[drewd]

Quote:

Originally Posted by pabbi1 Several build curiosities: a) What is the optimal (in your most humble opinion) voltage setting (using a STEPS) for the 12ae6a and the 12fk6 respectively?

24 Volts. The heaters in the tubes are designed for a 12 volt system and since they are wired in parallel, that gives them 12 volts each. The bias voltage should be set to 12V, but you can experiment a bit with that voltage. Your ear is really your best guide - and you may not hear any difference over a fairly broad range of voltages.

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b) I am using a wood front panel on a PARS metal case - is steel shielding (an easy option for me) likely to be needed?

Probably not. My STEPS is in an aluminum Hammond case and it sits directly under my Millett in another aluminum Hammond case. I hear no hum, even at full volume. I use it at work, where I'm surrounded by fluorescent lights, computers and electronic test equipment. Oddly enough, the only noise that I ever hear is from my cell phone, but that appears to be coupled through the headphone cable.

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c) The PARS metal case has an aluminum divider - does that need to be steel (an easy option) to shield the Millett board from the STEPS?

If you get hum from the power supply, then yes, it does need to be steel, or some other material that interacts with magnetic fields (mu metal, nickel, etc.)

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d) Which tube set is likely better for Senns (HD600 or HD650)?

I happen to like the 12FK6 best of all of the tubes that work in the amp, but you might have a different opinion. Since the tubes are pretty inexpensive, try a couple of different sets. I'd recommend starting with the 12AE6A and 12FK6.

Quote:

e) Do I need to adjust any resistor values to boost the gain for Senns (600/650)?

The amplifier does not use a feedback loop for gain. The gain is set by the constant current diode on the anode. You may want to reduce or even eliminate the 22.1 ohm output resistor. It was originally placed to protect the buffers from a direct short, but the BUF634s have internal protection, so it's not strictly required. The amp has plenty of gain for your Sennheisers.

Good luck!

-Drew

 

[drewd]

Quote:

Originally Posted by mrdon How does one connect the toggle switch to the pcb? Thanks!

There are two pads on the board labeled S1 and S2. They are for the switch - one wire to each pad. I'll update the build instructions to address that.

-Drew

 

[dsavitsk]

Quote:

Originally Posted by pabbi1 c) The PARS metal case has an aluminum divider - does that need to be steel (an easy option) to shield the Millett board from the STEPS?

I have a STEPS sitting about an inch to the side of my Millett. There is no shielding and no noise. I would wait until you have interference before you worry about it.

 

[pabbi1]

Thanks for the input... I have indeed purchased both sets of tubes, and see if there is a difference.

I was just curious since the earlier posts indicated 30v, and bias of 13.5 was working very well, but possibly at the expense of tube life (which I'm fairly insensitive to).

Mainly I'm asking questions because I'm waiting for parts...

 

[comabereni]

Quote:

Originally Posted by n_maher From what I've read and what I hear the bias setting is not super critical with the exception of not going higher than say 14V. I'm sure someone can clarify this. If it were me I'd just set it at 12V and forget it.

Many of the original Millett builders/users set their bias as high as 19V. I haven't read Pete's article in awhile, but I don't remember there being a 14V recommended ceiling. I've read most of the Millett impression posts, if not all of them, and there hasn't been a lot of comment on optimal bias settings for different model tubes--this should eventually make for some interesting discussion, i.e. we should all try different settings and find out.

-coma

 

[dviswa]

Hi Guys,

Did we rename the parts from the original Pete's schematic? From what I can see from his schematic there are no parts names either L or R, in contrast the PCB has plenty of parts named L/R. For somebody trying to follow Pete's schematic this is confusing.

Regards,
Dinesh

 

[drewd]

Quote:

Originally Posted by comabereni Many of the original Millett builders/users set their bias as high as 19V. I haven't read Pete's article in awhile, but I don't remember there being a 14V recommended ceiling. I've read most of the Millett impression posts, if not all of them, and there hasn't been a lot of comment on optimal bias settings for different model tubes--this should eventually make for some interesting discussion, i.e. we should all try different settings and find out. -coma

I'll vouch for that - I accidentally set mine at 20V with no damage. The 12AE6A tubes didn't work, but they weren't hurt. Interestingly, the 12FK6's worked OK.

As always, your ears are your best guide.

-Drew

 

[n_maher]

Quote:

Originally Posted by dviswa Hi Guys, Did we rename the parts from the original Pete's schematic? From what I can see from his schematic there are no parts names either L or R, in contrast the PCB has plenty of parts named L/R. For somebody trying to follow Pete's schematic this is confusing. Regards, Dinesh

Yup, we renamed them in the hopes of clarifying things a bit. That way you can see which part is for what channel and so on. The fluidlight sight has both a BOM and parts list that are coordinated with the production boards.

And I can completely see how it would be hard to follow Pete's instructions with these boards, which is why we rewrote the build instructions as well

.

HTH,

Nate

 

[dviswa]

I surely appreciate depicting symmetry where one exists, but I also prefer following schematics. Do we have a map or list of what became what. That would be really appreciated.

 

[n_maher]

Quote:

Originally Posted by dviswa I surely appreciate depicting symmetry where one exists, but I also prefer following schematics. Do we have a map or list of what became what. That would be really appreciated.

I'll get to work on it, as far as I know the answer right now is no.

 

[drewd]

Quote:

Originally Posted by dviswa I surely appreciate depicting symmetry where one exists, but I also prefer following schematics. Do we have a map or list of what became what. That would be really appreciated.

Uh oh...schematics. I will work on the schematic this week. In the interest of not screwing up Pete's original design, I worked exclusively from the board file.

-Drew

 

[dviswa]

Quote:

Originally Posted by n_maher I'll get to work on it, as far as I know the answer right now is no.

Quote:

Originally Posted by drewd Uh oh...schematics. I will work on the schematic this week. In the interest of not screwing up Pete's original design, I worked exclusively from the board file. -Drew

Nate, Drew,

You guys totally rock

 

[Erik S.]

In the parts list the Muse KZ 3-4030 is recommended for C2L/R, but does it fit since it is 12.5 mm in diameter while the diameter on the board is 10.5 mm?

Is there a noticable difference by using Holco or Roederstein resistors instead of of Vishays?

Gonna use some better parts on this Hybrid than the last one I built to see if there is a noticable difference. With that said, a Hybrid with Panasonic caps/resistors allover is pretty good

-Erik

 

[drewd]

Quote:

Originally Posted by Erik S. In the parts list the Muse KZ 3-4030 is recommended for C2L/R, but does it fit since it is 12.5 mm in diameter while the diameter on the board is 10.5 mm?

Yes, it will fit, it's just a bit of a tight squeeze.

Quote:

Is there a noticable difference by using Holco or Roederstein resistors instead of of Vishays?

I don't know - somebody made a comment that using carbon resistors in the audio path complemented the tube sound, but I have not tried that.

-Drew

 

[Emon]

So...I don't suppose anyone has an extra revised PCB lying around they would mind selling?