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Stepped Attenuator for 32.5

D

dspatterson

pfm Member
Hi, how difficult is it to install a ready built stepped attenuator, the one i have seen is 10K whereas the Nac 32.5 one is 20k. Is it just a case of soldering line in and out for both the channels.I would fit it into what is the selector socket side so loads of space behind.Does it need to be wired in between the 729output and the 321 input. The alps has 6 pins, can someone explain.


Thanks
David
 
Hi Neil, i cant see the full pic of the attenuator, rodderstein i think,to see the connection, do you recon it will be fairly simple and is 10k OK.

David
 
David , you might consider a Noble potentiometer as , I think it was Mr Tibbs, compared one to a stepped attenuator and considered the Noble pot just as good. Have a look on Hifi Collective.
 
Yeh, I hear the nobles are pretty good too - must get hold of a couple.

But Dave, if you go ahead the pot should be supplied with a wiring diagram. It's then pretty easy to trace the tracks on the 32 motherboard back to the points of origin, i.e., Ch 1 and Ch 2, In, out and ground. Simple link wires from the pot to the board will do the job.

You'll need to do that on the Noble too since I believe they are different spacings to the Alps.
 
indeed , the noble will need some short flying leads , but the pins on them correspond to the ones on the Naim mother board , ie if they could reach they would drop in.
 
I hope dspatterson does not mind me cutting in here.:)
Back n the mid 90,s I had intended upgrading my 32.5's volume pot. At that time the best replacement was supposed to be a Sfernice 100k linear pot (model PII)with a "law faking resistor". This was purchased from Russ Andrews but not available anymore as far as I know.
As I am intent on building my own 32.5 clone what is now best practice for this part? I have already got the Sfernice pot etc. But I still would like to know if this is still the best option? Anybody out there with experience of the differences in sound quality produced with the various different options now available?
Frank
 
OK so if i go for the Noble, options are 10K and 25K, what difference does the 10to 25 make is it the rate of volume inc to dial movement, which would be best (more scope on the volume control would be welcome)

david
 
Yes....go for the 25k as the 10k will give you little control @ low volumes.


DubbLinn said:
I have already got the Sfernice pot etc. But I still would like to know if this is still the best option?
Frank
Click to expand...

Difficult to beat.............so you might as well use it.

Paul.
 
Here is some example:

P9200246_s-1.jpg


This is a shunt stepped attenuator with Grayhill rotary switch like this:
42265462.jpg


You'll need to find the 12 positions, two poles, make before break variant (try in Ebay). some example from Farnell for the one pole switch:

http://il.farnell.com/4144557/electrical-circuit-protection/product.us0?sku=grayhill-71ad30-02-1-ajn

I use 15K Caddock for the Shunt position and 12 Holco resistors for the divider. Values depends at the sensitivity of the loudspeaker in use. (Since you can not use all the volume range with 12 steps). keep some 2.5db steps from the middle of the volume scale (lower volumes positions down to say -55 db you can use 4db steps).
I can send you an Excel file with the resistors and formulas.
This Grayhill switch is very small and can put easily in the NAC32/72. I use it for some years and it is very solid. some changes to the sound character can done easily by selecting other resistors.

Avi
 
zener said:
indeed , the noble will need some short flying leads , but the pins on them correspond to the ones on the Naim mother board , ie if they could reach they would drop in.
Click to expand...

This wasn't exactly true of the one i fitted last week to a 72. The pin layout is correct but the spacing is slightly different. It wouldn't drop in even if the pins were the correct length - it did sound good though.
 
Mine is a DACT CT-2. When I still had the motherboard I had to make up flying leads, but no more motherboard, so output of 729 to input of attenuator, then output to 321. Both grounds run to star ground point.

Colin
 
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