Bottlehead Forum

Bottlehead Kits => Crack => Topic started by: ccoolliinn on May 28, 2023, 03:53:28 AM

Title: Volume pot resistors
Post by: ccoolliinn on May 28, 2023, 03:53:28 AM

Having been using my Crack for many years now and still really enjoying it, I've decided to relook at fitting resistors to stop the volume getting too high too quickly with my Bayer Dynamic T90 headphones. I held off all this time just in case I tried other can's. I have two questions.
In the FAQ it says fit a 75K resister on both channel inputs to volume pot, but I'm unsure of the 33K position or amount.
As these are fitted into the signal path, is there a recommended make which would give the best sound quality.

Title: Re: Volume pot resistors
Post by: Paul Birkeland on May 28, 2023, 06:21:47 AM

At the bottom of the first post on the FAQ, there's a picture of a pot with the four resistors added:
https://forum.bottlehead.com/index.php?topic=4295.0 (https://forum.bottlehead.com/index.php?topic=4295.0)

Title: Re: Volume pot resistors
Post by: ccoolliinn on May 28, 2023, 06:52:23 AM

Hi thanks for the reply, yep I saw the photo. Just not clear on the 33k position, I can only see one but I guess the other one matches the top one on other channel.

Title: Re: Volume pot resistors
Post by: Paul Birkeland on May 28, 2023, 06:57:01 AM

Yes, the other one goes on the bottom row of lugs on the pot just like the one up top.

Title: Re: Volume pot resistors
Post by: ccoolliinn on May 28, 2023, 07:32:41 AM

I understand the 75k resister job in reducing signal but what is the job of the 33k.  ???

Title: Re: Volume pot resistors
Post by: Paul Birkeland on May 28, 2023, 08:03:02 AM

Here's a helpful reference:
https://goldpt.com/preattenuation.html (https://goldpt.com/preattenuation.html)

The second resistor set keeps the input impedance of the Crack around 100K and increases the amount of attenuation. 

Title: Re: Volume pot resistors
Post by: ccoolliinn on May 28, 2023, 08:12:38 AM

Thanks, very interesting link. Have you any recommendations on best resisters for the job quality wise. Bit of a minefield with so many to chose from online.

Title: Re: Volume pot resistors
Post by: Larpy on May 28, 2023, 08:15:03 AM

Quote from: ccoolliinn on May 28, 2023, 03:53:28 AM

As these are fitted into the signal path, is there a recommended make which would give the best sound quality.

Vishay/Dale CMF series metal film resistors are inexpensive but excellent quality.  I suggest 1% tolerance since these will be used in such a critical position.

Title: Re: Volume pot resistors
Post by: ccoolliinn on May 28, 2023, 08:57:55 AM

https://www.hificollective.co.uk/catalog/75k-05w-audio-note-tantalum-resistor.html     

This looks okay.

Title: Re: Volume pot resistors
Post by: Larpy on May 28, 2023, 12:03:28 PM

More than OK.  Those are highly regarded.  And pricey.  But you only need 4 of them.

Here in the U.S. we can buy Vishay/Dale CMF resistors for less than a dollar each.  They're usually plenty good for me.  I don't know that I would hear a difference between them and boutique resistors.

Title: Re: Volume pot resistors
Post by: ccoolliinn on May 28, 2023, 02:05:45 PM

I agree, but as I only need 4  ;D