• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

Sowter 9335 as input - hard noise when switching

Jump to Latest
J

jev

Member
Joined 2004
#1
My recent build is a SRPP pre-amp which has too much gain for me so I will probably rebuild it into something like this Muchedumbre Buffer Preamp – wauwatosa tube factory

But I think with two halves of the 6sn7 I am using in the SRPP

Now my question is as follows:
- I use Sowter 9335 as volume control
- Switching is by relays kit from Dantimax, this works fine
- However there is a lot of hard noise while switching, really annoying. Is this because of the high gain? Or because of the relays?
- Also do I still need a grid resistor after the Sowter?
 
#4
Hm, the website says it is made to be used with TVCs. I don't really understand your description of the noise. I assume it isn't a switching sound from the relay but something coming through the speakers? A single hard sound or something else?
 
#5
A very hard clicking sound. May be if I reduce the gain it will be bearable

But would be interested if I can mitigate it somehow

Pretty sure the Dantimax kit does not use make before break. So what happens at the switching moment. Probably the + / live secondary of the TVC is in between the taps. The secondary common / grounded wire stays always connected to ground
 
Last edited:
#6
Inductors (including TVC) don't like to suddenly became open-circuited, just like capacitors don't like to suddenly became short-circuited. Hence you do need make-before-break switching with TVC.
RelVol2 doesn't provide that indeed - there is a thread here on diyAudio with people angry for that reason, even with resistive attenuators.

What you can try though is putting another resistor of several hundred kOhm across the whole TVC secondary (between the "max volume" and "ground" taps).

BTW, where is you grid leak resistor located exactly - "after the Sowter" as stated or after the relays close to the tube grid, where it should be?
 
#7
Is it possible that your signal source(s) that drives the Sowter 9335 has a DC offset voltage?

Even a small DC offset voltage into a transformer volume control, may cause noticeable transients whenever you switch to different attenuation levels.

Some sources of DC offset voltages are direct coupled IC op-amp outputs, leaky coupling caps, etc.
Measure the signal source output without a load.
Any DC offset will become a current into the transformer input.
 
Last edited:
#8
TG said:
Inductors (including TVC) don't like to suddenly became open-circuited, just like capacitors don't like to suddenly became short-circuited. Hence you do need make-before-break switching with TVC.
RelVol2 doesn't provide that indeed - there is a thread here on diyAudio with people angry for that reason, even with resistive attenuators.
Click to expand...
Thanks I will look into this thread!
 
#9
TG said:
What you can try though is putting another resistor of several hundred kOhm across the whole TVC secondary (between the "max volume" and "ground" taps).

BTW, where is you grid leak resistor located exactly - "after the Sowter" as stated or after the relays close to the tube grid, where it should be?
Click to expand...

OK will try this asap
 
#11
TG said:
BTW, where is you grid leak resistor located exactly - "after the Sowter" as stated or after the relays close to the tube grid, where it should be?
Click to expand...
Yes sorry for the confusion I meant after the RelVol2 and just before the tube grids

Would the value of the grid resistor change anything? I will may be experiment a little
 
#13
The click sound come from relè.
I got same problem with volume from Tent labs.
It is a common problem. It comes from a electrostatic signal on contacts of relè.
There is a type from Matshusita that is fine for that use
I have to find the model. It is pin compatible with the standard signal relè

Walter
 
#14
Thanks, I also have another RelVol with resistors which also had this problem but much less. I suspect the gain of my pre amp which is now too high also does not help. I will work on it a bit the coming time

If you find the Mathusita relay please let me know..
 
#17
jev,

It is difficult to troubleshoot a circuit that is both:

1. At a distance
and . . .
2. Without a schematic.

Since we probably will not travel to your location . . .
Would you please post a complete schematic?

I use a stepped volume control with many relays. There are several models of that volume control.
Shunt resistor model
Divider resistor model
Tapped transformer model

None of them have noticeable clicks.
 
#18
It's now like this. Tapped transformer from Sowter with a relay based switching
 

Attachments

  • Dia1.JPG
    Dia1.JPG
    33.4 KB · Views: 193
You must log in or register to reply here.
Top Bottom