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Post by Deleted on Jun 30, 2009 10:18:24 GMT
Thanks Jon for the feedback.
It is interesting that you still think it is acceptable with an input impedance of only 7k5. I wonder how the TVC will compare when you get it sorted.
I also note you talk about the LS as an attenuator where everyone else is focused on the LS as a passive pre. I'm sure it will prove a great attenuator for a active pre-amp.
regards
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jonclancy
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Post by jonclancy on Jun 30, 2009 20:22:12 GMT
Yes, I think there is still plenty of mileage to go on this design. Weren't Dartzeel trying to patent an Optocoupler volume control on one of their new designs?
Cheers
Jon
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Post by rowuk on Jul 24, 2009 17:22:33 GMT
Why not a couple in parallel to get lower resistance values? It would also make it easier to "match" for stereo. 4 of these things don't take up that much space.
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jonclancy
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Post by jonclancy on Jul 25, 2009 22:03:50 GMT
Mine were supplied matched, so not an issue for me.  You'd need 8 per unit because this design uses shunt to ground with an LDR as well. Interesting idea, mind you. |
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Post by Deleted on Jul 25, 2009 22:28:30 GMT
Jon
yes, an interesting idea. A couple of things that I would like to know though.
1. How does Lightspeed compare with an upmarket attenuator like the DACT 2.
2.What are the distortion figures for these LDRs.
3.What is the typical capacitance of the LDR selected for this project.
4.What is the bandwidth of the Lightspeed attenuator project as posted.
(from memory, A DACT2 has a -3dB bandwidth of 50MHZ)
I haven't trawled right through the rather lengthy DIYAudio thread, so perhaps some of these figures may have already been mentioned.
SandyK
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robertkd
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Post by robertkd on Jul 25, 2009 23:31:22 GMT
Jon yes, an interesting idea. A couple of things that I would like to know though. 1. How does Lightspeed compare with an upmarket attenuator like the DACT 2. 2.What are the distortion figures for these LDRs. 3.What is the typical capacitance of the LDR selected for this project. 4.What is the bandwidth of the Lightspeed attenuator project as posted. (from memory, A DACT2 has a -3dB bandwidth of 50MHZ) I haven't trawled right through the rather lengthy DIYAudio thread, so perhaps some of these figures may have already been mentioned. SandyK cheez so I guess know one knows what a "T" type attenuator is then? rockgrotto.proboards.com/index.cgi?board=m&action=display&thread=4066&page=1#48162 ;D |
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Post by Deleted on Jul 26, 2009 0:04:31 GMT
Robert
Fair suck of the sav! It's hard enough to get properly matched pairs of these LDRs, let alone in triples ! Most of the guys building this want a proven design that works, and preferably with devices that are prematched. Of course you can do better as you pointed out, but at a substantially higher cost, and there is also a lack of ready made PCBs etc. I doubt that too many have even noticed your original post, where you asked a similar question to what I just asked.
Alex
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robertkd
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Post by robertkd on Jul 26, 2009 1:41:39 GMT
Robert Fair suck of the sav! It's hard enough to get properly matched pairs of these LDRs, let alone in triples ! Most of the guys building this want a proven design that works, and preferably with devices that are prematched. Of course you can do better as you pointed out, but at a substantially higher cost, and there is also a lack of ready made PCBs etc. I doubt that too many have even noticed your original post, where you asked a similar question to what I just asked. Alex ouch!  |
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Post by Deleted on Jul 26, 2009 1:56:50 GMT
Robert
;D
BTW, any further progress on DACs and other items you acquired recently from Flea Bay ?
Alex
P.S.
Blame "Topic: Rev this place up a bit?"
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Will
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Post by Will on Jul 26, 2009 9:01:47 GMT
I must say that this design intrigues me, and the "novel" (to me) approach is interesting. Given that you would need a clean supply (JLH PSRR springs to mind), the only other special bits are the LDR's. What's the typical cost of a set of matched ones? The rest of the components used in building it are 'bits box' friendly, and it could be made up on Veroboard. For those that want a pcb, that is far from being a problem....
Although the figures are interesting/important, I cant help thinking that the proof is in the listening.
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robertkd
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Post by robertkd on Jul 26, 2009 9:55:53 GMT
Robert ;D BTW, any further progress on DACs and other items you acquired recently from Flea Bay ? Alex P.S. Blame "Topic: Rev this place up a bit?" well no really, kinda finding the both DAC's to be pretty damn good as I left them last, as here rockgrotto.proboards.com/index.cgi?board=c&action=display&thread=3736&page=11#48997the 8 stacked TDA1543 with moded output stage is also still going strong as is the FET head phone amplifier. As far as ebay shyt waiting on another 2 by AKG perception 220 microphones to mary up to the 2 i already have. oh for some REAL ambience recording  Next need to get some form of I/O so I can record 4 channels (plus) and do some surround sound recording. I'm also on the look out for a video camera  all that plus trying learn to TIG weld you know the lay the stack of dimes, dam aluminium is freaky stuff to weld  |
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jonclancy
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Post by jonclancy on Jul 26, 2009 13:35:09 GMT
Hi Alex, Yes, I think most of the figures are out there and in the DIYA thread. There was a big conversation discussing the distortion figures, and the differences between the Mk1 and Mk 2 LS (one pair and 2 pairs of LDRs). www.diyaudio.com/forums/showthread.php?s=&postid=1807338&highlight=#post1807338www.diyaudio.com/forums/showthread.php?s=&postid=1260039&highlight=#post1260039www.diyaudio.com/forums/showthread.php?s=&postid=1520950&highlight=#post1520950www1.silonex.com/audiohm/www1.silonex.com/datasheets/specs/images/pdf/104539.pdfI haven't heard a DACT 2, but I do have a TKD Stepped Attenuator that I understand is in the same sort of league. I need to collect my TX2575 naked Vishays sometime, then I'll be able to install the Bobo Crump mod. This configuration was used in the CTC Blowtorch, and is highly regarded. I haven't been able to find the bandwidth figures, but maybe I just like listening to 2nd harmonics!!  Ah well, off to work now! Cheers Jon Jon yes, an interesting idea. A couple of things that I would like to know though. 1. How does Lightspeed compare with an upmarket attenuator like the DACT 2. 2.What are the distortion figures for these LDRs. 3.What is the typical capacitance of the LDR selected for this project. 4.What is the bandwidth of the Lightspeed attenuator project as posted. (from memory, A DACT2 has a -3dB bandwidth of 50MHZ) I haven't trawled right through the rather lengthy DIYAudio thread, so perhaps some of these figures may have already been mentioned. SandyK |
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jonclancy
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Post by jonclancy on Jul 26, 2009 13:36:21 GMT
Just buried in the thread, Robert, and missed it! ;D |
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Post by jonclancy on Jul 26, 2009 13:38:22 GMT
I must say that this design intrigues me, and the "novel" (to me) approach is interesting. Given that you would need a clean supply (JLH PSRR springs to mind), the only other special bits are the LDR's. What's the typical cost of a set of matched ones? The rest of the components used in building it are 'bits box' friendly, and it could be made up on Veroboard. For those that want a pcb, that is far from being a problem.... Although the figures are interesting/important, I cant help thinking that the proof is in the listening. Hi Will, I used and ALWSR set to 5V and a 12V wallwart supply. If you drop Uriah (udailey) a PM over at DIYA, he'll be able to tell you what the deal is with the next batch of matched LDRs. |
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Post by Deleted on Jul 26, 2009 21:19:31 GMT
Hi Jon That group of posts by Nelson Pass is quite revealing, and no, it's not all 2nd harmonics. Perhaps they are in there somewhere but I didn't notice any bandwidth figures. As Nelson Pass noted : "The distortion of the active buffer is about .003% on a clear day at 1 V, which is less than you will be experiencing with the LDR portion of the circuit." Alex www.diyaudio.com/forums/showthread.php?s=&postid=1520950&highlight=#post1520950 |
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robertkd
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Post by robertkd on Jul 27, 2009 0:08:31 GMT
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Post by Deleted on Jul 27, 2009 2:17:33 GMT
I found the attached quote in AudioCircle Forum. Anybody else using the LSA eithout a buffer noticed such a problem ?
Alex
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Re: WTB: the best passive preamp there is.
« Reply #46 on: November 03, 2008, 03:35:37 PM »played the passive game for a while. clarity beyond belief, detail but for my system just not enough weight or slam compared to the actives. To date the most affective was the TAP followed by the S&B. The Promitheus was promising but the build quality and customer service is lacking.
At first the amazment of the clarity and silence was addictive. After listening to my favorites for a while the love affair grew old. just missed the air, decay body of the active."
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jonclancy
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Post by jonclancy on Jul 27, 2009 9:33:19 GMT
Certainly enough bass with my speakers... I think I'll have to dob a B1 together sometime and plop the two together. |
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Post by jonclancy on Aug 7, 2009 20:30:14 GMT
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Will
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Post by Will on Aug 20, 2009 23:31:26 GMT
A set has been ordered.
I'll report back later!
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Post by jonclancy on Aug 26, 2009 12:35:47 GMT
Looking forward to it, Will. Hope I don't get proved to be a Cloth-Ears!! Update: Just got my LS off the 'scope. I noticed it was a bit "left-wing-down" when listening, so decided it was time to sort it!! I fitted two trim pots in my build and wouldn't recommend this. It isn't really necessary and adds an unneccesary construction/setup variable. Just build it up, measure the channels (or listen) and put the trimmer on the louder channel. In mine, the Left is loud, and I really ought to remove and jumper the Right trimmer!!  I now have the channels balanced to 2mV P-P at the standard 12 o'clock listening position. The dual-ish (1-4) channel scope and split RCA plug adaptor I bodged up for the function gen made life much easier!! I'm looking ofrward to turning it up tomorrow - first (quiet) listen tonight hinted at a soundstage back where it should be. When are your LDRs arriving, Will??? Cheers Jon |
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You'd need 8 per unit because this design uses shunt to ground with an LDR as well. Interesting idea, mind you.
