Converting a small 18 watt derrived amp to NR

General discussion area for tube amps.

Moderators: pompeiisneaks, Colossal

Post Reply
User avatar
chopstuck
Posts: 399
Joined: Fri Apr 25, 2008 5:09 pm
Location: Here next to my tracking bracelet.

Converting a small 18 watt derrived amp to NR

Post by chopstuck »

When removing the reverb from a complete amp circuit like a ***erati JR what else has to change to make a NR ?

The lesson of the Princeton NR is being taken to heart. Remove too much and you emasculate the amp.

In the case of the JR, the amp sounds sweeter without the reverb.

I plan to remove the reverb driver circuit but what else ? How does the recovery stage add to the amps character ?
Heavens, an unused PI input !
azatplayer
Posts: 556
Joined: Thu Feb 26, 2009 7:59 pm
Location: Great Southland

Re: Converting a small 18 watt derrived amp to NR

Post by azatplayer »

The reverb circuit starts from the master volume return. It ends at the voltage divider on the phase inverter input.
The return wire on the master pot runs to a 1meg resistor, unpick that wire at the 1meg end.
At the .02 coupling cap entering the PI, theres a 1k resistor that attaches to a divider network. Disconnect the 1k from the network.
Now attach the loose wire from the master pot, to the loose 1k resistor.
Circuit now bypassed. You can just leave it all there and pull the tubes if you like.
You could also put in a pull pot at the master, to engage it back in. Which would be ideal.
Ive owned both of these amps, great amps both. Very versatile. I think having the verb switchable would be the best of both worlds for sure.
Don
User avatar
chopstuck
Posts: 399
Joined: Fri Apr 25, 2008 5:09 pm
Location: Here next to my tracking bracelet.

Re: Converting a small 18 watt derrived amp to NR

Post by chopstuck »

Thanks for the tip ! I will give that a try. So you think that when the reverb circuit is bypassed in this way it is equivalent to the NR ? More sustain etc..
Heavens, an unused PI input !
azatplayer
Posts: 556
Joined: Thu Feb 26, 2009 7:59 pm
Location: Great Southland

Re: Converting a small 18 watt derrived amp to NR

Post by azatplayer »

You know, everything makes a difference. The reverb circuit is twice as busy as the tonestack, takes up more room on the board as well. Plus 2 tubes and a driver. The signal gotta pass thru a lot of real estate to get from the master to the phase inverter, so its gotta make some difference.
The rest of the amp is the same, so what folk say about the NR having more grunt is valid.
I see the good doctor is now offering a tonestack bypass mod as an extra.
Will give it a massive boost. Probably too much of a boost i think, but cool option all the same.
Anyways, this simple trick will get you where you want to be to see for yourself, and will take you about 5 minutes to do. Good luck, let us know what you think!
Post Reply