[John Wilson]

Light Dependent Resistors Light Dependent Resistor - Electric Circuit http://www.biltek.tubitak.gov.tr/gel..._NSL19_M51.pdf

 

[amphead]

LDR, sounds like an interesting mod for the MAX. I'm certainly tempted to try it. If the standard MAX hammond case is modified a little, it should fit. Using MrMajestic2s case would seem to fit even easier. Ouch my wallet.

 

[BoilermakerFan]

Quote:

Originally Posted by amphead /img/forum/go_quote.gif LDR, sounds like an interesting mod for the MAX. I'm certainly tempted to try it. If the standard MAX hammond case is modified a little, it should fit. Using MrMajestic2s case would seem to fit even easier. Ouch my wallet.

I think it will fit in the longer case, with room for the Alien DAC on the other side. Just have to remote mount the potentiometer to the front.

 

[mik000000]

I have finished my max otherthan the tube sockets. Can i apply power to check voltages (and tube led brightness) without tubes installed? or will that damage the transistors?

 

[tomb]

Quote:

Originally Posted by mik000000 /img/forum/go_quote.gif I have finished my max otherthan the tube sockets. Can i apply power to check voltages (and tube led brightness) without tubes installed? or will that damage the transistors?

It won't damage anything, but you won't have any voltage through the buffer without the tubes. Unlike the revMH Millett, though, which took the LED power from the heater circuit, the MAX's will light up fine without the tubes.

EDIT: Scratch that. You will get voltage through the buffers, but it will be greatly reduced. That makes it dangerous to attempt biasing the buffers. The MAX I just checked had almost a 30mV difference between no tubes and with tubes - with the complete w/tubes condition having a much higher bias reading.

 

[tomb]

Volume Pots -
The Opti-Vol could be an interesting option for those ultimate MAX builds or for anyone who's contemplating wiring an offboard pot. However, it's probably for someone who's interested in an advanced build. Besides the fit problem - as Fran mentioned , you have to power it too: + and - 15VDC @ 13ma. As best I can tell, Gary Ball is referring to -15VDC and +15VDC. I don't know that for sure, but looking at his other stuff, when he quotes "+/- VDC," he's also referencing AC and CT transformer options. That makes me think he's really talking a voltage divider from a 30VDC supply. I could be wrong about that - because obviously, Fran has one working. If true, though, it would be very difficult to get that kind of voltage from a regular MAX.

For those wishing to compare with the ALPS and other pots, Tangent's tests are here: http://www.tangentsoft.net/audio/misc/pot-curves.zip

If you are interested in looking at Tangent's spreadsheet in that zip file, the formula for minimum dB is LOG(E2)*20, where "E2" is the cell on the ALPS worksheet tab. For some reason, Tangent left that off of the ALPS sheet. For instance, the minimum dB range (volume range) for the Panasonic EVJ is -43.5dB. One of those fake ALPS attenuators is -48dB, while a DACT CT2 is -46dB. When you plug that equation into the ALPS page, it results in 84.3dB, easily the best of the lot. The SKA Opti-Vol quotes a dB control range of 50dB.

The average channel difference is much better on the DACT and even the fake ALPS Stepped Attenuators. That could be the reason stepped attenuators seem to sound better, but I'm no expert on pots. It does seem that the ALPS tests quieter than the rest. It would be nice to see some tested data on the Opti-Vol.

Another thing to consider - part of the reason the ALPS is nicknamed the "Blue Velvet" is the feel that you get when turning the knob. One of the features of the Opti-Vol is its inexpensive potentiometer. I believe that means you would give up the positive feel of the ALPS, but not having tried an Opti-Vol, I can't say that for certain. Looking at the pics, though, it looks like a push-on type shaft. It's possible he may be able to substitute something different, but I don't know.

I'm not trying to be skeptical per se, just mentioning some of the things that perhaps should be considered before anyone goes abandoning the long-accepted ALPS.

MiniMAX -
The Opti-Vol will not fit in the MiniMAX, btw, which will have precious little room for anything but the specified parts in the Lansing case. Colin has been working on the board design lately, btw - we've traded comments on a couple of layouts. He is currently working on making sure the new, smaller 0.18uf Vitamin Q's will fit without tombstoning or kneeling. The new MiniMAX board will also accomodate 0.22uf Wima's all around, something different than the proto, which used 0.1uf's. The 0.22uf's impart a bit more smoothness.

As for the 0.18uf 96P series VitaminQ, I've been testing it lately with an ES version MAX. When using FK6 tubes, it closely approaches the detail of Black Gates - very closely. So, I may be editing some of the "Can't Miss Builds" a bit.

MAX Review -
Meanwhile, you might check out the nice Mini-Review Colin found in the Head-Fi Amplifiers section. I was hoping he'd post it himself, but maybe he's been too busy with school and work lately. He and I have both been a little sick of late and you know how that puts you behind with work and school.

Mini Review: PPX3 and Bada PH-12 with comparisons to the Millet Max

I wonder if that was user Listen2This's MAX? I think he helped organize that Lawrence, Kansas meet.

 

[Fitz]

Quote:

Originally Posted by ruZZ.il /img/forum/go_quote.gif good pot is important

Indeed.

 

[mik000000]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif It won't damage anything, but you won't have any voltage through the buffer without the tubes. Unlike the revMH Millett, though, which took the LED power from the heater circuit, the MAX's will light up fine without the tubes. EDIT: Scratch that. You will get voltage through the buffers, but it will be greatly reduced. That makes it dangerous to attempt biasing the buffers. The MAX I just checked had almost a 30mV difference between no tubes and with tubes - with the complete w/tubes condition having a much higher bias reading.

understood, but i can verify the power supply stage, and get the led's working before i solder in the tube sockets?

 

[tomb]

Quote:

Originally Posted by mik000000 /img/forum/go_quote.gif understood, but i can verify the power supply stage, and get the led's working before i solder in the tube sockets?

YEP

 

[kvant]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif ...you have to power it too: + and - 15VDC @ 13ma. As best I can tell, Gary Ball is referring to -15VDC and +15VDC. I don't know that for sure, but looking at his other stuff, when he quotes "+/- VDC," he's also referencing AC and CT transformer options. That makes me think he's really talking a voltage divider from a 30VDC supply. I could be wrong about that - because obviously, Fran has one working. If true, though, it would be very difficult to get that kind of voltage from a regular MAX.

I haven't seen the schematic of the OptiVol, but I think that it is reasonable to assume that you could power it single rail and lift the signal up between the rail and ground with a capacitor and a couple of resistors. The rail we have on board here should be just fine to power it then.

Quote:

Another thing to consider - part of the reason the ALPS is nicknamed the "Blue Velvet" is the feel that you get when turning the knob. One of the features of the Opti-Vol is its inexpensive potentiometer. I believe that means you would give up the positive feel of the ALPS, but not having tried an Opti-Vol, I can't say that for certain.

Well, I have a bunch of Panasonic EVJs and they feel pretty good too. Anyway, is the feeling while turning the knob that important feature of a pot? Besides that, there is another pot from ALPS known as Black Beauty. I don't know what is beautiful about it, but since it is typically hidden inside an enclosure, you don't get to admire it too often. I guess there is only that much information in a nickname.

 

[tomb]

Quote:

Originally Posted by kvant /img/forum/go_quote.gif I haven't seen the schematic of the OptiVol, but I think that it is reasonable to assume that you could power it single rail and lift the signal up between the rail and ground with a capacitor and a couple of resistors. The rail we have on board here should be just fine to power it then.

Yes, if there were 30VDC to work with - there's not unless you build a transformer-supplied MAX. I did mention a voltage divider - again, another reason why I stated perhaps it's an advanced build.
Quote:

Well, I have a bunch of Panasonic EVJs and they feel pretty good too. Anyway, is the feeling while turning the knob that important feature of a pot? Besides that, there is another pot from ALPS known as Black Beauty. I don't know what is beautiful about it, but since it is typically hidden inside an enclosure, you don't get to admire it too often. I guess there is only that much information in a nickname.

Perhaps the push-on shaft is enough to bother your sensibilities?

For what it's worth, I agree that the EVJ has a nice feel as long as you're not looking at it.

 

[kvant]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif Yes, if there were 30VDC to work with - there's not unless you build a transformer-supplied MAX.

I don't quite understand this statement. What voltage do you have after the regulator? 27V? There is surely enough wiggle room with the OptiVol so that 27V will do. I mean, the signal we are attenuating is line-level, some 3V peak, so there is hardly a real need for such a high rail. That +/-15V is probably just a convenient value, which is typically available in a preamp.

Quote:

Perhaps the push-on shaft is enough to bother your sensibilities?

Well, yes, that looks... ugly. But then again, chances are that one can buy a pot with slightly different part number that will be absolutely equivalent, just with a more convenient shaft.

 

[tomb]

Quote:

Originally Posted by kvant /img/forum/go_quote.gif I don't quite understand this statement. What voltage do you have after the regulator? 27V? There is surely enough wiggle room with the OptiVol so that 27V will do. I mean, the signal we are attenuating is line-level, some 3V peak, so there is hardly a real need for such a high rail. That +/-15V is probably just a convenient value, which is typically available in a preamp.

I'm certainly no expert on the Opti-Vol. If you state that it will perform to specifications with only +/-13.5V, then I won't dispute that.

Quote:

Well, yes, that looks... ugly. But then again, chances are that one can buy a pot with slightly different part number that will be absolutely equivalent, just with a more convenient shaft.

Well, yes - but doesn't that get you back into the selection-of-a-quality-pot business all over again?


EDIT: It wasn't my intent to debate about this - only to offer some opposing items that didn't seem to be considered. It might be an interesting thing to try.

 

[kvant]

Quote:

Originally Posted by tomb /img/forum/go_quote.gif If you state that it will perform to specifications with only +/-13.5V, then I won't dispute that.

Just found a post by Greg Ball on his forum that clears the fog, check post #125 at 'http://ska-audio.com/Forum/YaBB.pl?num=1178438672/120'

 

[fran]

On the optivol:

You only need single rail voltage. The standard kit comes with a current limiting resistor sized for 30VDC supply - which is whats available in Gregs other DIY amp offerings. It will work of any supply >6VDC - you just need to resize that resistor. If you want to do that, you know that the thing needs 13mA, you will know your voltage, plug the 2 into an online ohms law calculator and it will give you the right resistor. I told Greg what I wanted it for and he included the appropriate resistor in the kit for me. I am using one in my 24V aikido (at 24V) and I'm using another in a valve preamp and I have it running off the 6.3VDC heater supply. Both work perfectly.

So to summarise:

1. Single rail voltage anywhere from 6VDC upwards. Cleaner the supply the better. Resize resistor to suit voltage.

2. The pot is a basic one, but feels pretty OK to me. Don't think you would really notice it any different to an alps blue if you weren't told. Feels way better than a stepped pot.

3. It is a simple push-on type splined pot, if you want to use a knob with screw fixing you may need to slip a shim into the slot in the shaft to stop it closing under the screw.

4. It is very easy to build, certainly if you can build a max you can do this.

5. It most likely won't fit in the standard hammond case, but since I don't have one I can't say for sure. It might just clear the board but that wouldn't leave you much room for in/out wiring.

6. Cost seems to be AUS$28 which from XE.com turns into US$25. Way cheaper than a stepped pot and not that much more than a alps blue ($16+shipping)


As usual YMMV. Not on a crusade here or anything! Alps pot is very well supported and thought of here and elsewhere. I suppose this would be good for someone who wanted to do something a little different or who had used the alps before and would like to experiment a bit.


Fran