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Old 20th February 2011, 01:33 PM   #251
qusp is offline qusp  Australia
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yeah i mentioned those, imo they are te best option on the market at the moment when it comes to steppers. did you buy it direct or through pcx? pcx has the option of using zfoil shunt resistors which is cool, though easy enough to do yourself. so as you are se, you just went with a stereo model yes? shunt or series? and heres an interesting question, will you actually recieve the model you ordered? have they sorted their development phase out? i prefer the look of the old model, but this one is still very cool. i would be buying the shunt version and breaking out a few ASMP smd zfoils for the shunt resistors. at least from pcx they tell you what is in stock
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Old 20th February 2011, 01:50 PM   #252
opc is offline opc  Canada
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jdkJake,

That's exactly the stepped attenuator I was thinking of! They were from Poland, but I couldn't for the life of me remember what the name of the company was.

I think I'll actually be ordering one of those just to have around. They're beautifully made, and as you said, the more steps, the better with stepped attenuators.

I wonder if they would do a ladder type balanced attenuator with the 8-pole version?

Cheers,
Owen
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Old 20th February 2011, 02:32 PM   #253
IanAS is offline IanAS  England
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They have two resistors in the signal path.

That's one two many.

Plus doubling the copper track, solder, contacts.

In about 1996 I made one for a friend with just one series Vishay and a bunch of switched shunt resistors; Vishay VSH.

I used a Shallco switch I bought from Michael Percy. IIRC, guaranteed for 25 years, 2mOhms contact resistance, 10 amps. Solid silver alloy, not plated, silver greased.

I eventually found that even a switch that good was not good enough and I just used one single volume level with a Vishay series and shunt in the leads at the amplifier end.

Audio Synthesis used this Shallco switch in their 'Passion' passives.

I do have a volume control now, it's software I presume, in windows or in maybe the the CMedia DSP on the Auzentech PC sound card. It seems to have no degradation in sound quality. I have a 32 bit resampler that can be used as an adjunct to Winamp specially to set the volume, but with the system as it currently is, I can't tell any difference with it on or off.

Last edited by IanAS; 20th February 2011 at 02:59 PM.
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Old 20th February 2011, 11:34 PM   #254
jdkJake is offline jdkJake  United States
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Quote:
Originally Posted by qusp View Post
yeah i mentioned those, imo they are te best option on the market at the moment when it comes to steppers. did you buy it direct or through pcx? pcx has the option of using zfoil shunt resistors which is cool, though easy enough to do yourself. so as you are se, you just went with a stereo model yes? shunt or series? and heres an interesting question, will you actually recieve the model you ordered? have they sorted their development phase out? i prefer the look of the old model, but this one is still very cool. i would be buying the shunt version and breaking out a few ASMP smd zfoils for the shunt resistors. at least from pcx they tell you what is in stock
I bought it direct. Communications with Arek of Khozmo was excellent. He was very prompt answering email and answered all of my questions. I have not received the part yet, but, so far, the experience has been fine. Heck, I haven't received my "Wire" kit yet, so, I guess I will see who is faster; Canadian Post or Poland Post. For the record, Canada had a head start.

BTW, I specifically requested the SMD model shown on the web page I linked in my previous post. They still offer the other model, which, is far more configurable in terms of resistor-brand choices:

High Quality Audio & Industrial Attenuators

Again, I went with the SMD version as it felt more appropriate for this amp design. They will custom configure a part to your specifications, you just need to ask. It appears they build to order anyway, so, I cannot see it taking much longer unless any custom/unique parts have to be acquired. I went for the stereo version at 50K. It is a series resistor into a ladder shunt to determine the final attenuation value.

Quote:
Originally Posted by opc View Post
I wonder if they would do a ladder type balanced attenuator with the 8-pole version?
They might. Drop them an email. Arek is pretty easy to deal with and respond quickly (at least he did with me).

Quote:
Originally Posted by IanAS View Post
They have two resistors in the signal path.

That's one two many.

Plus doubling the copper track, solder, contacts.
Perhaps, but, I still need an attenuator for my intended use, so, this will have to do as a compromise. IMO, I think it is more appropriate than log or shunted linear pot, at least in terms of potential accuracy and channel matching. Since I am going single-ended, I might be able to get away by not populating R2/R5 and R8/R11. The series resistor of the attenuator could act as a surrogate for this position, thereby "eliminating" one of the resistors from the signal path. Too early to tell yet, I will have to play around a bit and see what works best.

Should be a interesting build regardless.
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Old 21st February 2011, 04:20 AM   #255
qusp is offline qusp  Australia
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actually i prefer the idea of the smd version anyway, shorter signal paths and all that. plus the asmp zfoils are actually cheaper than the leaded version and melf are easy to find and easy to replace. they really are very cool and if i needed a pot i would be getting one of them. i may look into them for my daox or circlotron, plus they are just so god damn sexy
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Old 22nd February 2011, 02:05 AM   #256
qusp is offline qusp  Australia
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so opc, does the tab on the buffer need t be soldered to the board? or will silver epoxy, or just contact with the 'heatsink' be enough? because i was thinking of tinning the pad lightly and then heating the tab to try and solder it there. is this how it works in your board? i have always had a small amount of overhang to solder it to.
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Old 22nd February 2011, 04:52 AM   #257
L-Train is offline L-Train  Canada
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When I built mine, tinning the pad lightly and heating the tab is exactly how I did it. Here's the technique I used to solder the buffer tab:

1) Apply flux to the PCB and lightly tin the entire pad, leaving a slightly elevated "bump" or "ridge" of solder at the top of the pad. This will be useful later to determine that the solder underneath the buffer has melted when we're soldering the tab. Apply more flux to the pad.

2) Apply flux to the back of the LME49600 buffer, but do not tin it (I didn't, at least). Carefully place the buffer on top of the pad, making sure you give yourself enough room at the bottom of the buffer's 5 pins to apply solder to both the pad and the pin later on. The buffer should be raised off of the PCB slightly (a fraction of a millimeter) near the top of the tab due to the solder "ridge" we made.

3) Using a chisel tip on your iron, set your soldering station to 375C and overflow the tip with solder. Put pressure on top of the buffer with a pair of tweezers to hold it down. Place the chisel tip flat-face down on the PCB right above the buffer such that the side of the tip is in contact with the top edge of the buffer's tab. Slowly run the side of the tip "up and down" the top edge of the tab to heat it up to the solder's melting point. After ~5 seconds or so the buffer should "drop" oh so very slightly, and it's at this point that we know that the solder underneath the tab has melted. Keep running the iron against the tab for ~1-2 more seconds to make sure all of the solder underneath has melted, then remove the soldering iron. Remove pressure from the top of the buffer once you give enough time for the solder to solidify.

One more tip for builders: I found it much easier to solder the components in the order of resistors, op-amps, then ceramic bypass capacitors. The height of those caps gets in the way of soldering the op-amps precisely, but if you solder them afterward they are generally placed on the outside, giving your iron much more room.

Hope this helps!
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Old 22nd February 2011, 06:19 AM   #258
qusp is offline qusp  Australia
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yeah technique is fine, have done with other components, nice post though. i agree as with anything smd that doesnt have a stuffing order specifically given for testing is simply smallest to largest components. sometimes i have struck boards that will have a through hole under the pad that needs to be tinned and then soldered from the other side of the board.

Last edited by qusp; 22nd February 2011 at 06:22 AM.
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Old 22nd February 2011, 03:28 PM   #259
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I am yet to receive my kit.
Is anyone else still waiting?

=/
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Old 22nd February 2011, 07:08 PM   #260
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I too, am still waiting for my boards to come in. patience is a virtue!
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