Active tone control question?

[triode17]

I checked out those vector boards. Pretty cool. Do you get them anywhere specific? I take it that they make different layouts.

Kennyg

They're not cheap (used to be), but I get them from Mouser Electronics. I like the fact that you can easily change a part if you need to. If they are installed on the top side, you don't even have to remove the board from its chassis. I use the T28 size clips for tube circuits, T42 size for SS.

 

[triode17]

Kenny-As a follow-up, here 's the way I wired the tone control pots. I connected all the clear, polystyrene caps. directly to the pots (RC assembly). Then, I built the board from the RC assy, back to the rest of the tone control board. I had to draw it out on paper a few times to get just the right layout, but it works beautifully.

 

[Kennyg2209]

Kenny-As a follow-up, here 's the way I wired the tone control pots. I connected all the clear, polystyrene caps. directly to the pots (RC assembly). Then, I built the board from the RC assy, back to the rest of the tone control board. I had to draw it out on paper a few times to get just the right layout, but it works beautifully.

Cool, I'm using silver mica caps, but I'll still be able to solder them right to the pots . I'm going to have plenty of room around them. Ya, I've already been drawing it out on paper also. I printed out a couple copies of the pot layout to scale so I can get it right. Thanks!


Kennyg

 

[Kennyg2209]

Kenny- You have way too much wiring to the pots. on this thing. I built his "Tone Control You Can Love" circuit and made the same mistake. The pot. wires were too long and can pick up whatever is floating by in the air. So I rebuilt the circuit on a Vectorboard with the tone control caps. on the edge of the board. This way, the leads to the pots. were kept at no more than 2". That made the difference and the circuit works great, good range and smooth control from mid. rotation to either side. Also, those plug in breadboards are too flaky, too easy for one connection to come unplugged, unnoticed. I use Vectorboard, 'flea clips' and bus wire.
You can test the mid. rotation of the controls by injecting a 400 Hz square wave and adjusting them until you get a good , square waveform. If they are not straight up, you have the wrong controls.

How was your frequency response from 20hz to 20khz? Did you run a sweep with the pots at midpoint into a scope? Mine is not too good. It's only good from 8k to 18k. Everything else drops off . It's probably my layout. The breadboard. All three pots are responsive. I don't have a vector board, but I have some good regular prototype boards. I think I'll lay it out on one and solder it . My amp is very linear and I don't want to compromise that . I would like it right before I put it in a chassis .


Kennyg

 

[Kennyg2209]

How was your frequency response from 20hz to 20khz? Did you run a sweep with the pots at midpoint into a scope? Mine is not too good. It's only good from 8k to 18k. Everything else drops off . It's probably my layout. The breadboard. All three pots are responsive. I don't have a vector board, but I have some good regular prototype boards. I think I'll lay it out on one and solder it . My amp is very linear and I don't want to compromise that . I would like it right before I put it in a chassis .


Kennyg

My bad. It ended up the sweep generator I was using has an issue. I should have been checking the input also. I was only testing the output. I tried a different one and it's good, linear.


Kennyg

 

[triode17]

My bad. It ended up the sweep generator I was using has an issue. I should have been checking the input also. I was only testing the output. I tried a different one and it's good, linear.


Kennyg

1. Kenny, here are some notes I have from when I built the two band version: Z out is 2k Ohms, but that's only at 1 kHz. Now, I've learned to measure impedance at 20 Hz, 1k and 20 kHz. The circuit drives a Balance control of ( I am not sure) 100k Ohms at the most, so it doesn't seem to be a problem. A 10kHz square wave, tone controls set flat is just 2 uSec. There's a 1 dB loss , set to Flat. High freq. extension is -3dB @ 115 kHz. Low end is probably -3 dB @ 15 Hz. My only complaint is that the Treble boost is only 6 dB and the cut is 9 dB. I wrote to Max Robinson about this and he said the range can be increased by lowering the 220k resistor from the Treble pot.
2. As far as building it goes, any board will do as long as it's all soldered together. Terminal strips are an option as well but keep the pot. wiring on the edge, with no more than 2" leads and you won't lose and high end.