Adjusting the preamp drive level on an M3

[Guest]

Hello everyone,</p>

</p>

I'm the proud new owner of a M3 and a Leslie 47 single-speed. Everything on it seems to work and sound great, except for two things. One is that the pedal decay and attack switches don't work (but I'm not too concerned with that right now). The other is this: when I play the organ at a medium to high volume, the tone becomes grainy and a little distorted. This would be ok if it happened with the volume pedal fully depressed with the drawbars at 8, but it happens way before that. </p>

I read on the <u>HammondWiki</u> about the procedure involved in adjusting the preamp drive, but there is one thing I don't understand. It says that, "the preamp drive level is set by adjusting a trimmer swell capacitor
accessible behind a removable plug located on the cover of the box
containing the swell capacitor." But then, in the directions, there is no mention of removing the plug or of how to remove it. </p>

Since I don't really know what I'm doing, I'm very wary about accidentally damaging something. I tried to pull the little plug out of the back of the expression capacitor cover box, but it does not seem to want to come out. Should I really yank the plug and pull it out, or do I actually just turn the plug? I tried turning the plug, but it didn't seem to make any diference in the volume. </p>

Also, if you have any other suggestions about what might be causing the graininess of tone, please let me know. Maybe it's not the setting of the preamp drive at all. The tone is the same whether I run the sound through the internal speaker or through the Leslie, and it makes no difference if the Leslie is plugged into the M3 or not.</p>

Thanks for your help!</p>

Dan
</p>

[Guest]

Re: Adjusting the preamp drive level on an M3



Dan:</P>


This is Dan also. I just got an M3 too. Sorry I can't help you just yet but give me a couple of days and I should have an answer for you. In the mean time, hopefully "theAdmiral" will pop in and provide an answer. We'll get it solved one way or another. In the mean time, if I was you, I would yank the tubes and try to get them tested locally. Your local music store should have access to an amp tech that will be able to test them. The distortion may not be the product of a maladjusted expression capacitor. Given your discription it may well come from an earlier stage. Also, please post a picture of the speaker and give us a serial number and the model number of the amp. It will be AO-??-? and stamped either on the top or side of the chassis. TheAdmiral is surveying the change from field coil speaker to perminant magnet. </P>


Welcome!</P>

[johnny b3]

Re: Adjusting the preamp drive level on an M3



Dan is correct about checking the tubes, and that the distortion may not be caused by the preamp adjustment.</p>

However, Its worth a try - and you can remove the little silver cap by prying it off with a small flat-head screw driver. Thats it! Its not held on very tightly, just insert the screwdriver and twist...
</p>

[geoelectro]

Re: Adjusting the preamp drive level on an M3

[quote user="dleisawitz"]

Hello everyone,</p>

</p>

I'm the proud new owner of a M3 and a Leslie 47 single-speed. Everything on it seems to work and sound great, except for two things. One is that the pedal decay and attack switches don't work (but I'm not too concerned with that right now). The other is this: when I play the organ at a medium to high volume, the tone becomes grainy and a little distorted. This would be ok if it happened with the volume pedal fully depressed with the drawbars at 8, but it happens way before that. </p>

I read on the <u>HammondWiki</u> about the procedure involved in adjusting the preamp drive, but there is one thing I don't understand. It says that, "the preamp drive level is set by adjusting a trimmer swell capacitor
accessible behind a removable plug located on the cover of the box
containing the swell capacitor." But then, in the directions, there is no mention of removing the plug or of how to remove it. </p>


Thanks for your help!</p>

Dan
</p>

[/quote]</p>

First, this in not a "Drive Level Control", just referred to that way. It's a feedback control. Feedback is used in amplifiers for stabilization. The factory says to turn it all the way in (clockwise) and then turn it CCW 1 1/2 turns. This is the factory setting and will have the preamp/amp work normally. As it turns out, turning it more than that will in fact cause it to be louder, but it also changes the tone. I recommend setting it to the factory recommended setting.</p>

The plug will pop off with a small screwdriver. You will not hurt anything.</p>

If you still have distortion, you may have other problems. I would look first at power supply, then output section like bias etc.
</p>

George
</p>

[Guest]

Re: Adjusting the preamp drive level on an M3



Thank you, Dan, Johnny &amp; George for all your help,</p>

[img]/Users/danielleisawitz/Desktop/DSCN2080.JPG[/img]</p>

I adjusted the trimmer, but it didn't fix the slight distortion problem. So, maybe it is the tubes. I'll have them checked out. Here is the info that Dan asked for:</p>

Amp model no.: AO-24110-1</p>

Amp serial no.: 549-6619</p>

Speaker model no.: AO-21270-0 </p>

Speaker ser. no.: 14557 285835</p>

The amp might be from an M100, because "M-100" is hand written on top of the swell capacitor box. The man I got the organ from told me that he replaced the amp which had been damaged with one from another organ. </p>

I can't figure out how to post a picture in a post, so I'll just set the photo of the amp as my avatar, so that you can see it.</p>

Thanks again for all your helpful advice,</p>

Dan
</p>

</p>

[johnny b3]

Re: Adjusting the preamp drive level on an M3

You need to host your pictures on the internet in some capacity (I use flickr). Then hit the icon of the tree in the reply window. Paste your picture link and make sure it ends in the extension of the file, (ie. .jpg or .gif) as sometimes when you view a pic on a hosting site the address will have some extra characters on the end.

[TheAdmiral]

Re: Adjusting the preamp drive level on an M3



Your amp is not an original M3 amp. M3's have AO-29-(?)(some number from 1-13). I can't tell from the picture as it's too small for good details.</p>

You're getting good advice already so no need to add anything at this time.
</p>

[Guest]

Re: Adjusting the preamp drive level on an M3



Let's try this:</P>


</P>

[Guest]

Re: Adjusting the preamp drive level on an M3

Ok. I just set up a Flickr account. Here is the url:


http://www.flickr.com/photos/35065844@N08/?saved=1


You'll find photos of the amp, the speaker, and the id plate. Any info you guys could give me would be really appreciated!

Thanks,
Dan

[Guest]

Re: Adjusting the preamp drive level on an M3



The look of that amp is consistent with a late model AO-29 with perminant magnet speaker. Which you have. I don't know what amp went in the M-100 so I cannot say for sure. This is a very dificult problem to diagnose on the internet. Not so difficult on the bench. http://www.captain-foldback.com/Hamm...cs/M3_late.gif</P>


Carbon comp resistors drift to higher resistances with age. Individual stage gain is set by a number of factors. Voltage at the supply side of the plate load resistor, the resistance of the plate load resistor, the cathode bias level and the input impedance of the following stage. Of these, perhaps the most important components that could raise stage gain (causing distortion going into the phase inverter with expression pedal advance, would be the plate load resistance of V4B and the grid leak resistor (load)into V3B. Behold the schematic:</P>


</P>


I would be looking at R-38 first. Make sure it hasn't drifted to 400K or higher. Also, make sure thatpin 8 of V4 does indeed measure 1.5volts DC or very close. Around the phase inverter (V3B) I would want to know if indeed there is 90VDC between the junction of R39A,R41, and R42. If it's higher I would change all three components to new metal film resistors. Check the stage input voltages at R38,&lt;edit&gt; R43, they needn't be spot on, just in the ball park. As long as I was in the area I would change out C-21, C-24, and C-25 just as a matter of course. C-22 is almost certainly ceramic and won't have changed any over time. For C-21,24,and 25 I would use sprague 715 series poly caps available from http://www.tubesandmore.com </P>


This post assumes that you are qualified to work on high voltage equipment. Voltages at the plates of these tubes are lethal. Before tackleing a project of this type, be sure to acquaint yourself with all safety measures employed when working on high voltage circuits. </P>

[johnny b3]

Re: Adjusting the preamp drive level on an M3



Wierd...</P>


Did M-100's use the same amp as the M3?</P>


Here is a pic i've found from a M100</P>


http://www.mantor.info/Hobbyhjornet/..._M102_rear.jpg</P>


I've never observed an amp from the M100 but i'd say it looks identical with every respect (at least on the outside) to a M3 amp (later models with PM speaker)</P>

[Guest]

Re: Adjusting the preamp drive level on an M3

The photo you've posted Adam has an AO-44 reverb amp and both your picture and the OPs have a mysterious black box behind the expressioncapacitor that mine doesn't have nor does NYCfarmboy's. I don't know what that is.

[TheAdmiral]

Re: Adjusting the preamp drive level on an M3



That mysterious black box is the cover to the accelerator!</p>

Your's should have one unless it was taken off.</p>

I think the amps are the same but they must have given the M100 a different AO number to clarity.
</p>

[Guest]

Re: Adjusting the preamp drive level on an M3



</p>

Thank you so much for your detailed advice. Unfortunately, I have to admit that I have absolutely no idea what you are talking about. I've never worked with electronics before, and I don't even know how to read schematic diagrams like the one you posted. So, I will have to aske someone who knows their way around these things to take a look at your message and then check it out for me. In the meantime, I'm going to start studying a little bit, and try to teach myself how to interpret these diagrams. Hopefully, getting the tubes checked will do the trick.</p>


</p>

[Guest]

Re: Adjusting the preamp drive level on an M3

[quote user="dleisawitz"]


</P>


Thank you so much for your detailed advice. Unfortunately, I have to admit that I have absolutely no idea what you are talking about. I've never worked with electronics before, and I don't even know how to read schematic diagrams like the one you posted. So, I will have to aske someone who knows their way around these things to take a look at your message and then check it out for me. In the meantime, I'm going to start studying a little bit, and try to teach myself how to interpret these diagrams. Hopefully, getting the tubes checked will do the trick.[/quote] Well, as you describe the problem it seems likely that it originates after the "expression" pedal capacitor. Those are the things I would have your tech look at in that regard, but he's going to have a signal generator and scope and willbe able to follow the problem through the amp to see just exactly where it originates. To be honest, about 90% of all old amp problems are power supply related; having nothing to do with the area I pointed out. If you can't find a Hammond Organ tech in your area you may try a guitar amp guy with some experience. Check with the local music stores and see where they send amps for repair. I would think that the other switching problems really do call for a Hammond guy, which I ain't. Perhaps E&amp;Me here on the board has some ideas. </P>