C-lator hum

[ynor]

In case you need any PT i can search and find something - Norway is in europe (by trade if i remember), any EU shop should be good, and also my local winder can send it there.

Thanks! I'll PM you when we get to the end of this

[martin manning]

Given that Classictone has now gone, you will have no trouble with Twin 100w or Bassman 50 w transformers from Hammond and you can order them from Mouser

Those are cheaper yes, but the prices I got on the MMs are not that much more and are direct dropins without the need to drill new holes in the chassis. But are these Hammonds just as good (and safe from vibrating laminates) as the MMs?

Hammond is a very reputable manufacturer of high quality products. IMHO Mercury is more interested in building cachet to support their price point.

[ynor]

Ok I unsoldered all the secondaries (HT 135 V and 6.3 V heaters), and there is still hum. Gets a bit better if I lift the ground but still hum is introduced when I power on the unit. Can we with that conclude that the hum originates from the PT?

20240320_174141.jpg

[martin manning]

Shure is looking like the transformer is the problem. Which ground did you lift? The Earth? Can you isolate it from your chassis so the core is not making electrical contact?

[ynor]

Unscrewed the mains ground from the chassis.

Now I'm extending the leads of the PT and will try it outside the chassis.

[martin manning]

Unscrewed the mains ground from the chassis.

That breaks the connection from the neutral wire to the chassis via the earth ground... Provided that is the way things are in Norway.

[martin manning]

BTW, as you are trying this, see if you can control the hum with the C-lator return level knob. That should effectively ground the power amp input when you have a cable from the C-lator return to the power amp in, and the return is full CCW.
Compare the noise level of a a cable plugged into the power amp in with its other end open (not connected to the C-lator). That will be loud.

With my D'lator connected to my ODS, D'lator output to power amp in cable only, I can completely kill the hum with the return level pot.

[bepone]

Unscrewed the mains ground from the chassis.

Now I'm extending the leads of the PT and will try it outside the chassis.

do do this, pull out the sucker

Ok I unsoldered all the secondaries (HT 135 V and 6.3 V heaters), and there is still hum. Gets a bit better if I lift the ground but still hum is introduced when I power on the unit. Can we with that conclude that the hum originates from the PT?

but what does this mean humm is where?
is c-lator now connected to your amp? and you are hearing hum in main amp on the speakers?
or c-lator is on the table, not connected to anywhere? and you are hearing the hum, like only PT mechanical hum?

[ynor]

CAUSE OF PROBLEM IDENTIFIED!

As I postulated in my opening post it is caused by the proximity of the PT to the rectifier! Move it far out of the chassis and this hum is gone! Power on/off makes no difference. Now there is of course some other noise inducted when turning up the return level, but the mains hum is gone by moving the PT far from the chassis. Move the PT above the tube makes a huge hum!

I'm sure better XT can be used inside the chassis, but not this one and probably the reason HAD had them mounted outside.

20240320_185751.jpg

I cannot thank you guys enough, going great lengths to solve this puzzle with me. I've learned a lot in the process, so it has not been waisted time for me at least

Now to consult the manufacturer.

[Richard1001]

Good to hear you found the problem. I don't really understand why Nik has changed things and put the transformer inside the chassis. But he is a very helpful guy so i'm sure it will be solved.

[sluckey]

CAUSE OF PROBLEM IDENTIFIED!

As I postulated in my opening post it is caused by the proximity of the PT to the rectifier! Move it far out of the chassis and this hum is gone!

I seem to remember that was suggested a long time ago. Glad to see you finally give it a try.

https://ampgarage.com/forum/viewtopic.p ... 14#p463914

[bepone]

I'm sure better XT can be used inside the chassis, but not this one and probably the reason HAD had them mounted outside.

ok now inside you can fit not so tall toroid , or R core, but must be custom wound,
rare to find them with exact voltages

[ynor]

CAUSE OF PROBLEM IDENTIFIED!

As I postulated in my opening post it is caused by the proximity of the PT to the rectifier! Move it far out of the chassis and this hum is gone!

I seem to remember that was suggested a long time ago. Glad to see you finally give it a try.

https://ampgarage.com/forum/viewtopic.p ... 14#p463914

Yes it took some effort to finally get it done. Thanks!

I'm sure I'll bother you more pretty soon. Thinkering with this is fun And I have many plans on modding my OTS. The first being getting rid of that annoying hum in that amps speakers on standby (upgrading transformers). Then I'll convert from skyliner to classic tone stack. But have to get this C-lator working first because for me, tone can't be evaluated and the amp properly played without a working buffer in the loop, so I'll start there!

[martin manning]

This might be an option for your C-lator: https://www.toroidal-transformer.com/sh ... 22va-.html
The height is critical because you cannot have a conductive path (i.e. a bolt) through the torroid contacting the top and bottom of the chassis. This would make a single shorted turn. A non metallic bolt might be an option, or a carefully selected flat head bolt of the right length.

Note the ground scheme was not the problem, that has already been proven, and I suspect you are not the first to encounter this problem with a C-lator.

[ynor]

Note the ground scheme was not the problem, that has already been proven, and I suspect you are not the first to encounter this problem with a C-lator.

Correct, moving those grounds around made no difference in this unit. I think I'll put it back to original state, ask Nik for a return and ask for a previous model instead as this one doesn't have the chassis cutout for outside mounted transformer and I still question that transformer unit without bells. Wouldn't that be fair?