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Volume control for M3

post #1 of 19
12/8/09 at 9:28am
Thread Starter 
I am looking for a volume control for an upcoming M3 build. I need it to have superior tracking at low volumes, as I will almost definitely use it with IEMs. Thus, I am looking at stepped attenuators or digital ones. I was hoping this would be a cheap endeavor, but it looks to not be. So, what is out there that is cheap? Oh, and it has to be balanced (there went the cheap part).

I found the digital attenuator thread a week or so ago and it pointed to an alps logarithmic pot. On these log attenuators, are the less big steps near the low volumes or the high ones?

Thanks,
Nkk

EDIT: here is the Alps pot:
http://cgi.ebay.ie/ws/eBayISAPI.dll?...m=260438855634

I do not think it is stepped. Does anyone know if it has good channel matching in the lowest volumes? If not it looks like I am forced into paying at least $80, probably much more.
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post #2 of 19
12/8/09 at 11:03am
Keep your gain low if you're only going to use IEMs. You could likely use just unity gain.

You could also skip the bass boost and use that control as a variable gain control (documented on the M3 pages) to allow for different headphones.
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post #3 of 19
12/8/09 at 3:11pm
Uhm... that Alps RK27 is 6-gang (6-channel so to speak), you only need 2 channel.
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post #4 of 19
12/8/09 at 4:07pm
I think that your best bet if you want cheap steppers would be to use dual stereo steppers from ebay. That would probably be under $80. Not sure about the quality tho...
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post #5 of 19
12/8/09 at 4:18pm
Steppers are great for channel matching, but still aren't probably a good option for IEM's - the step size between the low steps are just far too large.

DACT CT2 for example...... the low steps where you will probably want to operate with IEMs are mute, -60dB, -50dB, -46dB, -42dB.
Goldpoint might be even worse. Mute, -62dB, -53dB, -46dB, -41dB.

So chances of finding a suitable listening level are quite slim without other modifications.
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post #6 of 19
12/8/09 at 5:32pm
Quote:
Originally Posted by Beefy View Post
Steppers are great for channel matching, but still aren't probably a good option for IEM's - the step size between the low steps are just far too large.
with relay steppers, at least with DIY, you can pick the # of relays or bits you want. usually up to 8 but at 8 bits you have 256 steps. I'm working on a 7bit version for myself and that gives me 128 steps. I like 1db steps and that's a *whole* lot of range, right there. on the PGA chips, they allow you to go from -96 to +32, which is also 128 steps of range, just mapped up to the gain range rather than stopping at 0, which is what relay steppers do (nonbuffered kind).

even using the -96 .. 0 range of the PGA chips (so, using less then 128 click stops) at 1db spacing seems fine for all kinds of loads.

mech switches are not the answer. solid state (chip) or relay is the answer.
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post #7 of 19
12/8/09 at 5:38pm
Big fan of the PGA chips here. When I get around to building an M3 that'll definitely be in there.
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post #8 of 19
12/8/09 at 5:38pm
Quote:
Originally Posted by nkk View Post
I am looking for a volume control for an upcoming M3 build.
here's a teaser: my own DIY digital volume control and an M3 under it:



I'm still working out the noise issue, though. location of the vol control board 'matters' and so does the analog op-amp (inside the vol control chip) dual-rail power supply. and even the +5v digital side of the chip. I might have to do more isolation to lower the noise floor (its fine for speaker use but you do hear the PGA noise in phones, in *this* build. in other builds, it seemed a lot quieter to me, as I remember and also tested.)

so one word of advice, plan extra room inside the box to keep the digital parts away from the analog parts (esp. near the inputs of the analog sections). I think my box, while nice and compact, puts the digital stuff too close to the analog side of things. that's never a good or desirable thing. next time, I'd go a size or two higher and reposition where the vol control and controller would go.
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post #9 of 19
12/8/09 at 5:44pm
Quote:
Originally Posted by linuxworks View Post
mech switches are not the answer. solid state (chip) or relay is the answer.
Well, those Khozmo 48 step ladder attenuators looked the part for a while, but I'm still unsure as to whether any have shipped yet......

But I do tend to agree that there needs to be more options in the relay and SS realm, and I myself am leaning towards the SS. Although many might scoff at the idea of their signal passing through what is essentially an OPAMP, I would wager that it is better than the multiple mechanical connections of steppers and relays.
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post #10 of 19
12/8/09 at 5:58pm
Thread Starter 
Quote:
Originally Posted by FallenAngel View Post
Uhm... that Alps RK27 is 6-gang (6-channel so to speak), you only need 2 channel.
For balanced? Did you read my OP? I know 6 is still greater than four, but I am fine with 2 unused channels for that price.

Quote:
Originally Posted by cobaltmute View Post
Keep your gain low if you're only going to use IEMs. You could likely use just unity gain.

You could also skip the bass boost and use that control as a variable gain control (documented on the M3 pages) to allow for different headphones.
The thing is it will also drive an updoming K701 or HD650. I am thinking I am just wiring a gain switch into the gain resistors position. Since I have sort of given up and am getting panels or panels express, it makes very little extra work for me.

Quote:
Originally Posted by Beefy View Post
Steppers are great for channel matching, but still aren't probably a good option for IEM's - the step size between the low steps are just far too large.

DACT CT2 for example...... the low steps where you will probably want to operate with IEMs are mute, -60dB, -50dB, -46dB, -42dB.
Goldpoint might be even worse. Mute, -62dB, -53dB, -46dB, -41dB.

So chances of finding a suitable listening level are quite slim without other modifications.
And that answers my log scale question. That is just annoying. Thanks for the info.

Quote:
Originally Posted by linuxworks View Post
with relay steppers, at least with DIY, you can pick the # of relays or bits you want. usually up to 8 but at 8 bits you have 256 steps. I'm working on a 7bit version for myself and that gives me 128 steps. I like 1db steps and that's a *whole* lot of range, right there. on the PGA chips, they allow you to go from -96 to +32, which is also 128 steps of range, just mapped up to the gain range rather than stopping at 0, which is what relay steppers do (nonbuffered kind).

even using the -96 .. 0 range of the PGA chips (so, using less then 128 click stops) at 1db spacing seems fine for all kinds of loads.

mech switches are not the answer. solid state (chip) or relay is the answer.
Like the Joshua Tree? A bit more than I wanted to spend, but whatever. After I looked at everything, my budget became a lot less strict.

Quote:
Originally Posted by linuxworks View Post
here's a teaser: my own DIY digital volume control and an M3 under it:

[Image cut for space]

I'm still working out the noise issue, though. location of the vol control board 'matters' and so does the analog op-amp (inside the vol control chip) dual-rail power supply. and even the +5v digital side of the chip. I might have to do more isolation to lower the noise floor (its fine for speaker use but you do hear the PGA noise in phones, in *this* build. in other builds, it seemed a lot quieter to me, as I remember and also tested.)

so one word of advice, plan extra room inside the box to keep the digital parts away from the analog parts (esp. near the inputs of the analog sections). I think my box, while nice and compact, puts the digital stuff too close to the analog side of things. that's never a good or desirable thing. next time, I'd go a size or two higher and reposition where the vol control and controller would go.
Thanks for the info. Mine is balanced, so my case will be large regardless, so I will take heed of your recommendation.

Thanks,
Nkk
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post #11 of 19
12/8/09 at 6:11pm
Quote:
Originally Posted by nkk View Post
The thing is it will also drive an updoming K701 or HD650. I am thinking I am just wiring a gain switch into the gain resistors position. Since I have sort of given up and am getting panels or panels express, it makes very little extra work for me.
I plan to do something like that with the gain controlling R's in the m3. at the very least, a few click stops of low/med/high gain and then let the real vol control work inside that range.

Quote:
Like the Joshua Tree? A bit more than I wanted to spend, but whatever. After I looked at everything, my budget became a lot less strict.
I'm working on my own (along with AMB). I have no idea what the parts will cost in the end, but it does not appear to be *that* much. the costly items, in my stepper build, are the relays themselves and that's only because latching relays (what I prefer to use) cost a lot more. figure $4 per relay. the resistors are not significant and the controllers might be a few dollars each and you'd need 2 or 4 i2c chips and some buffer drivers, but all that is still low count and low cost stuff. the relays (and the # of them needed) is the big cost item. figure $4 or so per relay per bit per 'side' of the channel (so 2x that for balanced use). that's the lion's share of the cost of the parts, at least.

but we don't have boards ready yet and there's no date on when it will happen (its in progress but so are a few other things related to this series).

if you are really into saving money, this *could* be built up on perf board (I did!). and then you don't have to wait for boards, you just build it and my opensource arduino firmware can control it (also free).

I would also consider the PGA chips as you may find they do what you want and take up a LOT less room (if you need balanced you can gang them up fairly easily and they all 'listen' on the same bus for vol control changes).
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post #12 of 19
12/8/09 at 6:16pm
Quote:
Originally Posted by Beefy View Post
Well, those Khozmo 48 step ladder attenuators looked the part for a while, but I'm still unsure as to whether any have shipped yet......
I wouldn't give those guys a dime. Based on what I see on Audiogon they've changed their design to be pretty fugly and they still won't reply to my emails.

My thought would be that if it's an amp for IEMs that lowering the gain and perhaps adding a voltage divider on the input would be good places to start while still allowing for the use of a cheap and simple pot like the RK27.
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post #13 of 19
12/8/09 at 7:33pm
Quote:
Originally Posted by n_maher View Post
My thought would be that if it's an amp for IEMs that lowering the gain and perhaps adding a voltage divider on the input would be good places to start while still allowing for the use of a cheap and simple pot like the RK27.
Ditto.

se
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post #14 of 19
12/8/09 at 7:36pm
Thread Starter 
Quote:
Originally Posted by linuxworks View Post
I plan to do something like that with the gain controlling R's in the m3. at the very least, a few click stops of low/med/high gain and then let the real vol control work inside that range.



I'm working on my own (along with AMB). I have no idea what the parts will cost in the end, but it does not appear to be *that* much. the costly items, in my stepper build, are the relays themselves and that's only because latching relays (what I prefer to use) cost a lot more. figure $4 per relay. the resistors are not significant and the controllers might be a few dollars each and you'd need 2 or 4 i2c chips and some buffer drivers, but all that is still low count and low cost stuff. the relays (and the # of them needed) is the big cost item. figure $4 or so per relay per bit per 'side' of the channel (so 2x that for balanced use). that's the lion's share of the cost of the parts, at least.

but we don't have boards ready yet and there's no date on when it will happen (its in progress but so are a few other things related to this series).

if you are really into saving money, this *could* be built up on perf board (I did!). and then you don't have to wait for boards, you just build it and my opensource arduino firmware can control it (also free).

I would also consider the PGA chips as you may find they do what you want and take up a LOT less room (if you need balanced you can gang them up fairly easily and they all 'listen' on the same bus for vol control changes).
Any idea on when it will be done? As in, before spring break time this year, or after? I am trying not to annoy you too much here, but with your knowledge and useful gadgets, you are way to big of a resource for me not to pester a bit.

Quote:
Originally Posted by Koyaan I. Sqatsi View Post
Ditto.

se
And that will not detrimentally affect using it with an HD600/650 or K701? The gain will be on a switch, but the divider?

Thanks
Nkk
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post #15 of 19
12/8/09 at 8:57pm
for the pga solution, I got jumpstarted from some really tiny boards from 'error401'. his post:

http://www.head-fi.org/forums/f6/min...ontrol-280515/

I took that board and hacked it to interface to my arduino as:



and that worked quite well for a long time, for me. I used it to control vol for tv, movies and headphone/audio use. the board also works with the intended firmware, I'm sure, but I never tried - I intended to use that board with my own controller and firmware. but if you don't need an lcd, you can go with *his* firmware and use a rotary encoder, alone.

if you feed a low noise power supply into this circuit, you should get good results. when I perf-boarded my PGA chip, it wasn't so good; but a decent pcb layout makes this chip work pretty well. and, at times, it WAS handy having some gain (esp. for tv watching or movies with DD5.1 downmixed to 2.0; the audio was often 10db lower than it should be and the PGA chip offers 32db of real gain if you need it. relays never offer gain )
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