Normal hum from 760?

[Tee]

When I turn on my 760 it immediately starts humming. Like a gigantic refrigerator. I guess it's normal. It's not supposed to stand there dead silent. But as I have it in my living room which isn't huge it feels kinda loud. Unless I'm playing the organ it's gets annoying. I guess I wouldn't notice it on a gig in a big room. But how loud is normal? Is there something I could do to reduce it?

Kalli

[Brendon Wright]

My one is barely audible.
Methinks you gotta replace all the 'lectrolytics, the cans especially....

[tonewheel1966]

Did you read my 760 post from yesterday? I had a bad ground. Try running a wire from one of the two black wires in the power supply (one goes to your 9 pin socket) and clamp the other end under one of the screws that hold the amplifiers to the heat sink. Mine is now silent when all the volumes are maxed. If not try Brendon's advice although I was told by a tech that these rarely fail on SS amps compared with the tube amps.

Cheers

Dave

[andyg]

Mine was overhauled just before I bought it five years ago and is still as quiet as a mouse. I'd go with TW first and then Brendon. My caps were all OK.

[CEB]

Does it hum with the organ shut off? This probably isn't the issue but just in case.... Is organ and speaker pulling it's electricity from the same outlet / circuit? If not do then do that. Then trying flipping the polarity on one of the devices. You can also try a ground lift if one of the devices are grounded.

It probably won't work since you are at home. Thought just in case you may want to look at the easiest things first in case you have thought to try this. When you are sharing circuits with neon / florescent lights / Ice Machines / freezers / cotton candy machines and things other things with motors you run into some interesting electricity issues.

[Tee]

I'll continue as it has only been a day, not two months!

I found that if I turn on the leslie without the 9-pin cord cable connected it runs silently. As soon as I connect the cable I get the hum.
So it's not like Tonewheel1966 problem which was more pops. Mine is best described as hollow hum or buzz. It gets a little bit louder when I turn my M3 on.
But no Leslie cable, no hum. Does that tell us something?

[jimmywilliams]

Tee,

Please tell us how you are turning the Leslie on if you do not have the 9-pin cable attached. The Leslie gets its power through the cable, to pins 8 and 9. Are you running AC power diectly to those pins with nothing else attached?

The design of the 9-pin cable itself lends itself to hum issues because the two sides of the power AC, and the audio signal, run together in the same cable.

You would also have to rule out if the hum is originating in your instrument itself (try running to another amp, etc.).

Without knowing the details of your hookup and how you are getting signal to the Leslie, we are only guessing.

- jim

[Tee]

Actually my 760 has an electric cable coming out in the back, appears to been made that way from the factory in Denmark that handled the European market.

[jimmywilliams]

Sorry didn't realize this was a European model. Don't know what to tell you ... Andy were the UK models similar? Any ideas how he can troubleshoot this?

[Clarion]

When I turn on my 760 it immediately starts humming. Like a gigantic refrigerator. I guess it's normal. It's not supposed to stand there dead silent. But as I have it in my living room which isn't huge it feels kinda loud. Unless I'm playing the organ it's gets annoying. I guess I wouldn't notice it on a gig in a big room. But how loud is normal? Is there something I could do to reduce it?Kalli

Sounds a whole lot like when I bought my new Hammond H-100 way back in 1972. It had loud background hummmm big-time! Contacting Hammond, met with the typical response of a company about to declare bankruptcy: There is nothing wrong with your organ; that is the way we designed them!!

Bottom line: adding a couple of 100 mfd capacitors in parallel with the power supply fixed everything!

[Tee]

Sorry didn't realize this was a European model. Don't know what to tell you ... Andy were the UK models similar? Any ideas how he can troubleshoot this?
No sweat Jimmy, how could you have known :-)

I'll try to clarify a little better:

-To get the signal out of my M3 I have an OBL-2 line output box from Goff installed. It's fed via its alligator clips at the speaker, the speaker still active though.
-From the 1/4" output it goes into a Dr. Fishsticks controller (which is not plugged to AC outlet and therefore passive) and from there ...
-through the 9-pin cable to the Leslie. It's a long way to Tipperary!
What I found out today is that if the Leslie is connected to the Dr. Fishsticks with the 9-pin cable and I unplug the 1/4" from the Dr. Fishstick (so that the M3 is NOT connected to it) I get yet a louder hum.

Am I making myself any clearer?

Leslie on it's own: No hum
Leslie connected to Dr. Fishsticks: much hum (very loud)
Leslie connected to Dr. Fishsticks connected to M3 (turned off): hum
Leslie connected to Dr. Fishsticks connected to M3 (turned on): more hum (loud)

It's only mystery!

[Hamman]

Hum in both bottom and upper speakers? or one or the other? I have a 770 that is the same but with a wood cabinet and it had a hum on the upper treble driver....after isolating where the hum/light buzz sound was coming from I tied a seperate ground wire from the upper drivers amp to the frame on the power supply and it killed the hum. It now only hums/light buzz for about 15-20 seconds as the tube pre-amp in the C2 is warming up

[Tee]

Hum in both bottom and upper speakers? or one or the other?
Interesting question. I had to check! It comes from both.

[TheAdmiral]

Try this: disconnect the organ from everything. Unplug the 9 pin Leslie cable from the connector at the organ. Run test wires directly from the speaker on the organ to the input pins on the cable. How does it sound? If you still have hum it's probably in the organ amp. What is the serial number of your organ and complete AO-29-??? number?. Some are wired differently.

[jimmywilliams]

Admiral,

It sounds to me like Tee does not have a 9-pin socket on the organ. It sounds like he is using a line-out tap from the organ (audio/ground). The 9-pin interface into the Leslie (in his case, to route the audio into the leslie as well as to control motor speeds) is the Fishsticks controller.

Now he is describing getting hum at the Leslie when nothing is connected to the audio input of the Fishsticks controller while the Leslie is turned on. That is most likely normal, because (a) I don't think the Fishsticks controller uses a shorting jack. So you basically have an open audio input there and that is probably picking up all sorts of hum through the long cable. (b) That 9-pin cable is not shielded and there is also no guarantee that the two sides of the audio line are right next to each other throughout the entire length of the cable - any separation will make that long length of unbalanced audio cable act as an antenna from what I understand. Let me know if I am mistaken.

Tee,

Since you have a 1/4" output from the organ, try running that into another amplifier. Make sure the amplifier settings are as flat as possible. If you don't get the hum there, then most likely the organ is OK. But you must be running that line out pretty "hot" to drive the Leslie power amp - be careful when running into a regular amp that already has a pre-amp stage (Leslie amps do not).

If you have another shorter 9-pin cable try using that to connect to the Fishsticks controller instead and see if you notice a difference.

The optimal setup in your case would be to have the Fishsticks controller unit as close to the Leslie as possible, connected via the shortest possible length of 9-pin cable. There is no need to have the Fishsticks unit hooked up to such a long 9-pin cable. The longest part of your audio chain should be a shielded 1/4" musical instrument cable that connects the organ line-out to the Fishsticks input. You should have enough leeway to run the second piece of the Fishsticks 9-pin interface - the motor speed pedal - close to your organ (or maybe you have his "violin" switch on your organ instead??).

In any case it sounds more like either an audio ground and/or audio interference issue rather than a Leslie power supply problem. If it were in the power supply filters, the hum would be apparent even when nothing was connnected to the Leslie - and this does not appear to be the case.

And we never asked the basic question - did it always make the hum, or did it used to work OK and then you started getting the hum later?

[andyg]

Just picked up on this thread again today. To answer Jimmy's question, this is non-standard for a 760 as far as the UK is concerned. I don't think even the Scandinavian countries banned AC in leslie cables way back then, but maybe this one was modified.

I have to ask if it wouldn't just be simpler to bypass all the Fishsticks stuff and the 1/4" out and connect the 760 the way it was meant to be - driven straight from the organ's speaker with a simple connector kit. Speed switching is just earth switching so I make it just signal, earth and two wires for the speed switching to go to the leslie as it's AC is already there. But hey, that's just me - follow the above advice from Jimmy! I too think that this is an audio ground problem somewhere.

[Tee]

Andy, when you say "connect the 760 the way it was meant to be" what do you mean? There is only 9-pin input to the Leslie, no 1/4". Should there be ?

[andyg]

The 760 was designed to be connected with a connector kit, a 9501 is the correct one for an M3. Looking at the schematics, it's a pretty 'standard' 760 9-pin kit like the one that connects my T402 to my 760. http://www.fishorgans.com/leslie_kits/009501_kit_for_Hammond.pdf

The 760 was never meant to be driven from a low-level 1/4" input, but from a hot speaker level signal. Once you start playing with that, you're liable to introduce nasties like hum, IMHO. The 9-pin leslie wiring is explained here, in case you're not familiar with the original. http://www.captain-foldback.com/Leslie_sub/pinouts.htm

[Tee]

Thanks for the info Andy. It all seems like rocket science to me although I'm getting a little better at doing things myself inside the M3. But I think I'll go with the ground problem to start with, a.k.a. Jimmy's advice.

Jimmy, I bought the Leslie about 2 years ago from a guy way up in north Sweden. It had not seen much use for quite some time. So he was really selling it as is. But it looks very well. Like new. But yeah, since I got it it has had this hum. At first I just thought it was supposed to be like that. But it is a bit too loud for a constant hum. It works OK on recordings if I make sure to drive it hot.

But I agree, this sounds like a ground problem. I must figure it out.

[jimmywilliams]

Andy, the Fishsticks controller is the basic interface into the Leslie - it takes the audio input and also has the speed control buttons via a separate pedal. So you can view it as a connector kit of sorts.
What I don't understand is why Tee is using a line-out tap off the M3 instead of just running a line directly from the speaker into the Fishsticks controller. The Fishsticks controller doesn't care what comes into its 1/4" input; whatever comes through is just going to go to the ground and audio input pins on the 9-pin socket.

[Tee]

What I don't understand is why Tee is using a line-out tap off the M3 instead of just running a line directly from the speaker into the Fishsticks controller.
The reason is: because it was there. I didn't have a Leslie at first. I installed the line-out thing after I got the M3 to be able to hook it up to things, amps, D.I into my DAW.
When I got the Leslie, over a year later, I thought it was easiest to get a kit so I could plug a 1/4" into it and get 9-pin out.

Do you think I should bypass it and take the signal straight from the speaker?

[andyg]

Yes I would, as you've got the Fishsticks, I'd send the hot speaker signal to it as Jimmy said. Either that or make/buy a 9501 kit.

[Hamman]

Andy, the Fishsticks controller is the basic interface into the Leslie - it takes the audio input and also has the speed control buttons via a separate pedal. So you can view it as a connector kit of sorts.
]What I don't understand is why Tee is using a line-out tap off the M3 instead of just running a line directly from the speaker into the Fishsticks controller. The Fishsticks controller doesn't care what comes into its 1/4" input; whatever comes through is just going to go to the ground and audio input pins on the 9-pin socket[/U].

Ditto that!

[jimmywilliams]

I must point out that tapping directly off the speaker lead to the Fishsticks controller will work - provided that you also keep the organ speaker itself in circuit (which is what I assume you were doing).

If you ever plan to disconnect the organ speaker entirely, you would need a console load resistor. I am not sure if the 9-pin fishsticks controller has one.

[Tee]

Thanks Jimmy! I'd keep the speaker going anyhow..when the Leslie runs you don't hear the speaker but it can be nice to have it.

What's the best way to tap the signal from the speaker lead to Fishstick? I'm not having much luck in Googling it.

[jimmywilliams]

Tee,

You can do it the same way you connect your line out to the speaker leads. Just use a 1/4" cable like you would use to connect a speaker cabinet to an amp head. Remove one end and connect directly to the speaker terminals - or alternately wire up a 1/4 jack to the speaker leads and use a normal 2-ended 1/4" cable. Put the positive (tip) lead of the cable on the positive terminal of the speaker and the ground (sleeve) end on the negative speaker terminal.

See how that works for you.

In any case I would still use a much shorter 9-pin cable for the reasons already stated.

[Silverfox]

Did you read my 760 post from yesterday? I had a bad ground. Try running a wire from one of the two black wires in the power supply (one goes to your 9 pin socket) and clamp the other end under one of the screws that hold the amplifiers to the heat sink. Mine is now silent when all the volumes are maxed. If not try Brendon's advice although I was told by a tech that these rarely fail on SS amps compared with the tube amps.

Cheers

Dave

Hi

I'm new to the site. I've got a similar problem with a 760. In the past it has worked ok but connected to a replacement T500 Hammond its got a AC hum. Please would you post a link to your last mail. I'm convinced its a ground problem and I know the T500 has in a past life had half moon switches and some fiddling done. Are the chassis in the T500 and 760 both at ground potential.

Do the black wires connect direct to the amp chassis?

I spotted another enquiry about a Leslie with an independant mains supply. Through one of the search engines check Captain Foldback and Leslie. In it there is a description of the Danish units. Like the majority I thought it all came down the one scary cable.