digital attenuator

[ujamerstand]

Well, yes - the Z-foil resistors with leads from (eg) Parts Connexion are $16 to $17 each. So the SM versions are likely to be about that too. But if this attenuator is to match up to the KG Blowtorch, it's gonna need some pretty fancy resistors.

I'll get a quote and see how nuts this option is likely to be.

That's about $1200 for 4 channels. It surely has to sound better than a quad RK50!

[kevin gilmore]

4PDT relays now discontinued. So the kgitsojc has to have significant changes

anyway. If i change the amplifiers to all surface mount only, the board can

be a bunch smaller.

The L.I.T.E attenuator with the silver resistors is also in the $1400 range.

Edited April 17, 2011 by kevin gilmore

[MASantos]

Surface mount is great as long as the resistors aren't the really tiny ones. Smaller board is always nicer.

[kevin gilmore]

None of the surface mount resistors i can find are less than 10 ohms

or more than 1 meg, so this limits the attenuator to a 25k or 50k version.

[luvdunhill]

None of the surface mount resistors i can find are less than 10 ohms

or more than 1 meg, so this limits the attenuator to a 25k or 50k version.

Look at current sensing resistors for the less than 10 ohm.

[Max]

None of the surface mount resistors i can find are less than 10 ohms

or more than 1 meg, so this limits the attenuator to a 25k or 50k version.

I had this problem too. I actually settled on 24K to get closest values using Vishay SMM0204 range of resistors from Mouser but I bet you US folks have a better range to choose from.

[Beefy]

Surface mount is great as long as the resistors aren't the really tiny ones.

I'll second this. I did 0805 resistors for Marc's PGA23** volume board, which was just manageable. 1206 as being discussed here is a touch bigger, which I would think would be ideal for most folks.

[kevin gilmore]

I could squeeze in thru hole resistors .4 inch holes.

The 2 inches would probably stay the same, but it would be

about .5 inches wider.

[MASantos]

I could squeeze in thru hole resistors .4 inch holes.

The 2 inches would probably stay the same, but it would be

about .5 inches wider.

I think that SMD resistors are much easier to work with since you don't have to be flipping the board and cutting the leads all the time.

Fine tweezers and a bit of practice and it's much faster than soldering through hole resistors. The smallest I did where 0506 and those were on the limit of size, but the 1206 ones are quite nice to work with.

[Craig Sawyers]

I've been talking to Charcroft, and asked them to quote for a set of Z-foil 10k attenuator resistors in either 2512 or 2010 size. There is a good chance that they can trim down to 6R34 and up to 169K. I've asked them to quote for one set, and ten sets.

Basically they hand trim to order in darkest Wales - they buy the basic chips from Vishay. Same game with the leaded Z-foils too.

I'll let you all know when I know the awful financial truth.

[luvdunhill]

I could squeeze in thru hole resistors .4 inch holes.

The 2 inches would probably stay the same, but it would be

about .5 inches wider.

careful about "solder stealing" if you add TH parts, since there is the possibility of these being machine assembled.

[Kerry]

Just got the pricing back on 4 & 6 layer boards:

130 pieces of the 4 layer design will come to $6.24 each.

130 pieces of the 6 layer design will come to $8.93 each.

Really just amazing to me. I'd be leaning to the 6 layer boards given the price, but I'm open.

[Beefy]

For the sake of a couple of bucks, might as well go the whole hog IMHO.

[ujamerstand]

The new 6 layer board already cost less than the original estimate. Might as well go with the one with better layout.

[Pars]

Do the other two layers actually buy you anything other than additional complexity and more opportunity for internal shorts?

BTW, regarding z-foils, etc., y'all be crazy...

[luvdunhill]

yes, impedance control.

[n_maher]

I respectfully suggest a small run of 10 boards for prototyping. With that many layers it'd almost impossible to fix a mistake manually.

[Craig Sawyers]

Do the other two layers actually buy you anything other than additional complexity and more opportunity for internal shorts?

BTW, regarding z-foils, etc., y'all be crazy...

The problem with multi-layer boards is not with shorts, but with imperfect through-hole plating to internal layers. So the problem is opens, not shorts.

The reason that the best possible resistors are important is that there are so many of the buggers in an R/2R ladder, and the number change as you adjust the volume. So yeah - it looks like financial madness, and probably only strictly necessary in the very best high resolution amps - but let's see what Charcroft come up with. At the end of the day this will be similar in cost to an RK50.

[kevin gilmore]

This should satisfy even the biggest whackjobs out there.

Had to add .1 inch so that it is now 2 x 5.1 inches.

3 different resistor sizes including the stupidly priced

thru hole resistors on .4 inch centers. Someone please check

this one thoroughly for errors.

I could probably increase the resistors to .5 inch with no

trouble, but they can't be more than .1 inch wide.

http://gilmore.chem.northwestern.edu/attenuatorsmt15.pdf

If you blow up the pdf to 400% it should display correctly.

(well at least on my screen)

edit: if you go with the thru hole resistors, and put

some of them on the bottom like you would with the smt ones,

then you can go to resistors that are up to .150 inch wide.

Edited April 18, 2011 by kevin gilmore

[MASantos]

The problem with multi-layer boards is not with shorts, but with imperfect through-hole plating to internal layers. So the problem is opens, not shorts.

The reason that the best possible resistors are important is that there are so many of the buggers in an R/2R ladder, and the number change as you adjust the volume. So yeah - it looks like financial madness, and probably only strictly necessary in the very best high resolution amps - but let's see what Charcroft come up with. At the end of the day this will be similar in cost to an RK50.

I'm not sure about others, but I am participating based on the estimate price of 88-108$, and even if it goes up to 150$ it's a good price for such a attenuator, but making them in the RK50 range would definitely put me out. I suspect some other folks would either cut down the number of assembled boards or just bail out.

While the z foils are the absolute best in terms of performance, will it really make a difference when the other resistors in the preamp circuit, power amp, etc are "of less quality"?

[Kerry]

Regarding manufacturing issues, here's the process.

We can get what's call a first article, before the full run of boards. This will allow us to build a board and make sure that everything works as we want.

I have an option of assembling myself or asking them to do it for us. It will cost for them to do it, but I also want to make sure that the assembly process is tested as well, so I'm leaning in this direction (I've already included this cost in my earlier pricing).

All boards will be electrically tested and is already included in the price above. They manufacture extra boards to make sure they can cover the fallout.

We'll have them assemble the boards (about 70 or so) based on a tested board and assembly. Even with this they are suggesting that there is a 1% - 3% fallout. We'll need to order some extra to cover this (again - already included in my earlier costs).

I agree that a 6 layer board is more complex, but I think we should be safe (though I don't have direct experience here). Regarding rework, I suppose it could make it more easy to damage the boards.

[luvdunhill]

Is the electrical test before or after assembly?

[Kerry]

Before assembly.

[Craig Sawyers]

I'm not sure about others, but I am participating based on the estimate price of 88-108$, and even if it goes up to 150$ it's a good price for such a attenuator, but making them in the RK50 range would definitely put me out. I suspect some other folks would either cut down the number of assembled boards or just bail out.

While the z foils are the absolute best in terms of performance, will it really make a difference when the other resistors in the preamp circuit, power amp, etc are "of less quality"?

I think that Kevin has made the board as flexible as possible for widest resistor choice. Regarding what resistors, I absolutely agree that the super-expensive ones will probably only be justified with equally high quality amps. Such as the T2 and KG Blowtorch clone to name two. So regular few cent metal film resistors are probably just hunky dory for the majority of applications. FWIW I've put myself in for two built ones and four bare boards - and I expect the built ones will be made with the resistors in the BOM - ie regular metal film. I will probably do something moderately crazy with the other four for the T2 or similar.

Edited April 18, 2011 by Craig Sawyers

[kevin gilmore]

The JFW step attenuators i have in all of my NMR's are 50 ohm, and

go all the way to about 800mhz. They have the red prp resistors in them

and the resistors are about $5 each in massive quantities. Lots

of resistors to pick from, anywhere from about 8 cents each to

about $20 each.