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PAS 2 - New volume control issues

Guys, there is NO WAY a volume pot will cause distortion. The key is two things: 1. Is the ALPS an audio taper (log)?
2. You disconnected circuitry for the loudness circuit that is not meant to be left open circuit.

The ALPS pots (I use the blue a lot) are excellent and track well. They are also tough and can handle a hacksaw on the shaft so long as you clamp it to prevent rotation. As for cutting off the locating pin you can break it off with pliers or cut it but you must cover the openings with painter's tape to prevent crap getting in.

Lastly the ALPS blue sometimes needs the metal body earthed to a signal ground at the input stage if the chassis is floating. This affects only hum and not sound quality.
 
Thanks for the suggestions and additional info. I think I'll end up purchasing one from China and see how it goes.
gadget73 said:
I suppose theres no reason you couldn't wire the loudness into one of those too is there? Just tap it at the appropriate place?
Click to expand...
Yep, that's what was suggested and what I plan to do.

It's possible the ALPS pot wasn't faulty and I just didn't like the sound of it with the loudness circuit removed. But it really sounded bad. Gonna go in a different direction anyways.
 
I actually may consider doing this with mine. It has a 100K Alps that I put in a while ago. Works fine and all, but it should be 250K, and the loudness isn't hooked up.
 
gadget73 said:
I actually may consider doing this with mine. It has a 100K Alps that I put in a while ago. Works fine and all, but it should be 250K, and the loudness isn't hooked up.
Click to expand...
When I end up getting one of the Chinese attenuators from the auction site I'll let you know what I think about it.
 
I broke down pretty quickly and got 250k 23 step attenuator from China and wired it up. It sounds excellent, with noticeable improvement in clarity over the stock volume control. Channel balance is perfect, so no more twiddling my balance control every time I set the volume! I wired it with the loudness components at first, but there was a really large jump in the volume once the control hit the spot where they were wired in. In the photos, you can see the loudness still attached with extended spliced wires. I ended up removing the loudness components, and now the control gives me really good contour between the steps through my entire listening range.
IMG_6571.jpg IMG_6572.jpg

I'm very happy with this attenuator, and it beats the ALPS pot and original control by a mile for sound quality and operation. It was not hard to install, especially after having switched the control four times already, and the seller provided a good diagram locating input, output, and grounds. I'd recommend it to anyone with a PAS trying to replace a wonky volume control, and I got mine from seller atop_authentic_auction (no affil), though there are several who offer similar products.
 
stanko said:
I'm with you on that, pots today suck.
Click to expand...
Now I order GoldPoint attenators when ever I'm redoing an important project. For the $150 bucks it solves a multitude of problems. Mainly crappy VC pots and poor tracking.
 
Wish I could justify spending that much, but that'd be more than I paid for the preamp! I bet those Goldpoints are great, but for $25, this one works great.
 
I bought one of those 23 step attenuators last year. It worked well in a preamp I built. The only problem for me was 23 steps wasn't quite enough for my application. I had that one more click and it was too loud problem. I do use the smaller ones now with SMD resistors with 28 or more steps. I don't buy volume controls with wipers anymore. Good to hear it fixed your tracking problem.
 
I tend to listen at relatively low volumes. A big reason I've been reluctant to go with a stepped control is exactly what you describe, worries about it being too granular.

Are the ones with SMD parts pre-loaded or do you have to assemble yourself? Doesn't sound like much fun if you have to put it together. Leaded parts would be annoying enough.
 
Lavane said:
I bought one of those 23 step attenuators last year. It worked well in a preamp I built. The only problem for me was 23 steps wasn't quite enough for my application. I had that one more click and it was too loud problem. I do use the smaller ones now with SMD resistors with 28 or more steps. I don't buy volume controls with wipers anymore. Good to hear it fixed your tracking problem.
Click to expand...


There is a resistor calculation program that allows you to vary the per-step dB throughout the range. I generally group mine closer together at the low level end for finer adjustments at quiet listening levels and go to larger jumps as the volume increases.
 
This 250k attenuator is pretty smooth and gradual in my PAS, especially at lower listening levels. It's set up to be a log taper as you go I believe.

I'm sure a custom built attenuator would be even better, but it would take me a good while to assemble one, not to mention keep the resistors in order...
 
I looked at the pictures and that's nice you had plenty of room for the stepped attenuator to fit, great to
see it worked out for you.

I bought many Alps pots from e-bay and one time I did get one that sounded awful, may have been one
of those counterfeit ones, the other Alps pots that I got sounded good although I think the stepped attenuators
sound better.

The stepped attenuator that I used in the preamp I built worked very nicely at low volume levels although
there are certain preamps that have to much gain and would be difficult to adjust the volume exactly where
you want it at the lower levels.

I have an Eico HF-85 and it has a lot of gain so the stepped attenuator may not have fine enough control
at the lower levels for the Eico, I do like Arts suggestion about the resistor calculation program to create
your own volume control curve, I may give that a try one of these days but for now I am very happy with
the tube preamp I built with the stepped attenuator volume control.
 
Since were on the subject of stepped attenuators I have a few questions.
1) I have an Aikido octal line stage kit that I have been collecting parts for. I can't find anything in the instructions on what size attenuator to use. (25K, 50K, 100K, 250K) How is that calculated?
2) From what I have seen, there are three types of attenuators, series, shunt and ladder. The ladder type has twice as many resistors and generally cost quite a bit more. For those of you that have used the different versions, can you really hear a difference?
I'm sold on the idea of using stepped attenuators, I just don't know what I need or want.
Thanks for any advice.

BillWojo
 
I have only tried the ladder type stepped attenuators so I really don't know which one will sound better,
maybe someone else has tried the different ones and can answer that.

I can give a PDF file that has some helpful info on the three different types of stepped attenuators for you
to read.

As to what value pot to use maybe you could buy some cheap pots to try the different values or hopefully
someone has built that Aikido octal line stage and knows exactly which value pot worked the best for it.
 

Attachments

BillWojo said:
2) From what I have seen, there are three types of attenuators, series, shunt and ladder. The ladder type has twice as many resistors and generally cost quite a bit more. For those of you that have used the different versions, can you really hear a difference?
Click to expand...

You can.

The three types:
Series Stepped: All resistors are in a line and the switch moves between them. Noise is additive.
Shunt: Switch selects a divider resistor with a common shunt. Problem is highly variable load from one end to the other.
Ladder: Switch selects pairs. More accurate but more expensive.

While I was writing this I see a detailed guide was posted. Excellent work, BrokenHill!
 
Keep in mind,the more complicated ladder attenuator was developed long ago,when resistors were much noisier than today.And companies like Shallco and Daven (still?) made some of the most over the top switches you will ever see.

Cost and complexity considerations aside,my thought is that with modern,low noise tight tolerance metal film resistors,any alleged advantage of the ladder over the series attenuator will be nullified by the additional switch contact.

I do not for one second believe that even an entire string of series connected precision resistors can ever generate as much noise as a single mechanical contact.

Clearly,my preference is the series string.Simple to design,inexpensive and easy to construct.It is also electrically ''equivalent'' to a potentiometer,with no input/output impedance considerations. Seriously,do we really need these for our old PAS preamps??

Mastering_Daven-300.jpg
stereo_023.jpg
 
I can see the advantage with carbon comps, especially if the goal is minimal noise. Modern metal films, even in series should be considerably less noisy than a standard pot and probably comparable to a ladder of CC resistors.

Also agreed about the benefit or lack of. The tubes themselves make an amount of noise that is probably a fair bit greater than what the control will.
 
So it looks like a modern series type of attenuator would be fine as long as it used good resistors. It also sounds like the shunt type is to be avoided because changing anything in the source could throw the system out of balance.
Thanks

BillWojo
 
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