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jrhughes 
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Joined: 24 Mar 2010 Location: Hampshire Status: Offline Points: 145 |
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 Topic: AttenuationPosted: 02 Nov 2011 at 6:53pm |
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Hi,
I have a DAK Novo (built last year - love it) to which is connected a Cambridge Audio DacMagic and AKG K702 headphones. The sound is incredibly detailed and wonderful, but the DacMagic's line output is very high. This means most of my listening is rarely above the 8 o'clock position, where the audio balance from the volume control is ever so slightly off. I know that this is a known issue with volume pots, in that the L-R balance may not be ideal at very low positions. It also means that the volume level is quite difficult to control as it's all bunched up within the first few degrees of rotation. I bought a pair of Rothwell in-line attenuators and these solve one problem but introduce another. With them fitted, the volume control is likely to be in the 9 - 10 o'clock position which completely solves the balance issue, but I can't get over the fact that they affect the sound too much. They appear to compress the soundstage, which I find surprising as I thought they were supposed to be just a "static" volume control. No matter how much I try to convince myself otherwise, I feel that something is missing when they are in place, so they are back in their box. Is there anything I can do to attenuate the level a little, without resorting to expensive attenuating cables, and that won't affect the quality I get from these components?
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Graham Slee
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Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16314 |
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Posted: 02 Nov 2011 at 7:25pm |
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Yes!
As this is DIY, break the signal tracks somewhere convenient between phono jacks and the volume control to insert a series resistor. Then solder another resistor across the pot input and ground connections. Do this to both left and right channels (obviously, but the answer is for others too). The resistor values are best chosen to provide a near match to the existing input resistance which is 50k volume fully down to around 30k volume fully up. Let's give it 10dB attenuation. I'll choose 27k as series resistor and 15k to go across the pot so you'll have an average 38k input resistance. No need for great expense here unless you're overly worried about channel balance - carbon film resistors off the same "bandoleer" should be closely matched although they have a tolerance 5% away from that rated. Tyco CR25 resistors sound beautiful to my ears and are also dare I say it... cheap! I'm steering you away from 1% metal film because mostly they sound sh*t because of outsourcing to a far eastern laundry. After all the world is in the final throws of capitalist/communist/whatever greed. It is a complete b'stard for us in sourcing good sounding metal films (please - no suggestions - we already tried them) so it's going to be a bigger one for you.  |
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jrhughes
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Joined: 24 Mar 2010 Location: Hampshire Status: Offline Points: 145 |
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Posted: 02 Nov 2011 at 11:07pm |
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Graham, thanks very much for your reply.
What you describe sounds very much like the description of how the Rothwells work (a simple, two resistor potential divider per channel) and, from what you're saying, the choice of resistor is very important here. I hadn't realised they could make so much difference but the ones used in the Rothwells turn my headphone setup from amazing to OK - they take the edge off, certainly. Maybe they are not matching well to this setup, or maybe they use the type of 1% metal film to which you refer  If you think the Tyco ones won't affect the sound quality in a negative way, as the Rothwells clearly do, then I may be brave and do this. Thanks again, Jason
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Graham Slee
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Retired Joined: 11 Jan 2008 Location: South Yorkshire Status: Offline Points: 16314 |
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Posted: 03 Nov 2011 at 8:06am |
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Just did a quick web search and it looks like the only places you'll get real Tyco CR25's is RS Components or Farnell which are trade only unless you can somehow sneak in under the radar...
The toy shops sell the stuff from the laundry - why do you think there are all those tents outside St Paul's? |
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That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps
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hotmog
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Joined: 14 Jun 2010 Location: Worcester Park Status: Offline Points: 178 |
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Posted: 03 Nov 2011 at 11:08am |
I'm not trade, but I had no problems opening an account with Farnell to purchase a replacement 12V 3.5A power adapter for my Maxtor external backup HD a couple of years ago. The original one had expired after being liberally "scent-marked" by one or more of our Siamese cats, and it was the only place I could find a similar one. BTW, they're not allowed in the front room so the Solo/PSU1 is not at risk, and there are now barricades to prevent feline access behind all the computer stuff. |
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jrhughes
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Joined: 24 Mar 2010 Location: Hampshire Status: Offline Points: 145 |
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Posted: 03 Nov 2011 at 11:10am |
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Hmmm. Ok then - in which case I think I'll leave it alone. There's no way I'm going to risk even a small compromise to the quality of the sound by using sub-par resistors.
This has taught me a lot. I had thought that these attenuators would be transparent (as the blurb says) but they are clearly not. Cheers
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Graham Slee
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Posted: 03 Nov 2011 at 3:36pm |
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You could always take them out if they were not right for you and bridge the breaks with the bits of trimmed off resistor leads - we do things like this in R&D all the time, the offcuts of bits of wire won't alter the sound. Or you could try some of the "toy-shop" resistors including metal films if you like - knowing you can reinstate it to as it were.
Edited by Graham Slee - 03 Nov 2011 at 3:38pm |
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