Attenuator for Passive pre amp, best sounding solution - diyAudio
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Old 22nd April 2014, 08:11 PM   #1
UMarcus is offline UMarcus  Germany
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Default Attenuator for Passive pre amp, best sounding solution

Hi,
i want to build a passiv pre amp and looking for the best attenutator solution.

On my list there are following :

1. Potentiometer ALPS (motorized)
2. Relay based Attenuator with resistor array
3. IC based volume control (MUSE 72320)
4. Auto Transformer
5. Lightspeed Attenuator


It should be possible to remote the volume, so i exclude the switch based solution which is near to relay based solution (?)

Did anyone could advise or had compare the different attenutator solutions ?
Is there a noticeable sound difference herable (maybe in a high end system) ?

Thanks, regards
Marcus

Last edited by UMarcus; 25th April 2014 at 06:30 PM.
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Old 22nd April 2014, 08:16 PM   #2
Zen Mod is offline Zen Mod  Serbia
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best when buffered on input

for my ears , superior to , say, Penny-Giles attenuator , TKD and similar
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Old 23rd April 2014, 06:59 AM   #3
UMarcus is offline UMarcus  Germany
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Hi Zen,
wow, looks great. Thank you for your response and pointing me to that. This sounds interessting, i have to update my mind.

Which buffer design you prefer for balanced signals ?
Is the signal dc decoupled by using an auto transformer ?

Thanks,
Marcus
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Old 24th April 2014, 11:57 AM   #4
thommy is offline thommy  United Kingdom
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Would you add an LDR attenuator to that list?

I have just built one of the Stereo Coffee attenuators and am very pleased with it. Have it between DAC and power amps, takes nothing away from the sound other than gain.

It works for balanced signals and cost me $160. It's capable of switching between 3 balanced inputs which makes it great value for money. You could attach an output buffer if needed but I use it without and get fantastic results.

There's no remote with the kit, but any remote controlled pot of the correct impedance will control the LDRs.
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Old 25th April 2014, 06:33 PM   #5
UMarcus is offline UMarcus  Germany
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Quote:
Originally Posted by thommy View Post
Would you add an LDR attenuator to that list?

I have just built one of the Stereo Coffee attenuators and am very pleased with it. Have it between DAC and power amps, takes nothing away from the sound other than gain.

It works for balanced signals and cost me $160. It's capable of switching between 3 balanced inputs which makes it great value for money. You could attach an output buffer if needed but I use it without and get fantastic results.

There's no remote with the kit, but any remote controlled pot of the correct impedance will control the LDRs.
Hi Thommy,
many thanks for your response, the LDR are not on my scope, i add it to the list.

Do you compare some solutions with the LDR ?
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Old 27th April 2014, 11:39 PM   #6
Neilsan is offline Neilsan  New Zealand
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I've had a Goldpoint 25kohm attenuator for a while after trying other "passive pots" over the years, and love it.But now I've gone to one of the Stereo Coffee LDR's and it's definitely a step up sound-wise.
Have a look at this thread.
Light Dependant Resistor 3 Input Preamp Kit
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Old 30th April 2014, 05:24 AM   #7
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A transformer is the best sounding attenuator. Resistive attenuators will add more loading to the source, reducing its dynamics as well as increasing the impedance seen by the destination component.
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Old 30th April 2014, 06:20 AM   #8
UMarcus is offline UMarcus  Germany
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Many Thanks for your input Guys.

Somebody know a remote control transformer solution ?

Would it be possible to combine the transormer with a µC controlled relais array ? Drawbacks ?

Last edited by UMarcus; 30th April 2014 at 06:35 AM.
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Old 30th April 2014, 07:48 AM   #9
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I don't know of a commercially available one but sure this would be an excellent DIY project, combining hi-tech uC with low-tech trafo I think relays probably wouldn't be needed, MOSFET switches might well do the job well enough.
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Old 30th April 2014, 08:05 AM   #10
Calvin is offline Calvin  Germany
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Hi,

I´d say a transformer is certainly not the best solution, as the ´best´ always depends on the circumstances, as price, resolution/steps, precision, etc. etc.
- Due to its inductive nature a Autoformer is a nonlinear device. Typically the resolution restricts to a few large steps and size is large. Beeing specialty devices cost is high. Most offers use mechanical switches offering only low comfort, though relais may be used for more handling comfort. Voltage range and power can be high. Due to low comfort, it doesn´t lend itself well to multichannel use.
- Integrated chips like the Muses excel in compactness, number of steps and probabely also in handling convenience, especialy in multi-channel applications. It may be argued about the (sound) quality of silicon resistors and numerous MOS-switches which add THD. Voltage range and power capability is typically small but sufficient for Audio.
- Potis are still the workhorses and come in countless styles. They are compact and may offer some comfort if motorized. Interchannel balance and dB-linearity may be from mediocre to good. For a passive Preamp their varying and rather highish output impedance may be troublesome depending on the load. Typically only short cable runs and higher impedance loads are suitable. Cost and quality may vary over a huge range. Voltage range may be high, Power is typically low, due to the filigrane wiper contacts.
- LDRs offer a compact, low parts number count solution. Number of suitable parts is low, tolerances are high and need screening. Technically an elegant solution allowing for easy handling and comfort and multichannel use.
- Resistor array offer a high dedree of precision. Depending on the chosen number of Steps the number of parts and cost may be high. Build size is not compact.
If intended for a passive Preamp a network should be chosen that offers a lowish and constant output impedance. If a bit-wise weighted network is chosen to reduce the number of switches and resistors, the resistors need to be very tightly tolerated. Only then is a high level precision in dB linearity achieved. Each step itself offers the highest linearity of all solutions as a high quality resistor is without doubt the most linear device one could use. Interchannel balance is excellent and handling and comfort may be high. Adopts well to multi-channel useage. Voltage range and Power can be high.

The final signal quality of the listed solutions depends on the quality of the parts and their implementation. And each of the different techniques has proven good results as well as inferior results. Factors like cost, build size and especially comfort and easy of handling should not be understimated in the evaluation process.

I´ve made excellent experiences with bit-wise weighted switched resistor networks. Sonically its as neutral as one could wish for. At typical listening levels no more than 2-3 resistors are within the signal path. Imho one couldn´t come much closer to the proverbial piece of wire. If it sounds limited in dynamics, its implementation certainly is flawed. Done right the dynamics are outstanding (... as the resistors are the most linear and lowest limiting devices).

jauu
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