• 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.

A Heretical Unity Gain Line Stage part III

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Algar_emi

Algar_emi

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Three PCB set is done, ready to assemble. Rather nice looking :D
 

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Algar_emi

Algar_emi

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Take note that these PCB's were designed to allow for a lot of options, choice of caps casing, use of transformer surge reducer TH1, HV relays or not, etc...
So make sure to read the Parts List and look at the schematics before assembling the PCB's. You may need to install jumpers at some places, if you don't use some optional parts.

I'll try to write a small document listing all the options but it is not done yet.

GROUNDING CONNECTIONS:
This preamp use a very specific Grounding scheme. There is a lot a separate GND (HV, HTR, Signal, Power, etc...) that need to be correctly connected for optimum performance. You need to correct all the PCB correctly. I'll put together a schematic for the connection but it is not done yet either...
 
Algar_emi

Algar_emi

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And the Regulators PCB completed as well. Just a few parts are missing until I select the correct leds resistors and timing capacitors.
I'll start testing them in a few days.

The big film caps are held in place using silicone to reduce microphony effect.
I also found the cap's leg connected to the outer film layer and connected this leg to ground for best noise immunity.
 

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SY

SY

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Josh, my soon-to-be-published preamp article (I think it's in the June AX) is indeed balanced output. But at the time I built the Heretical, I would have had to rework my electronic crossover (which the preamp drives).

In all honesty, I've never found much of a difference between balanced and unbalanced in using short-ish (<3m) interconnects at line level, despite the theoretical superiority. There are some interesting reasons, which I'm sure have already occurred to you, to use a balanced drive at high level, like 20V, to the power amp. One of the nearly-finished projects I have is an EL84-based unity gain balanced-in power amp, sort of a tube analog to the First Watt F4. But the only place I think that balanced has a REAL advantage in home audio is between cartridge and RIAA amp.
 
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