C-lator hum

[martin manning]

Also, removing the send/return cables does not remove the hum. Signal is then running straight through from send to return jack. But when one jack is plugged in either send or return (loop interrupted) the hum is slightly reduced if I remember correctly. Makes be believe the hum is injected into the signal path somewhere?

What I was asking is if the C-lator is connected to the amp, is the hum affected if you remove either of the "preamp out" or the "power amp in" cables.

Are you sure you have a good heater ground reference?

Absolutely not. How can I exclude that as a cause?

The heater circuit will either have a heater winding center tap connected to ground, or 2x ~100 ohm resistors, one from each side of the heater winding, connected to the chassis. Make sure that those connections are good by measuring from the tube heater pins to ground. You should see a very low resistance or 100 ohms, depending upon which type of ground reference it has. If the hum is present with the tube removed, i doubt that this is the cause.

[ynor]

What I was asking is if the C-lator is connected to the amp, is the hum affected if you remove either of the "preamp out" or the "power amp in" cables.

Ah I see. Will try removing either one and see what happens. When the C-lator is completely removed from the amps fx loop the hum is removed though.

Can try the C-lator on another amp by the way, as I'm not sure if the grounding between the amp and C-lator can be a part of the problem..?

The heater circuit will either have a heater winding center tap connected to ground, or 2x ~100 ohm resistors, one from each side of the heater winding, connected to the chassis. Make sure that those connections are good by measuring from the tube heater pins to ground. You should see a very low resistance or 100 ohms, depending upon which type of ground reference it has. If the hum is present with the tube removed, i doubt that this is the cause.

Yes the hum is present without the tube. This one has 2x 100R resistors. Will measure the resistance of those connections tomorrow. Thanks!

[bepone]

I can feel the need for one of these growing...

If not on hand, no need to buy.. you can use multimeter on AC V selector , on capacitor node. You can find easily humm if existing in RMS value.. this humm is inserted directly in signal chain and amplified, because triode stage has bad PSRR (power suply ripple rejection).. In dumblelator builds there is no choke like in amps which serves like great filter to supress rippple and if is power supply not made properly, with many RCRCRC stages , there you can find it in the signal.

[ynor]

What I was asking is if the C-lator is connected to the amp, is the hum affected if you remove either of the "preamp out" or the "power amp in" cables.

Just tried: Hum is introduced when connecting the C-lators out to the "power amp in".

So:
No C-lator = no hum.
C-lator in to " Preamp out" = no hum.
C-lator out to "Power amp in" & "Preamp out" disconnected = hum.
C-lator in & out connected to amp fxloop = hum.

[martin manning]

What I was asking is if the C-lator is connected to the amp, is the hum affected if you remove either of the "preamp out" or the "power amp in" cables.

Just tried: Hum is introduced when connecting the C-lators out to the "power amp in".

So:
No C-lator = no hum.
C-lator in to " Preamp out" = no hum.
C-lator out to "Power amp in" & "Preamp out" disconnected = hum.
C-lator in & out connected to amp fxloop = hum.

Ok, so with the C-lator disconnected from the amp, do you measure any AC on the C-lator output (on the power amp in cable)?
What happens if you put a patch cord into the C-lator's send and return (FX) jacks? Maybe you have a bad switching contact on one of those that is leaving the recover stage grid open.

[rogb]

What I was asking is if the C-lator is connected to the amp, is the hum affected if you remove either of the "preamp out" or the "power amp in" cables.

Just tried: Hum is introduced when connecting the C-lators out to the "power amp in".

So:
No C-lator = no hum.
C-lator in to " Preamp out" = no hum.
C-lator out to "Power amp in" & "Preamp out" disconnected = hum.
C-lator in & out connected to amp fxloop = hum.

Ok, so with the C-lator disconnected from the amp, do you measure any AC on the C-lator output (on the power amp in cable)?
What happens if you put a patch cord into the C-lator's send and return (FX) jacks? Maybe you have a bad switching contact on one of those that is leaving the recover stage grid open.

I was just going to say that, had that problem a number of times with switching jacks in amp in/out and Dlator. Check those very carefully.

[Richard1001]

I was looking at the transformer mains and high voltage wiring. Could you take a picture of the side of the transformer where the wires are connected?

[Charlie Wilson]

Are potentiometer casings referenced to ground?
CW

[Richard1001]

I was looking at the transformer mains and high voltage wiring. Could you take a picture of the side of the transformer where the wires are connected?

The reason i ask this is that it looks like the high voltage and mains wiring are crossed.

On my Ceriatone transformer mains connections are at the bottom, high voltage are the two top left lugs and the filament are the top right lugs

IMG_20200712_002236~2.jpg

If your transformer has the same connections, the high voltage and mains voltage coil seem to be wired in series.

Screenshot_20240315_070440_Gallery.jpg

But pictures can sometimes be misleading so maybe you could check the wiring.

[ynor]

Ok, so with the C-lator disconnected from the amp, do you measure any AC on the C-lator output (on the power amp in cable)?
What happens if you put a patch cord into the C-lator's send and return (FX) jacks? Maybe you have a bad switching contact on one of those that is leaving the recover stage grid open.

Measuring AC voltage on the C-lators output reads 00.0 V (on 200VAC setting, the most sensitive) , but I dont think my cheap DMM is capable to read mV.

Using a patch cord between the send and return is giving the same hum (and audio) as not having the cord plugged, so I think the switching is ok. But leaving ONE jack in either the send or return (breaking the connection between send and return) reduses the hum some, but still there.

[erwin_ve]

Are potentiometer casings referenced to ground?
CW

Did you check?

[ynor]

I was looking at the transformer mains and high voltage wiring. Could you take a picture of the side of the transformer where the wires are connected?

Looks correct to me. Mains on 240V, high voltage on the top left 135 V (black goes to standby switch, red to rectifier), and heaters on the top right 6.3 V.

20240316_140200.jpg

[ynor]

Are potentiometer casings referenced to ground?
CW

Did you check?

My cheap DMM reads 0.6 Ohms between the pot casings and the signal ground.

[ynor]

The heater circuit will either have a heater winding center tap connected to ground, or 2x ~100 ohm resistors, one from each side of the heater winding, connected to the chassis. Make sure that those connections are good by measuring from the tube heater pins to ground. You should see a very low resistance or 100 ohms, depending upon which type of ground reference it has. If the hum is present with the tube removed, i doubt that this is the cause.

Resistance between pin 4 and signal ground: 50 ohm. Between pin 5 and ground: 50 ohm. Pin 9 and ground: 50 ohm.

[ynor]

Also 50 ohm between each of the two heater taps on the PT to safety ground