jerrydyer · Post by **jerrydyer** » Tue Feb 20, 2007 4:52 pm

that was thinlizzy. I was just making the statement that my send level acts more like a blend level. Clockwise more effects but no raise in volume. Counterclockwise more dry and a little louder. Works great for me. I just asked about a 2.2k instead of the 1.5k and 22uf. No problems really just playing around.

joshwilson3 · Post by **joshwilson3** » Wed Feb 21, 2007 1:17 am

Do you guys have a recommendation for an on/off switch? I wouldn't want a toggle switch. But like a small push button on/off switch. I think the push button would work better on the back of the chassis vs. a toggle switch.

novosibir · Post by **novosibir** » Wed Feb 21, 2007 3:42 am

thinlizzy wrote:Has some one a schematic for al simple on/off switch with a led that does'nt make a pop sound while switching.

Email with a schem w/ true bypass switch, but w/o LED already sent!

Larry

novosibir · Post by **novosibir** » Wed Feb 21, 2007 3:43 am

antosimoni wrote:as I'm tryin' to have the least influence of the loop on the head sound can I use a switch to make the entire loop switchable on/off?? if yes how I've to do it??

joshwilson3 wrote:Do you guys have a recommendation for an on/off switch?

Email with a schem w/ true bypass switch already sent!

Larry

thinlizzy · Post by **thinlizzy** » Wed Feb 21, 2007 5:26 am

jerrydyer wrote:that was thinlizzy. I was just making the statement that my send level acts more like a blend level. Clockwise more effects but no raise in volume. Counterclockwise more dry and a little louder. Works great for me. I just asked about a 2.2k instead of the 1.5k and 22uf. No problems really just playing around.

????? what was I?? I read all Larry's mail very carefully....