12BH7 in 12AU7 cathode follower circuit

[perkri]

Less than 3% difference is pretty darn good, not a discrepancy.

One of my many personality defects - needing things to be the same 🙂

 

[perkri]

That makes sense. So a small discrepancy in the resistor value, can have an effect of measured voltage because of the divider being created. Thank you.

 

[NIXIE62]

For example, my BK 393 multimeter has a 10Meg input impedance. If you look at the simulation above, you connect a 10 Meg resistor from grid to ground (my multimeter), and the grid voltage goes from 69V to 56V.

Multimeter + R6 are parallel to R5, shouldn't change much. It can also be measured directly on R5 to GND.

 

[jcalvarez]

R5 to GND yes, but if you measure directly the grid, then the multimeter is in series with R6 and the voltage source, which is the intersection of R5 and R4. You get a voltage divider if you measure at the grid.

 

[ranshdow]

I’m not sure how different it would be from my existing Hiraga 30w class a?

Not all Class A sounds alike. I'm pretty sure every FW amp and clone is class A & they all sound different. I've never heard a Hiraga anything so I can't help there.

 

[perkri]

Oh, I know they sound different. My comment was that I wasn’t sure how different they would sound.

 

[perkri]

Finally have some time to myself to get back to working on this.

Adjusted the B+ down to 307 from the 324 I was seeing before.

I’ve drawn out the schematic with the new values suggested in place. I think I got the right changes made?

Measured the output impedance, and it’s approximately 1.2kohm. Using the 20x multiplier for power amp input difference, I’m safe w all my amps, except the VFet.

It was suggested to lower the value of the volume pot, I’m presuming a 100k is suitable?

Hoping to order the resistors this week.

Thanks,

P

 

[perkri]

I also looked up the Salas board. I don’t think I can shoehorn the board into this build? If I redo this in a bigger chassis, I will for sure look into it.

Was also contemplating converting to DC heaters???


Thanks

 

[perkri]

Ordered the resistors. Hope to have them soon. Going to do one channel at a time so I can A/B the difference.

Thanks!

 

[perkri]

Parts arrived, and finished doing the suggest changes last night. Did not have a chance to do a proper listening comparison yet, but first impressions are it’s sounding “fuller”.

Won’t be able to do a deeper analysis until next week when I’ll do some side by side listening to see how it is working now.

I’ve left the bypass cap in place for now, but will be trying it with and without it in place as suggested.

After doing the changes, B+ dropped about 50v, so I changed the power supply resistor and it’s back up to 300v.

I’ll map out all the voltages next week as soon as schedule allows.

Thanks!

P