pot used for shunt attenuator

CButterworth · « **on:** 21 Jul 2004, 03:38 pm »

Hello,

I have a great sounding (IMO) AKSA55 that uses a DIY passive preamp for source selection and signal attenuation. In the preamp, I have a 50K Alps Blue Velvet which is wired in shunt mode so that the actual signal only passes through a single Vishay-Dale resistor (33K, I think).

After reading about stepped attenuators, I was thnking of building my own. Many reports talk about them as being far better than other types of pots. But, in shunt mode where the positive signal does not pass through the pot, would I notice any difference between my Alps and a stepped attenuator - afterall the positive signal only passes through a single resistor that is entirely independant of the pot/stepped attenuator?

Thanks,
Charlie

JoshK · « **Reply #1 on:** 21 Jul 2004, 03:53 pm »

Good question, I would also like to know from people with experience here.

Vinnie R. · « **Reply #2 on:** 21 Jul 2004, 07:12 pm »

Quote from: JoshK

Good question, I would also like to know from people with experience here.

In my experience (using a DACT and a alps pot), the difference in sound quality is very minor at best, BUT, when the pot wears out and gets scratchy, you will hear this as distortion. With a good stepped attenuator, you won't get this.

Regards,

Vinnie

Malcolm Fear · « **Reply #3 on:** 23 Jul 2004, 03:14 am »

Hi Charlie
If you're going to build your own stepped attenuator, why don't you go for a ladder type. That way you will only have 2 resistors in circuit at any one time.

Lost81 · « **Reply #4 on:** 23 Jul 2004, 04:18 am »

Excuse my ignorance, but can someone explain to me what "shunt mode" mean?

Quote from: Vinnie R.

when the pot wears out and gets scratchy, you will hear this as distortion. With a good stepped attenuator, you won't get this.

I can attest to that. The pot in one of my units has worn out and I can hear noise from the speakers. Quite sad. Unless I hack the circuit board, I don't think I can install a larger better pot in there.

-Lost81

JoshK · « **Reply #5 on:** 23 Jul 2004, 01:35 pm »

Shunt mode as I have read is where their is one hi-quality resistor in the signal path and then the pot is wired between the signal and ground. I am guessing this makes the pot work backwards where is most resistance position of the pot leads to the highest volume (least amount of signal escaping to ground) and visa versa. With the pot in the signal path the least resistance leads to the highest volume (least attenuation).

I have a ladder type attenuator in my preamp and wholely agree that it is a great method. It is however, moderately expensive to do with high quality. Shunt mode seems to be less expensive than ladder type and yield better results than standard pot in the signal path as I can gather from reading up.

I still would like to know the answer to the previous question of whether, in shunt mode, a stepped attenuator (obviously the cheaper series stepped attenuator rather than a ladder step) would result in better sonics than an alps-like pot. Would it lead to better channel tracking?

Guess I will have to try it out for myself. Maybe when I get down wiring up my DIY preamp I will play around with different pots.

Vinnie R. · « **Reply #6 on:** 23 Jul 2004, 02:23 pm »

Quote from: JoshK

Would it lead to better channel tracking?

The answer is YES. You will get better channel tracking because
the resistance from L and R signals to ground of the stepped attenuator will be more precise (discrete resistors) than a pot can achieve.

JoshK · « **Reply #7 on:** 23 Jul 2004, 02:25 pm »

That is what I thought, I'd imagine that might be the only reason though.

CButterworth · « **Reply #8 on:** 23 Jul 2004, 03:29 pm »

Thank-you for all the replies. I can certainly accept that standard pots are likely to become scratchy with use and age - a good quality stepped attenuator should work for much longer. I remember that the Goldpoint webpage had a good discussion and illustrations of the different types of attenuators - shunt, ladder, etc.

It would be great for someone with access to both stepped and pot type attenuators to make a side-by-side comparison and post the results somewhere.

Regards,
Charlie

markC · « **Reply #9 on:** 26 Jul 2004, 09:39 pm »

I swapped out the stock alps pots in my Decware ztpre for goldpoint ladders. The ladders are much more accurate and the improvement in sound quality was worth it imo. They are not cheap by any means, but I did buy them in kit form to save a few xtra bucks. I enjoy diy anyway. The ZTpre uses 2 volume controls in lieu of a balance contol and also makes it a true dual mono. B4 the Goldpoints, I used to get a wandering centre image, now it's locked in solid. They also provide a much clearer sound, which I believe is the result of the signal only having to travel through 2 precision resistors @ any volume setting rather than all the nasties of a potentiometer.