M3/145 trouble shooting distortion

[johnny b3]

http://www.sendspace.com/file/09edkb</p>

Have a listen to that clip (small 400k mp3 file). I have unplugged the woofer to enhance the clarity of the problem.
</p>

On some drawbar configurations we get this ugly scratchy noise from the driver. First I play a chord, adding one note at a time on the bass end of the swell manual. The very first note is not affected, but the noise starts as soon as the 2nd note is deppresed.</p>

Then I play another chord on the great manual to show that the bad sound does not occur.</p>

I'm guessing the driver cone is wearing thin, or on its way to driver heaven...something like that. But I dont understand why I can still play clean on some drawbar settings and not get that sound. Only certain combinations of frequencies cause the problem.
</p>

</p>

More problems include:</p>

- bass pedals are REALLY quiet</p>

- the pre-amp adjustment control in the swell box does not change the sound of the organ's output. I can turn it endlessly in either direction. </p>

(geoelectro - this is the same organ on which you helped me fix the percussion)</p>

</p>

Thanks!
</p>

[tonewheel1966]

Re: M3/145 trouble shooting distortion



Hi Johnny</P>


I have this on the treble driver on my Leslie 710. It is called the "wasp in a glass" sound. Basically your treble driver has warped and is vibrating against a solid part of the assembly. Have a look at the UK retrokeys site run by Mark Ashfield. I bought my RT3 from him and he told be about this problem. He recommended BT productions a US site who do a really good replacement. I tried to get you the URL but the site is down temporarily. If you look at retrokeys though there is a section on this.</P>


Cheers</P>


Dave</P>
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[johnny b3]

Re: M3/145 trouble shooting distortion



I found this link: </p>

http://www.retrokeys.co.uk/maintenance.html</p>


How does one adjust the driver whilst installed in the cabinet, as the site recommends?</p>

[geoelectro]

Re: M3/145 trouble shooting distortion




To me it sounds like amplifier distortion. Adding bass pushes the amp more and the distortion being higher frequency clipping is heard mostly in the treble driver. I would check the amp out fully. You can find info on voltages etc. on my site at;
Benton Electronics</p>


Check the Leslie 147 link. One specific thing to check is the second stage of power supply filtering. That point supplies the output transformer and tubes. DC wise it may appear OK, especially if the preceding point reads OK. However, that stage can be bad so that the AC component can escalate when signal is driving. If you look at the AC reading there at idle, you should see about .1Vac. Playing it so that you get the distortion you should still see less than 1Vac. A bad filter section can allow that point to go well beyond 1Vac under a load. This will result in lots of distortion.</p>

Other wise, check voltages and perhaps try another pair of output tubes. The cathode voltage of 25Vdc is the first thing I look at.</p>

BTW. Driver problems usually are frequency dependent. You can run the manuals one note at a time and usually find a note or range of notes that buzz.</p>

George
</p>

[tonewheel1966]

Re: M3/145 trouble shooting distortion



I think I have amp distortion on my 122Ras I get a distortion on both drivers when I play the 888000000 type reistrations. I found this out after emailing Mark at Retrokeys. The 710 problem is only on the upper driver. I have been looking at Georges site and will be doing these bits next week. Failing that I will re-tube the Leslie 6550swhen budget allows.</P>


Cheers</P>


Dave</P>

[Hammond101]

Re: M3/145 trouble shooting distortion

[quote user="johnny b3"]


- the pre-amp adjustment control in the swell box does not change the sound of the organ's output. I can turn it endlessly in either direction. [/quote]</P>


Yes! That is amplifier distortion and it sounds like too much growl to me. I would check out that trimmer cap in the swell box and see what is going on there. From your audio clip it sounds like the preamp section of the AO-29 is overdriving the output stage and majorly so IMO. The treble driver in the 145 sounds fine to me. They buzz when bad, first only at certain frequencies, then it expands to darn near everything. The sound is a buzz and not a break-up as you have in your rig.</P>


If you still have a speaker in the M3 you should be able to hear that distortion there as well. As George suggests the output stage of the amp could need some work but I'd look at the swell box first.</P>


H101</P>

[johnny b3]

Re: M3/145 trouble shooting distortion



I haven't checked the trim cap yet, but i've set up the leslie amp and have been conducting a few tests.</p>

</p>

First, one of the 6550's started glowing bright red. I swapped its position with the other 6550 and it still glowed, even when in the different socket.</p>

I swapped both 6550's for different tubes and the glowing happened again. One tube was known to be weak (white powder) and the other never glowed red before, but now it did glow quite bright.
</p>

With both sets of tubes the Cathode voltage starts at 25, but as the amp heats up it quickly climbs to 55 VDC.</p>

The 150ohm cathode resistor gets quite hot (not sure if that is normal), but I tested it and it reads close to 150ohm (IIRC ~152).</p>

The bypass capacitor is also fine...</p>

last but not least...pin 2 on OC3's 470 ohm resistor is reading at 235!</p>

Is this my culprit for raising the supply voltages?</p>

During this testing with tube set #2, the one with white powder broke (glass broke). Its brother, which was glowing, was paired up with the other 6550 which glowed originally. This time, the original glowing tube did not glow, but the set#2 tube did glow. (instead of both...which leads me to believe that atleast ONE of these tubes is good. I'm sorry, i know this would be much easier with a known good pair).</p>

</p>

Tomorrow I'll pick up a 470 ohm resistor and see if that keeps the cathode voltage in check.</p>


</p>

[tonewheel1966]

Re: M3/145 trouble shooting distortion

[quote user="johnny b3"]


During this testing with tube set #2, the one with white powder broke (glass broke). Its brother, which was glowing, was paired up with the other 6550 which glowed originally. This time, the original glowing tube did not glow, but the set#2 tube did glow. (instead of both...which leads me to believe that atleast ONE of these tubes is good. I'm sorry, i know this would be much easier with a known good pair).</P>
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<P mce_keep="true">Sorry to interrupt the thread. I broke the white powdery thing next to the 6550s on my 122. What is it and what does it do. My 122 still works but wondered if the can be replaced. You do not see them on Goff with a tube set.</P>
<P mce_keep="true">Cheers</P>
<P mce_keep="true">Dave</P>

[johnny b3]

Re: M3/145 trouble shooting distortion



</p>

That white thing? it sticks up next to the 6550?</p>

Thats the cathode resistor, 150 Ohm.</p>

Unsolder the ground wires and test its resistance. I would assume it will need to be replaced.</p>

[tonewheel1966]

Re: M3/145 trouble shooting distortion



Cheers Johnny,</P>


What are the symptoms a a dead/damaged cathode resistor? The internal loop is intact it's just the shell that vapourised!</P>


Thanks</P>


Dave</P>

[johnny b3]

Re: M3/145 trouble shooting distortion



Replaced the 470ohm resistor at OC3, no change in .</p>

Swapped for good tubes = bingo. Shot tubes.
</p>

[johnny b3]

Re: M3/145 trouble shooting distortion



I had my personal leslie amp (with new tubes) out for testing, heres what I got:</p>

470 ohm resistor on OC3 read 500ohm. (didn't bother changing it as it is within its tolerance).
</p>

Yellow wire of choke transformer at diode section (1st stage?) read 450VDC, other yellow wire at pin 5 of OC3 read 440. (I assume these are higher because of a higher input voltage (120 vs 117VAC)
</p>

My preamp plate voltages are reading 150...and are supposed to be 115VDC. I'm using a 12AT7 instead of 12AU7. Is this reading too high?
</p>

</p>

Any thoughts?</p>

[johnny b3]

Re: M3/145 trouble shooting distortion



As in the "fuzzy sound" thread, the output tubes on this 145 were "going thermal" and replacing the tubes fixed the problem. All the voltages check out.
</p>

The M3 preamp volume pot wasn't broken, it was simply unscrewed very very far counter-clockwise. I closed it and heard a much cleaner sound on the internal speakers. </p>


We're still getting the "wasp in glass" sound even though the amp checks out and the organ preamp is now in check. It plays fine otherwise - does this rule out the driver or amp?</p>

Also i still have not fixed the other 2 issues:</p>

1) the pedal volume is very low. I remember it being louder when the organ was acquired, even though all the tubes are new</p>

2) when percussion is engaged, the top manual volume drops noticeably. This is also a new problem which was not occuring when I originally fixed the 1st percussion problem (no decay/reset)</p>



Unrelated - the studio finds the foot switch speed control mechanism
too loud (standard DPDT foot plunger switch). Can anyone suggest a
quieter foot switch that can handle AC mains? I want to keep it left foot operated - as opposed to the switches that mound on the swell pedal.
</p>