Metropoulos Forum

Hello everyone!

Is it possible to do One Wire/Cascade Mod wiring Bright channel into Normal? Is it safe for amp? Should it sound more bass that standard mod?

Thank you!

I tried this one about a month ago and this cause high pitched oscillation when High Treb channel knob higher than 3, no matter using shielded or unshilded cable when wiring. Any recomendations on this?

Thanks!

You may need to adjust some component values to reduce the gain a bit or adjust the voltage divider between stages to cut a bit if the gain. Do you have grid stoppers on each stage? If you are able to post some pics we may be able to offer some suggestions.

I had a similar problem. The amp was unusable for a lot of the volume knob sweep (the know adjusting the cascaded signal). I later added a 470K resistor to ground at the unused tag of the push pull switch in this diagram (the one I used, below) to form a voltage divider that reduces cascaded gain by ~ 50 %. The volume knobs are now useful throughout out their range, but sounds best with cascaded gain knob around 80% of max. No oscillations or squeals anymore.

Here is the layout I am referring to. The unused tag is ta the lower left of the push-pull switch.
http://i1329.photobucket.com/albums/w55 ... 117520.jpg

Note that this is the normal channel cascaded into the bright channel, but will probably work for your topology. Give it a shot. Should only take a few minutes.

danman wrote: ↑

Tue Dec 29, 2020 6:29 pm

You may need to adjust some component values to reduce the gain a bit or adjust the voltage divider between stages to cut a bit if the gain. Do you have grid stoppers on each stage? If you are able to post some pics we may be able to offer some suggestions.

Thank you for response. Mine is stock 1959HW (schematic attached) with master volume mod that not affects preamp section at all. So what ways it may be solved?

https://i.ibb.co/WVnXCyP/45828-B7-C-B11 ... AA3335.gif

The first thing to check is the amp's lead dress or how neat the wiring has been done. When adding extra gain with the cascaded stages, the preamp wiring must be done correctly to avoid an oscillation issue. Make sure the wiring is short and neat and all signal wires that cross each other do so at a 90 degree angle. Try gently moving some of the preamp wires around a bit with an insulated tool such as a chopstick and see if you find a position that quiets the amp. If proper lead dress and shielded wire does not help, you could look at cutting a bit of the gain by changing some component values or adding a voltage divider between stages. Adding grid stoppers may also help to stabilize the amp. If you could post some pics of the wiring, I could point out a couple of places that you could add snubber caps which will also help.

Try this from SDMs site (1959 RR1wireswitch.jpg)

It works. I've used it on two amps

You may need to experiment a little with cathode cap and resistor (Ck/Rk) on the normal channel (ie lower the cap and slightly raise the resistor to something like 4n7uF and 1k5 and play with the resistor shunt on the pot for best effect.

https://drive.google.com/drive/folders/ ... zd3STVYd3c

Thanks for everyone!

My problem gone after wiring grids inputs with coax cable with grounding screen on the pot side. Deadly quet now.

Good to hear!