would it help the sound quality if the Lightspeed would have a constant impedance at output, e.g. 5kOhm?
Tolu said:
No, as long as the input of the power amp is highish 100k and the input capacitance is below say 200pf, the source is low impedance and strong (current).
The Lightspeed Attenuator as I make them for my customers, is (series AND shunt) and has a fairly constant impedance of around 7K.
If you made a cheaper version (series OR shunt) to save on LDR's and the "extreme" headache of matching 4 LDR's, a series with a shunt resistor or a shunt with a series resistor, then yes in these the impedance does change quite a bit, and do not sound as good. They were my MkI Lightspeed Attenuators that were sold a few years back, but all have now been upgraded up to MkII status, (series/shunt)
Cheers George
Hi George,
thanks for explanation.
Do you have a trick how to get the min volume lower? My Lightspeed has a lowest volume of about -56 dB. That's not quiet enough sometimes in connection with my power amp.
I think the 100k pot for the shunt part is too little, or? There is still too much current for the LDR.
thanks for explanation.
Do you have a trick how to get the min volume lower? My Lightspeed has a lowest volume of about -56 dB. That's not quiet enough sometimes in connection with my power amp.
I think the 100k pot for the shunt part is too little, or? There is still too much current for the LDR.
Hi Thomas, most people have no problem with the minimum volume, it's a whisper, if you have built it to the circuit that i have posted, but if you have a very high gain power amp (eg .5volt to clip) or very efficient speaker (eg 100db), then yes the minimum volume can get above a whisper. You could drop the gain of the amp, (raise the feedback) but it must be done, so it doesn't become unstable. or (not the best) lower the output of the source.
The problem is with the range of the NSL-32SR2S LDR's, (min and max darkness/light impedance) and there are no better ones for this yet on the market that are also matchable.
Cheers George
The problem is with the range of the NSL-32SR2S LDR's, (min and max darkness/light impedance) and there are no better ones for this yet on the market that are also matchable.
Cheers George
And don't forget to vote a "Passive Preamp" forum.
Were second from the top now, of getting it.
We need it, as us passive nutz are all over the place
http://www.diyaudio.com/request/
Cheers George
Were second from the top now, of getting it.
We need it, as us passive nutz are all over the place
http://www.diyaudio.com/request/
Cheers George
Tolu said:
Tolu,
To achieve silence you can put a stereo mute switch between the outputs of both channels and ground.
Switched pot.
Another option is to use a switched pot to control the current. I found some local, stereo and mono. They also allow you to turn off LDR's to extend life if not used for long periods.
George
Another option is to use a switched pot to control the current. I found some local, stereo and mono. They also allow you to turn off LDR's to extend life if not used for long periods.
George
If I have 3 meters of interconnect cable between lightspeed and amp do you think will be more proper if I use a buffer after the lightspeed to have a good drive possibilities?
Tolu said:
No, because as it is the LDR's are pushed to their safe max in my published circuit.
Yes but better to reduce the three to one if you can, and use low capacitance interconect < 100pf per footfelixx said:
Cheers George
Thx George....but what about the distance between the source (cd-payer) and preamp?.....1 meter more or less?
felixx said:
There you can have longer, 2mt, because of the lower output impedance of the cd player, so long as it's not tube output.
Cheers George
I am extreamly interested in this project. Is there anywhere to buy 4 pre-matched vactrols? I only want to build one for myself and can't really see a use in having a bunch left over from matching.
Greyskale said:
Forget about the Vactrols, wrong resistances and totally unmatched. The only one is the NSL-32SR2S from Silonex these are matched/sorted sort of, you still need to get around 10-15 to get a good match of 4, and the only place cheap enough for this small quantity is here Allied Electronics. Buy some Panadol, (the big box) while your at it.
http://www.alliedelec.com/Search/Pr...SC=NSL-32SR2S&R=699-3011&sid=4754988062CD617F
Cheers George
georgehifi said:
These are actually what I was going to pick up 😀
I don't believe I've ever seen Panadol in the US... headache inducing project?
Greyskale said:
These are actually what I was going to pick up 😀
I don't believe I've ever seen Panadol in the US... headache inducing project?
Vactrol: (Perkin Elmers's name), not so good for this project.
Panadol (Paraceteamol) mandatory, take 2 every 4 hours while matching LDR's, they should give them out in a kit from with the LDR's.
Cheers George
Hi
I bought 12 pieces at RS components which were from 3 grades (C, D, F) and got 2 pairs which were very close in their resistance curve.
So, if you can get 8 pieces of one grade it will be far enough to match.
The matching process is a little bit like knitting or nut picking. You can do it with your brain at stand-by
I bought 12 pieces at RS components which were from 3 grades (C, D, F) and got 2 pairs which were very close in their resistance curve.
So, if you can get 8 pieces of one grade it will be far enough to match.
The matching process is a little bit like knitting or nut picking. You can do it with your brain at stand-by
Lightspeed with Meitner MTR-101
Hi, I recently acquired a pair of Meitner MTR-101 mono block amps. I was thinking of building an Aikido Line stage, but am intriguted with the Lightspeed. Would the Lightspeed Attenuator work well with the Meitner MTR-101 mono block amps?
Thanks
Kris
Hi, I recently acquired a pair of Meitner MTR-101 mono block amps. I was thinking of building an Aikido Line stage, but am intriguted with the Lightspeed. Would the Lightspeed Attenuator work well with the Meitner MTR-101 mono block amps?
Thanks
Kris
Re: Lightspeed with Meitner MTR-101
The Meitner MTR-101 has an input impedance of 22k, which is too low for the Lightspeed, but it can be changed to 100k easily, then it should only be turned on with a source (Lightspeed) connected, as the dc offset may rise if the input has nothing connected. Still safe.
Cheers George
kvardas said:
The Meitner MTR-101 has an input impedance of 22k, which is too low for the Lightspeed, but it can be changed to 100k easily, then it should only be turned on with a source (Lightspeed) connected, as the dc offset may rise if the input has nothing connected. Still safe.
Cheers George