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-   -   Valve Wizard Tube Phono Preamp (https://www.diyaudio.com/forums/tubes-valves/332603-valve-wizard-tube-phono-preamp.html)

spoontex 16th January 2019 12:04 AM

Valve Wizard Tube Phono Preamp
 
Hello,

I build this phono preamp from valve wizard:

The Valve Wizard

When I finished the build I connected to my amp and I notice that the left channel sounds louder than right channel. Okey, time to connect an oscilloscope and insert 1khz signal, and yes, the left channel sounds louder than right channel. I try to adjust the internal trimm, but its not enough, I check all the components over and over, I change the tubes, for new ones. The only way I can adjust more or less precisely is if I elevate the heaters to 7v and down the HT to 200 or 220 vdc.

I have paralell heaters
RIAA split
V1 and V2 ECC83
V3 ECC82 I tryied a ECC88 to

And ideas?

V1 and V2 arenít matched, but I supose that the prupose of the trimm is for it...

Thanks.

rayma 16th January 2019 12:42 AM

Quote:

Originally Posted by spoontex (https://www.diyaudio.com/forums/tubes-valves/332603-valve-wizard-tube-phono-preamp-post5666170.html#post5666170)
the left channel sounds louder than right channel.

Likely it's just that the tubes vary in gain. There's no nfb to normalize their gains. Try measuring the 1kHz gain of each tube stage, disregarding the RIAA network to see where the gain difference is, first or second stage. If you have plenty of gain,
try removing the cathode bypass capacitors and see if this makes the gain similar enough between channels.

Alllensoncanon 16th January 2019 03:24 AM

Do the tubes look the same. Perhaps it is mis-label. Regardless, you can add a small resistor between V2 cathode and the trim balance pot on the loud channel. That should do it.

stocktrader200 16th January 2019 04:56 AM

reverse the phono inputs and test again. The cart may not be uniform output.

spoontex 16th January 2019 08:46 AM

Morning,

new readings. I follow the input signal, from the first component.

C2 ( left channel ) have more signal than C22 ( right channel ).


Voltage readings from V1:

1: -1.045
2: 1.615
3:
4: 210
5: -4.05
6: 1.942
7: 1.585
8:
9: 228.1

V2
1: -1.078
2: 0.400
3:
4: 138.8
5: -4.06
6: 1.956
7:
8:
9: 141.1

V3
1: -1.010
2: 29.56
3: 30.07
4: 248.8
5: -4.06
6: 1.980
7: 26.20
8: 26.78
9: 250.6

tristanc 16th January 2019 10:18 AM

1 Attachment(s)
Here are my voltages for comparison. Not sure they're much use. I used a 5751 in the 1st position and ECC82 in 2nd & 3rd. Pretty much identical readings on both channels. I had to do a minor adjustment to get channel balance.

Alan4411 16th January 2019 11:27 AM

Quote:

Originally Posted by spoontex (https://www.diyaudio.com/forums/tubes-valves/332603-valve-wizard-tube-phono-preamp-post5666503.html#post5666503)
Morning,

new readings. I follow the input signal, from the first component.

C2 ( left channel ) have more signal than C22 ( right channel ).


Voltage readings from V1:

...

Are you sure you are reading the pins correctly?
Those voltages do not make any sense?

Alan

spoontex 16th January 2019 11:31 AM

Sorry I read upside down.

pin 1 is 9 etc...

sorry!

Alan4411 16th January 2019 12:48 PM

I see that!

So I will use your method of numbers. (Clockwise from the top of the socket :-).

Pin 2 should be very similar to pin 7 on each valve. That's the cathode (3 and 8 from below).
Pin 4 should be very similar to pin 9 on each valve. That's the anode (1 and 6).

So what looks wrong?
1: -1.045
2: 1.615
3:
4: 210
5: -4.05
6: 1.942
7: 1.585
8:
9: 228.1

V2
1: -1.078
2: 0.400 should be much higher 2 to 5 volts ?
3:
4: 138.8
5: -4.06
6: 1.956
7:????
8:
9: 141.1

V3
1: -1.010
2: 29.56
3: 30.07 this should be the same as you have on pin 4 of V2 so ~ 140v.
4: 248.8
5: -4.06
6: 1.980
7: 26.20
8: 26.78 this should be the same as you have on pin 9 of V2 so ~ 140v.
9: 250.6

So check what you have on V2 pins 2 and 7 again.
Then look why you do not have 140 volts on the grids of (pins 3 and 8) of V3.
Once you have fixed that, the voltage on pins 2 and 7 will go up to about the same too.
Alan

spoontex 16th January 2019 05:43 PM

Okey,

I have made new measeures:

Now, it correct valve pins.

V1
1: 242.1
2: X
3: 1.548
4: 2.046
5: -3.90
6: 239.9
7: x
8: 1.552
9: -0.922

V2
1: 154.6
2: x
3: x
4: 2.063
5: -3.89
6: 138.8
7: x
8: x
9: -0.913

V3
1: 251.9
2: 24.40
3: 26.96
4: 2.103
5: -3.80
6: 251.7
7: 26.70
8: 26.25
9: -0.840


I haven't any reading on V2 pins 2, 3, 7, 8...


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