Page 3 of 5

Re: T Attenuator Termination Kluge

Posted: Fri Aug 02, 2019 11:48 am
by JR.
How much difference does 44 ohm make?

Clearly 700 ohm is unacceptable, but 30-45 ohm may be OK?

JR

Re: T Attenuator Termination Kluge

Posted: Fri Aug 02, 2019 12:35 pm
by mediatechnology
Paul -

Rather than adjust it at the top-most position try adjusting it at the lowest, -∞ attenuation.
If you can get <2-3Ω on the bottom end and 30-40Ω, at the top, the top "hop-off" is pretty low relative to the wiper to ground resistance value which is the element value. (Was it 10K?).

If Rhoptop is 40Ω and the element value below it is 10KΩ then the tracking error, at the top, is very small. (0.035 dB; 0.4%).
If Rhopbottom is 40Ω then the attenuation at the bottom stop is only 48 dB.
Optimize the wiper angular adjustment for the bottom.
You should be able to get 2-3Ω if not better at the bottom or something is broken.

Re: T Attenuator Termination Kluge

Posted: Fri Aug 02, 2019 2:39 pm
by Gold
I have the fader after the bridged T attenuator. 30-40 ohms is throwing off the termination and therefore the gain steps. I could put the fader before the bridged T attenuator. I suppose 40 ohms is a low enough source impedance not to cause problems.

I just got some more documentation it says the top of the throw should be “0dB attenuation” but gives no resistance value or range. I think P&G thinks this is normal. I’m not spending anymore time on these pieces of shit. They were only like $600 each. I’m waiting for a TKD quote.

Re: T Attenuator Termination Kluge

Posted: Tue Aug 06, 2019 11:18 am
by Gold
I got a quote of $145 each for three 4 channel TKD 2500 attenuators. I only need two but I suppose a spare is okay. Maybe a minimum order type thing. It's round about $500. I payed more for one RF15 so I'm not complaining. This price includes a custom version. I asked for a single detent at the fully clockwise position to aid in level calibration. These pots will only be used for fades. Not level adjusting.

Re: T Attenuator Termination Kluge

Posted: Tue Aug 06, 2019 11:21 am
by mediatechnology
$145 seems like a very fair price.

Re: T Attenuator Termination Kluge

Posted: Tue Aug 06, 2019 11:31 am
by Gold
My experience with TKD 2500 series has been great. I used them for the Dual Class A headphone amp. They are better than the RF15 in every respect except maybe look and feel. The RF15's feel really expensive. They usually elicit oohs and ahhs from anyone who touches them.

Re: T Attenuator Termination Kluge

Posted: Mon Aug 12, 2019 10:32 am
by Gold
The TKD pots are on the way. It’s a 30 day lead time. Now I have to figure out what to do with the RF15’s. I think they may be manufacturing bad mojo. Bad mojo drops off according to the inverse square law but is still too much.

Re: T Attenuator Termination Kluge

Posted: Mon Aug 12, 2019 2:27 pm
by mediatechnology
Gold wrote:
Mon Aug 12, 2019 10:32 am
Bad mojo drops off according to the inverse square law but is still too much.
+1. Well put.

Re: T Attenuator Termination Kluge

Posted: Mon Oct 07, 2019 12:01 pm
by Gold
The TKD pots arrived today. Teeth clenched, wish me luck.

Re: T Attenuator Termination Kluge

Posted: Mon Oct 07, 2019 3:16 pm
by Gold
Although the invoice said there was a detent at the fully CW position there wasn't. It's frustrating but I think I'll keep them. The series resistance of these are all between 12Ω and 14Ω. That's much better.

On the spec sheet it says Max Attenuation 50dB and Cutoff Better Than 80dB. At the fully CCW position I'm getting 56dB attenuation. I was hoping I'd have more like 80dB attenuation at the fully CCW position. I tried a few different grounding schemes with no change.

I have an unbalanced Out from the Dingo board feeding the 5K bridged T attenuator. The output of the T Attenuator feeds the TKD pot. The output of the TKd pot returns to the unbalanced in of the Dingo. The unbalanced input is terminated with a 5K resistor.

Should I be able to get more than Max Attenuation spec at the fully CCW position?