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Old 10th July 2009, 03:35 PM   #1
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Default Need opinions about this tube circuit

Hello

Maby I've post it in the wrong section, since there is no reply, I ask my question here in the tube section.

I have done a I/V tube ouput for a Nos TDA1541A dac, I use 12AX7 tube because I have many of this tube.

Any suggestions about my schematic, is my circuit are ok ?


http://www.diyaudio.com/forums/attac...amp=1247210460

Thank you

Bye

Gaetan
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Old 10th July 2009, 06:29 PM   #2
DougL is offline DougL  United States
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Three questions,

How much gain do you need?
What is the input impedance of the stage you are trying to drive?
Or what is the output impedance are you targeting?
How long a cable / how much capacitance are you driving?

12AX7 may or may not be appropriate, depending on your answers.

HTH

Doug
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Old 10th July 2009, 08:55 PM   #3
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I would AC couple the input.

I think the cathode 200R resistors are way too low for a 12ax7.
I use 1k2 with 12au7 that will drive much more current.
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Old 10th July 2009, 09:20 PM   #4
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Yes, about 1K is needed. Also, I would use much smaller value of a feedback cap (like 30K) connecting it after a coupling cap from the upper cathode, then one more coupling cap to output.

Also, consider grounding grid operation feeding input signal to cathode, all above apply.
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Old 10th July 2009, 09:22 PM   #5
SY is offline SY  United States
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Why an SRPP in this application? The voltage swings are low and the load isn't particularly reactive. There's a distortion penalty to using this topology.
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Old 10th July 2009, 10:40 PM   #6
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Quote:
Originally posted by DougL
Three questions,

How much gain do you need?
What is the input impedance of the stage you are trying to drive?
Or what is the output impedance are you targeting?
How long a cable / how much capacitance are you driving?

12AX7 may or may not be appropriate, depending on your answers.

HTH

Doug

Hello Doug

I need between 40 to 50 times gain.

The input impedance of the stage I am trying to drive are arround 35k ohm.

This tube stage will be in the same case than the power amp, so the cable will be a max of 4 inch long and will be video type cable.

Thank

Bye

Gaetan
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Old 10th July 2009, 10:43 PM   #7
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Quote:
Originally posted by SY
Why an SRPP in this application? The voltage swings are low and the load isn't particularly reactive. There's a distortion penalty to using this topology.

Hello SY

I did chose SRPP in this application because it was seem more simple to do. But it can be another type of circuit.

Thank

Bye

Gaetan
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Old 10th July 2009, 10:56 PM   #8
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Hello

There is this other tube circuit, but I suspect that the resistors values are not right.

Suggestions ??

Thank

Bye

Gaetan
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Old 10th July 2009, 11:06 PM   #9
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If you look up the datasheets for 12AX7 and 12AU7 then they give examples of circuits with resistor values.

If you want advice on circuits then you need to tell us what the signal comes from and where it goes to so we can work out input and output impedances.
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Old 10th July 2009, 11:17 PM   #10
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Try this one. Choose a gate stopper accordingly to the device you use.

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