[jboehle]

I'm using the RK097 switched 10K ohm pot from Tangent's store, what are optimal values for R1 & R2?

What is optimal PIMETA gain for Grado phones, using the aforementioned pot?

Also, looking for suggestions on a good balance between sound quality and battery life when using Grados. How are you guys and gals configuring your PIMETA (OPAL/R/G, stacked buffers, R11, class A bias, gain, total cap in C2/3)?

 

[n_maher]

Quote:

Originally Posted by jboehle I'm using the RK097 switched 10K ohm pot from Tangent's store, what are optimal values for R1 & R2?

I'd use the stock values but socket the resistors so you can play around with them if you want.

Quote:

Originally Posted by jboehle What is optimal PIMETA gain for Grado phones, using the aforementioned pot?

As low as the opamps you use will allow. So we need to know what you plan to do for opamps before recommending anything.

Quote:

Originally Posted by jboehle Also, looking for suggestions on a good balance between sound quality and battery life when using Grados. How are you guys and gals configuring your PIMETA (OPAL/R/G, stacked buffers, R11, class A bias, gain, total cap in C2/3)?

I personally prefer single buffers running wide open (220 ohm R11), w/ class A bias, gain of 2 and OPA627s. For caps I used [4] 470uf Panasonic FM series caps. Depending on what you use for a battery config (single 9v, multiple AA/AAA, [2] 9V, etc.) your battery life will vary wildly. Here's my office PIMETA that uses a TREAD power supply:

Note that in the picture I still had the AD8620/10 combo which I found a touch dry with my KSC35s, YMMV and the AD's don't use nearly as much current as the 627s.

HTH,

Nate

 

[jboehle]

Quote:

Originally Posted by n_maher So we need to know what you plan to do for opamps before recommending anything.

I've been thinking about 1x BUF634 each for BUFL/R, and OPA2134 (as a start) for OPALR.

Is it worth trying to use something like LM6171 in for OPAG and not using a BUFG? Or is the LM6171 too hard to get stable? Thinking of battery life here.

Quote:

Originally Posted by n_maher Depending on what you use for a battery config (single 9v, multiple AA/AAA, [2] 9V, etc.) your battery life will vary wildly.

I want to use 1x or 2x 9V. I would like to get at least 10 hours out of the batteries. 20 hours would be more useful (and cheaper).

 

[n_maher]

Quote:

Originally Posted by jboehle I've been thinking about 1x BUF634 each for BUFL/R, and OPA2134 (as a start) for OPALR.

Quote:

Originally Posted by jboehle Is it worth trying to use something like LM6171 in for OPAG and not using a BUFG? Or is the LM6171 too hard to get stable? Thinking of battery life here.

Based on those two statements I think you've got to decide what you're really shooting for. Again, I can only tell you what I would do based on the amps that I've listened to so... If you're thinking of eliminating the ground buffer I'd switch to the MINT design. If you're going to build a PIMETA populate all three buffers. Also, if you're concerned about battery life try running the buffers in a somewhat restricted bandwidth mode by using a higher R11 value (like 1k or something). You can calc how much current draw that will save you. As far as opamps go I'd just make sure to use sockets so you can change them at a later date. And I'd also go with the 2227/134 combo maybe since Tangent seemed to think that the 2227 sounded a bit better and also runs to slightly lower supply voltages.

Quote:

Originally Posted by jboehle I want to use 1x or 2x 9V. I would like to get at least 10 hours out of the batteries. 20 hours would be more useful (and cheaper).

If you want to get 10hrs out of a single 9v you'll have to do some digging to find out what the typical current capacity of a non-rechargeable 9v is and then also consider how the voltage drops over time. And you'll also want to look into the potential bad things that can happen if you wire two batteries in parallel to increase total capacity (not voltage). You also might to consider rechargeable batteries since the cost of 9v's will add up quick.

HTH,

Nate