@George !
I finished my balanced Lightspeed MKII following the schematics and the directions you kindly provided. The beast works really amazingly after the last connected wire ! Even without any tweaking it outperforms my last auto-former interface without any doubt !...
Despite the 10 K input impedance, the output levels reached are largely enough. I think that aside the impedance problem, one other parameter is of some importance : the sensitivity of the amps. With very sensitives amps the Lightspeed will perform much better... I tried with two different amplified monitors both with 10 k input impedance, the results are much better with the one displaying 100 dB SPL for -6 dB !...
Then, please can you tell me how to tweak the 1K variable resistors to optimize this indeed beautiful and incredible interface ? For low levels I noticed a degradation of the audio quality (disappearing for louder levels), do you have observed this problem previously ? And of course, any suggestion to correct this will be welcome...
Thanks for this and for all the support you already provided to everybody on the present thread !
My Best.
I finished my balanced Lightspeed MKII following the schematics and the directions you kindly provided. The beast works really amazingly after the last connected wire ! Even without any tweaking it outperforms my last auto-former interface without any doubt !...
Despite the 10 K input impedance, the output levels reached are largely enough. I think that aside the impedance problem, one other parameter is of some importance : the sensitivity of the amps. With very sensitives amps the Lightspeed will perform much better... I tried with two different amplified monitors both with 10 k input impedance, the results are much better with the one displaying 100 dB SPL for -6 dB !...
Then, please can you tell me how to tweak the 1K variable resistors to optimize this indeed beautiful and incredible interface ? For low levels I noticed a degradation of the audio quality (disappearing for louder levels), do you have observed this problem previously ? And of course, any suggestion to correct this will be welcome...
Thanks for this and for all the support you already provided to everybody on the present thread !
My Best.
ondesx said:
Remember you only insert one 1k trimpot on the louder of the two channels
To calibrate the matching finer after I've hard wax potted the 4 X NSL32SR2S together, and the wax has cooled completely. I use a 1khz sine wave from an Audio Frequency Generator at around 1v and view both channels on my Oscilloscope and adjust the 1k trimpot so both sine waves are averaging the same level at different volume control settings.
You could do this using a good DMM best if you have two. Or it will be almost as much of a headache as matching the LDR's.
As for your low level listening, sounds like you need higher input impedance on your amps, as I remember you said they were 10k? this is too low for the Lightspeed Attenuator ( I find it compresses the dynamics). Or it could be that you need an active "Loudness" button that all pre's could do with at low levels.
Cheers George
Hi again George,
Thanks for the trimpot calibration procedure : I'll do it asap as I can approach an oscilloscope !...
For the low level audio degradation I mean it appears a sort of "grain" or distorsion with a very audible blurring of the sound. This behavior totally disappears rising the output level. It remains also some hum on the left channel even rising the output level... Well I suppose some tweaking with a much better PSU and pot will improve the things... (I presently use a mobile phone charger...
).
Usually, for impedance mismatch, the first observed degradation affects the lows, but this is not the case here, since I have plenty of bass (much more than with my trannies !) provided I turn CW the pot to a higher level...
Anyway the firsts results are encouraging !
Have a nice Sunday.
Thanks for the trimpot calibration procedure : I'll do it asap as I can approach an oscilloscope !...
For the low level audio degradation I mean it appears a sort of "grain" or distorsion with a very audible blurring of the sound. This behavior totally disappears rising the output level. It remains also some hum on the left channel even rising the output level... Well I suppose some tweaking with a much better PSU and pot will improve the things... (I presently use a mobile phone charger...
).Usually, for impedance mismatch, the first observed degradation affects the lows, but this is not the case here, since I have plenty of bass (much more than with my trannies !) provided I turn CW the pot to a higher level...
Anyway the firsts results are encouraging !
Have a nice Sunday.
You've got to remember with my production Lightspeed Attenuators I always ask the customer their amp and cd player output and input resistances if something does not gel I let them know what to do about it.
You have an amp that is 10kohm (bad) and the Lightspeed is around 7kohm ( if made like my production ones), the to two added together will load the CD player's output with 4.1kohm.
If you have a high output impedance or weak solid state or tube output on your CD player this load will not be kind to it.
Analogy: Look what happens to an amp that finds a speaker hard to drive because of it's load, at worse it can clip, but it usually before that happens it sounds thin lacking in body and edgy.
Cheers George
You have an amp that is 10kohm (bad) and the Lightspeed is around 7kohm ( if made like my production ones), the to two added together will load the CD player's output with 4.1kohm.
If you have a high output impedance or weak solid state or tube output on your CD player this load will not be kind to it.
Analogy: Look what happens to an amp that finds a speaker hard to drive because of it's load, at worse it can clip, but it usually before that happens it sounds thin lacking in body and edgy.
Cheers George
My DAC have 100 ohms of output impedance in XLR balanced mode and outputs 5.5 Volts !... (2.5 V and 50 ohms in single-ended mode).
I hope improving the PSU and pot will solve part of the remaining drawbacks... Wait & See !
I'll post a picture of the developing prototype to morrow...
Thanks for all Georges.
All the Best,
I hope improving the PSU and pot will solve part of the remaining drawbacks... Wait & See !
I'll post a picture of the developing prototype to morrow...
Thanks for all Georges.
All the Best,
Low Impedance Amp Input
Hi Ondesx,
The First Watt F3 amp has the similar lousy low input Z of about 9kR and "strangles" the Lightspeed sound - have added a simple JC buffer (k170,j74 fets) and all is fine - can't do without it.
the B1 buffer also does a good job and you get to choose the series capacitor "colour" to your taste - the JC is direct, but needs better supply.
Hi Ondesx,
The First Watt F3 amp has the similar lousy low input Z of about 9kR and "strangles" the Lightspeed sound - have added a simple JC buffer (k170,j74 fets) and all is fine - can't do without it.
the B1 buffer also does a good job and you get to choose the series capacitor "colour" to your taste - the JC is direct, but needs better supply.
Thank you James. I did a try before going to bed yesterday night with a very simple operational amplifier mounted in follower mode (a couple of LME 49720) and the observed phenomenon at low level remain... I concluded that there isn't an impedance issue !
Moreover, the impact and intensity of the lows are just amazing, that wouldn't be the case with an impedance mismatch, or this mismatch just appears for low levels ?
Perhaps somebody knows what happens if one use a too high or a too low power supply ? Anyone tried batteries instead ? With a charger, it'll be perhaps the best solution isn't ?
I'll try with different PSU now and we'll see...
For an enough high level, all is pretty good, the sound is just incredible, better than with my third opus of auto-transformer (which still reached a very very good audio quality indeed, much better than most active preamps, even some swiss made costly gear...). We have more presence, transparency, the sound stage is very large, the voices are more natural, with a very good stability for high frequency at high levels, the dark side is the mixing errors are more evident too !...
Enclosed a picture of my first balanced LS opus !
Moreover, the impact and intensity of the lows are just amazing, that wouldn't be the case with an impedance mismatch, or this mismatch just appears for low levels ?
Perhaps somebody knows what happens if one use a too high or a too low power supply ? Anyone tried batteries instead ? With a charger, it'll be perhaps the best solution isn't ?
I'll try with different PSU now and we'll see...
For an enough high level, all is pretty good, the sound is just incredible, better than with my third opus of auto-transformer (which still reached a very very good audio quality indeed, much better than most active preamps, even some swiss made costly gear...). We have more presence, transparency, the sound stage is very large, the voices are more natural, with a very good stability for high frequency at high levels, the dark side is the mixing errors are more evident too !...
Enclosed a picture of my first balanced LS opus !
Attachments
Hello George,
As explained in one post above, the anomaly at low levels is not just a lack of bass, but really a degradation of sound becoming like a not well tuned FM radio station, with very audible crackling and duplication of the sound (a sort of echo), do you see what I mean ?
I'm quite sure this is not due to an impedance mismatch... When I increase the volume, this phenomenon disappears totally and the sound becomes clear, punchy, with very consistent bass and a beautiful transparency, presence and details, well a quite perfect audition indeed, better at this point then with my best auto-former !...
An issue will be found undoubtedly.
PS : sorry but it seems your last post has been removed...
As explained in one post above, the anomaly at low levels is not just a lack of bass, but really a degradation of sound becoming like a not well tuned FM radio station, with very audible crackling and duplication of the sound (a sort of echo), do you see what I mean ?
I'm quite sure this is not due to an impedance mismatch... When I increase the volume, this phenomenon disappears totally and the sound becomes clear, punchy, with very consistent bass and a beautiful transparency, presence and details, well a quite perfect audition indeed, better at this point then with my best auto-former !...
An issue will be found undoubtedly.
PS : sorry but it seems your last post has been removed...
ondesx said:
Yes I did delete, I jumped the gun I wanted to wait for more info from you before I commented.
You have a real big problem, I fear maybe you have faulty NSL32SR2S's, your post back a while, you stated that the impedance range you got was
Quote:> I finally did the job ! I found 2 groups very close from each other with resistances ranging from 35 to 110 ohms for 2 to 5 Volts. The third group had a larger dispersion (from 20 ohms for the lowest value to 140 ohms for the highest) <:Quote
This to me sounds very very odd as the full light to total dark reading of these units from the specs is 40ohms to 5megohms, and you got 20-120ohms????
I have never ever had one that goes down to 20ohms ?
And as far as the upper reading of 120ohms you got, this is 4,000 x less than spec.
Cheers George
Well, George I think my English is far from to be perfect unfortunately and I am sorry for this but anyway I must do with it...
Of course, for the full 5 Volts I got more than this 110 ohm (or 140 ohm) values ! The range reported was for matching purposes only (5 points measured for each of the 20 NSLs). After these measures I got the 3 groups, I built my LS with the first group (i. e. having the closest values for the 5 measured points).
It's almost impossible that the NSLs are faulty, since I suppose if it's the case I'll never reach such a degree of audio quality (see waht I said about it on two posts above) as soon as the voltage control through my 100k pot is increased to reach even not so louder levels...
Then otherwise the NSL can be only partly faulty I think the issue is not to be searched neither from the NSL themselves nor to the impedance mismatch... I observed that the open value of my phone charger even supposed to be 5 V 300 mA indicates 5.6 volts on my DMM. I need to try a regulated PSU or batteries to be more confident with this point.
Of course, for the full 5 Volts I got more than this 110 ohm (or 140 ohm) values ! The range reported was for matching purposes only (5 points measured for each of the 20 NSLs). After these measures I got the 3 groups, I built my LS with the first group (i. e. having the closest values for the 5 measured points).
It's almost impossible that the NSLs are faulty, since I suppose if it's the case I'll never reach such a degree of audio quality (see waht I said about it on two posts above) as soon as the voltage control through my 100k pot is increased to reach even not so louder levels...
Then otherwise the NSL can be only partly faulty I think the issue is not to be searched neither from the NSL themselves nor to the impedance mismatch... I observed that the open value of my phone charger even supposed to be 5 V 300 mA indicates 5.6 volts on my DMM. I need to try a regulated PSU or batteries to be more confident with this point.
It becomes obvious now after all this that you do not have good power supply, so comments about low level sound of the Lightspeed is not of the Lightspeed it self but the phone charger power supply you are using.
As I have stated many times on this thread the production Lightspeed Attenuator that I make has first 12vdc Linear Regulated 300mA supply that is then fed to a second 5vdc Linear Regulated supply, I also have stated on the forum and in the instructions that a Switch Mode type (phone charger) regulated supplies are not to be used, they have too much HF garbage in them, that can be detrimental to the sound.
Cheers George
As I have stated many times on this thread the production Lightspeed Attenuator that I make has first 12vdc Linear Regulated 300mA supply that is then fed to a second 5vdc Linear Regulated supply, I also have stated on the forum and in the instructions that a Switch Mode type (phone charger) regulated supplies are not to be used, they have too much HF garbage in them, that can be detrimental to the sound.
Cheers George
Attachments
Well George, with another PS the sound is now quite perfect ! I face a new incident (as it wasn't the case yesterday night...) : I have a noticeable balance mismatch with my left channel much louder than the right one (no tweak has been performed yet on the trimpot since I haven't any oscilloscope at home). I correct the drawback for the moment by changing the input sensitivity of my left monitor, but I need to determine what's wrong now ! Any suggestion welcome as usual !
Looking again the figure you provided few post ago, I noticed you draw a double pot... In the design I follow initially (i. e. the balanced one) you just drawn a single pot. Is there any possibility to introduce some balance mismatches with the mono pot ? Do you think a double pot will be a better solution ?
I'll modify my new PSU with some rectifiers to achieve a more stable 5 V supply...
PS : Please James may you elaborate on your comment ?
Looking again the figure you provided few post ago, I noticed you draw a double pot... In the design I follow initially (i. e. the balanced one) you just drawn a single pot. Is there any possibility to introduce some balance mismatches with the mono pot ? Do you think a double pot will be a better solution ?
I'll modify my new PSU with some rectifiers to achieve a more stable 5 V supply...
PS : Please James may you elaborate on your comment ?
Hi guys. I am new to the forum, however I've been hearing a lot about Lightspeed Attenuator, since I started looking for a passive preamp.
Please forgive my ignorance, but one needs a ton of time to read through all these 66 pages of discussion - a luxury that I can not afford with my 9mo old on my hands now.
I was wondering whether someone is offering the complete Lightspeed Attenuator kits, with or without the remote control.
On some pages that I've managed to look through I see some references to purchasing kits, but no links to the actual product.
I googled it and the only kit that's coming up (through other forums) is SKA Optivol (http://www.ska-audio.com/diy/optivol.html).
Is this the only one and the one by George?
Thanks for clarification.
Please forgive my ignorance, but one needs a ton of time to read through all these 66 pages of discussion - a luxury that I can not afford with my 9mo old on my hands now.
I was wondering whether someone is offering the complete Lightspeed Attenuator kits, with or without the remote control.
On some pages that I've managed to look through I see some references to purchasing kits, but no links to the actual product.
I googled it and the only kit that's coming up (through other forums) is SKA Optivol (http://www.ska-audio.com/diy/optivol.html).
Is this the only one and the one by George?
Thanks for clarification.
Now it's my turn to help others !...
Then welcome MindaLT... I ordered and built the OptiVol from Greg Ball. It's a NSL 32 too, but an hybrid one (not a series-shunt like the George Lightspeed MKII). It works pretty good but I experienced a very low output level. Things are bettered using his VBuffer (or any buffer you may have, i. e. an OP AMP in follower mode)...
The George's LS is the simplest electronic schematics that you will ever have on hands. The difficulty is the matching of the LDR and to deal with a nice 5 V regulated PSU.
Anyway, I built the LS MKII in a balanced version and this thing rocks really. I didn't experienced the level limitation observed with the OptiVol. Anyway, it's relatively easy to derive a LS MK II from the OptiVol : you just have to exchange the 27 k resistor by another NSL and provide an inverted current, et Voila !... In this case with one OptiVol you can control a single-ended stereo amplifier from your DAC or CD player. For Balanced stereo you need... 2 Optivols !
Hope this helps.
Then welcome MindaLT... I ordered and built the OptiVol from Greg Ball. It's a NSL 32 too, but an hybrid one (not a series-shunt like the George Lightspeed MKII). It works pretty good but I experienced a very low output level. Things are bettered using his VBuffer (or any buffer you may have, i. e. an OP AMP in follower mode)...
The George's LS is the simplest electronic schematics that you will ever have on hands. The difficulty is the matching of the LDR and to deal with a nice 5 V regulated PSU.
Anyway, I built the LS MKII in a balanced version and this thing rocks really. I didn't experienced the level limitation observed with the OptiVol. Anyway, it's relatively easy to derive a LS MK II from the OptiVol : you just have to exchange the 27 k resistor by another NSL and provide an inverted current, et Voila !... In this case with one OptiVol you can control a single-ended stereo amplifier from your DAC or CD player. For Balanced stereo you need... 2 Optivols !
Hope this helps.