[doobooloo]

Hmm...

The ebay seller asked for my eBay name and when I emailed it to him he hasn't replied yet...

In the meanwhile, BrianGT of diyAudio is organizing a group buy on the Series R Elma ladder attenuator - and he says the entire attenuator will cost less than $90 with resistors!

What a deal! Here are two images he posted:

I have signed up for one of these units...

[edit]

Link to thread: http://www.diyaudio.com/forums/showt...5&pagenumber=1

 

[morsel]

A word of warning about that design: It appears heinous to assemble, with no room for error, as one would be hard pressed to get it apart again once soldered. While they are slightly less cool looking and more bulky, ladder attenuators without captive resistors are more readily serviceable.

I like the concept of ladder attenuators, but the Elma or HeadRoom series attenuators with SMD resistors have a short signal path, are less complex, and replacing a resistor or two is not so bad.

 

[doobooloo]

But, the question is, how often would I need to replace resistors once assembled successfully?

I guess there is a risk of putting a wrong resistor in during assembly and realizing only after I've soldered everything in, but I think the chances of that are rather low...

 

[morsel]

You may find you want to rescale the dB steps someday. And anyone can make the mistake of putting in the wrong resistor. It happens to the best of us.

Moderators, there is a bug in the web forum software that is mangling the URL for the Elma series attenuator in my previous post by inserting a <BR> in the middle of it.

 

[JohnFerrier]

Agree: tedious amount of soldering. Not for everyone. Make sure they go in the right order. Check twice, solder once. "Voodoochile" spent 7 hours assembling his. I think he bettered my time by a few hours. I assembled mine yesterday...finished 2:00am this morning.
Voodoo's thread: http://www4.head-fi.org/forums/showt...threadid=60553

Disagree: short signal path. Sounded good when I read that several months ago, but thinking about it now, not sure what the benefit is. These are resistors. Inductance of any extra lead length is on the order of micro-henrys and lead capacitance will be lower than 1pF. As far as resistance, the most important aspect is that they match left and right...so if the leads are the same... Not sure why someone would need to replace SMT resistors...not a wide selection with similiar form...

Holco resistors are nice, though probably hard to find all values with old stock values (OS supposively equals non-ferrous end caps). Old stock parts have thicker leads. New stock parts seem to be more accurate. I imagine Roederstein parts would be very good too.

Grayhills: no news.


JF

 

[morsel]

Quote:

Not sure why someone would need to replace a SMT resistor...

As I said, you may want to rescale the dB steps someday. I was not suggesting "boutique" SMT resistors. See you in 3 weeks, I'm going out of town and will not have much Internet access.

 

[JohnFerrier]

Agree: there probably are cases that the scaling is not perfect. Guess a person should try to get the db scale right the first time. However, it not easy to know in advance what all the requirements are...

Enjoy time away.


JF

 

[doobooloo]

The difference between the Elma switch Voodoochile used and the one pictured above is that the PCB board on the one above is specifically designed to be for a ladder audio attenuator, so I assume it's really just plug-and-solder sort of a deal... Should be a little easier to put together.

 

[Voodoochile]

The switch I used was purpose-built for a ladder attenuator by Elma. Even the shorting contacts are a different bounceless design than their normal shorting contact, to avoid any bounce-induced clicking while turning. Also, there is an extra wiperless deck that serves as the common ground between the two channels, between the in and out decks for both channels.

From left to right, the decks are like this:
Left in, left out, left & right signal ground, right out, right in. In the picture linked above, you can see four decks with wipers and one in the center without. That extra deck actually made assembly easier, I thought, keeping you limited to one layer of resistors. I see the common ground ring on your PCB deck, which is cool, but the thought of threading those resistors into that narrow space in two layers makes me a little buggy. My hands and fingers are just too big I guess!

As for assembly time, I mainly depends on how fastidious you are with parts matching, sorting, getting organized, lead forming as needed... the actual soldering is maybe a couple hours. I would select the part, make sure it was the proper value, confirm the location, the reconfirm everything

.
I wanted to be darn sure I was not desoldering and swapping any of these Holcos after assembly.

 

[doobooloo]

Ah - I apologize! I didn't know that yours was specifically designed to be an audio attenuator.

Anyhow, how easy is it to take the decks apart? The thing is, I'm wondering how I can get the resistors in place on the PCB design if I can't somehow take the thing apart...

 

[Voodoochile]

I don't know if it is easily disassembled or if it assembled with the idea that it will not be taken apart again. I would probably make a big difference in assembly time. Then again, pre-inserting all the resistors, then trying to get them all to align with the holes in the next deck might be trouble, too.

Perhaps sliding the end (the end away from the knob) further into the rear deck to clear the front lead end, then swinging the resistor into place and sliding it back towards the knob end to insert the forward lead into the forward deck would work. Careful pre-trimming of the leads needed, but ought to go pretty well. Certainly the outer layer would go well.

 

[Super-Gonzo]

Quote:

Originally posted by doobooloo In the meanwhile, BrianGT of diyAudio is organizing a group buy on the Series R Elma ladder attenuator - and he says the entire attenuator will cost less than $90 with resistors!...

I signed up for one of these switches as well. Too bad the resistor kit he's making isn't 50k... it would be nice to not have to go to the trouble of ordering the resistors myself.

 

[JohnFerrier]

FWIW: Elma switches are not make before break (as someone previously indicated) and can make a slight clicking sound between positions. Make before break would be kind of odd anyway as the impedance would be changing up and down. Regardless, nothing annoying with the Elma switches.


JF