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Old 18th April 2003, 12:44 AM   #1
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Default Relay volume control kit -- shameless plug

This is only slightly off-topic ...

Most of you builders will likely need a decent volume control, and since the PassLabs transistorized volume control is likely unbuildable for most of us (it is still sort of secret, patent pending, and nobody seems to have made much effort into building a controller for such a beast)

Here is the link: http://www.dipchipelec.com/apox.htm, an effort which started here on this board (Trading Post forum, but the guys are just too nice to post off-topic Remote relay volume control kit.)

I am particularly pleased with the Apox-1 and have put in my order . According to my measurements, mechanical switching of attenuators measures so much better than any method I was able to try (including saturated base BJT) + it does not require you to shunt to ground. This last point could be very helpful to Pass DIY'ers of the Balanced Zen pre-type ilk (can be used anywhere you want -- at input, output and of course between sources of input devices).

I firmly believe most (if not all) audiophile issues have been adressed in this design and look forward to receiving mine which will be used as a 6 channel tracking preamp for a digital crossover speaker system I am building (solves a huge problem for me). I have no economic interest in this project.

Petter
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Old 18th April 2003, 08:15 AM   #2
uli is offline uli  Austria
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Sensational link!!!!!!!!!!!!!!!!!!!!!!!


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Old 18th April 2003, 02:26 PM   #3
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Question 1 or 2, thats the question...

Hi Petter,

i am thinking about Apox1 too, but wich value for the resistors will i need for a Aleph P1.7?
And, is Apox1 or 2 better for me? What do you think?

Reinhard
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Old 18th April 2003, 07:52 PM   #4
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Hi,

Is the P1.7 a stock unit? Have not really looked at that schematic for a long time so I don't know what is optimal, so I went and took a look.

So it looks like the gain is developed across about 3.2KOhm resistance for each leg. In addition, each leg has a series element of 100 Ohms on the way out.

The volume control is close to what Apox 1 was like in the beginning and it is quite clever even though I much prefer the direct shunting. In the 1.7, however you will need something to pull the ac coupled output down to ground anyway (R64 provides such duty), but shunting is definitely still a good thing (if for no other reason than it saves relays).

If I take the worst possible cases, the output is downloaded very heavily at 62 (+100) in series and about 100 total in shunt. This is probably not how it was intended to be run, but illustrates the point.

I can't give you definite ideas, but I would recommend that you first of all nuke the 100 Ohm series resistor, and work with the spreadsheet to figure out optimal values. I plan to be making some comments on that later and I am sorry that I an unable to provide better recommendations for you at this point. The reason why it is somewhat problematic to provide optimal suggestion is that the volume control is direcly on the output which means that it is by itself responsible for output impedance.

Normally, I would have preferred to have the volume control between stages. You can still do that -- that is in fact what the Apox-1 is designed for.

You can also try this trick: Place the Apox-1 before the output capacitor -- shunting between phases, and you will not load the output capacitor with the volume control This will probably help a little as well.

Petter
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Old 18th April 2003, 11:54 PM   #5
jleaman is offline jleaman  Belgium
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I too have the p1.7 pre-amp. Im thinking about useing it and doing up a apox. Any Sujestions.
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Old 19th April 2003, 05:07 PM   #6
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Well I say use the Apox-1 in probably 10K mode (each phase at the highest attenuation) to shunt between phases BEFORE the output capacitors. You should be able to pull that one off pretty easily, simple remove the 100 Ohm resistors and place the Apox input/output across that.

I don't know what pot you are using today to set volume (if you are doing it at the output) -- but if you are happy with that you have a pretty good idea as to what will definitely work.

If you are doing the volume stuff at the input, especially if you have high output sources such as modern digital equipment, you are pretty much free to do what you want in terms of ranges on the Apox.

Petter
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Old 24th April 2003, 10:59 AM   #7
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Hi all,

I do not want to upset anybody involved in this design , but just for your information I did design (and publish) relay-resistor volume control circuit, that uses direct binary-2-log (or BCD-2-log) conversion, has constant input impedance independent of the attenuation settings and uses just 1 relay per binary bit, so 6 relays make 64 steps in 1 dB with perfect precision (only limited by the resistor array tolerance). It could be controlled by a simple and noise-free CMOS logic and (if BCD) could directly display the attenuation with 7-segments LED using just a simple BCD-7 decoder. Unfortunately it is a commercial design and I am no longer working for the company who has rights to it. However, if there is enough interest here I may be able to persuade the company to offer a ready made module - stereo pair, 5V 200mA max supply, logic level inputs, BCD 2-digit control, 80 steps in 1 dB + complete mute (more than -120 dB), 10 K input impedance , 0.05 dB precision over the range, less than 0.02 dB imbalance between channels, output impedance roughly as of a normal 10 K pot. Probably in the area of $150 each. Any takers?

Al
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Old 24th April 2003, 12:01 PM   #8
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Hi Al,

No offense taken. I hope the following does not sound defensive.

1) I don't think that we have ever stated that the design is original. I hope that we have not violated any patents. If so, we would be happy to work out a royalty payment. .

2) The specs on your unit sound quite impressive. I would expect ours to measure as just as good.

3) I don't see any mention of a remote control interface and no input switching. The goal of our project was to incorporate all of these elements together. Granted, a remote interface could be easily added by one of those remote to digital output interfaces.

4) If you look closely at the cost of our unit, the volume boards themselves are actually less expensive than $150.

Sure, I think that we have a good system. Is it the best. No. Are you free to market your own product. Absolutely! That is free market capitalism.


Best Regards,

Dale
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Old 24th April 2003, 12:53 PM   #9
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Dear Dale,

Quote:
Originally posted by harvardian
Hi Al,

No offense taken. I hope the following does not sound defensive.

1) I don't think that we have ever stated that the design is original. I hope that we have not violated any patents. If so, we would be happy to work out a royalty payment. .

2) The specs on your unit sound quite impressive. I would expect ours to measure as just as good.

3) I don't see any mention of a remote control interface and no input switching. The goal of our project was to incorporate all of these elements together. Granted, a remote interface could be easily added by one of those remote to digital output interfaces.

4) If you look closely at the cost of our unit, the volume boards themselves are actually less expensive than $150.

Sure, I think that we have a good system. Is it the best. No. Are you free to market your own product. Absolutely! That is free market capitalism.

Do I like that you posted in this thread? NO

Best Regards,

Dale
1) My design is not patented and it is published. I deliberately did it to avoid all the hassle. So not to worry .

2) I am quite sure that it will be. Almost

3) No remote, and it is not a complete unit .

4) That is good, and I am happy that you have a price advantage. I probably would not benefit at all from any sales of my design anyway... .

Don't be mad. I suspect that I have to apologise - it would be more appropriate to start a new thread and not post here. Sorry.

Moreover I am happy to see that your design is near the completion. You've done a good job. I did not follow all the details - it is a very long thread after all. So - here is a question/advice - is the micro in your unit works all the time? It is much better to put it to sleep when its operation is not required. If you already done so, well done. I was just surprised to see so much interest in the relay-resistor configuration and decided to show off a bit. That's all. It may be even possible that you will have a look at the module and can design the driving electronics for it, if you wish, as my design offers some advantages, thought for a higher price. Partly it is a result of a custom made laser trimmed down to 0.1% resistor array.

Good luck

Al
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Old 24th April 2003, 08:36 PM   #10
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Al,

If your design is published, I would be very interested in checking it out. Showing off is a good thing

Petter
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