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FS: T-PAD attenuator 600ohm from Avdo!

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I too am confused about what you are doing Ian.  Is it loaded 600 ohms resistive?  That makes an enormous difference in the attenuation amount for given rotation. 

You want 200 instead of 800 at the half point, connect the - leg to the opposite end.  Right?  What am I missing?  The throw is going to be off for any made with off the shelf wafer tapers. 

Perhaps someone has one of these and a Hairball/CAPI and can compare 50% rotation resistances. 

If you want a true T-pad, vintage used is the only option in a continual rotation part. 


 
OK, I see there is some confusion. I am feeding it from a transformer output and loading it with a bridging input. So the driving impedance is relatively low and the load impedance is relatively high. Even loaded with 600 ohms, the attenuation is only 6dB at the mid point because the 1K pot is effectively a rev log.

Cheers

Ian
 
Ian,
The task was to achieve a smooth attenuation of the signal.
This makes it. I really don't understand why you decided that half of it should be how many decibels!?
I think for the price it works quite well! Maybe his work doesn't meet your any desires!
The most important thing in his work is that he not spoil the sound!

Thanks!
 
avdo said:
Ian,
The task was to achieve a smooth attenuation of the signal.

That is what I am saying. It does not achieve a smooth attenuation of signal. In the first half turn you get only 6dB of attenuation. Normal attenuators will give you 14dB to 20dB of attenuation at the mid point.

Also, I think the reason is that the 1K log pot has been fitted in backwards so it operates like a reverse log pot. I am suggesting there has been an assembly error.

Cheers

Ian
 
Ian,
Can you show how do you do this test?

I don't see this when I use it. May be, if you used others T-Pad, may be there is the same about you tell!
You want to tell that I need to flip 1K resistor?

Thanks!
 
avdo said:
Ian,
Can you show how do you do this test?

Attached is a schematic of your T pad at the mid point. R1 and R2 are the two 500ohm pots, each at 250 ohms. R3 is the 1K pot which measures 800 ohms at the mid point. R4 is the 600 ohm load. V1 is the source signal which has a source impedance of 150 ohms. Under these conditions, the attenuation is only 7dB. If the 1K pot was a proper LOG type it would be 200 ohms at the mid point. This gives an attenuation of 11dB at the mid point. This is still too little in my view but it is better than 7dB.

Now, my only assumption is that with the control fully clockwise, you want no attenuation and you want the attenuation to increase and the signal to decrease as you turn it anti-clockwise.

Cheers

Ian

P.S. and if the log pot is 100 ohms at the mid point, which is what I would consider to be normal, the attenuation at the mid point is 14dB which is about right for audio use.
 

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Ian,
I have tested T-Pat from CAPI,
It not has the same characteristics that you write here.
I can't understand what do you use for testing.
When I did it, I used t-pad calculator. All steps we checked and created a table.
I had 3 times of t-pad, checked all this, and choosed last t-pad.
I use it, my friends use it. And we don't have any problems with this!

If you some special t-pad, that you want, we can produce it for you. Are you realy planing to buy it?

Thanks!
 
What Ian says makes sense, mechanically. Look at the pictures. The middle wafer (assuming it to be 1k) is physically reversed in relation to the other two. If someone spec'd a 1k log, and then it was flipped over, wouldn't that make a rev log?
 
thanks. Can you confirm that the middle wafer is in fact a true Log Taper.

At 50% rotation, a 1K Log taper will measure 10% of total resistance, i.e. 100 Ohms.

with +/-20% tolerance, your part should measure between 80 Ohms and 120 Ohms.

is this the case?

Also (attached is a 'generic' taper graph.)

is it possible to post a similar graph using your new part?
 

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envelope said:
thanks. Can you confirm that the middle wafer is in fact a true Log Taper.

At 50% rotation, a 1K Log taper will measure 10% of total resistance, i.e. 100 Ohms.

with +/-20% tolerance, your part should measure between 80 Ohms and 120 Ohms.

is this the case?

Also (attached is a 'generic' taper graph.)

is it possible to post a similar graph using your new part?

I think I can do this,

We use this
57038-220116160438.gif


Thanks!
 
Guys, Hello again everybody!
I pulled a few pieces out of the box, last order. Checked. All upside-down resistor 1K!!!!
I compared them with the first resistors that I currently use.
They are different!
Ian was right! Ian, please, sorry me! I am testing your and don't understand what he's telling me! My all from old order work well! All I sent you was from one of the box! I have not tested, could not even think about what might happen!
I am very sorry!
Don't worry! I will contact the factory and find out why it happened! Tomorrow all write!
I hope we can decide it in the coming days, I will send to all new resistors!

Thanks! Will inform you soon!

PS. Ian, please, sorry me!!! And thanks to you a lot!
 
Ian, thanks!!!
I will check it at first, when I decide this!
I will send to you again how many do you need!

Please, sorry! I am very not pleased that I did!
 
avdo said:
Ian, thanks!!!
I will check it at first, when I decide this!
I will send to you again how many do you need!

Please, sorry! I am very not pleased that I did!

Do not worry about it. Life is too short. I just tried to take one apart hoping I might be able to reverse the 1K part but the shaft is permanently fixed to the last 500R pot so this is not possible.

Just send me a couple of the correct ones.

Cheers

Ian
 
Side note:

If you could make these with a smaller shaft diameter, I'd buy a bunch of them.
 
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