Hammond M3 Chorus question

[geldo79]

Hi,

I have a question concerning the chorus on one of my m3s. Normally, by activating chorus, the sound gets more highs. In my case, it is the other way round. The normal channel produces a very nice and rich tone, with lots of highs and leakage present. When i activate chorus, the sound gets a bit dull compared to the normal channel. I'd like to have at least the same amount of highs in the chorus/vibrato channel. I already switched the 6au6s, but that does not seem to be the source of the Problem. Any ideas? Or would it make sense to buy two new 6au6s? BTW, in my AO29, two caps (C1 und C6) were removed to pronounce the highs of the amp. I don't think that is has anything to do with it....just for completeness.

Greetings
Christian

[enor]

Does your chorus sound nice and swirly, or is it more of an amplitude modulated "quasi-tremolo"?

[geldo79]

It sounds nice and correct....only the high freq drop compared to the normal channel does not feel right....

[Sweet Pete]

The chorus resistor (in the switchbox) should be changed.My B2 along with an M3 had those symptoms."Lost sparkle"
Geo suggested I try a new resistor.It worked in both cases.
IIRC it's a 12K. Older B2 had an 18K,changed it and pleased with the results at 12K.
Some folks hang a 100K potentiometer off the connections.

[geldo79]

Well....my organ was an m2 which i converted into an m3. Thus, it had an 18k resistor. I already installed an 100k pot which made the chorus depth a lot better. But if the 18k resistor, which is still in place, has lost sparkle, i would have to change it anyway i guess!? I'm afraid that changing that resistor is a lot of work? )-; If I remember right i will have to disassemble some parts to get to the switchbox.

greetings Christian

[geldo79]

hmm....but is it really possible that an old resistor steals high freqs?

[enor]

I doubt it. I was leaning towards drifted capacitors in the delay line.

[David Anderson]

There is a 12AU7 section in the vibrato channel not present in the normal channel. Have you tried replacing this 12AU7?

[geldo79]

Not yet. I'll try.

[geldo79]

Another question concerning the caps. I think I noticed the difference between normal and vibrato channel after recapping the twg. Would that make sense? Should the line box caps always be replaced when changing the twg caps?

[enor]

Another question concerning the caps. I think I noticed the difference between normal and vibrato channel after recapping the twg. Would that make sense? Should the line box caps always be replaced when changing the twg caps?

Well, they are the same type as the generator caps; so if your generator caps have drifted enough to justify replacement - so will the line box capacitors.

[geldo79]

Yes enor..no doubt. But technically speaking: do the line box caps affect the highs? Or should I expect something else from drifted line box caps like changes in modulation depths or something else?

[enor]

They make the vibrato appear more "muddy" and "undefined", for lack of a better word. Whether it also translates to a loss of HF ... I haven't thought about that. I always replace them anyway on wax organs, just to get the nice chorus back.

[geldo79]

Ok thanks. I'll try two things. I'll replace the caps and change the 12au7. Then I'll report the results. Btw, The twg caps had drifted a lot, and replacing them made the organ sound much brighter. If the line box caps drifted the same amount, it should help to replace them.

[enor]

Ok thanks. I'll try two things. I'll replace the caps and change the 12au7. Then I'll report the results. Btw, The twg caps had drifted a lot, and replacing them made the organ sound much brighter. If the line box caps drifted the same amount, it should help to replace them.

Most commonly, the wax caps will have drifted to about 2 times their nominal value.

[geldo79]

I read some information about low pass filters. If i understand it right, the inductance/capacitor pairs inside the line box are low pass filters. And a low pass filter will cut off high freqs and delay the signal. The values of the coils and capacitors are chosen in that way, that the cut off frequency is higher than the highest frequency of the organ. Thus the line box should only delay the signal. But when the values of the caps drift to higher values, the cut off frequency should be lowered, so that in principle it would be possible to cut out high freqs. Right?