722/822 Solid State Amp problems

[pm115]

Hi all,

Looking for some advice. I have a fairly road worn HL822 Rotosonic Leslie, coupled to a B200. Its a pretty good sound, when its working, but there's a few problems.

First, there is some crackling noise (doesn't matter if I am playing or not) which stops when I gently tap the amplifier back panel with my fingers - so it must be something loose. The louder I play - so the more the cabinet vibrates, the more likely it is that the noise comes back - until I tap it again. No idea where to look, there is nothing obviously loose on the amp circuit boards, oh and this affects the rotary channel only.

Second, the stationary channel has developed terrible distortion - only recently, and as my electronics knowledge is limited (or non-existent) I don't know where to look for problems. I'm quite happy to start changing components, and this does seem to be a simple amp design, but again, I don't know where to start.

Any advice from this forum would be very very appreciated.

Thanks

pm115

[BlueOliveB3]

First thing to do would be to get a can of DeOxIt, disconnect the Leslie from the mains, and clean the volume pots on each amplifier board as well as all connectors. It would also be a good idea to get fresh thermal grease for the output transistors, clean the old grease off, DeOx the transistor sockets, then reapply thermal grease. Be sure to reinstall the insulators on the heat sink (back panel) as well, you don't want the transistor cases to come into electrical contact with the heat sink as this will cause the magic smoke to be let out. If the insulators are damaged during this process replace them, any good electronics supplier will have them.

But start with cleaning the pots and any mating connectors internally. That may clear it up right there.

At some point you'll want to replace the main electrolytic capacitors in the power supply, if you feel up to it. 5000uF/50VDC caps. They will bite if charged, so make sure they're discharged by measuring DC voltage across their terminals before replacing.

TP

[pm115]

First thing to do would be to get a can of DeOxIt, disconnect the Leslie from the mains, and clean the volume pots on each amplifier board as well as all connectors. It would also be a good idea to get fresh thermal grease for the output transistors, clean the old grease off, DeOx the transistor sockets, then reapply thermal grease. Be sure to reinstall the insulators on the heat sink (back panel) as well, you don't want the transistor cases to come into electrical contact with the heat sink as this will cause the magic smoke to be let out. If the insulators are damaged during this process replace them, any good electronics supplier will have them.

But start with cleaning the pots and any mating connectors internally. That may clear it up right there.

At some point you'll want to replace the main electrolytic capacitors in the power supply, if you feel up to it. 5000uF/50VDC caps. They will bite if charged, so make sure they're discharged by measuring DC voltage across their terminals before replacing.

TP

Thanks for that - I am suspicious of the output transistors anyway, because the connectors on them don't seem very firm, but I have taken them to bits yet, I'll watch out for the insulators too - don't want blow things up and make matters worst :-D

[pm115]

Just been reading that these power supply capacitors mentioned by BlueOliveB3 are often the problem with strange noises. Anyone know where I can get new ones, in the UK preferably ? Surely these aren't rare parts ?

Thanks to all

[Wes]

Any electronics supplier should have suitable caps.

digikey.co.uk
uk.farnell.com
www.maplin.co.uk

etc

Wes

[Guest]

Hi all,

Looking for some advice. I have a fairly road worn HL822 Rotosonic Leslie, coupled to a B200. Its a pretty good sound, when its working, but there's a few problems.

First, there is some crackling noise (doesn't matter if I am playing or not) which stops when I gently tap the amplifier back panel with my fingers - so it must be something loose. The louder I play - so the more the cabinet vibrates, the more likely it is that the noise comes back - until I tap it again. No idea where to look, there is nothing obviously loose on the amp circuit boards, oh and this affects the rotary channel only.

Second, the stationary channel has developed terrible distortion - only recently, and as my electronics knowledge is limited (or non-existent) I don't know where to look for problems. I'm quite happy to start changing components, and this does seem to be a simple amp design, but again, I don't know where to start.

Any advice from this forum would be very very appreciated.

Thanks

pm115

In my experience the usual suspects are dc leaking triacs, powers transistors and crossover capacitors!
Exactly same specs are on the market, costs about total of 15 gbp with postage and give full restoration of speaker with this symptoms!

St.chanel distortion may be a result of a torn speaker cone already because you play loud and not of too many other things but the above mentioned

I bet a pint of Guinness that after the job's done you'll wonder on why people hate transistor Leslies but install transistor preamps in there b3s.

Cheers
Boyan

[pm115]

Hello Boyan,

Many thanks for taking the time to reply. Since I started this thread, I have found a couple of things wrong (loose wire on one of the inputs, and a loose output plug) and having fixed these, things are much improved - though I am still getting some noise that a quick 'tap' on the amp fixes. But what interests me most about you response is your suggestion that I can overhaul the stationary channel for just a few pounds!

As I said, I'm not an electronics whizz, though I'm handy enough with a soldering iron. Would you advise me to check the leslie parts list, order up the potentially faulty components and just go ahead and start swapping them out until I find the issue ?

Thanks once again for the advice

pm115

[Guest]

Based on what I did with 720 and 130 revival, I suggest the following:
1. Check your Leslie cable/Leslie plug. Check for a cable or particles or loose belt that may touch the rotating drum thus producing that noise.
2. Check all cable shoes especially those on PCB for broken soldering.
3. Look at your part list for triacs. They cost like couple of pounds and you may replace them directly-3 solders on each. I think they are two.
4. Check cables going to/ from your power transistors. Check/fasten transistors on the base/heat sinks. You may buy new power transistors as they are less 2 pounds each and change all of them: 2 per amp x 4 amps. This will dramatically restore the power and temperament of your amps, reduce hum, kill pops and spikes, and improve speed switching.
5. Check speakers on the stationary channel - unpleasant distortion could be caused by torn one.
6. There are five audio filter capacitors - just before the 3 speaker sets(bass doesn't have any) on the schematics. They are also responsible for pops and spikes! Can't see the values from my iPod screen but you have to find something close or exact as value to rebuilt! These are more expensive and you may do that last!
7.This could be done first - try to readjust gain trimpots on each amp accordingly to the service manual - you need one.
That is the most complicated Leslie I've seen and my 720 was kind of only half of it! If you are lucky you may revive it with a couple of triacs(6 soldering ), 8 power transistors (bolt on) and gain realignment! Or just the last one if you are more then lucky!

I would start with those as I did on half this Leslie - my 720! The result is proven (YT) and was great! But having said that, this was not a 722/822 just one half.

Cheers
Boyan

PS. With multimeter you may check the voltages at various locations as explained in the SM and schematics in order to shorten the list of usual suspects! But regardless of the results, the above revival parts list will restore the box to its original power and tone. That is why I always start with!
It's good to spray clean trimpots and cable shoes as well! Carefully when pulling out c. shoes from PCB - fragile soldering!