[Beefy]

Quote:

Originally Posted by MoodySteve /img/forum/go_quote.gif Regarding replacements for the RK27, there's the Noble AP25 (available on eBay), the TKD 2CP-2511 and the Audio Note Noble equivalent (both available at Parts Connexion). Allen-Bradley probably has some usable ones, though you'd have to look in industrial catalogs (they don't target audio).

For not much more - relative to the total project cost anyway - you can get a DACT for $129 from Headamp.

 

[tintin47]

I am not trying to build a budget beta, but I just don't think that I have a good enough ear to warrant $130 on a potentiometer. The main thing that I want is something that feels nicer than the RK27.

 

[MoodySteve]

The DACT is a stepped attenuator, not a pot, so it's probably not suitable for what you want anyway.

 

[tintin47]

^ I know. I don't really differentiate between them in my brain. The function is the same even if the design isn't. I should have bid more on those dual mono goldpoints during the silent auction.

 

[m1abrams]

Quote:

Originally Posted by MoodySteve /img/forum/go_quote.gif The DACT is a stepped attenuator, not a pot, so it's probably not suitable for what you want anyway.

Why not? A stepped attenuator works very well for volume control. It does have a different feel when using it. I have not used a DACT one so not sure how they "feel".

 

[m1abrams]

Quote:

Originally Posted by tintin47 /img/forum/go_quote.gif I am not trying to build a budget beta, but I just don't think that I have a good enough ear to warrant $130 on a potentiometer. The main thing that I want is something that feels nicer than the RK27.

hmm what about the RK27 do you not like? So that people can use that to suggest something.

Personally I find the RK27 to be very smooth for feel. Maybe using a larger knob would make it feel better? Smaller knobs tend to have a rougher feel when turning the pot.

 

[MoodySteve]

Quote:

Originally Posted by m1abrams /img/forum/go_quote.gif Why not? A stepped attenuator works very well for volume control. It does have a different feel when using it. I have not used a DACT one so not sure how they "feel".

I was under the impression (from talking with tintin at the meet) that he was only interested in potentiometers, not steppers, so that's why i said it wouldn't be what he wanted. I personally prefer to have continuously adjustable volume control, as opposed to the discrete volume levels of stepped attenuators. I also like the smoother feel of non-detented pots.

He also stated that his budget was around $70 max.

 

[nattonrice]

If you listen quietly then the rk27 can be a complete pita.
The one I had on an amp of mine had this very annoying channel in-balance which only righted itself at a volume that I didn't like.
Naturally a stepped attenuator like the DACT does not have this problem and will have essentially perfect matching at the lowest level.

Something to keep in mind.

 

[Beefy]

Yeah, I certainly wouldn't use an RK27 for super sensitive phones or with a high gain amp.

But I wouldn't use a DACT under the same circumstances either. Sure, channel matching is extremely good, but the step size is very large at the low end...... your first two steps after mute are -60dB and -50dB, then 4dB steps up to -34dB, then 2dB steps up to 0dB.

So anything quieter than -34dB will be very hit and miss.

 

[Pars]

TKD CP2500 (or 2511) ~$65 or so. Michael Percy Audio, PartsConnexion (which is having a 20% sale currently). Seductively smooth, and good sounding.

 

[tintin47]

Thanks, everyone, for attempting to answer my poorly formed and incomplete question. I was posting from my phone and I had to go unexpectedly.

Beefy and Nattonrice are dead on. The real problem I have with the RK27 is that it is terrible and frustrating to use before about 11 or 12 oclock on the dial. I listen quietly and I use sensitive phones. On my CK2III with a gain of 4 I never get past 11 oclock with my grados, and usually it is around 10. I can't simply build a 2x gain beta because I just bought the HE5, for which I think I'll need a gain of at least 5x if not more. So I'd like a potentiometer that is accurate (or at least channel balanced) from end to end.

I have no problems with a stepper and it might be very nice, but I am worried about the step size on the low end as Beefy pointed out.

 

[boinger]

Its been a while since i did any work on my beta.. but im having some problems

I have to turn the volume up pretty high to get any sound... im using a joshua tree attenuator...

and when it is very low i here an extremely loud pop in my headphones before i can hear anything...

and there is also lots of sound distortion its not very clear.. also the volume in the right channel is almost non existent...

i have it setup as a test bed right now .. any idea where i should start ?

 

[MrMajestic2]

Quote:

Originally Posted by boinger /img/forum/go_quote.gif Its been a while since i did any work on my beta.. but im having some problems I have to turn the volume up pretty high to get any sound... im using a joshua tree attenuator... and when it is very low i here an extremely loud pop in my headphones before i can hear anything... and there is also lots of sound distortion its not very clear.. also the volume in the right channel is almost non existent... i have it setup as a test bed right now .. any idea where i should start ?

Make sure that the Joshua Tree is working like it should first.

 

[johnwmclean]

Check the psu, is the voltage right? If ok, then double check the wiring to the amp boards. Run each board through an initial check and see what you have.

 

[ShinyFalcon]

Make sure that your β22 hasn't malfunctioned. Lack of bass is a sign of high DC offset, popping from 0 -> low volume can be high DC offset, no sound might indicate a bad board.

To check your Tree, disconnect your tree and measure resistance from IL to OL, IR to OR, etc and make sure the resistances across (IL/OL) / (IR/OR) channels are the same as the volume goes up/down. Make sure OL, OR and OG are not shorted to each other.

If your heatsinks on your β22 are all equally warm, the β22 are probably fine assuming DC offset is low.