Metropoulos Forum

Is the lack of a normal channel mix cap the only thing adding the mud to the normal channel? I'd like to shape the tone of that channel a bit so I'd actually use it.

thoughts?

The mixer section is part of it but remember that the resistance values and any bypass caps there affect BOTH channels at the same time because of their common point right before V2, depending on how the channel volume pots are set. Change one channel and the other can be affected. There is a path to "back to ground" for mid and high frequencies (depending on bypass cap value) through the other channel's bypass cap and volume pot rather than on to V2's grid.

In other words, depending on the resistance of the individual volume pots to ground (what volume they are set to), part of one channel's signal can bleed to ground through the other channel's pot. Add a bypass cap to the normal channel mixer and that channel will get brighter but the bright channel can also lose treble. Hopefully this makes sense. I may not have described it very well.

Obviously the different cathode resistance and bypass caps on V1 as well as any bright caps on the volume pots add to how each channel can be more different or similar to the other.

I recently reshaped mine - into 2203 preamp (left the 2n2 cap though and used 250pf for the mixer).
No mud whatsoever
Not the answer you wanted to hear but try it out!

YMI5150? wrote:Is the lack of a normal channel mix cap the only thing adding the mud to the normal channel? I'd like to shape the tone of that channel a bit so I'd actually use it.

thoughts?

The mix cap is a big part of it.
The other part is the 330uf cap. Way, way too big.
The final "mud" factor is the .02 coupling cap.

If you have a PPIMV and you want to get a thicker, fatter, gainier tone, bring your normal channel closer to the specs of the bright channel, then jumper them internally. I use a 1000pf mixer cap, a 1uf cathode bypass cap and a .002 coupling cap. It'll holler. This is one thing that Ben "stuntdouble" turned me on to.

SteadyEddie wrote:

YMI5150? wrote:Is the lack of a normal channel mix cap the only thing adding the mud to the normal channel? I'd like to shape the tone of that channel a bit so I'd actually use it.
thoughts?

The mix cap is a big part of it.
The other part is the 330uf cap. Way, way too big.
The final "mud" factor is the .02 coupling cap.

The 0.022uF coupler is not a problem on this channel and the mixer cap has the influences that Toner covered. A bypass cap on the normal pot can help tune the treble peaking ability of the pot if you want. By all means replicate channel 1 on channel 2 but I think if you want to be able to jumper channels and tone shape that way is simply change the cathode bypass cap to something that shelves in the normal human hearing range!

IMO best thing to do which keeps a lot of the character of the amp is simply replace the 330uF cap with a similar rated 4.7uF electrolytic. It keeps the 'normal' character but removes so much of the mud. The 820R gives the gain you want, but if you want cleaner and less gain (think Fender) then a 25uF cap and 1k5 cathode resistor also works.

I went through the options but settled on a 4.7uF/820R on my JTM45 clone, you might prefer one of the other options. If you crack the amp open and fire the soldering iron up you can try all of the options back and forth in a couple of hours. I have not wanted to mess with my split cathode amps as I usually plug straight into hi channel 1 but am tempted to try the 25uF/1k5 route (nowadays it will be 22uF/1k5).

thx. dropping the V1a cathode is working nicely. got rid of the 250 in place of a 10uF and its close. I may increase the resistor to clean it up a bit. Just need to decide what i want from this channel.

Cheers