I don't know if this is the correct place (I didn't found a place for pre-amps). A few days ago I started a thread asking about a passive volume control, but thinking well I guess that maybe this is not the ideal solution for my case...
I have a great pre-amplifier which only thing that bugs me is the sliding control that won't allow me a smooth operation. To make things still "better" it doesn't have a separate balance control, instead it has TWO sliding controls for volume (left and right).
Years ago when I had an identical pre-amp to this one the solution I found was to buy a second pre-amp (with a rotating volume control) and put it in series with the first pre-amp. Beside to have a lot of inputs available I left the sliding pre-amp at the maximum volume (with the -20dB button pushed) and controlled the volume in the rotating pre-amp.
I was about to do it again but I know that this is not the ideal situation because having a pre-amp pushing signal into another turns easier to induct distortion. Also I was thinking and maybe the passive control is not a good idea either because there is impedance issues and it may cause noise and also the high frequencies to be cut specially in low volumes.
From my very small knowledge in electronics I am realizing that maybe the ideal would be an active volume control but with 0dB of gain to avoid distortions.
Said that, there is someone that could point me a good (and yet as simple as possible) circuit to do this and that I could try to assemble myself in home?
I am opened to other suggestions.
Thanks a lot!
I have a great pre-amplifier which only thing that bugs me is the sliding control that won't allow me a smooth operation. To make things still "better" it doesn't have a separate balance control, instead it has TWO sliding controls for volume (left and right).
Years ago when I had an identical pre-amp to this one the solution I found was to buy a second pre-amp (with a rotating volume control) and put it in series with the first pre-amp. Beside to have a lot of inputs available I left the sliding pre-amp at the maximum volume (with the -20dB button pushed) and controlled the volume in the rotating pre-amp.
I was about to do it again but I know that this is not the ideal situation because having a pre-amp pushing signal into another turns easier to induct distortion. Also I was thinking and maybe the passive control is not a good idea either because there is impedance issues and it may cause noise and also the high frequencies to be cut specially in low volumes.
From my very small knowledge in electronics I am realizing that maybe the ideal would be an active volume control but with 0dB of gain to avoid distortions.
Said that, there is someone that could point me a good (and yet as simple as possible) circuit to do this and that I could try to assemble myself in home?
I am opened to other suggestions.
Thanks a lot!
Oi amigo, tudo bem?
The main problem is not the volume control circuit itself but how will you adjust it, mechanically.
Obviously you want a rotary control instead of those sliders, which look cool but are impractical, specially with such a short travel..
The basic solution would be to disconnect those potentiometers, add some wires to carry signal to an external stereo volume pot , mounted on a small box on top of the preamp and back.
Correct technically but will need some 6 pin connector added to the preamp back and some PCB surgery .
Plan B and way more practical would be to build a stereo volume control inside an external case, and connect it between preamp and power amp, no need for a second preamp at all.
No need for it to be active, at all, since preamp has low impedance out and power amp has highish impedance in, I bet a 10K Log/Audio stereo potentiometer will be fine.
You can still use the sliders as a sort of semi-fixed gain control, set them at a comfortable level, and then use the rotary one.
IF you happen to connect a very loud or very weak signal source, then you adjust it _once_ with the sliders and then go on with the rotary one for everyday use.
Balance control is not much used these days, if you NEED one it can be easily added.
You will not have noise or treble loss problems since we are talking 10k impedance (in fact output impedance will always be less than 2k5, go figure) , signal level is high and we hav 30/40 cm tops cable length.
The main problem is not the volume control circuit itself but how will you adjust it, mechanically.
Obviously you want a rotary control instead of those sliders, which look cool but are impractical, specially with such a short travel..
The basic solution would be to disconnect those potentiometers, add some wires to carry signal to an external stereo volume pot , mounted on a small box on top of the preamp and back.
Correct technically but will need some 6 pin connector added to the preamp back and some PCB surgery .
Plan B and way more practical would be to build a stereo volume control inside an external case, and connect it between preamp and power amp, no need for a second preamp at all.
No need for it to be active, at all, since preamp has low impedance out and power amp has highish impedance in, I bet a 10K Log/Audio stereo potentiometer will be fine.
You can still use the sliders as a sort of semi-fixed gain control, set them at a comfortable level, and then use the rotary one.
IF you happen to connect a very loud or very weak signal source, then you adjust it _once_ with the sliders and then go on with the rotary one for everyday use.
Balance control is not much used these days, if you NEED one it can be easily added.
You will not have noise or treble loss problems since we are talking 10k impedance (in fact output impedance will always be less than 2k5, go figure) , signal level is high and we hav 30/40 cm tops cable length.
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You could take a look at the thread on the Douglas Self preamp design. Carl Huff has developed some excellent PCBs for it. It's an active volume and tone control that can be configured for unity gain.
Doug Self Preamp from Linear Audio #5
Doug Self Preamp from Linear Audio #5
Oi amigo, tudo bem?
The main problem is not the volume control circuit itself but how will you adjust it, mechanically.
Obviously you want a rotary control instead of those sliders, which look cool but are impractical, specially with such a short travel..
The basic solution would be to disconnect those potentiometers, add some wires to carry signal to an external stereo volume pot , mounted on a small box on top of the preamp and back.
Correct technically but will need some 6 pin connector added to the preamp back and some PCB surgery .
Plan B and way more practical would be to build a stereo volume control inside an external case, and connect it between preamp and power amp, no need for a second preamp at all.
No need for it to be active, at all, since preamp has low impedance out and power amp has highish impedance in, I bet a 10K Log/Audio stereo potentiometer will be fine.
You can still use the sliders as a sort of semi-fixed gain control, set them at a comfortable level, and then use the rotary one.
IF you happen to connect a very loud or very weak signal source, then you adjust it _once_ with the sliders and then go on with the rotary one for everyday use.
Balance control is not much used these days, if you NEED one it can be easily added.
Hola que tal!
Yeah, the idea is the plan B. The only problem is that I fear that a passive control may dull the signal...
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Actually I want exactly the opposite: NO gain.
Also I don't want any tone control, just volume.
Actually I want exactly the opposite: NO gain.
No gain = 0dB = x1 gain = unity gain
I mentioned it because you wanted active device that is simple to create. Simple in relation to the link I sent means the circuit and related PCBs are available and the design is proven. Beyond that, Carl's PCBs are large and easy to work with.
In addition, the circuit had a defeat option for the tone controls. So you end up with an input selector and active volume control with an option for unity gain (0 dB) from a proven circuit by a well-respected designer (Douglas Self).
The thread is also active and any questions have probably already been asked or are promptly responded to by experienced builders.
Got it. Actually I was thinking in something still more simpler and smaller -- just a single pot in an active circuit with no gain. I have very small knowledge in electronics, so my GUESS when I asked specifically for 'active' is that an active circuit would be less subject to degrade the original signal than a passive circuit. My concern is that using a simple 10K passive pot may cut high frequencies specially in low volumes...
I think that the project you gave me the link is way too much for my needs and also way too expensive ($50). Considering the shipping and taxes it would easily reach $100. For less I could order a Chinese "hi-end" tube preamp or even buy a solid state second hand preamp with a rotating control and hook it in series with my existing preamp.
Cost here is a variable that I cannot ignore in this equation. I am not willing to spend more than $10 in parts to assemble such circuit. But if I cannot do that I probably will prefer to pick an off-of-the-shelf solution. In fact I didn't totally discard this option yet...
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"My concern is that using a simple 10K passive pot may cut high frequencies specially in low volumes..."
That's actually where a simple pot is at its best, with the least output resistance that would attenuate highs
due to load capacitance. The pot would be at its worst at a setting of half resistance (-6dB), seldom used.
This half of maximum setting gives the maximum possible output resistance (1/4 of the pot value)
That's actually where a simple pot is at its best, with the least output resistance that would attenuate highs
due to load capacitance. The pot would be at its worst at a setting of half resistance (-6dB), seldom used.
This half of maximum setting gives the maximum possible output resistance (1/4 of the pot value)
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I was checking the stores around and I found the Alps RK27 that was suggested by a friend of mine as being of superior quality (for 'audiophiles'). However in this store they have only the 50K pot. What would be the disadvantage of using it instead the 10K one in a passive circuit?
I agree with JMFahey. There's nothing magical about an active volume control. I think what you're really after is a passive attenuator with a buffer stage following it. The B1 is a great example of this.
Here's a link to the First Watt article discussing it: B1 Buffer Preamp
The DIYAudio store has a PCB solution based on this here: Mezmerize B1 Buffer
For the actually attenuator, you can use a simple pot like an Alps RK27 (break boards available) or go fancy with a stepped attenuator like Gold Point ($$$).
Or go really fancy with autoformers (AVC) like those from Intact Audio. Not cheap though. ZenMod has espoused the virtues of the AVC solution. You can read his blog for details.
If the Douglas Self preamp I referenced in a previous post doesn't appeal to you then I suspect some version of the B1 is probably what you're looking for.
"they have only the 50K pot. What would be the disadvantage of using it instead the 10K one in a passive circuit?"
The 50k pot would have five times the output resistance of a 10k pot (at the same setting),
and so it would have 1/5 the bandwidth of a 10k pot, all else equal.
It appears the RK27 series is currently only made in a 100k value. Some NOS 50k versions may still be available.
The 50k pot would have five times the output resistance of a 10k pot (at the same setting),
and so it would have 1/5 the bandwidth of a 10k pot, all else equal.
It appears the RK27 series is currently only made in a 100k value. Some NOS 50k versions may still be available.
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Ohhhhh!!! It DOES sound like magic for me!
I think that by 'active with 0dB gain' I was meaning a volume control circuit feed by some current, and therefore able to sustain the quality of the input signal. I think that this is probably what I was after!
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The issue is that any active device can alter the signal. There's no free lunch.
Signal attenuation is probably one of the most complex topics in line stage design. There are a myriad of solutions to address this each with their own trade-offs. Even a simple pot has a wide range of options and price points.
The simplest solution likely to achieve good results at the lowest price point is probably a B1 with an Alps RK27 pot. You could start with just the pot and see how you like it. You can also read the B1 article I linked to understand what role the B1 plays when inserted between the pot and amp.
Signal attenuation is probably one of the most complex topics in line stage design. There are a myriad of solutions to address this each with their own trade-offs. Even a simple pot has a wide range of options and price points.
The simplest solution likely to achieve good results at the lowest price point is probably a B1 with an Alps RK27 pot. You could start with just the pot and see how you like it. You can also read the B1 article I linked to understand what role the B1 plays when inserted between the pot and amp.
What does '1/5 the bandwidth' mean in practical terms?
The output impedance of the device driving the pot and input impedance of the following stage impact the pot's taper.
Rod Elliott has a good article explaining this: Beginners' Guide to Potentiometers
In particular, he states:
The B1 buffer specifically addresses the impedance of the following stage. It provide the pot with a very high impedance to avoid loading the pot while at the same time providing a low output impedance to the amp to avoid unnecessarily forming an voltage divider which attenuates the signal. . Note: You don't necessarily need the B1 to implement this. Any unity gain stable opamp can provide this. It's likely what you'll find on eBay. But there are many users on this site that prefer discrete solutions. Hence the popularity of the B1.
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You're looking for the "Analog Line Level" forum on this site. It's under the "Source & Line" group. Perhaps the mods can move this thread there.
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