Crack 1.1 replacing volume pot with stepped attenuator, novice help

[Tomunizum]

Hello all. I recently purchased the crack 1.1 kit and I was doing some reading and planning ahead of time for the build as well as upgrading it.

Goal is to drive my HD6xx from my desktop PC in the USA.

I was reading from other posts that a 100k stereo ladder type stepped attenuator would be used in this case.

~Such as this one by Dale on eBay: "1PC HIFI 24-Step Stereo Attenuator Potentiometer 10K 50K 100K Dale Resistance"

Using this I was trying to figure out how I would wire this given the manual and what I could find online.

Disclaimer:
I have only a Undergraduate level understanding of circuits that I learned in my basic physics class / lab a few years ago, so I really do not know much of what is going on but I am doing my best to understand.

I have attached images of my understanding and of how I was thinking of wiring it. Hopefully they are somewhat clear and helpful.

If you would be so kind , I would greatly appreciate if you could let me know if this seems okay, if I am missing something, or anything else that you think I should know.

I apologize if this has been addressed already, I could not find a wiring diagram on the forum and any links that seemed to point the right direction were expired.

Thank you for any time that you are able to dedicate towards my request for help.

John Burns

 

[Paul Birkeland]

I would suggest building the amp stock first.  Once you have gone through that process and have the kit up and running properly, then you will have greater confidence in getting that stepped attenuator properly installed.  Building the kit stock will also reveal a problem that will arise with the drawings you posted.

 

[Tomunizum]

Hmm, I'm curious what you are referring to. Looking at the completed diagram in the manual, I see that one single black wire runs through both RCAs and terminates at the upper lug of the pot after going through the lower one, which differs from my drawing in that I drew separate ground wires. I was thinking that if I could still use one single ground wire to connect to the attenuator I would but was unsure and 2 as I have not seen it any other way. If you are referring to something else, I am unsure.

I agree that it would be probably a good idea to complete it stock to familiarize myself and determine if I can produce something functional, but I wanted to be efficient and save some time de soldering, repositioning, etc.

In any case, I will plan to build stock as you suggested but if information as to how I should wire an attenuator should present itself to me, I will likely still consider this route.. haha.

Thank you for the feedback.

John

 

[Paul Birkeland]

Yes, the separated grounds will be a big problem.

The issue with putting the stepped attenuator in from the beginning is that debugging the amp may require you to pull it back out and put the factory pot in its place. 

 

[Tomunizum]

Okay, gotcha.

And regarding troubleshooting using the stock build, that is a great point. I wont introduce any variables until I know what I have out of the box is functioning as expected.

I will build stock first.

I will keep looking for info and help on wiring the attenuator in the meantime.

Thank you very much.

John

 

[Paul Birkeland]

You can also make your life way, way easier by just substituting a TDK or PEC pot in place of the stock pot.  They can be wired up exactly the same.

 

[Tomunizum]

Thank you,

Between a good quality stepped attenuator, TKD, or PEC, what would you say is the perceivable difference, if there is any?

John

Edit: spelling

 

[Paul Birkeland]

You'll have to travel down that road on your own.  You'll definitely notice that the higher dollar audio pots have better channel balance and do sound better, but at the same time that a stepped attenuator is another jump up.  The big question with the stepped attenuators is whether you have enough steps down low, and that isn't something you ever have to worry about with a carbon pot.

 

[Tomunizum]

That I shall.

Thank you for the info, I'll just have to dive in and see what I seem to enjoy more.

John