Skylark clone question

[mumford]

So I just finished building a skylark clone. It sounds pretty good but the low end feels a bit overly stiff/choked. I'm using a ss rectifier with 2 15v zeners on the PT center tap to pull down the voltage. I'm wondering if over filtering is the culprit--I'm using an 80 uf and 2 40 uf caps. I don't have NFB hooked up yet. Thoughts on what is making the low end so constricted?

[mumford]

It's a GA5, one 6v6 and one 12ax7. Basically a tweed champ with slightly different plate and cathode resistors.

[Firestorm]

What kind of OT? With SE, it's typically hard to get good low end w/o a hifi or near-hifi transformer.

[mumford]

It's a magnetic components champ OT. It's not weak so much as too stiff.

[mumford]

What I'm looking for is a bit spongier.

[overtone]

yup, my guess is the filtering is too high.
Last year I knocked up a GA5, the LP version before the Skylark.
I went with a solid state rectifier, the filtering at 20 10 10, as per the old schematics, into an ancient really crappy looking OT.
The response of the amp is more than perfect and the mains filtering is fine.
Best, tony

[tubeswell]

Yes. "Overfiltering" will take away the sponginess.

[rp]

if that's the old, very cheap MC champ OT it's a dink. I'm lazy about going through the A-B thing with jumpers but I did it here, pure mud, 100% dink. Noticed MC recently offered an upgrade which should be better. The Allen one is terrific & w/ 4&8 ohm taps. The Edcor I put in a 5C1 is killer too but the 5C1 is a unique animal and I'm only familiar with my clone so can't extrapolate to 5F1 or BF.

Over-filtering can do what you don't like. Was the GA5 really 80/40 40, if not why not try stock or 5F1 or BF filtering and see what you get? 5F1 16/8/8 is not too little, I often run mine w/ the Allen through a Brit G12H30 Anni and you can't ask for more from 5 watts.

[mumford]

I've never had a problem with a MC transformer before, but after adding NFB, I have to admit it's a lot darker than I expected. Adding a 0.68 uF bypass cap on V1b helps quite a bit, though. I may have to tweak the NFB resistor to compensate.

[rp]

I've never had a problem with a MC transformer before

it's not MC as a whole, just that one OT of theirs that's lame. They kind of acknowledged it by offering an upgraded version. Champs (prolly Skylarks?) are dark, muddy OT doesn't help.

but after adding NFB, I have to admit it's a lot darker than I expected. Adding a 0.68 uF bypass cap on V1b helps quite a bit, though. I may have to tweak the NFB resistor to compensate.

Bypass on V1a is essential, on V1a & b not so nice in a champ, .68-4.7 depending on pickups, not much difference from 4.7-25, actually not much after 2.2. For 15 minutes work you might try making the GA5 into a 5F1 and see if it sounds any better. No sure what the Gibson had but if you're using an 8" I've not found a modern 8 that's bright enough for a champ. Build it for a 10/12" you'll have much more choice to voice it.