Re: Tricks for 70's D-ODS Clones

[mlp-mx6]

IIRC, if you put the resistor between the "ground" lug and the wiper lug on a linear pot it "log-ifies" the curve. On an already-log pot it would be "more loggy". (LOL!)

Much about this on RG Keen's site - http://www.geofex.com/ - look for "Secret Life of Pots"

[Darkbluemurder]

I tried 100k and 150k before the Drive pot and both sound good to me.

Since I have a 250kA level pot I did not use a series resistor in front of it and used a 220k from the pot wiper to ground to simulate a 150k into a 100kA level pot. That works good for me although the modded Concert gets pretty loud at 2 (1 equals 0 with the Fender knobs).

I bought West's 250KA "Worlds Best" pots(?!?) and intend to put 168K resestor across the pot to bring it to 100K. I'm interested in how much of the audio curve remains after this mod, and may well experiment with a ten turn calibrated knob I have to see how the resistance stacks up to regular audio curve. I don't have the scheme handy but I'm not sure how you've simulated a 100K pot with what you describe. You may want to try the other approach to get a somewhat more usable drive control.

FWIW
Dan

Dan,

in fact the net value of the pot is closer to 120k with a 220k to ground. 180k in parallel with 250k would have made 100k. But you are right - I made a calculation in an excel spreadsheet and it does not work exactly the way I thought. Still useable but I will probably change it to Rev A specs for accuracy sake.

DBM

[George Adzich]

Dan,

I am glad that you asked the question about changing the value of the 250K pot to 100K by the addition of a resistor "across" the pot.

I too, thought that this would approximate a 100K pot - it does not. It actully creates a weird anti-log variation.

I also experimented with the technique of placing a resistor from the wiper to the ground lug. This is slightly better but is still different than a true 100K pot.

In the example that "darkbluemurder" gave of not needing the 150K resistor in series with the "level" pot because of this method, I think that he will find some issues if running the level pot fully open. He will no longer have any series resistance. I am not certain what the effects this will have, but it is definitely different than the 150K resistor in the circuit.

I ended up buying a couple of PEC 100K audio pots from Mouser to go with my set of Clarostat pots that I also purchased from Westlabs. The quality is excellent and the dimensions and the price are the same. It is going to be tough to go back to Alpha pots after using these........

I hope this saves you some time and frustration.


-George

[Darkbluemurder]

In the example that "darkbluemurder" gave of not needing the 150K resistor in series with the "level" pot because of this method, I think that he will find some issues if running the level pot fully open. He will no longer have any series resistance. I am not certain what the effects this will have, but it is definitely different than the 150K resistor in the circuit.

George,

You are correct - this is what I noticed yesterday when I did my calculations. Since I did not turn the level control past 2 on the dial (about 9 o'clock) it wasn't an issue.

BTW: are you able to turn the level control past 5 or 12 o'clock? My band certainly would hate me for that.

DBM

[skyboltone]

Thanks George, and it will. Great trick with linear taper pots I guess but not so good here. I'll change my parts list and save the frustration.

Anyone ever just run the 250K instead of 100K and suffer the consiquences?

Cheers.
Dan

Dan,

I am glad that you asked the question about changing the value of the 250K pot to 100K by the addition of a resistor "across" the pot.

I too, thought that this would approximate a 100K pot - it does not. It actully creates a weird anti-log variation.

I also experimented with the technique of placing a resistor from the wiper to the ground lug. This is slightly better but is still different than a true 100K pot.

In the example that "darkbluemurder" gave of not needing the 150K resistor in series with the "level" pot because of this method, I think that he will find some issues if running the level pot fully open. He will no longer have any series resistance. I am not certain what the effects this will have, but it is definitely different than the 150K resistor in the circuit.

I ended up buying a couple of PEC 100K audio pots from Mouser to go with my set of Clarostat pots that I also purchased from Westlabs. The quality is excellent and the dimensions and the price are the same. It is going to be tough to go back to Alpha pots after using these........

I hope this saves you some time and frustration.


-George

[George Adzich]

DBM,

You had asked if "I can turn the Level control up past 5 (12 o'clock)".

I am able to do this, but I run a Master Volume as well. I can usually always turn up my amps to full blast, but I only use a pair of 6V6 tubes - approx. 18 watts. I also used a Concertina Splitter on my clone which is kind of different and sounds SWEEEEET!

No if you are asking if I actually do this as a practice - NO. I do not have a band to contend with but a wife and a 9 month old baby - LOL.


Cheers to All,

George

[Darkbluemurder]

DBM,

You had asked if "I can turn the Level control up past 5 (12 o'clock)".

I am able to do this, but I run a Master Volume as well. I can usually always turn up my amps to full blast, but I only use a pair of 6V6 tubes - approx. 18 watts. I also used a Concertina Splitter on my clone which is kind of different and sounds SWEEEEET!

No if you are asking if I actually do this as a practice - NO. I do not have a band to contend with but a wife and a 9 month old baby - LOL.


Cheers to All,

George

I see - I don't have a global Master Volume on my amps.

Meanwhile I changed the level control to a 100kA and put a 150k resistor in front of it just like in Hybrid A. I know I should have done that right away because it works better. Now the amp is pretty much Hybrid A except for a 0.022uF instead of 0.01uF after OD1 and 0.01uF instead of 0.005uF after OD2. I just like it better that way.

The big ticket however was changing the Fender Reverb to the 1 tube reverb described here in the forum. What a difference that made!