So I did the short plug. I honestly couldn't tell any difference. Another observation I mae is I get some weird nuances while sweeping the volume knob. Almost sounds like sweeping a filter from low to high. It its not a uniform "sweep" so to say.
When the 'phono' input is utilized the sound is more consistent. No funny effects from the knobs. I dunno, maybe it's my guitar. I did notice however that the hum is more prevalent when the bass is boosted.
When the 'phono' input is utilized the sound is more consistent. No funny effects from the knobs. I dunno, maybe it's my guitar. I did notice however that the hum is more prevalent when the bass is boosted.
Funny that 🙂
But is telling you that (some) of the hum is getting in via the pre-amp section.
Unfortunately there's got to be a dozen ways to get hum into a 12AX7 (or similar)
As I think I mentioned earlier (or maybe it was in another thread) instrument amps aren't something I normally deal with and so I did a double take when I looked at the mic input on the diagram in post #1
It looks like the MIC socket has an extra connection that the plug barrel uses to add a 0.47uf cathode bypass into circuit, presumably to give some HF lift. Never seen anything like that before.
The phono socket does appear to have a shorting option now I look closer although that input is still 100's of k away from the MIC input.
I suspect the hum and all is normal.
It looks like the MIC socket has an extra connection that the plug barrel uses to add a 0.47uf cathode bypass into circuit, presumably to give some HF lift. Never seen anything like that before.
The phono socket does appear to have a shorting option now I look closer although that input is still 100's of k away from the MIC input.
I suspect the hum and all is normal.
Yes, the extra finger on MIC does "something". It may kill NFB, or reduce the tone-control range. I'd have to work-out that odd tone/NFB leg, and I'm not up for that.
If this will be "only" a gitar amp, I'd cut a lot of that phono network right out. The amp already has a "design flaw": vol pot at pickup level. This means you get (nearly) all hiss and all hum all the time, even when turned-down. (You may turn-up the hum around the jack and pot and the pot hiss.) There were a few commercial g-amps which did this (not "good" ones). Look at any of the Fender Champs (similar tube lineup), Leo put the vol pot between 1st and 2nd stages. Turn-down lost 1st stage noises.
I would not go back and hack the V-M with vol pot between stages. You want that, Epi Valve Jrs (Champ clones) are readily available. The V-M gain-staging is "different", and with the world over-run by Fender(/Marshall) clones, we need to preserve those differences for future players.
If this will be "only" a gitar amp, I'd cut a lot of that phono network right out. The amp already has a "design flaw": vol pot at pickup level. This means you get (nearly) all hiss and all hum all the time, even when turned-down. (You may turn-up the hum around the jack and pot and the pot hiss.) There were a few commercial g-amps which did this (not "good" ones). Look at any of the Fender Champs (similar tube lineup), Leo put the vol pot between 1st and 2nd stages. Turn-down lost 1st stage noises.
I would not go back and hack the V-M with vol pot between stages. You want that, Epi Valve Jrs (Champ clones) are readily available. The V-M gain-staging is "different", and with the world over-run by Fender(/Marshall) clones, we need to preserve those differences for future players.
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