U47EF Oliver Archut version

[Spencerleehorton]

Ah ok, I’ll give that a wurl and see how I end up

 

[Spencerleehorton]

i think what I’ll do is build another U47 same as this one and do a P2P and try this gnd scheme, then A B the two, see which one I like better.

 

[Spencerleehorton]

Have a few EF80 to try and compare so I knocked up a couple of P2P/turret U47.

 

[kingkorg]

Have a few EF80 to try and compare so I knocked up a couple of P2P/turret U47.
View attachment 111445

Why are you using 1G resistors?

 

[Spencerleehorton]

There are 3x1G resistors on the schematic

 

[Spencerleehorton]

I have some 400meg I could use?

 

[Spencerleehorton]

 

[kingkorg]

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.

 

[Spencerleehorton]

Ah ok, I’ll stick with original values R1 100meg and R2 60meg and see how I get on.

 

[Spencerleehorton]

version two coming together now, made a very ruff body, will clean up once ive got it all working, found a 7 pin connector for the mic but have another on order which will fit better.

 

[MasterEvan07]

version two coming together now, made a very ruff body, will clean up once ive got it all working, found a 7 pin connector for the mic but have another on order which will fit better.

View attachment 111705

I'm glad I'm not the only one with a messy workspace...

 

[Spencerleehorton]

I will adjust the diagram layout and schematic to show exactly how this next version will be.
I’ll also document the psu and any other alterations as well as final voltages.

 

[Khron]

I'm glad I'm not the only one with a messy workspace...

Was it Einstein that allegedly said "a cluttered desk is a sign of a cluttered mind"..?

 

[Spencerleehorton]

i'll get round to it as its in a corner in my drum room which needs to be tidy once this is complete!!

 

[Spencerleehorton]

could someone check this please, hopefully got this right!!

 

[Spencerleehorton]

will add on voltages once tested V2



Did another version to make use of the other turret board

 

[Spencerleehorton]

i missed a GND connection!!! corrected.

made a little mount for the tube socket to hold it to the strutts, seems to work ok, will need to mount the reed relay on the top of the capsule plate.

 

[Spencerleehorton]

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?

 

[Spencerleehorton]

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.

 

[rock soderstrom]

Swap the tubes and test your heater voltage. How clean is it? Does the hum go away when you turn off the power?