• 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.

Universal tube preamp PCB, ECC99/6N6P/ECC88/ECC85/6922/6DJ8 etc. MU follower or SRPP

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#22
jean-paul said:
As expected, sorry. It is often assumed one can not hear RF so it is not an issue. EMI and RF are nasty in audio though and in semiconductor stuff sometimes the cause of "listening fatigue" and this intermittent or depending on the time of the day/temp etc. Even when devices look nice and have blue LEDs 🙂 Not measuring = not knowing.

BTW I do like your design so no negative criticism except a few quibbles like lacking volume control and PSU. Nice design.
Click to expand...
There are to much options for volume control and power supply.

For the tube preamp are a lot of applications where you do not need a volumecontrol. Such as outputstage for DAC or CD player, or inputbuffer for classd amp.

About the power supply i started a thread in the power supply section https://www.diyaudio.com/community/...s-design-for-tube-preamp.388367/#post-7073834 to make a high voltage preamp smps. I think about linear supplies there is a lot to find here on DIYaudio. I myself also used in the past the maida regulator or a LR8n regulator with or without fet.

In this thread i like to talk only about the preamp.
 
#23
I just realised there has been no discussion about heater elevation and looking at the schematic the heaters are floating unless you connect one side to HT0V somewhere. With many of the tubes you could use in this circuit, their Vhk spec is may be low for the upper triode if the heaters are grounded with a 265V HT voltage. The normal solution is to elevate the heaters to around 25% of the HT voltage.

Cheers

Ian
 
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#26
Koifarm said:
I am aware about the specs for elevating the heater supply. But as Jeam Paul stated my SMPS share GND between anode and heater supply. Luckily it is forgiven by the 6n6p tube.
Click to expand...
Yes, some tubes will be OK others may not. You need to be careful with a regular 6DJ8 for example because the two triodes have different Vhk specs, but if you use an EH6922 instead you should be OK. Just something to be aware of.

Cheers

Ian
 
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#27
Koifarm said:
I am aware about the specs for elevating the heater supply. But as Jeam Paul stated my SMPS share GND between anode and heater supply. Luckily it is forgiven by the 6n6p tube.
Click to expand...
Reproduce luxman cl34 heater supply and heater wiring It's totaly silent and it has a small secret that will help you every single time you meet weird constraints! By the way...you can go opposite way too, lowering the fillament potential below ground!
 
#34
Koifarm,

In reading the SMPS operation description, the HV section has a turn-on delay of approx. 30 seconds behind the filament heater turn-on. And the HV has an adjustment range of 10% (approx. 247V - 273V). Will cattle be powered from it? :rofl:
Can you confirm if this is accurate?
Thanks.
 
#35
Mine SMPS has not the 30sec delay. It starts high voltage after heater supply is on.

I use the 6n6p SRPP stage now for 14 years as an outputstage. It is in a cd player, straight from a I/V resistor after two PCM1794 DAC’s.
 
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#40
A package arrived in the mail today

20220729_190252.jpg

Looking forward to building this up and testing it. Plan is to build as SRPP for 6DJ8s

.. dB
 
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