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Old 6th March 2012, 07:00 PM   #1
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Default How to build good stereo volume control?

Hi!

I got a HRT2+ usb dac to my Audioromy FU29 onto a pair of Tannoy 607's (Mark II-series).

My problem is that the output signal from the HRT2+ dac is 2.25V, with the result that the volume knob on the Audioromy only can be operated some steps up from 0. Typical action: Silence, whisper, Loud, Concert level. I really hate using digital volume control on the pc because it mess with my sound! It might be just me, but I rather keep the digital volumes at max.

I want to build a passive stereo volume control with rca connectors in and out, so that it is easy to move around.

Another story is that I need a input selector with rca connectors too. Is it a good idea to make this into one unit? 2 selectable inputs, only one input used at a time.

My plan is to purchase a suitable plate, install the recommended components, use point-to-point wiring where needed, then make a suitable cabinet for it so that it look nice and all with a adjustable knob or something like that. (or two knobs with line selector built-in)

Do anyone want to recommend parts and sketch up a simple wiring diagram for it? If simple is possible.

I wish it to have as little as possible impact on my listening experience.


Hope that someone want to look a little into it and guide me onto a good path.


Best regards
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Old 6th March 2012, 07:26 PM   #2
GloBug is offline GloBug  Canada
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I'm was pondering a similar project using LDRs (Light dependent resistors)

I don't have a "need" for switching but might add one for fun, to plug in an ipod etc.

Search for a couple threads like "light speed attenuator" or "LDR volume" etc. See if it works for you.
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Old 6th March 2012, 07:39 PM   #3
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Seems odd that the VC on the Audioromy behaves like that. I'm sure it would be much more convenient to use the built-in selector and VC on the Audioromy. I use my laptop as a source for my tube amp. My output voltage is almost 3V. I keep the digital volume on the PC at 100%. I have no issues with smooth volume control operation on my tube amp.

The description you give on the response of the Audioromy VC almost sounds like a linear control and not logarithmic.

Do you have a schematic that can be posted?

Last edited by scott17; 6th March 2012 at 07:50 PM. Reason: comment on logarithmic
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Old 6th March 2012, 08:59 PM   #4
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Quote:
Originally Posted by GloBug View Post
I'm was pondering a similar project using LDRs (Light dependent resistors)

I don't have a "need" for switching but might add one for fun, to plug in an ipod etc.

Search for a couple threads like "light speed attenuator" or "LDR volume" etc. See if it works for you.
Thanks, I'll look into it when I get some extra minutes.. Please share your schematics if you like, here or PM. Also if you choose to add in a switching function. Let me know how it works when operative.

Quote:
Originally Posted by scitizen17 View Post
Seems odd that the VC on the Audioromy behaves like that. I'm sure it would be much more convenient to use the built-in selector and VC on the Audioromy. I use my laptop as a source for my tube amp. My output voltage is almost 3V. I keep the digital volume on the PC at 100%. I have no issues with smooth volume control operation on my tube amp.

The description you give on the response of the Audioromy VC almost sounds like a linear control and not logarithmic.

Do you have a schematic that can be posted?
Hi.
My setup is PC-USB dac-Audioromy.
The VC response is very rough. But how much can you ask for the price? From full left: no sound, 1step-no sound, 2step, little lower than desired volume, 3rd step little higher than desired listening volume (when people around).

With my modified Yaquin MS-12 preamp connected, this is no problem, with it's optional 0,3V or 0,7V outputs, but I do not want to use that in my "office" setup.

At higher listening levels this is less of a problem, but I never get to 50% operation on the VC.

I would guess it got somewhat linear behaviour. Sorry, no schematic for it..
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Old 6th March 2012, 10:00 PM   #5
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Quote:
Originally Posted by Join View Post
The VC response is very rough. But how much can you ask for the price? From full left: no sound, 1step-no sound, 2step, little lower than desired volume, 3rd step little higher than desired listening volume (when people around).
What about just replacing the volume control pot?
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Old 7th March 2012, 01:36 AM   #6
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You probably don't need a volume control, just a fixed attenuator which you can build into the cable from the DAC to the amp with 4 resistors and some shrink wrap.

Say, a 1k2 and a 6k8 in series (connect one end of the 6k8 to the 1k2) across each channel. Connect the 6k8 to the signal (from the DAC) and the 1k2 to the ground. Continue the ground to the amp and connect from the junction of the resistors to the signal input on the amp. This will cut your volume into the amp down to a fraction.

You might have to mess with the values a bit. The smaller you make the 1k2 (or the bigger the 6k8) the quieter. Keep the total (1k2 + 6k8) resistance to ~10k.
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Old 7th March 2012, 06:26 PM   #7
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Hi guys,

After some reading, I really have started drooling over the Lightspeed attenuator mentioned, (LED/LDR)

That would perfectly "fix" the issue I got, right?

Quote:
Originally Posted by scitizen17 View Post
What about just replacing the volume control pot?
That might not be a bad idea, after all the original pot might not be of the best quality. What info do I need to get a suitable replacement? Remote controlled options?

Quote:
Originally Posted by counter culture View Post
You probably don't need a volume control, just a fixed attenuator which you can build into the cable from the DAC to the amp with 4 resistors and some shrink wrap.

Say, a 1k2 and a 6k8 in series (connect one end of the 6k8 to the 1k2) across each channel. Connect the 6k8 to the signal (from the DAC) and the 1k2 to the ground. Continue the ground to the amp and connect from the junction of the resistors to the signal input on the amp. This will cut your volume into the amp down to a fraction.

You might have to mess with the values a bit. The smaller you make the 1k2 (or the bigger the 6k8) the quieter. Keep the total (1k2 + 6k8) resistance to ~10k.
It sounds better to me to have a easy way to adjust it. If there is new equipment connected it will need adjustment?
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Old 7th March 2012, 07:20 PM   #8
Marra is offline Marra  United Kingdom
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You will like the LDR type attenuator it gets out of the way of the music;detailed and dynamic.
dvb-projeckt provides details of the pcb he used to supply in post 366 of the following thread. Salas excellent DCB1 works extremely well with the ldr if you need a buffer.

Optical Volume Control Professional PCB
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Old 8th March 2012, 02:50 PM   #9
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Quote:
Originally Posted by Join View Post
That might not be a bad idea, after all the original pot might not be of the best quality. What info do I need to get a suitable replacement?
Measure the linearity and total resistance with an ohmmeter. Something is not right with that control. It should control the volume smoothly with the input level you indicated.
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Old 8th March 2012, 03:18 PM   #10
AndrewT is offline AndrewT  Scotland
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Your problem is too much system gain from source to speaker.

Have you read
What is Gain Structure?

There is an easy and still pretty cheap solution that avoids changing the system gain.

Buy a 10k stereo log pot.
Wire up the output (wiper and ground) to the receiver (or output RCAs).
Wire up the ground to the input RCA.

Now to the last RCA to pot connection:
Wire a 100k resistor from RCA Hot to Pot Hot input.

At maximum rotation of the volume control the signal coming out of the pot is ~-20dB below the input signal.

If the 10k pot alone could achieve a range of -0dB (at max) to -60dB (at min) then this modified version with the two extra resistors (one for each of the stereo channels) will achieve a range of -20dB (at max) down to -80dB (at min).

This pair of resistor will cost just a few pence.

If you have a source that outputs a much lower signal and the modified pot requires near max rotation to get a noisy signal at the speaker, there is another simple and cheap solution.
Add a two pole, single throw switch, suitable for audio signals. A DPDT switch or relay can be used but a spare pair of terminals will be redundant.
Wire the switch across the 100k resistor. This brings back in the "normal" range of the unmodified vol pot.

The only disadvantage I am aware of is slightly increased noise due to throwing away 20dB of excessive gain.

Use the switch to flick between "normal" pot and "modified" pot.

BTW,
you can use any value resistor for the "modified" version. 20k will give less attenuation of the TOO LOUD source, 300k, or even 1M0, will give more attenuation of the TOO LOUD source.
__________________
regards Andrew T.

Last edited by AndrewT; 8th March 2012 at 03:24 PM.
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