DIY 10dB attenuators

pete_mac

Super Member
I've also made up two sets of 10dB attenuator links for both of my Sansui amps. These fit between the pre-outs/main-ins and help to improve the resolution of the volume control. It's extremely common the volume control knob on vintage amps to be extremely sensitive when used with CD players and modern digital sources. Most of these amps are specc'd with 150mv input sensitivity, so if you run equipment with 1-2V output. it's clear that there is quite a mismatch!

Constructing a pi attenuator is pretty straight-forward. Input your desired attenuation and input/output impedance here http://www.random-science-tools.com/electronics/PI_attenuator.html (in my case, 47000ohm for each, and 10db) and it spits out the resistor values that you need. Thanks to skippy124 (Dad) for putting me onto this one!

I managed to fit the three resistors within one of the RCA plugs which makes it quite neat. I pillaged some CAT6 cable that I had lying around and used two orange/white twisted pairs per link. Some techflex tidies them up nicely.

Very happy with the result - to my ears, they add no colouration and the music is just as dynamic as before. If anything, the amp may sound nicer at lower listening levels now, as I'm actually a 4-5 clicks on the volume knob, rather than 1-2 like before. The amp seems to prefer this - it just sounds 'right'. From what I've read, this will also bring the signal-to-noise ratio for the amp back into spec.

I can also easily remove these links from the signal path due to the switch on the rear panel of the Sansui which connects and separates the internal jumpers for the pre-outs/main-ins. Too easy really!



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Some (most?) Sansui units have a front panel control that accomplishes the same thing...I take it that this particular unit does not.
 
Some (most?) Sansui units have a front panel control that accomplishes the same thing...I take it that this particular unit does not.

Correcto dear sir! There's no 20dB attenuation switch on the AU-517 and AU-317 which are the two units that I fitted attenuators to.

I've got an AU-719 in the works which has the 20dB attenuation switch.
 
if i am not mistaken could these be used as interconnects from cd deck etc ? instead


Absolutely... they sure could!

I was considering making up a longer 1m cable for this exact purpose, however I already have nice interconnect cables that I use between by DACs and amps and I didn't want to ditch those.

There are some pre-made cables with attenuators built into them (the same resistor network that I made) and there are also attenuator adaptors which have a male RCA on one end and a female RCA on the other end. I preferred to make my own though.
 
just a thought if you was to build a passive mixer like i did for a 12 volt system years ago you could have a vol control / gain . and a switch for the inputs
 
just a thought if you was to build a passive mixer like i did for a 12 volt system years ago you could have a vol control / gain . and a switch for the inputs

True. I just went with the most straight-forward approach for my specific needs. I've got ample inputs on the Sansui and they are switchabe from the front of the amp, and I don't need any level-matching between sources - just an overall attenuation of the signal that the amplifier section sees.
 
True. I just went with the most straight-forward approach for my specific needs. I've got ample inputs on the Sansui and they are switchabe from the front of the amp, and I don't need any level-matching between sources - just an overall attenuation of the signal that the amplifier section sees.

nice neat job well done .i am hoping to do some neat jobs now i have built my new electronic workshop and been given some reading glasses its great to see small things again
 
I am totally lost.:yes:

Whoops... I missed your earlier question!

These attenuators do the same thing as the muting/20dB switch found on many amps. The switch attenuates (reduces the strength of) the signal prior to going to the 'power amp' section of the amplifier. At least, I think it does... I should check the circuit diagram to confirm that it occurs as part of the preamp section.

By attenuating the signal going to the power amp, each increment on the volume knob (particularly with stepped knobs like on many Sansuis) will give a smaller increase in volume. It gives you better overall volume control/resolution.

I could never get my AU-317 quiet enough for night-time listening. Now, with the attenuators, it's perfect.
 
Ah, to be honest I thought it was a switch for letting you take a phone call or something. Now I know what it really is, thanks.:thmbsp:
 
I might have to build a pair of these for a friend that has an over-powered amp for his ultra-sensitive speakers. How would I figure out the ideal input/output impedance? Just looking at the equipment specs?
 
I might have to build a pair of these for a friend that has an over-powered amp for his ultra-sensitive speakers. How would I figure out the ideal input/output impedance? Just looking at the equipment specs?

Yep, that's your best bet :)
 
I might have to build a pair of these for a friend that has an over-powered amp for his ultra-sensitive speakers. How would I figure out the ideal input/output impedance? Just looking at the equipment specs?

It's not really an issue of power. A small amp with high gain could exhibit the same problem. That said, yes, attenuators will cut the gain and should help.
 
Great thread! I wanted to build these things before, to protect my speakers and to sustain the DAC SNR. Right now I have DAC -> power amp. I forgot to include R1 of the attenuator in my drawing.

I might have to build a pair of these for a friend that has an over-powered amp for his ultra-sensitive speakers. How would I figure out the ideal input/output impedance? Just looking at the equipment specs?
In each connection you want to have the output impedance of the previous device insignificant w.r.t. the input impedance of the next device. This is to avoid a voltage drop at the source side.

This is an example I plan for. I cannot guarantee these values are good choices but maybe someone can check them.
My DAC has 560 Ohms output impedance and amp 25 KOhms input impedance.
19.4 dB attenuation
Input R = 18.3 KOhms
Output R = 800 Ohms
R1 = 5.6 MOhms
R2 = 18 KOhms
R3 = 820 Ohms.
 
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