Zero Loss fx loop in Express?

[freakshow__]

Does anyone have pictures or a layout to install the Metroamp Zero Loss loop in an Express build? Thanks for any help guys!

[xtian]

What are you trying to achieve? As we've recently been discussing, Express begins to distort first at the power tubes, so an FX loop sounds useless to me.

[freakshow__]

need it for volume lowering/boosting via a clean boost pedal....not effects/distortion.

[martin manning]

I added a trim pot to my Express going into the third stage. You could arrange a two-level attenuator on a relay at that point for a switchable boost.

[pdf64]

need it for volume lowering/boosting via a clean boost pedal....not effects/distortion.

So what’s the rationale for a clean boost being better in an fx loop than at the regular input?

[freakshow__]

guys...just want to add a zero loss loop in an Express. Not looking to complicate things anymore.

The rationale? have you put a boost in front of a high gain amp before? it does nothing....putting it in a loop boosts volume bigtime.

This is what "I think" I need to do to add the zero loss loop? See the attached layout. I have noted where I am to add in purple between gain stage 3 and the PI.

Does this look right?

EXPRESS LOOP.jpg

[pdf64]

The rationale? have you put a boost in front of a high gain amp before? it does nothing....putting it in a loop boosts volume bigtime.?

Can’t compare a non master vol amp with a cascading overdrive preamp, it’s an apples and oranges thing. With the express, most of the clipping occurs after anywhere a loop could be inserted.

[freakshow__]

well, I tried it as I had in my layout picture. It works but it's not right. The sound is greatly distorted, it sounds kind of like crossover distortion. Hmmmm

[pdf64]

A voltage survey would be a good idea.

[romberg]

need it for volume lowering/boosting via a clean boost pedal....not effects/distortion.

Ah! I pretty much don't use effects at all. But this is the one thing I have used an effects loop for (sorta). It is nice in a band situation to be able to step on a pedal and instantly increase your volume a bit for solos and the like. The only goal is to get louder not increase distortion.

I have a diy "effects pedal" that I plug into some amps effects loops for just this purpose. The pedal consists of a simple 1M pot (voltage divider) and a foot switch. The pot you can adjust to lower the overall volume of the amp. In effect it is acting like an additional master volume. Then the foot switch simply bypasses the pot for a volume boost. This works pretty well for amps that generate their overdrive in the pre-amp. However as others have pointed out, the express is a different story.

If I was going to try and have the same foot switchable volume boost trick going on with one of my expresses I think I might try one of two things:

• Install a PPIVMV into the express. With this type of master volume you can then overdrive the phase inverter first instead of the power tubes. This does of course not sound exactly the same. But it is a reasonable compromise IMO. And it does leave some extra headroom for a volume boost. However the signal is now split in two and one would need to install two effects loops or some kind of foot switch controlled relay (and extra dual ganged pot). I think it could be done. But it would probably be more trouble than it is worth.
• Use an external volume attenuator that features a foot switchable volume boost. I'm almost certain I've seen such a thing advertised before. Such an attenuator might be the most straight forward way to implement a foot switchable volume boost for an express.

[10thTx]

The best "boost" pedal I've found working quite well for me in an active FX loop is actually an EQ pedal. Every OD pedal, distortion pedal and fuzz pedal I've tried in an active FX loop sounded horrible to me.

With respect, 10thtx

[freakshow__]

Got it to work guys.....

If you ever want to do it, buy the Metroamp zero-loss loop. Then insert it in between the .1uF cap (C9) and 1meg resistor (R10) on the schemo. You need to remove the jumper and put the loop in its place. You also need to add a .022uF 400-600v cap after the loop, this is where it connects to R10 on the turret board. If you don’t add that cap it will not work...it will be greatly distorted.

All this is basically shown in the Two-Rock ‘ruby’ schematic that is floating around the internet. It’s not very clear....but those are the 2 cap values on it.

Now as far as getting the volume boost in the loop, you gotta set the boost pedal low, so it actually lowers your volume when on, and boosts your volume when you turn it OFF. I know it’s not a ‘pure’ trainwreck tone by doing this.....but it does the trick and the guy I did it for loves it. Enjoy!

[Mark]

Another option is what Zinky did on the Tone Master amp where he used a post P.I. master volume and switched it out of circuit. This might be a more transparent option.

https://www.thetubestore.com/lib/thetub ... ematic.pdf