Videoshielded
Modify or Die!
- Joined
- Jun 22, 2001
- Posts
- 132
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- 11
I’m getting ready to upgrade my MG Head DT by putting a pair of constant current sources (CCS) on the plates of the driver tube. As long as I had to disassemble the amp to pull the plate load resistors and put in the connecting leads for the CCS circuit boards, I did a couple other mods I’ve been putting off:
Coupling caps – I pulled out the Auricaps I’ve had in there for over a year and replaced them with Dayton film and foil caps from Parts Express, part number 027-458. They cost $1.38 each; the Auricaps are about $7.75 each. Both are true film-and-foil caps (as opposed to metalized film caps, which don’t sound as good IMHO).
Shunt pot – I shunted the Alps volume pot with a pair of Caddock MK132 resistors, size 47K. The easiest way to do this is solder one resistor so it connects the input of the pot (the one with the wire from the RCA jack on the back of the chassis, duh) to the wiper of the same channel of the pot (center terminal, connects to the “input” terminals on the circuit board); then do the same thing with the other resistor on the other channel of the pot.
Just for giggles, I also redid the negative feedback circuit so I can switch it on or off with the “high-low” toggle on the front panel. Then I put everything back together and tack-soldered the plate load resistors back in, so I could be sure everything was working well before I add the CCS boards this weekend.
The Dayton caps are good – just as good as the Auricaps, I think. I’ve used them in other projects and been similarly impressed.
The shunt pot mod – amazing. I’m on record as hating volume pots. It’s astounding how cruddy they make things sound. But there’s really no room for a resistor-attenuator in this chassis; even the DACT looks too big. The shunt mod helps a whole, whole lot. Best example I can give is one track I like on a Latin jazz CD recorded in Havana; it has a strange background noise in the studio that I could never quite sort out. Some kind of percussion, but I couldn’t tell what. Turns out, it was raining like hell. Now I know.
Coupling caps – I pulled out the Auricaps I’ve had in there for over a year and replaced them with Dayton film and foil caps from Parts Express, part number 027-458. They cost $1.38 each; the Auricaps are about $7.75 each. Both are true film-and-foil caps (as opposed to metalized film caps, which don’t sound as good IMHO).
Shunt pot – I shunted the Alps volume pot with a pair of Caddock MK132 resistors, size 47K. The easiest way to do this is solder one resistor so it connects the input of the pot (the one with the wire from the RCA jack on the back of the chassis, duh) to the wiper of the same channel of the pot (center terminal, connects to the “input” terminals on the circuit board); then do the same thing with the other resistor on the other channel of the pot.
Just for giggles, I also redid the negative feedback circuit so I can switch it on or off with the “high-low” toggle on the front panel. Then I put everything back together and tack-soldered the plate load resistors back in, so I could be sure everything was working well before I add the CCS boards this weekend.
The Dayton caps are good – just as good as the Auricaps, I think. I’ve used them in other projects and been similarly impressed.
The shunt pot mod – amazing. I’m on record as hating volume pots. It’s astounding how cruddy they make things sound. But there’s really no room for a resistor-attenuator in this chassis; even the DACT looks too big. The shunt mod helps a whole, whole lot. Best example I can give is one track I like on a Latin jazz CD recorded in Havana; it has a strange background noise in the studio that I could never quite sort out. Some kind of percussion, but I couldn’t tell what. Turns out, it was raining like hell. Now I know.