which TKD faders for Soundcraft Sapphyre?

[alia]

I have to replace some faders on my Soundcraft Sapphyre and ready to order the TKD faders, but not sure which series to buy - 6000, 7000 or 9000. Basic specifications are the same. Any ideas?

[alia]

Anyone use tkd faders? Which series?

[nid]

I'm posting here because we have a relevant issue. To answer the question of which TKD model, Jim Williams had advised us to get the CP7101 faders.

To our problem now... we just got 34 Log faders and it seems we should have got Linear... I'm at a loss of what can be done now. Not even the unity point is correct and the attenuation is much much faster. Does anyone know about circuit modifications so that a Log taper can work with the same behavior as the old (Linear as it turns out) fader did??? I could post schematics if needed.

thanx!
NICK

[brianroth]

A schematic would be handy.

Best,

Bri

[nid]

As it turned out, the old faders are also LOG. The thing is that the tapers of the old Alps carbon faders and the new CP faders of TKD are a bit different. The new bunch is still in the box and we try to see if there is a way to line them up correctly (which seems unlikely, unless it can be done electronically by a circuit mod) or send them back and find other ones.

Trouble for no reason... a lesson for anyone planning to upgrade old faders on their desk.

I wonder, has anyone ever replaced faders with different taper and then somehow repainted the marking on the desk? Or use some kind of sticker on every strip?...

[brianroth]

You can make some minor modifications to the taper of any pot by adding resistor(s) that "pull up" the wiper to the input/high side of the pot, or adding R from the wiper to the ground/low side of the pot.

Otherwise, you might have to concoct some sort of panel overlay with the correct markings.

Best,

Bri

[nid]

The unity position with the new faders is about 4dB higher than the original position. Do you think it's possible by mod to "move" it that much lower? Don't forget it's already 10dB from top. I'll scan the schematic tomorrow so you can see what's going on with the original circuit. Thanks!

[brianroth]

You should be able to "pull down" the levels by 4 dB with a resistor between the wiper and the low/ground side of the pot. Now, how that impacts the attenuation "law" along the rest of the pot's travel is unknown.

I noticed that TKD's docs included "X dB attenuation at X mm" along the stroke:

http://www.tkd-corp.com/02_products/...1_cpa-7101.pdf

I'm assuming that is with the wiper being loaded into a relative high-Z buffer, although there is no indication of their test setup's loading. But, by studying that drawing and comparing it to the scale of the original pot you might be able to see how far off everything is.

Best,

Bri

[nid]

I attached the schematic.

[nid]

There is a 104.2mm version of the TKD faders that is close to the law we need. It is CPA7201. But can a 100mm fader be replaced with a 104.2mm fader?

Why are there two types in the first place anyway??? I guess there is some historical explanation for this... like for so many other stupid variances in this world.

[brianroth]

Originally Posted by nid

I attached the schematic.

You can "play" with the value of R100 (47k) to see if you can "tug" the taper of the slidewire to a point that is satisfactory. Decreasing the value "pulls down" the "wiper position".

Best,

Bri

[JohnRoberts]

Deja vu... I wouldn't expect to get dramatically different answers here.

re: 104mm I doubt somebody would manufacture a "100mm" fader that wouldn't fit in all the 100mm console channels applications out there, but if they can't get the taper right who knows.

If you have one in hand, try it... if it doesn't fit it will be pretty obvious.

JR

[nid]

OK we got one 104.2mm fader as a sample and it fits exactly in the slot. Also the taper is very close to the old Alps taper. So we'll go ahead replacing the whole desk with this type of faders. The model number is CPA-7201.