U47EF Oliver Archut version

GroupDIY Audio Forum

Help Support GroupDIY Audio Forum:

This site may earn a commission from merchant affiliate links, including eBay, Amazon, and others.
I have some 400meg I could use?
For some reason people publishing these various u47 schematics, replicas, etc, believe 1G resistors are an upgrade. Same goes for higher value plate>transformer coupling caps.

These determine crucial low cut points in the circuit, and can affect the sound tremendously. There is also the issue of grid current with tubes, one more reason not to use 1G. 1G will let subsonics straight through the tube and potentially overdrive it, the transformer too.

If you are after accurate replica i would stick with original values. Changing these crucial component values will impact the sound way more than any specific tube, or capacitor type used.

It's kind of difficult to go against Oliver's schematic, but there are very clear reasons why you wouldn't want 1G there. I have no idea why he went for it.
 
well, so far on V2 of this U47, using the same PSU as V1. only difference from V1 is that on V1 i have put a cathode bypass 5k trim set to 2k and a 33uf electro cap. V1 has no noise and loads of level and sounds wonderful using the EF800 tube.
V2 is using the EF80, now powered up and has hum. i have followed the schematic with as close values as i have, the 100M i have used a 200M and the 60M i have used another 200M. all other values are the same.
pin 3 on mic socket is Heater GND and goes to heater gnd rail which then goes to chassis on IEC, pin 7 on mic socket is audio GND and goes to B+ gnd rail which then goes to chassis on IEC.
The XLR pin 1 goes to chassis as per the advice.

i have 4 other EF80 to try and see if the problem is the valve but i doubt it.

may have to cathode bypass this one as well, just very frustrating that i cant get the original basic circuit working without hum?
 
I have cathode bypassed and no hum now, need to check voltages and see where i am but quite a lot of hiss, going to try another tube, transformer and capsule and see if any better.
So far its sounding pretty lifeless and dull, fair bit of microphonics, which i could dumb down with tape and a tube rubber ring.
but so far the EF800 wins by a mile.

update:

changed tube and hiss pretty much gone, but valve really microphonic, will order another EF800 as i think it sounds so much better.
 
Last edited:

Latest posts

Back
Top