Bigbottle Phonostage Builders thread.

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nielsek

Member
Joined 2014
Enjoyed listening to my records yesterday with this phonostage. I have only MM cartridges, but planning to get MC one also.
When turning off the phonostage I get a big thump from the speakers, even if my preamp/receiver is not turned on the input. I measured the output voltage of left and right channels with multimeter. When turning off the unit, there is a spike between 0 to -5V. Is this normal behavior or I should be worried?
 
N

nielsek

Member
Joined 2014
Vivant said:
That will be normal behaviour as the internal supply collapses.

You shouldn't get a noise if the input is deselected.
Click to expand...
Unfortunately when it's turned on the input, it's even worse. The receiver shuts down and goes into diagnose mode when turned on afterwards. That's what got me scared in the first place and I started to investigate how it works when selecting other input and measuring the voltages.
Anything I could do about it?
 
Bigman80

Bigman80

Member
Joined 2018
nielsek said:
Unfortunately when it's turned on the input, it's even worse. The receiver shuts down and goes into diagnose mode when turned on afterwards. That's what got me scared in the first place and I started to investigate how it works when selecting other input and measuring the voltages.

Anything I could do about it?
Click to expand...
I have never had an issue like that.

Just leave it on lol

Seriously, I know they do soft starts, what about soft stops?
 
S

slav

Member
Joined 2010
nielsek said:
Unfortunately when it's turned on the input, it's even worse. The receiver shuts down and goes into diagnose mode when turned on afterwards. That's what got me scared in the first place and I started to investigate how it works when selecting other input and measuring the voltages.
Anything I could do about it?
Click to expand...

I've had that problem long time ago when I built NOS DAC with tube output , you need simple muting circuit like that small board with transformer on the top of the photo:
SmYrENq.jpg


it requires small transformer , relay few caps , diodes and resistors . Relay is NC and when turned on outputs stays shorted to ground for a time set by capacitors time constant, it also allows time for filaments to warm up before you get output active - once capacitor charges it opens the relay.

There are many variations of these circuit , search for preamp muting on this forum or you can buy muting PCB from Pete Millet but it's completely different/better animal to what I've done :
Muring Relay PCB
 
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S

slav

Member
Joined 2010
Thump is a result of capacitors on transformers secondary charging through the lowest impedance path , capacitor on mains won't do anything .
Switching in sequence is fine if one remembers about , muting circuit would be my option as it prevents fairly high voltage appearing on output
 
N

nielsek

Member
Joined 2014
Muting circuit seems like an interesting project. Not a fan of adding another power supply, but as I understand, it's possible to power it from the preamp also(Preamp Muting Circuit | audioXpress).

Measured the voltages with tubes fitted and V2 & V3 are quite off. Should I investigate more?
I'm using MM mode, tubes are NOS TESLA PCC88 7DJ8 and 6N2P-EW NOS.
V1 1&6 81 83
V1 3&8 2 2
V2 1&6 113 110
V2 3&8 0,82 0,85
V3 1&6 204 205
V3 3&8 116 113
 
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