M3 percussion volume too soft

[geldo79]

Hi,

I have a question concerning the percussion volume on my m3. It seems to me that neither the "normal", nor the "soft" volume produces a percussion volume which sounds ok to me. From other m3's I know that the "normal" setting produces a relatively loud Percussion tone, which is too loud in my opinion. On my m3, the volume of the "normal" setting is softer, but still too loud. On the other Hand, the "soft" setting produces a too soft sound. I can hardly hear the difference between percussion on and off, e.g. using the 888000000 setting, fast decay, and 3rd harmonic. I tried adjusting the percussion cut off potentiometer on the amp, but i did not help. Also, changing the tubes of the percussion circuit did not help. Any ideas?

Greetings Christian

[enor]

Wax capacitor organ?

[enor]

Step one: rebuild your amp
Step two: if the problem persists - recap your generator.

[geldo79]

In the amp, I already replaced all electrolytic caps. Of course some other component might need to be replaced.I could of course replace all caps and resistors....but...lots if work )-;

And I already recapped the generator.

[enor]

Old resistors drift just as badly as old caps!

If all seems well in the amp, experiment with the mixing resistor (R63). It hangs off terminal P and is connected to ground. A 47k pot here, wired as a rheostat, becomes a simple but effective percussion volume control.

[geldo79]

Good hint. I'll check the value of R63...and the other resistors.

[geldo79]

The R63 resistor on my m3 is a 47k resistor (not 33k as mentioned in the service manual). It measured ca. 51k. I replaced it with a 100k pot. Strange thing is, I can reduce the percussion volume by increasing the resistor value. But decreasing the value has only little effect. Percussion gets louder only to some point, but decreasing the resistor value further does not lead to louder percussion. I could also remove the resistor completely, and i would have a normal percussion volume. Is this behaviour normal?

[Alek Z]

If you've changed the tubes and adjusted the percussion decay, the only other easy fixes I can think of would be to clean the tube sockets, and or clean the percussion adjuster pot. If these things don't help you may be in for quite a project. It's likely a resistor in the percussion circuit. Look for resistors that show signs of damage or burns first. You may want to look through the entire amp for this as there may be problems with input voltages to the percussion tubes (which just to clarify are the 3 rightmost tubes, 2 x 6C4 and a 12 AU7), which could run across the chassis. If you don't find anything like this, you'll have to start taking out resistors and caps in the percussion amplifier. The other simple fix to avoid this painstaking process would be to just set your drawbars lower, to get the relative levels you want. Then you can just play louder, and if it won't go loud enough, adjust the gain control inside the expression control box to increase output voltage (as well as drive, which isn't always a bad thing in my opinion). Good luck with the issues, I hope you can fix it before having to go through the process of checking resistors and caps, that's always my last resort. Oh, if possible you could also try replacing all the tubes, if you have a ton of spares around like I do haha, particularly the 5U4 rectifier, but it's likely something isolated in the percussion circuit due to the fact that it's completely separately amplified and mixed back in to the intermediate amplifier, and the volume of the percussion is relatively lower. I wish you the best of luck, and I hope I have offered some solutions.

[enor]

Note that I wrote "if all seems well in the amp" prior to suggesting the mix resistor. Step one is to make sure the amp itself is operating normally, THEN start fiddling with the mixing!

[geldo79]

Hmm....I think my skills in electronics are not sufficient to tell "if all seems well in the amp" )-; I think I'll compare the behaviour with my other m3.

[delaware dave]

This happened on my B3 10 years ago. Soft was barely audible and normal was the volume of what soft should be. I changed three tubes out on the AO28. Bingo, the level returned to normal.

[fmbeaumont]

My M3 percussion is not working. I swapped v3 and v9....no effect. Cleaned percussion on/off switch. If a hold a upper manual key and toggle the percussion switch I get one percussive blip. Any advice here? Thanks

[enor]

You have a short in the manuals, or in the percussion switch assembly - probably due to crystalline "hair" growth, also known as "dendrites". There's plenty written on the subject in this forum if you search for the term "dendrites". Common problem, easy fix!

[fmbeaumont]

Any zapping info specific to just the M3?

[enor]

No, nothing specific.

[fmbeaumont]

Thanks, I'll check it out

[geldo79]

I did two things now concerning the percussion volume:

1 : I jumpered R2 in the matching transformer to be able to have loud percussion without drawbar volume drop.

2.: I removed R50 from the percussion switch assembly and installed a 22k pot. Now the percussion volume for the "soft" position can be altered.

In principle, both mods worked fine. Only thing is, when I tune the pot to 0k, the percussion volume is still not as loud as for the "normal" volume setting. That i don't understand. Shouldn't R50 be the only difference between soft and normal percussion volume?

[enor]

"Normal percussion" breaks the connection to R50, in other words it causes infinite resistance to ground. Your pot can only accomplish 22k to ground, as its maximum - so it won't be as loud. (You're thinking backwards - the volume goes up with a HIGH resistance here, and when you set the pot to 0 it should also mean that the volume goes to zero).