| ralf |
Hi, All
hope you enjoy nice xmas days...
Has anyone experiences with led potentiometers like this one in TACT amlifier?
are there kits somewhere? is it difficult to build?
how do they sound?
Ralf |
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| Mad_K |
| Isn't this a digital unit? I'm guessing the volume is adjusted in the digital domain (IC). |
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| GRollins |
How Tact does it I don't know, but it is quite easy to build an LED volume control. I've got a Morley volume pedal for my bass rig that uses such a scheme; they've been doing it for years.
At least in the case of the Morley, I think the receiving element is a CdS cell. I've never heard anyone say whether CdS cells sound decent or not. I believe they have a tendency to fatigue when exposed to the same light level for a while, so the volume might not remain exactly where you left it. However, I can say from experience it doesn't change by enough to matter.
If you let your imagination stretch a bit, you can start getting into using phototransistors instead, which are superior in many ways.
I've got some notes on this sort of thing around here somewhere. I was looking into it from another angle a year or two ago but dropped it when a crisis popped up. I remember leaving more detailed notes than usual so that I'd be able to pick up the thread later when things calmed down. It looked--at least for my purposes--to be an interesting avenue for exploration.
Grey |
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| paulb |
Isn't the LED just displaying the setting? I agree with Mad_K, I think it's digital. PGAxxxx or something similar.
CdS cells? Can you still buy those things? Sounds like something out of an old Popular Electronics. |
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| Nisbeth |
CdS cell = LDR (light dependant resistor) - should be available almost anywhere.
/U. |
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| jcarr |
| Maybe you could get a resistor with a horrid tempco, wrap a Nichrome coil around it and start passing some power through the coil... :D |
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| tvi |
I posted this in the "Son of Dork: Attenuator" thread, might be of interest.
<a href="http://www.diyaudio.com/forums/showthread.php?threadid=3626&highlight=dorkus"><img src="http://www.diyaudio.com/forums/attachment.php?postid=38072"></a>
I think it is similar to the <a href="http://www.melosaudiorestoration.com/article-03.html">Photentiometer</a> used by Melos in thier preamps??
Try searching Vactrol with google
Regards
James |
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| FUCHSAUDIO |
New to the forum and I've been curious about this circuit and topology for a long time. I was wondering if anyone had technical info, or tried to make their own Phototentiometer ? I thought I'd seen a post by georgehifi about this.
I would appreciate any information out there. |
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| Nelson Pass |
I played with the Cadmium Sulfide elements (the ones used
by Randy Smith's Mesa) and while they are workable for
musical instruments, they had too much distortion for use in
"hi-fi", and the tracking you can achieve between 2 channels
was not good.
:bawling: |
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| Nelson Pass |
I just accidentally replied over in the referenced solid state
thread, but what I said was that I'd have to see these parts for
myself and measure them, as the samples I played with
(years ago now) had terrible distortion at line levels. |
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| EUVL |
> I just accidentally replied over in the referenced solid state thread
I answered too quick on the other thread before you moved this back here.
Would be most interested to know your findings, especially with the Silonex NSL-32SR3, which has supposedly the lowest distortion. I am sure you have much better measurement equipment that I (which is next to none). But I shall post some results as well when I get round to measuring my examples, hopefully before 5 October.
Patrick |
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| Nelson Pass |
I didn't test the Silonex parts, I tested VacTec's as I recall. It
would be nice if they are as good as those curves, so please
let me know what you get. |
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| EUVL |
My equipment is limited to a 16 bit digital scope and 12 bit functions generator, no distortion meter.
If you would be interested, I should be more than happy to send you one for analysis.
Patrick |
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| maxw |
| quote: | Originally posted by ralf
Hi, All
hope you enjoy nice xmas days...
Has anyone experiences with led potentiometers like this one in TACT amlifier?
are there kits somewhere? is it difficult to build?
how do they sound?
Ralf |
I'm not sure if you meant the LDR attenuator thing or just having a digital LED readout of the volume level but here are two places you can get kits that have digital LED readout of the volume level:
http://eshop.diyclub.biz/product_in...products_id=196
http://electronics.dantimax.dk/Kits...ards/index.html |
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| Rob Dingen |
Hi
I play arround with the Silonex NSL-32SR3 and did some measurements.
I put out 10Vpp and place the resistor in series with my distorsion analizer.
I leave the 10Vpp always the same and changed the resistor value.
200K = 2.75% 3e Harmonics
100K = 1% 3e Harmonics
50K = 0.3% 3e Harmonics
25K = 0.05% 3e Harmonics
10K = below 0.01%
So if you build a very good current regulator and keep it max at 10k you could build a nice Volume Pot.
At 20ma it's 50 Ohm so you have about -48 dB
Rob |
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| EUVL |
Would you be kind enough to repeat the test at 1Vpp, to see whether the amplitude dependence of the distortion is as posted by Silonex ?
Thanks,
Patrick |
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| Rob Dingen |
Hi EUVL
That's a bit difficult the input impedance from the analizer = 100k and it needs minimal 300mv RMS at the input.
So what I did is decrease the signal that its enough for the analizer and the THD drops.
At 100k was 1% and drops down to 0.07% and if you calculate i put aboud 600mv rms in about 1.8Vpp.
Rob |
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| EUVL |
I'll try to measure one next week, though I have no distortion analyser. So all I can measure is any deviation fron a straight line.
Patrick |
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| EUVL |
Have measured one example and the deviation from linearity is beyond the noise level of my 16 bit Handy Scope 3.
So I can only assume that Rob's figures are valid.
Patrick |
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| jev |
| Hi, I am building an Aleph P with these volume meters http://electronics.dantimax.dk/. Also use a programmable Philips remote control. Is not yet alive but the volume meter seems to work! |
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