I initially opted for an RK27 for my Dynalo build but as the build progressed I found an early revision Joshua Tree for 60$ that needed repairs. There was a subtle change in detail and maybe it sounded a tiny bit less lush. Most likely due to the impedance change "seen" by the DAC output. The resistors used in the relay board were regular 1%'ers.

There's no doubt that setting up a relay board is a bit of a hassle as it takes up a lot of enclosure space (2 pcbs + transformer), but in my opinion it's hard to get shorter signal path with regular potentiometers. There's also the issue of noise when the relays are clacking but I usually can't hear it through the music. I once saw a surround system preamp with five or more of these boards... It must sound like a machine gun range. There is, however one thing that I consider a big plus for relay based attenuators- they purr when you have DC coming from DAC outputs. When you have zero DC input you most likely won't hear a thing when adjusting volume (save for the steps when all the relays switch), but when I had 0.5VDC coming from my DAC due to misadjusted output buffers there was a distinct motorcycle sound/purr. Good for me that I had DC servo on my amp!

I also highly regard quality digital attenuation as found on Buffalo and other DACs, very convenient in my opinion. If I'd knew I settled for such a DAC I'd surely build my future headphone amps without any attenuators to keep shorter signal path. Heck, my Dynalo has preamp output that can be switched from passive to active! I might build a simple tube amp without an attenuator just for the kicks!

I also know that there used to be this Lightspeed attenuator project at DIYA. I remain skeptical about it because optical resistors do have noise characteristics among other things that are not superior to quality regular resistors. Also the guy who proposed the Lightspeed attenuator said that there is a diode effect in potentiometers where wiper touches the conductive material. I also have a hard time buying this.

Mike, are those offered in 4 chan versions?

I was poking around the web site after Mike posted it... seems you can create a custom pot.  I wonder how over the top you could go with these guys?

Damn! I came here to recommend the BBC Documentary "The Evil Weed"

From that pic, still not seeing how it's built better than the RK50  The RK50 is completely potted, and I'm seeing a set of screws on the Spec to hold it together. One thing that would get a lot more people interested in Spec is if they offer higher than 10k/20k input Z. I think P&G only offer 10k

If you must have something "now" the US dealer for P&G minimum purchase quantity is 2. I've played with the RK50 and RF15, and I would never pay RK50 prices again (even the "deal" at $580 is not so great in comparison). The P&G is similar to the RK50 in that it continues max attenuation a bit past 7 o'clock so there isn't imbalance even with the most sensitive headphones. The other thing is longevity is a well known with P&G; there is British professional gear from 40 or 50 years ago using their faders that still work.

Quote from: n3rdling on February 10, 2013, 09:58:28 AM

Mike, are those offered in 4 chan versions?

I was poking around the web site after Mike posted it... seems you can create a custom pot.  I wonder how over the top you could go with these guys?

Check out their clients.  They'll build anything you want as long as you buy enough of them.

From that pic, still not seeing how it's built better than the RK50  The RK50 is completely potted, and I'm seeing a set of screws on the Spec to hold it together. One thing that would get a lot more people interested in Spec is if they offer higher than 10k/20k input Z. I think P&G only offer 10k

The picture doesn't do it justice, I what's on the inside would matter more.     Like I said, it's a custom spec'd sample unit and Spectrum wouldn't let us keep it or buy it off them.