Cannot speak to interest, but here are the ones I'd use:

http://www.cardas.com/images/oem/PDF_DRAWINGS/GRFADBLPRT.pdf

not an engineering drawing. pretty much useless to lay out the board with.

why those morons can't post something useful is beyond me. When i asked,

i never got the engineering drawing. Measure and post please.

more editing, switched to the dip version of the lme49720 so that there

is less surface mount work required.

http://gilmore.chem....inputboard4.jpg

approximate pricing

lme49600 need 4 for balanced stereo $10.50 ea

lme49720 need 4 for balanced stereo $3.08 each (dip)

opa1632 need 2 for balanced stereo $5.88 ea

nc3fdh xlr male need 14 for balanced stereo $4.52 each (probably cheaper)

nc3mdh xlr female need 4 for balanced stereo $5.55 ea

ds2e-sl2-12v relays need 16 for balanced stereo $6.37 ea (digikey)

overpriced boards at $37.50 each in quantities of 10 (lil-knight is going to be much cheaper)

so about $375 plus resistors plus power supply plus chassis plus plus plus.

RK50 (don't ask)

my step attenuator (i don't remember how much)

arduino (cheap)

...

Edited November 26, 201114 yr by kevin gilmore

The 4CP TKD pots aren't that expensive and there is always the Alpha.

Yea the rk50 is up to 700 these days... There is also khozmo - a bit more expensive than a DACT at 289 (259 for smd version) but 48 steps instead of 24

KG attenuator FTW.

<snip>

Still think that when you need unbalanced inputs, you use the neutrik converters.

What neutriks are these?

these

http://www.mouser.com/ProductDetail/Neutrik/NA2MPMF/?qs=sGAEpiMZZMtUKTCHc2CNRBaiw9SrxpJs

and these

http://www.mouser.com/ProductDetail/Neutrik/NA2FPMF/?qs=sGAEpiMZZMtUKTCHc2CNRAvIKttWysf6

All these do is ground pin 3 so custom cables are easy to make. I made one for the T2 before I went and defiled the chassis with a range of connectors and a switch...

approximate pricing

lme49600 need 4 for balanced stereo $10.50 ea

lme49720 need 4 for balanced stereo $3.08 each (dip)

opa1632 need 2 for balanced stereo $5.88 ea

nc3fdh xlr male need 14 for balanced stereo $4.52 each (probably cheaper)

nc3mdh xlr female need 4 for balanced stereo $5.55 ea

ds2e-sl2-12v relays need 16 for balanced stereo $6.37 ea (digikey)

overpriced boards at $37.50 each in quantities of 10 (lil-knight is going to be much cheaper)

so about $375 plus resistors plus power supply plus chassis plus plus plus.

Cost is not prohibitive, IMHO, for a preamp of this class, just as long as someone doesn't go wild on exotic parts and connectors.

Neutriks are just fine, for example, but I'm sure there are people who'll find them "not hi-end enough" for them.

Judging by the attenuator, I think there'll be enough interest for a GB, thus making pricing even more attractive.

Will we be able to see measurements etc of the finished product?

The test setup already does distortion levels way lower than my 30+ year old measurement system.

That is not the point, i can take an lm741 and put oodles of feedback around it and measure .001%.

Still sounds like crap. Its the rise time, symetrical slew rates, overshoot, and all those other things

that make something sound good or not. These newer chips with real complementary silicon processses

really do sound great.

The quality of the resistors in the audio path is going to need to be of very high quality. I see that

Susumu .1% resistors are now available cheap, i'm going to have to listen to those. To maintain

the CMRR on the input stage is going to require very close matching of the resistors.

Probably a couple of months away from circuit boards. Then again, maybe sooner. Lil-knight is

going to have to do the boards, locally, the prices are way out of line, and the sales tax is also

way out of line.

As far as i know there are no better board mount xlr connectors made, regardless of price.

Everyone uses the neutrik.

The IRC RC55LF's at Mouser could work for through hole resistors. I'm sure some Vishay's will work as well.

Crazy audiophiles may think Neutrik isn't the best but they are just idiots.

Are there any comparable 5V relays? Seems like it would be better to have only 1 digital power supply and then the +/- 15 analog supply

This seems to be the same thing with a 5V coil, no?

http://search.digikey.com/scripts/DkSearch/dksus.dll?WT.z_header=search_go&lang=en&site=us&keywords=DS2E-SL2-DC5V&x=0&y=0

Yep, works fine with the dual coil latching 5 volt versions.

Hmm I guess the attenuator board uses 12V relays anyway so if you use that a 12V power supply is necessary anyway

Susumu are great. So are Neutrik.

I use the latter in all my builds and I really like the fact that they have the same D-Type cut-out for all sorts of connectors (RCA, XLR, RJ45, HDMI, BNC, you name it...).

People who'll be using the standard build (which includes the on-board Neutriks) could actually benefit from a real panel GB as well... I don't see much room for customization anyway and the tolerances will be minimal..

Hardest part will be agreeing on a case.

Thread has been quiet for a while. Any new news or developments?

need to check over the board one more time, then its probably ready to be made.

I was spending more time on the black hole

Sorry if this has been mentioned before but will there be an option (or an easy mod even) to allow for one of the preamp's inputs to be switched to "direct mode" (aka linked to the output without intervention of preamp/volume etc)?

i'm already using 8 bits for the relays, so the direct option is not going to happen

via hardware. Via software its easy, just pick the input, set the attenuator

for no resulting gain...

Thank you.

If there is no room on arduino to control an extra relay, it'll either have to be done manually (via switch - which will kinda ruin this elegant design) or via the way you propose.

I'm not interested in HC stuff but sometimes I listen with my DAC directly on my power amp. It'd be nice not having to stand up and fiddle with cables etc.

need to check over the board one more time, then its probably ready to be made.

I was spending more time on the black hole

That's great news. I'm in the need for a good balanced preamp, and this baby would fit the bill perfect.

What do you have in mind for the power supply?

Digital power supplies won't be too important, I was imagining two 78xx supplies for the digital stuff (7805 and 7812) or maybe dual lm317s. You are going to want something nice for the analog side though. I think KG mentioned using the dynahi ps somewhere, but I was also thinking amb's sigma22 would be a good option.

I was considering Sigma22 as well or even Salas shunts if current consumption is not too high but I'll wait for KGs recommendations.

lil-knight has the board files now, we are going to do a prototype board run to make sure

everything is perfect. Same thing with the black hole.

Sweet! I'm excited about this one.