L-Pad attenuator question

[Rockhorst]

This is just to double check:
I'm building a fixed resistor L-pad box for a 5W amp. I was under the impression that I should use isolated jacks, but I've only seen other builds that use non-isolated jacks. So connecting the grounds through the chassis of the box is ok?

[cooder]

I built one using metal jacks BUT I did NOT rely on the enclosure making the ground connection, I definitly put a dedicated heavy gauge (18 AWG) wire to connect both grounds on the jacks.
IMO opinion the correct thing to do.
Risking an open connection through missing ground and the speaker disconnected from amp while running is potentially and quickly bad news especially for the OT.

[Rockhorst]

Hey Cooder, thanks for the reply. My concern with that would be a potential ground loop? Is there any problem with using isolated jacks?

[cooder]

AFAIK groundloops in this situation are not a problem.
Groundloops in the front of the chain can induce hum on the very weak guitar signal, but the signal from amp to speaker is much stronger obviously and inducing hum through a ground loop doesn't happen there or other nasty side effects.
So no, I don't think in the case of an attenuator there would be a problem with using a dedicated ground wire AND have also a ground connection through chassis. Using isolated jacks would be fine too I guess, no problem as long as you definitly have a safe connection to make sure the amp always connects to speaker or other resitive load, but not an open connection.

[Rockhorst]

Seems you're right Cooder. Wired it up and no loop problems whatsoever. Additional question: did you try a treble bleed bypass? I've tried everything from 1u to 22u with little difference. My L-pad resistor values are 8 and 16 Ohm. I read that these values are about the same as the ESR on run of the mill electrolytics, which defeats their purpose here. I ordered some low ESR panasonics to see if it'll make a difference.
Any ideas?

[cooder]

Can't say anything about that as the attenuator I built is a little more involved than an L-Pad.
I built this one http://www.madbeanpedals.com/forum/index.php?topic=20290.0

[Rockhorst]

nice praying mantis
hadn't considered film caps in that range, might be a good idea (negligible ESR compared to electrolytics).

[cooder]

nice praying mantis
hadn't considered film caps in that range, might be a good idea (negligible ESR compared to electrolytics).

Yes I was lucky that I had those film caps floating around... you need at least 50 V rating i believe to be on the safe side including a good safety margin.
I could send you some of those 4.7uF film caps if you pay for the shipping...