My Passive Pre

[pre65]

Hi-try this-----

http://wduk.worldomain.net/forum/showthread.php?t=198




Philip

[Richard]

Yes, this is how it works,



Your stepper may work in place of the pot; it has in, out, and ground so invert it, like the pot here, and draw it out with values for each step to see what the input and output impedances will end up at. Then compare them with my advice re sources in the previous post.

If it works electrically you can then start trying different resistors etc for sound quality but you'll be stuck with the Dale resistors for the ground connection which may be the problem. The combination I liked most was Philips metalfilm for the series resistor and carbon film for the ground resistor (= Alps blue pot). Using a metal film pot or conductive plastic type (Panasonic, Omega) was too bright and hard and a cheapo carbon (Alpha) warmer but gritty/rough.

Rich

[pre65]

Hi-i use a shunted stepper in Pre 3.

Wired as per diagram.



Philip

[Greg.]

I believe (but happy to be corrected) that the Vishay dale R's are carbon. If so, they should be fine for signal grounding and the selection of something better as suggested for the actual signal should work well. The Phillips as sold by Maplin are good as are the Welwyn precision R55Y series sold by RS and Farnell These have the benefit of close tolerance matching. You can then go boutique but it'll start to cost (still pennies though). Certainly, the signal resistors need to be anything other than carbon which will produce a dull sound. Having said that, a boutique carbon has more life than a standard one and might be acceptable, but in general I'd recommend concentrating on the metal film option.

[Malka07]

Well i have done alot of reading on Psuedo Shunt...and now have a throbbing headache...but i think i am beginning to understand it.

Am i correct in thinking that the series R takes the signal to the amp and bypasses the pot/attenuator, the pot itself shunts some of the signal to ground thus achieving a level of volume that you want? This way there is only ever 1 resistor (per channel) in the signal path...and good quality Resistors can be used here.

If this is the case, then im definetely going to try this mod.
Maybe even test a few different resistors.

My only concern is that the dale attenuator i have is a 100k version, since i am using a cdplayer with 50ohm output and kat34 with 300mv input sensitivity, will i have a problem? as the faqs and a few members have stated that a 20k or 50k would be better with cd player???

Thanks again for all your help. I am hoping that soon you will all have a meet up, and that i will be invited bring my equipment along and see what you all think, give me idea's etc...

Im sorry for all the questions but i really am learning off of you guys. Hopefully soon i will be able to contribute to the site instead of just asking questions all the time

Alon

[JerryT]

Originally Posted by Greg.

I believe (but happy to be corrected) that the Vishay dale R's are carbon. If so, they should be fine for signal grounding and the selection of something better as suggested for the actual signal should work well. The Phillips as sold by Maplin are good as are the Welwyn precision R55Y series sold by RS and Farnell These have the benefit of close tolerance matching. You can then go boutique but it'll start to cost (still pennies though). Certainly, the signal resistors need to be anything other than carbon which will produce a dull sound. Having said that, a boutique carbon has more life than a standard one and might be acceptable, but in general I'd recommend concentrating on the metal film option.

Agreed and as you are only replacing two resistors you can have hours of fun experimenting with different types of resistor for a number of weekends (tantalum, Shinkoh, Riken, Vishay bulk foil etc. ) while spending less than hiring the latest movie DVD each weekend! Try this line on your significant other if you really want peace and quiet to hear the difference - but it will cost you flowers on Sunday

Hope this helps.

Jerry

Jerry

[Greg.]

Flowers on Sunday? Sunday is Fathers day

[Richard]

Originally Posted by Malka07

Well i have done alot of reading on Psuedo Shunt...and now have a throbbing headache...but i think i am beginning to understand it.

Am i correct in thinking that the series R takes the signal to the amp and bypasses the pot/attenuator, the pot itself shunts some of the signal to ground thus achieving a level of volume that you want? This way there is only ever 1 resistor (per channel) in the signal path...and good quality Resistors can be used here.

If this is the case, then im definetely going to try this mod.
Maybe even test a few different resistors.

Alon

Hi Alon, it's a potential divider, the signal out is in proportion to the ratio of the series and shunt resistors. It's nice to be able to hard wire the signal leg. Sound-wise, the ground resistor is as important as the series resistor and the pot character still shows through the series choice, e.g. there's a noticeable difference between using, say, a Panasonic and an Alps. Rich

[prince of darkness]

Originally Posted by Greg.

I believe (but happy to be corrected) that the Vishay dale R's are carbon.

Nope, metal films apparently.

http://www.hi-fi-insight.com/210/vis...attenuator.htm

[Malka07]

Hi, could someone please give me the formula for working out input and output impedances for each step of my attenuator(100k with 91k Series R)

Thanks

Alon