Effects loop pre or post MV?

crbowman · Post by **crbowman** » Fri Dec 11, 2009 4:52 pm

Hey Gang,
I'm working on a 70's style build based loosely on #40. As we know, #40 does not have a proper effects loop, just a pre-master vol preamp out. In you guys valued opinion, if I wanted to turn this into a full-fledged loop, would it be best to implement this by tapping right off the preamp out as it is now (pre-master vol), or to follow the more conventional implementation ala #124 and most others and do it post MV?
Is there any real advantage to having the loop output level controlled by the MV?

benoit · Post by **benoit** » Fri Dec 11, 2009 6:46 pm

crbowman wrote:Hey Gang,
I'm working on a 70's style build based loosely on #40. As we know, #40 does not have a proper effects loop, just a pre-master vol preamp out. In you guys valued opinion, if I wanted to turn this into a full-fledged loop, would it be best to implement this by tapping right off the preamp out as it is now (pre-master vol), or to follow the more conventional implementation ala #124 and most others and do it post MV?
Is there any real advantage to having the loop output level controlled by the MV?

I think it would make a pretty significant difference putting it before or after. It just depends on whether you pedals deal well with a wider range of levels. I would lean towards putting it pre MV, but that's mostly intuitive speculation rather than hard data and experience. It seems like you'd keep your tone more consistent with the pre MV loop. Can't hurt anything at all to try it both ways.

crbowman · Post by **crbowman** » Fri Dec 11, 2009 8:09 pm

benoit wrote:
crbowman wrote:Hey Gang,
I'm working on a 70's style build based loosely on #40. As we know, #40 does not have a proper effects loop, just a pre-master vol preamp out. In you guys valued opinion, if I wanted to turn this into a full-fledged loop, would it be best to implement this by tapping right off the preamp out as it is now (pre-master vol), or to follow the more conventional implementation ala #124 and most others and do it post MV?
Is there any real advantage to having the loop output level controlled by the MV?
I think it would make a pretty significant difference putting it before or after. It just depends on whether you pedals deal well with a wider range of levels. I would lean towards putting it pre MV, but that's mostly intuitive speculation rather than hard data and experience. It seems like you'd keep your tone more consistent with the pre MV loop. Can't hurt anything at all to try it both ways.

This was my thinking as well. I'll be putting my venerable old Roland Space Echo in the loop and this thing is pretty sensitive to input level. Seems that with the loop post MV, I'd have to tweak the input level control on the echo every time I tweaked the master on the amp which could be kind of a PITA.
Wonder why HAD usually implemented this post MV?

heisthl · Post by **heisthl** » Fri Dec 11, 2009 10:34 pm

Post MV insures you set the correct return level.

talbany · Post by **talbany** » Fri Dec 11, 2009 11:19 pm

Post MV also changes the load on the PI... 250k (or 440k w/220k on jack) vers 1meg which helps keep the low end tight after efx signal has been amplified..

Tony

crbowman · Post by **crbowman** » Fri Dec 11, 2009 11:44 pm

Thanks guys.
I was wondering about the load on the PI. So in you guys opinion, considering an older style PI circuit like #40 has, do you think the decreased load of the post MV loop would be an attractive option? I guess I could always try it both ways and report back.......

talbany · Post by **talbany** » Fri Dec 11, 2009 11:58 pm

crbowman wrote:Thanks guys.
I was wondering about the load on the PI. So in you guys opinion, considering an older style PI circuit like #40 has, do you think the decreased load of the post MV loop would be an attractive option? I guess I could always try it both ways and report back.......

Not really getting your question?.. 40 just has a pre out.. If your talking about adding full loop there it wouldn't change since the MV is still 1M...That Pi is set up a little cleaner than the later style so you may have some room to go up if you want to fatten things up.. Other than that it's pretty much the same beast in that respect

crbowman · Post by **crbowman** » Sat Dec 12, 2009 5:29 pm

Thanks for your help guys!
I think I got it figured out.

Structo · Post by **Structo** » Sat Dec 12, 2009 7:47 pm

Is there a schematic for #40 around?

Guitarman18 · Post by **Guitarman18** » Sat Dec 12, 2009 7:50 pm

Here you go Tom,

https://tubeamparchive.com/files/40_schematic_496.pdf

This is the thread ic-racer started on the subject,

https://tubeamparchive.com/viewtopic.php?t=5986

Cheers,

Paul.

Structo · Post by **Structo** » Sat Dec 12, 2009 8:13 pm

Thanks!

crbowman · Post by **crbowman** » Sun Dec 13, 2009 3:39 am

Keep in mind that there are some inaccuracies in the otherwise great schem and layout for #40 as provided. Marcos was good enough to provide us with some info gleaned from his own 70's style amp as laid out in this thread.
https://tubeamparchive.com/viewtopic.ph ... &highlight

That said, MUCH thanks to ic_racer for his great work on this.

Tube Amp Archive

Effects loop pre or post MV?

Effects loop pre or post MV?

Re: Effects loop pre or post MV?

Re: Effects loop pre or post MV?

Re: Effects loop pre or post MV?

Re: Effects loop pre or post MV?

Re: Effects loop pre or post MV?

Re: Effects loop pre or post MV?

Re: Effects loop pre or post MV?

Re: Effects loop pre or post MV?

Re: Effects loop pre or post MV?

Re: Effects loop pre or post MV?

Re: Effects loop pre or post MV?