Glam - Volume Drop

[daleykd]

Anyone else built the Glam and noticed a decent volume loss when engaged?  I get beautiful chorus, but the volume is too low.

EDIT: My TP is 6.9DCV, and I can't get it any lower with the trimmer.

Thanks,
Kyle

[drolo]

Not an expert in biasing FET's but lowering R2 might help.

[mjcyates]

My build also has a significant volume drop. My TP voltage is 5.99. What is the best way to get unity volume?

[madbean]

You can increase R9 to get more output. It's stock at 10k. Try 15k or 20k.

For Q1 bias, it's a bit unusual to not be able to dial in the right voltage with a 50k trimmer. But, you can use a 100k trimmer instead of 50k. However, changing R9 is probably easier.

[gordo]

Not noticing a drop in mine.  Usual suspects...checking all parts and swapping out tranny, 062 and the PT.  I'd suspect that 2N5457, and if you're like me you didn't socket it to save room in the enclosure.

[mjcyates]

Thanks for the replies. I will change R9 and see what happens.

[mjcyates]

Changed R9 to 15K and biased TP to 4.5 problem solved. This is a unique sounding chorus. I really like it. I don't know anything about biasing transistors so I don't know if 4.5 is good or not but it works!

[midwayfair]

I'm going to plop a partial explanation in here of what's going on since it relates to another post I was responding to:

The output impedance of Q1 is both R3 and the drain impedance, which depends on the trimpot setting. So while a lower bias point will give you more output from the FET, more resistance on the drain means less gain from the inverting op amp stage.

Increasing R9 bumps up the output of the entire pedal, but you could also adjust R3 if you need to adjust only the dry path and R8 if you need to adjust only the wet path.

[daleykd]

Glad to see this thread got a bit more traction and that I wasn't the only one.

The Glam has been sitting on my "to fix" pile and I haven't gotten to it.  My hope was in the next couple of weeks.

Thanks for all the input, guys!

[daleykd]

I finally got around to doing this (I'm slowly in the process of boxing up all the 1590G builds).

I increased R9 from 10k to 15k and the volume was much better, if not perfect.  However, I still couldn't get a decent bias.

I replaced the trimpot from 50k to 100k and was able to dial in 6V.

IT'S WORKING!  HOORAY!

[Willybomb]

Necro revival.

Thanks for this.  I'm playing around with my Glam properly in the box now, and the volume drop is pretty noticeable.  I'm probably going to replace it with a pork barrel anyway, but in the meantime.

[LateCentury]

I'm having this same problem with the Wigl. I'm not very adept at reading schematics... would increasing R9 on the Wigl have the same effect in a volume increase? Or would it be a different resistor?

[LateCentury]

I just built my Glam up and ran into the same problem. Swapping out R9 for a 15k, and increasing R3 and R8 don't really seem to do anything at all. The effect is very weak sounding, but maybe because of the overall volume drop.

I increased R3 to 27k, R8 to 18k and R9 to 15k. Am I going backwards?

[reddesert]

I'm having this same problem with the Wigl. I'm not very adept at reading schematics... would increasing R9 on the Wigl have the same effect in a volume increase? Or would it be a different resistor?

I can't answer your question about the Glam, but for the Wigl, no I don't think increasing R9 would have a useful effect. If anything I think it might give you less volume. The two circuits are pretty different and the Wigl doesn't have a FET that needs to be biased, so that eliminates one source of variability.

I built a Wigl and didn't notice a volume drop. You might look at the resistors R3-R4, R5-R6, R7-R8, and R9-R10. Each of these pairs should have equal value resistors. If one is different or if you have loose/shorted connections, it will change the gain of the stages.