Diy attenuated rca cable

[bunno77]

Hi all

 

May not be appropriate for this site but....

 

I'm hoping someone might be able to help me calculate resistors needed for attenuation of DIY RCA cables.*

 

My source output impedance is 47 Ohms and my amp input impedance is 22k Ohms. *

 

I am using a Geek Pulse DAC with McIntosh MA2275 integrated valve amp and at normal listening levels the dial is at about 8 O'clock. *Thinking maybe 8 to 12dB attenuation is needed? I have read about sonic benefits of having the dial higher on the power amp when matching old and new equipment. *

 

The formulas can be found here but the link to calculate resistors required seems to be broken

 

DIY passive attenuation - SqueezeboxWiki

 

Also I am planning to not terminate the shield at the amplifier/attenuated end of the cable to avoid possible ground loops. *

 

Any help, recommendations or directions to info/calculators for the resistor and which resistor brand would be greatly appreciated.*

 

*

 

Thank you very much*

 

 

 

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[bunno77]

Why do you think you need to attenuate the signal? If your normal listening level was at 11 o'clock or full on, then this might make sense. As long as you are not overloading your amps input stage, you will get a cleaner (higher s/n ratio) the higher you set your amps volume. There will be recordings that need more attenuation than others, and if your loudest is overloading the amps input, then you would want to cut the signal some.

 

think of it this way—the lower the input signal is, the more it needs to be amplified. Unfortunately, there is also a noise floor in the amp, that also gets amplified along with the signal.

 

your amp is integrated, so let's assume that the Mac designers have set the internal gain blocks at optimum for the circuit topologies. Your job is to feed the loudest signal you can into the input stage without overloading it in any way, then use the volume control to set your listening volume.

The point is to get the dial closer to 11 o'clock so that the amp is in a more optimal zone.

 

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[bunno77]

I think your Pulse uses a digital volume control. It is 32 bit. You should be able to attenuate the output fine.

Adding a fixed attenuators would only make sense if the Pulse had fixed output.

I have an Infinity Pulse and the volume control circuit is the best performing feature it has. Very clear, dynamic, and linear.

Yeah it's not bad but the pre amp stage in the McIntosh is better. I bypass the dac volume control.

 

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[bunno77]

With RCA connectors, you should always terminated the shield.

https://www.google.co.th/url?sa=t&source=web&rct=j&url=http://www.vandenhul.com/download/CAwdEAwUUkNEW0k%3D&ved=0ahUKEwiYwJbt5t_PAhVKMo8KHSQ1Co4QFggZMAA&usg=AFQjCNEs47xMnNa1kQ6Agc-FCUugXYLxHA

 

The plan is to do the same as this by Van Den Hul and its the same principle as I use with screened cables as an industrial electrician.

I will still terminate the shield but only at one end.

I am happy to be proven wrong though

 

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[bunno77]

Search for Harrison lab attenuators. Just get a couple of the right value.

 

The proper answer is one you have rejected. Use your digital volume control to put it in the proper range. It will do less damage than any hardware based method.

 

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Thank you very much.

The plan is to diy a resistor into the rca jack myself.

I was hoping it would sound better attenuated in the cable as I don't particularly like digital volume control and notice that attenuating via the dac doesnt quite sound as good.

But as you both suggest it's probably the lesser of two evils.

Or I could just leave it and be happy as it is.

 

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[bunno77]

When you write " the preamp stage in my Mac is better" are you trying out the digital volume by bypassing the preamp stage? If so, then try keeping it in, and if you want, with the volume as high as you want; and then compare to the digital volume control. It is very possible that bypassing your pre amp stage completely wouldn't sound as good.

Thank you very much Pooger. I have been looking at the vishay's.

The the pulse s infinity dac at full volume bypasses the pre.

A benefit of my integrated is I can use it as an integrated or as purely a power amp.

I have tried all the different combos.

Dac attenuation and just power amp is very transparent, detailed but a little fatiguing and less 'romantic' (I have also tried this into my halcro and it's amazing for hearing every single detail)

Dac attenuation and integrated adds a little harshness.

Dac bypassed and integrated is the best to my ears.

 

So I'm just trying to get the mac to perform a little better by being in its sweet spot.

I have been unable to find anything stating attenuated cables are detrimental to sound quality if done correctly and I plan to by the best resistors that will physically fit.

 

I have found a bit of info though claiming that an amp at 8 o'clock doesn't quite sing the same. It's also common with new front ends matched with older power amps.

 

 

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[bunno77]

I have also had a burson timekeeper in the system too which shares the same dac chip. It was a different story. It was better using its volume control in conjunction with the integrated.

The geek pulse dac was superior though. The burson also had a bit of bass bloating

 

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[bunno77]

If you didn't look at the Harrisons, they are built into an RCA adapter.

 

If you make your own, keep it as close to the amp input as possible.

 

I have quite a bit of experience with DIY attenuators and Vishay is the way to go. I also have at times altered the gain of gear to keep everything working in a good range. When I used tube gear that was always an issue with it being too sensitive.

 

However, once I used one of the Meridian 518 digital pre-amps for volume feeding into a good DAC, I abandoned analog volume control. It was no contest. I have tried other gear with analog vs digital volume a few times after that in my own or other people's systems. Digital volume properly done is simply more transparent. Now analog preamps might do something to the sound you prefer. So no arguing with your preference if you have tried it, and like it better without digital volume control.

 

Now having said all of that, I think you might do about as well to do some tube rolling. The 2275 uses one pair of the 12ax7's for line level signals (one pair is used for phono). Those can subtly alter the sound. I wouldn't be surprised if you couldn't use the digital volume for tweaking levels a bit, and swap to different 12ax7's to get the sound you prefer. I haven't been very active with tube gear for about a dozen years so I am not up to date on what is available. Some old NOS JAN 12ax7s (or 5751s which are basically milspec 12ax7s) might be worth a try, and Telefunken even more so if you can come across some. The old Sylvania tubes are good, but likely have a sound signature away from your preference. In my experience the 12at7 driver stage tubes don't make as much difference in sound as the 12ax7s are likely to cause. So just a suggestion that might pay more dividends.

Excellent information thank you.

I have done a little bit of tube rolling.

Currently running all re issue gold lions which made it a completely different amp.

I've tried a few others but no vintage tubes.

A manufacturer got back to me about attenuated cables and stated that it can take a little off the higher frequencies so I think I will abandon this little project and be happy with how it is.

Thanks again for your help

 

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