Pre-Classic Tonestacks

[Max]

I have learned these past few days it seems that there is a version with a change in the james config with a .005 cap plus the .02 cap connected to the tail

.


Marcos,

"a version": of the 2nd generation ODS or of the 3rd generation ODS?

Cheers,

Max

[marcos]

Hi Max,
2nd generation.

[Max]

Hi Max,
2nd generation.

Marcos,

thanks for the clarification.

OK. So please check again, if I did understand you right up to now:

a) All 2nd generation ODS you are familiar with but one (see below in b)) have this tone stack:

Treble: 500KL pot / 510pF treble cap
100k slope resistor
Mid: 250KA pot / .01 mid cap
Bass: 1 MA pot / .1 bass cap / .002 and .02 cap soldered at the bass pot’s terminals

b) There is one single 2nd generation ODS you know with a .005 and a .02 cap soldered at the bass pot's terminals.

c) You are familiar with only one 3rd generation ODS. This single 3rd generation ODS you are familiar with has the same tone stack as the 2nd generation in b), but without the .02 cap at the bass pot - it has only the .005 cap.

Did I understand this right?

Thanks again and all the best,

Max

[marcos]

Hi Max,
it is true that I have seen only one 3rd generation amp.
AFAIR it had the .005 cap on the Bass pot, but not the .02 cap.
Big difference because this cap drastically reduces lower mids in the
2nd generation tonestack.Also it had a 250 KL Treble pot instead of the
500 KL, again a big difference.
There might be several amps with a .005 cap instead of .002 in the
2nd generation amps, hard to tell from the pix I have.Some have orange drops, some ceramic caps, impossible to tell which value.
I hope some owners or techs will chime in to either confirm my theory
or correct me.That is the reason I started this thread.

Have a nice weekend Marcos

[Max]

Hi Max,
it is true that I have seen only one 3rd generation amp.
AFAIR it had the .005 cap on the Bass pot, but not the .02 cap.
Big difference because this cap drastically reduces lower mids in the
2nd generation tonestack.Also it had a 250 KL Treble pot instead of the
500 KL, again a big difference.

Hi Marcos,

thanks a lot.

OK, just to make sure again that I got you right.

The 3rd generation ODS you've seen had this tone stack:

Treble: 250KL pot / 510pF treble cap
100k slope resistor
Mid: 250KA pot / .01 mid cap
Bass: 1 MA pot / .1 bass cap / .005 soldered between the terminals 2 and 3 of the bass pot.

Did I get it right?

There might be several amps with a .005 cap instead of .002 in the
2nd generation amps, hard to tell from the pix I have.Some have orange drops, some ceramic caps, impossible to tell which value.

I've found a note of one or perhaps even two 2nd generation ODS with a 3nF (or 3.3nF) cap between terminal 2 and 3 in addition to the .02 cap between terminal 1 and 2.

Can someone else confirm such a James network for a 2nd generation, too?

I hope some owners or techs will chime in to either confirm my theory
or correct me.That is the reason I started this thread.

I'll try to dig out more, too, and report.

Thanks again and all the best,

Max

[talbany]

Hi Max,
it is true that I have seen only one 3rd generation amp.
AFAIR it had the .005 cap on the Bass pot, but not the .02 cap.
Big difference because this cap drastically reduces lower mids in the
2nd generation tonestack.Also it had a 250 KL Treble pot instead of the
500 KL, again a big difference.
There might be several amps with a .005 cap instead of .002 in the
2nd generation amps, hard to tell from the pix I have.Some have orange drops, some ceramic caps, impossible to tell which value.
I hope some owners or techs will chime in to either confirm my theory
or correct me.That is the reason I started this thread.

Have a nice weekend Marcos

Marcos/Max
As Max puts it the bass pot configuration is indeed James inspired.. In a passive stack all these caps attached to the bass pot as well as the R/J .005 are used to dump certain frequency's.. In the case of the James (concentrating on 100Hz - 1K depending on the caps value)..
The cool thing about the James configuration is it doesn't effect the amount of sweep it's directed more at certain frequency so you can really shape those frequency's you want to cut and yet not effect the total sweep..If you want to lift all frequency's (or pot) you can just lift the 10k resistor..So as you can see the James is perfect for shaping the frequency response of the bass control..Dumble obviously used this to his advantage either to shape the low/ low mid freq to a customers taste or guitar or speakers etc..Or to try and keep the amps consistent..

You can run it through the Tone stack calculator and see what I mean if you like..Click James stack..It's not identical but you get the idea..

Hope this helps!!

Tony

[Max]

After some more research I am now rather sure that these are the more "usual" 2nd and 3rd generation tone stacks you'll find in most of the 2nd and 3rd generation ODS:

2nd generation:

Treble: 500KL pot / 510pF treble cap
100k slope resistor
Mid: 250KA pot / .01 mid cap
Bass: 1 MA pot / .1 bass cap / .002 soldered between the terminals 2 and 3 of the bass pot and .02 cap soldered between terminals 1 and 2 of the bass pot / 10K tail

3rd generation:

Treble: 250KA pot / 510pF treble cap
100k slope resistor
Mid: 250KA pot / .01 mid cap
Bass: 1 MA pot / .1 bass cap / .005 soldered between the terminals 2 and 3 of the bass pot / 10K tail

Of course there will be some rare exceptions as these are custom made amps (a confirmed 250KA treble pot in one 2nd generation ODS as an example)

BTW: I can't confirm any still all original 2nd or 3rd generation ODS with a 1M treble pot or with a 500K bass pot.

Cheers,

Max

[Structo]

I don't know much about the different generations and I'm not so sure there is a definitive line that divides each era of amps into these generations.
I think they evolved more than anything as HAD went along and also got customers amps back for service he would tweak them with the latest idea.

But the .001uF cap across the 500K (1 & 3) Bass pot with a 10K tail seems to be a popular as well as common feature on quite a few schematics.