JMI Vox AC10 add-on top boost?

[seveneves]

This may be closer to what you have in mind...

Yes! Interesting. If you don't mind, could you help me to understand here... I would have suspected the DPDT to be located between the normal volume pot (R15 in the Thomas AC10 schematic) wiper and the 0.01 cap (C12). What's the downside to doing that vs. what you have here?

Also, it seems those 220k (R19 and R20 in your schematic) are mixer resistors (?) to the PI... maybe one would be required for the top-boosted normal channel but would one be required for the EF86 trem channel? There are no mixer resistors that I can see in the stock AC10?

[sluckey]

Yes! Interesting. If you don't mind, could you help me to understand here... I would have suspected the DPDT to be located between the normal volume pot (R15 in the Thomas AC10 schematic) wiper and the 0.01 cap (C12). What's the downside to doing that vs. what you have here?

The downside is the NOR volume pot will also affect the TB channel. If that's OK with you then move the switch. My circuit allows you to set the NOR volume then set to TB volume independently. This way you can match the TB volume to the NOR volume, or maybe set the TB volume a bit higher than the NOR volume, kinda like a BOOST.

Also, it seems those 220k (R19 and R20 in your schematic) are mixer resistors (?) to the PI... maybe one would be required for the top-boosted normal channel but would one be required for the EF86 trem channel? There are no mixer resistors that I can see in the stock AC10?

Yes they are mixing resistors. If you are gonna mix two channels together, you need two resistors.

The AC-10 doesn't use passive mixing resistors because the mixing takes place in the PI tube. Did you notice that each channel uses a different input to the PI?

[seveneves]

The downside is the NOR volume pot will also affect the TB channel. If that's OK with you then move the switch. My circuit allows you to set the NOR volume then set to TB volume independently. This way you can match the TB volume to the NOR volume, or maybe set the TB volume a bit higher than the NOR volume, kinda like a BOOST.

Ah, I missed that your schem has a volume within the TB circuit (R11)!

What I was hoping for was to just go straight from the Normal Volume wiper to the switch which would then allow it to go directly into V2A's (your schem) grid, pin 2 (if switched into TB via the DPDT; otherwise the Normal Volume wiper goes to 0.01 cap that is the PI input as stock factory).

Yes they are mixing resistors. If you are gonna mix two channels together, you need two resistors.

OK, I think I understand... would I still need based on my clarification above (i.e., bypassing the TB volume)? My (naive?) thinking is an incorporation of TB as a switchable inline "EQ/boost" to the normal channel, not it's own channel. Thus, ultimately just one channel and therefore no mixing resistor(s) required?

The AC-10 doesn't use passive mixing resistors because the mixing takes place in the PI tube. Did you notice that each channel uses a different input to the PI?

I do now! Thanks for the reminder.

[sluckey]

What I was hoping for was to just go straight from the Normal Volume wiper to the switch which would then allow it to go directly into V2A's (your schem) grid, pin 2 (if switched into TB via the DPDT; otherwise the Normal Volume wiper goes to 0.01 cap that is the PI input as stock factory).

You seem to already know what you want. Just go for it. It will work.

[seveneves]

Thanks for your confirmation, patience and understanding sluckey. I appreciate it and respect your knowledge and input (pun intended ).

[sluckey]

OK. Final revision. I think this is what you are asking for...

[seveneves]

Yes!!! Thank you sluckey for the schem!