https://www.tnt-audio.com/ampli/the_truth_e.html
Looks very simple and seems loved for transparent sound... has this been covered anywhere,
Looks very simple and seems loved for transparent sound... has this been covered anywhere,
It's always interesting to read about the importance of absolutely avoiding all kinds of active and passive devices in the signal path, only to see them inserting non-linear optical parts into same ...
Jan
Jan
Yeah, I agree, but some times I feel it is interesting to look into these little deviations from that path, in case there is some higher plane, imponderable (goodness ?), going on.
My guess is that those metal can heatsinked devices are some sort of BUF634 type or relative. With the LDR in between.
Of course compared to the inside of some of the Croft amplifiers...
EDIT: this century stuff from Croft is a lot better, I was referring to their last century stuff 😀
EDIT: this century stuff from Croft is a lot better, I was referring to their last century stuff 😀
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Yes, I feel quite uncomfortable looking inside, But I still want to know what is going on. It would seem so easy to do a proper version with linear / external supplies and a small neat circuit.... if it is really worth the effort of course.
There is the Truth. And there is the truth:
ASR: The Truth
And before we go on and on and on about the spectacular sound endorsements of the LDR, our very own colleague at Neurochrome has done extensive measurements of the Tortuga LDR units here. (And yes, I’ve auditioned this unit and the aforementioned unit, The Truth, and, no, I don’t own either).
And here: ASR: Tortuga Tube Buffer
Caveat Emptor. Beware that not only is the distortion (relative to other well designed preamps) high but as we introduce less and less attenuation (i.e. higher volume), the distortion only lowers to a certain point which is a serious impasse of these designs (look particularly at the IMD measurements).
They are not “distortion less” in any sense of the word but add their own flavor (i.e. “distortion more”). But that might be to your liking ;-)
For DIY, it’s fine - and perhaps linear supplies will clean it up somewhat.
You want little to no distortion? Look at Neurochrome’s Universal Buffer. Game. Set. Match 😎.
Best,
Anand.
ASR: The Truth
And before we go on and on and on about the spectacular sound endorsements of the LDR, our very own colleague at Neurochrome has done extensive measurements of the Tortuga LDR units here. (And yes, I’ve auditioned this unit and the aforementioned unit, The Truth, and, no, I don’t own either).
And here: ASR: Tortuga Tube Buffer
Caveat Emptor. Beware that not only is the distortion (relative to other well designed preamps) high but as we introduce less and less attenuation (i.e. higher volume), the distortion only lowers to a certain point which is a serious impasse of these designs (look particularly at the IMD measurements).
They are not “distortion less” in any sense of the word but add their own flavor (i.e. “distortion more”). But that might be to your liking ;-)
For DIY, it’s fine - and perhaps linear supplies will clean it up somewhat.
You want little to no distortion? Look at Neurochrome’s Universal Buffer. Game. Set. Match 😎.
Best,
Anand.
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Thanks for the links. My, I have been asleep for a few years with respect to LDR volumes, but some how my thoughts turn to them again. I think I have some of those tubular isolated LDRs somewhere.
The light speed is of course the "right" way to do things, but intrigued by truth, there are so many things "wrong" but still good reports of sound.... like a little mystery to investigate.
I was half expecting to find a full dissection of this truth, I looked here first and nothing jumped out at me, The ASR has just hit the spot. Oh unobtainium,
The light speed is of course the "right" way to do things, but intrigued by truth, there are so many things "wrong" but still good reports of sound.... like a little mystery to investigate.
I was half expecting to find a full dissection of this truth, I looked here first and nothing jumped out at me, The ASR has just hit the spot. Oh unobtainium,
Having been in the hobby for too many years to even remember, my take on this is not optimistic. If a device produces a very different, even dramatically different sound, there will be fans. No matter how poor that sound is, if it's sufficiently distinguished that's all it takes for winning devoted fans. Seen this happen with wire, amps, passive parts, carts, speakers. Fallen myself a victim once or twice.
After being slightly disappointed with the transparency of a buf634 i found some of those remarkable old BUF03s. Ok, those were even less transparent to my ears. The integrated buffers can certainly find some sensible use, especially when under the nfb loop of a good opamp and when driving heavy loads.
Perhaps better to not even discuss the actual photoresistors and their non linearities and long term drift. Little wonder they sound dramatically different to good resistors.
Edit. The presence of a BUF03 is only speculation. It may easily be an opamp.
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I was surprised to not see hot glue somehwere, but the quality of construction seems on par with what i would expect from Ed quality wise after dissassembling one of his loudspeakers (not inspiring).
This looks to essentially be a “Lightspeed” (LDR) clone, something that has been studied, discussed, and built many times here.
https://www.diyaudio.com/community/search/306926/?q=lightspeed&c[title_only]=1&o=relevance
dave
Thanks for these comments. Yes the BUF03 is named by Ed in the ASR thread.
I have too been round the block a few times, but haven't been down this particular cul de sac, I have done "passive", shunt, and recently got a TVC, which I have been quite impressed by. I do pay attention when people rave about things, you know, just in case. I particularly like the idea of simple things, that I can / could knock up in an afternoon, parts permitting.
I think I have enough information now to understand the circuit. I may or may not make one, LDR sweepable filters seems like an interesting potential application, that's probably been done already 🙂. I will have to form my own opinion, as to the sonic signature of the LDR.
I owned a Truth for about 9 years before I sold it to a friend and he loves the sound of it! Yes, it does look home brewed.
As a perpetual tweaker, I upgraded some of the parts in the Truth - especially in the power supply - and I thought it sounded slightly better.
I even visited Ed Schilling's home in rural South Carolina for him to hear it. Ed is a very unique character in this hobby, and an all-around nice guy!
From his "thehornshoppe" web site I can see that he has upgraded the Truth for the current version.
I replaced the Truth with a Tortuga Audio LDR based DIY unit. Like the Truth, It has a buffer before and after the LDR volume attenuator.
I used parallel JFET's in a constant current sink configuration for my buffers instead of the BUF03 which costs over $20ea from obsolete parts vendors.
As a perpetual tweaker, I upgraded some of the parts in the Truth - especially in the power supply - and I thought it sounded slightly better.
I even visited Ed Schilling's home in rural South Carolina for him to hear it. Ed is a very unique character in this hobby, and an all-around nice guy!
From his "thehornshoppe" web site I can see that he has upgraded the Truth for the current version.
I replaced the Truth with a Tortuga Audio LDR based DIY unit. Like the Truth, It has a buffer before and after the LDR volume attenuator.
I used parallel JFET's in a constant current sink configuration for my buffers instead of the BUF03 which costs over $20ea from obsolete parts vendors.
For me there are two factors. I live happily with a normal Alps blue pot in my pre amp, but I made a pre amp once with a shunt volume and shunt input selector. And it did feel like it sounded more secure and confident. Bit odd. So I am alway interested in contactless ways of adjusting things. Also I believe a lot of the line level sound variableness is caused by devices having problems driving cables. So my attention is piqued by the positive comments, maybe here, by luck or fluke, is a design that can drive a cable cleanly.
History question. I know Audible illusions popularised the light powered volume control and set the myth in place, but who was first to do this for audio?
So the conclusion is that these LDR components are quite distorting and not the best choice in the audio signal pathway if someone is pursuing lowest possible distortion?
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They are quite non-linear as can be easily seen in the data sheet. But IIRC the lightspeed implementration tries to hit the sweet spot by limiting the signal across the LDR and wrapping it all in a feedback loop. So it's really a case of applying a good measure of electrical engineering.
Could be acceptably clean.
I once designed a tracking notch filter that was tuned by an opto-coupler, and was extremely clean to below -130dB, but the tuning range was limited to +/-0.5%, which was enough for my purpose (tracking a Viktor oscillator). The signal level across the LDR was limited to 10mV so only a very narrow part of the non-linear transfer curve was exercised.
So, it depends.
Jan
Could be acceptably clean.
I once designed a tracking notch filter that was tuned by an opto-coupler, and was extremely clean to below -130dB, but the tuning range was limited to +/-0.5%, which was enough for my purpose (tracking a Viktor oscillator). The signal level across the LDR was limited to 10mV so only a very narrow part of the non-linear transfer curve was exercised.
So, it depends.
Jan