Buffalo DAC output stage

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jmanalo
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Post by jmanalo » Mon Feb 14, 2011 1:01 am

Nick,

Here is cathode voltages: On one channel it's 6.6V, 6.8V and 6.5V,6.4V at the other channel.
It sounds good though.

Thanks,

Joe

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Nick
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Post by Nick » Mon Feb 14, 2011 2:20 am

That sounds ok. Remind me what you have built, value of the shared cathode resistor. What the voltages on the grids are (it will be the +ve offset from the DAC. How is the power supply built?
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Post by Nick » Mon Feb 14, 2011 2:24 am

If you are using the Sowter transformers, you need to ensure that the current through both sides is within 0.5ma nothing will break if its not, but the bass response will suffer. Let me go back and see what I posted, I built it with a shared cathode resistor, and a balancing arrangement.

Ok, just checked what I posted. 6v or so sounds fine, if you have the 401 0.1% cathode resistors then thats 15ma per side, which is perfect. Have you adjusted the preset so there is the same voltage across each resistor on a pair? Anywhere from 15ma to 20ma is fine.

Simple way is connect meter across the two test points, and adjust the pot until there is less than 0.2v difference. Get the difference as small as you can (no signal from dac). then connect the two test points together and run with a shared cathode resistor.

If you describe the power supply we can see if the voltage drop is as expected. The entire thing will be drawing 60ma from the supply.
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Post by jmanalo » Wed Feb 16, 2011 5:09 pm

Nick,

The supply that I'm using is the Lampizator Board.

I used all the parts and same values from your circuit post on the top of first page of this thread and followed your test instructions. I used the 402R 0.1% (can't find 401) cathode resistors.
I adjusted the test points to .001V after warm up, then I connected the two test points.

FYI: I tried to add the link for the Lampizator Board at DIYaudio group buys but it won't let me post with the link.

Thank you much for your help.

Joe

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Post by Mike H » Wed Feb 16, 2011 5:51 pm

 
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Post by Nick » Wed Feb 16, 2011 6:49 pm

Ok, that makes sense, the 1k resistor in each chan will loose 30v on its own when you connect it to the output stage, so the numbers you have found make sense.

I would guess the output stage you have is drawing far more current than that board was made for, as long as the TX is happy with the 60ma or so it will be fine. A ECC83 SRPP as they are talking about in th ethread is probbaly pully 2ma, 6n1p not much more. The output stage we have is altogether a more hairy chested proposition :-)

I used a choke in the supply, that would be a option for you, replace the 1k resistor in each chan with a little choke. Say a hammond 156G in each side. The supply will be quieter for it and the voltage will sag far less. With the choke mentioned you will get 5 times the smoothing and a third of the voltage drop.
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Post by jmanalo » Wed Feb 16, 2011 8:20 pm

Mike,
Thanks for posting the link.

Nick,

Actually, I replaced that 1k with 1.8k to reduced the voltage to 170V to match your circuit.
The DVB guy is talking about 6n2p, that is what he is using on his board, that board is switchable for 6n6p, 6n2p and 12ax7 with the use of toggle switch.

I have the Salas Shunt Regualator that I'll add to the supply end and before your circuit. The regulator is on the same thread link aboved at post #190.

How low of the B+ voltage I can apply to the 8650? I know once I add the Shunt regulator, it will drop another 30V. Maybe I'll replace the resistor with less than 1k.

Thanks,

Joe

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Nick
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Post by Nick » Wed Feb 16, 2011 11:01 pm

Anything above 100v should be fine.
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Post by jmanalo » Wed Feb 23, 2011 5:39 pm

[quote="Nick"]
I used a choke in the supply, that would be a option for you, replace the 1k resistor in each chan with a little choke. Say a hammond 156G in each side.

Nick,

If I replaced the 1k resistor with 156G Choke, can I still connect the Salas Shunt Regulator?

Thanks,

Joe

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Nick
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Post by Nick » Wed Feb 23, 2011 9:29 pm

Dont see why not. What is the "Salas Shunt Regulator"?
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Post by jmanalo » Fri Feb 25, 2011 4:03 pm

[quote="Nick"] What is the "Salas Shunt Regulator"?
It's claimed by several users to improve the sound.

Nick,

I ordered the 156g Hammond choke, so, how I'll connect that in place of the 1k resistor?
Thanks,

Joe

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Nick
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Post by Nick » Fri Feb 25, 2011 4:28 pm

Just replace the resistor on the PCB with the two wires from the choke.
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Post by Mike H » Fri Feb 25, 2011 4:37 pm

Nick do "salas shunt regulator" in Google images Image
 
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Post by jmanalo » Mon Feb 28, 2011 11:39 pm

Nick,

Do I need to zero the voltage between TP1 and TP2 everytime I'll replace the (same type/model) tube?
Thanks,

Joe

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Post by Nick » Tue Mar 01, 2011 2:59 am

Yes
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