[dburna]

Just curious, Morten -- on what input impedance did you settle?

-dB

[tortugaranger]

Just curious, Morten -- on what input impedance did you settle?

-dB

We did beta testing from 10k to 50k. While 50k sounded good, the commensurate higher output impedance proved to be a problem for certain amps like the popular Job 225 and the NCore which exhibited unacceptable levels of hum (which nobody I've consulted with can explain). But for other tube and SS amps there was no problem.

After several iterations, I decided to standardize at 10k. It does the job of getting getting the impedance off the floor which is key to improving dynamics. And it achieves the general goal of having an 10:1 impedance bridging ratio between source and preamp with most sources having much less than a 1k output impedance.  Also, at 10k you don't get the hum problem mentioned above with certain amps.

Turns out there's a tradeoff between impedance and channel balance/matching. This is an artifact of digital control and the finite data set inherent with 8 bit (256) sampling. As impedance is increased, the dB error (spread) between left/right channel tends to increase. Mostly in the mid volume range but much less so towards min or max. At 10k impedance, this error is usually limited to a max of 0.2 dB and is mostly 0.1 or less. At  50k this can double. The benefit of tighter channel balance is superior stereo imaging thus further supporting the 10k.

On the other hand, if someone really wants/needs a higher input impedance I can certainly provide that upon request up to 50k. Beyond 50k, you start to push distortion which of course isn't good.

Best,
Morten

[tortugaranger]

Just a suggestion (I'm only a tour participant), but it would probably be a good idea if whoever has the LDR by about 12/20 just keep it and ship it to the next person just before/after Jan. 1st.  I'm not sure anyone will have time to give it a good/critical listen in this period, plus it's probably best for the shipment if it's not being moved from place-to-place during the busy holiday shipping season.

Whoever has it during that period would have an extended "Christmas bonus," but at least no one would get shortchanged.

Any thoughts? 

-dB

P.S. Based on the revised schedule, I don't stand to receive this until early 2014, so I'm not angling for an extended audition for myself.

I agree that whoever has the unit over the Xmas break should just hold on to it until after New Years. I figure everyone should spend a week or so with it anyway and getting quality listening time around family holiday time can be challenging.

Once Konut has put in the HiZ chip and refreshed his listening impressions, he'll move it on to rajacat and then its Nick B. We'll see where we are by then and figure it out from there.

[konut]

I have received, and successful installed, the new chip. Morten has included the quick flickering visual LED feedback when raising and lowering the volume. 
I am listening to Romeo and Juliet from the Telarc, Maazel and the Cleveland disc. The tympani really jump out at you with the new software. Truly spine tingling! The sound-stage has more depth and is more cohesive. Enough for now. More thorough impressions to come.   

[konut]

I have sent the tour sample on to the next tour participant, rajacat, and will be posting the second part of my review tomorrow PM.

[konut]

    This is part 2 of a review for the Tortuga Audio LDR1 passive preamp. I was able to audition the LDR1 for a full month before receiving the updated software chip. There had been a delay in sending out the chip as it was discovered there were certain anomalies with Class D amps. Once those were resolved the chip was sent out. Since I have W4S Class D amps, it was reassuring that this was checked out. Having the LDR1 for so long made it easy to hear the difference between the old software and the new software.
    The only difference in actual operation of the pre was that now when the volume was raised or lowered, the LED fast flickers. Tortuga had incorporated my suggestion. Nice!
    The purpose of the new software was to increase and optimize the input impedance thus resulting in better dynamics especially at lower volumes. In actual practice it did much more than that. Dynamically there was a sense of  increased transient response though not nearly as significant as the difference between my old passive and the old software. At lower volumes it was difficult for me to detect a significant increase in dynamics across the board. What was significant was a marked increase in low level detail, even at lower volumes. But the most improvement came in rendition of sound stage. At all volumes there was an expansion of width and depth as well as a greater perception of space. There was a smoothness to the presentation that gives a greater sense of reality, especially in live recordings.
     My GUESS as to whats going on is that the precision of the channel balance that the original software pioneered is further enhanced and made more apparent by the impedance optimization. Those spacial cues that are embedded in the phase relationships are made more precise by the channel matching and brought to the fore by the impedance refinement. Again, just a guess on my part.
    Having sent the unit on to the next participant on the tour, and going back to my previous pre, I noticed that the texture of instruments and voices are less refined. The subtle emotional nuances are less. There is a flattening of the sound stage and the sound sticking more to the speakers. Harrumph.
    Having worked in live sound for a few years and maintaining an interest in audio as a hobby for 40 years, I have come to appreciate that everyone comes to different conclusions as to what they hear and thus how they want their audio to be reproduced. Its a trial and error process hopefully with correlations between what is heard and what can be measured. That has been my experience anyway. What I have found is that low distortion, high signal to noise ratio, and flat frequency response are the preeminent determinants as to whether I will like a certain component. Others have come to different conclusions.
      The very nature of the recording process manipulates the sound running it through various circuits with all kinds of deleterious as well as beneficial effects, some recordings more than others. Some are of the opinion that since this is the case why not use every means at our disposal to manipulate the sound, when reproducing, to achieve pleasing results. Those that use passive preamps take an opposing view. The last thing we want to do is use anything that will obscure the waveform as its delivered by the source medium. The fewer circuits the better. While I have not personally auditioned a lot of passive pres, I can say that the LDR1 is as a transparent component as I have ever encountered. I will be curious of the findings of the rest of the tour participants as to how the LDR1 performs with their systems. Thanks to Tortuga for sponsoring the tour.         

[tortugaranger]

Hi Konut!

Thank you for the before/after reviews!.  I think your guesses are as good as any. For me, the sound stage improvement was an unexpected bonus. I wondered if others would notice.

Cheers!
Morten

[konut]

For me in order of impact; low level retrieval, sound stage, dynamics.

[Nick B]

The LDR arrived yesterday from Roy....rajacat...in fine shape. All I've had time to do is unpack it I will get going hopefully by this weekend after "I've had a chance to make merry" as Bob Cratchit would say. 
A Merry Christmas to all!!
Nick

[Randy]

The LDR arrived yesterday from Roy....rajacat...in fine shape. All I've had time to do is unpack it I will get going hopefully by this weekend after "I've had a chance to make merry" as Bob Cratchit would say. 
A Merry Christmas to all!!
Nick

Nick, I'm next on the list and will be good to go when you are ready to send it on.

Randy

[Nick B]

OK, Randy. Thanks for the heads up
Nick

[rajacat]

I decided to test the LD1 with several albums that I know well.
 I gave up rather quickly trying to  do quick comparisons between my hybrid tube pre and the LD1 because the continuous switching between them was too tedious and time consuming,  Audio memory is short too. I like to listen in larger swatches of time to get a more accurate overall impression.

The first thing that grabbed my attention was the improved separation of the left and right channels. This was just a hint of the overall better imaging with a more accurate placement of the various instruments in the left/right continuum. The Charles Dutoit Respighi disk http://ecx.images-amazon.com/images/I/910Kx2ODjiL._SL1500_.jpg with the full orchestra, exotic percussion  and huge dynamic range let me evaluate  the spatial imaging and detail retrieval. I heard low level detail that I hadn't noticed before as if I was missing a layer of sound. The very low self-noise of the LD1 indicates to me that this passive pre would be an excellent low volume performer.  The noise floor emanating from my single drivers was considerably less than with the tube hybrid pre.  In all fairness I suspect that some of this noise is because my current active pre has way too much gain for my 96db Omega bipoles. Nevertheless, I suspect that even if the gain was adjusted to the optimum, the LD1 would still be more transparent.

Bipolar speakers generally have a huge and deep soundstage but give up a little on pinpoint imaging. I noticed that the imaging did improve with the LD1 and the soundstage was less diffuse. I could place the various instruments more accurately.

At one point I did change the interconnects from the source ( Bolder SB3 >modded Mhdt Constantine dac) to the LD1 and to the amps (modded Heathkit W5m tube monoblocks) and discerned an upgrade to the sound.  The improved transparency should make all system changes more distinguishable. I initially used some Blue Jeans cables because they're very flexible and were of optimal length thereby making changes easier but compared to my other cables with higher grade copper they just didn't sound as good.

I also listened to Lucinda William's Car Wheels on a Gravel Road and again the very transparent nature of the LD1 resulted in the proverbial "lifting of the veil". I heard background detail that I hadn't noticed before. The LD1 must be a very good match for my rig. At first I was a little skeptical that it could provide the same slam as my active pre but this was unwarranted. I also thought that it might have a lean quality but this too didn't materialize. Plenty meat on the bones here.

The third album I used for evaluation was Ahmed Jamal's Blue Moon. Like most of Jamal's albums, the dynamic range is huge and the SQ is quite good. He can play very softly and then escalate to crashing the keyboard.  Once again better transparency with no loss of texture.The LD1 improved the sound quality of all the music I listened to in much the same way and I gained a new appreciation for the SQ of my tube monoblocks.

It's too bad I didn't have more time with the LD1. I miss it already. Sometime in the near future I'll undoubtedly purchase the kit. I would recommend it for anyone with a similar rig to mine. I want to thank Morten for setting up the tour and for refining the use of light dependent resistors in audio gear.

...Roy

[tortugaranger]

It's too bad I didn't have more time with the LD1. I miss it already. Sometime in the near future I'll undoubtedly purchase the kit. I would recommend it for anyone with a similar rig to mine. I want to thank Morten for setting up the tour and for refining the use of light dependent resistors in audio gear.
...Roy

Hi Roy,

Thank you for participating and for taking the time to draft(twice!) and post a review. Getting feedback...good or bad...is very useful. Thankfully it's been mostly positive. It's been quite a revelation to hear what's possible with LDRs especially with the improved input impedance.

I find the biggest challenge in marketing our LDRx passive preamps is with people who have tried passive preamps in the past and were disappointed...and all their friends who heard about it. It's hard to argue with someone's personal experience when it's been negative. Hopefully, the positive experiences from this tour will help to reopen the whole passive preamp debate and even...dare I suggest it...change a few minds! 

Cheers!
Morten

[Nick B]

Hey guys,
The holidays really set me back and I apologize for the delay. I should be done by this weekend and will get the LDR to Randy
Nick

[Nick B]

I am shipping today.

[Randy]

I am shipping today.

Got it.

[Nick B]

First off, my apologies for having the unit so long. I was hoping not to have to get into this, but I do owe you guys and Morten an explanation. I had eye surgery in mid December and was recovering and enjoying the holidays. I had a setback and needed another procedure. The restrictions were no stooping, bending, straining  etc. So I had my wife hook up the cables (an interesting experience   )  and I heard the dreaded hum...presumably a ground loop. I had my wife check all the connections and I double checked what I could, but the problem persisted. We then hooked up my Audience preamp and the same thing. Since I wasn't able to crawl behind the cabinet, I just wasn't able to pursue it further.
I will comment then on the fit and finish and some misc items.The unit is nice, but it's a little bit of a "plain Jane". I would need muliple inputs and would therefore prefer a wider chassis so that the connections are not quite so close together. That's especially useful when I use locking RCA's that are wider. As I'm into aesthetics as well, I'd order it without the blue letterig and either put a gold colored  inlay in myself or have someone do it. It would match my beloved Basis Ovation turntable. The remote worked fine, but a digital volume readout would really be really nice also
I've been in this hobby...passion... for over 25 years and the guys at Audio Circle and Audio Nevosa have really helped me get a great sounding system. So I can say without hesitation that I would buy the LDR 6 based on the comments so far. It's exactly what I'm looking for. Right now I'm in California for another surgery within the next few days, so if you have some good vibes or prayers, pls pass them along. 
Nick

[tortugaranger]

First off, my apologies for having the unit so long. I was hoping not to have to get into this, but I do owe you guys and Morten an explanation. I had eye surgery in mid December and was recovering and enjoying the holidays. I had a setback and needed another procedure. The restrictions were no stooping, bending, straining  etc. So I had my wife hook up the cables (an interesting experience   )  and I heard the dreaded hum...presumably a ground loop. I had my wife check all the connections and I double checked what I could, but the problem persisted. We then hooked up my Audience preamp and the same thing. Since I wasn't able to crawl behind the cabinet, I just wasn't able to pursue it further.
I will comment then on the fit and finish and some misc items.The unit is nice, but it's a little bit of a "plain Jane". I would need muliple inputs and would therefore prefer a wider chassis so that the connections are not quite so close together. That's especially useful when I use locking RCA's that are wider. As I'm into aesthetics as well, I'd order it without the blue letterig and either put a gold colored  inlay in myself or have someone do it. It would match my beloved Basis Ovation turntable. The remote worked fine, but a digital volume readout would really be really nice also
I've been in this hobby...passion... for over 25 years and the guys at Audio Circle and Audio Nevosa have really helped me get a great sounding system. So I can say without hesitation that I would buy the LDR 6 based on the comments so far. It's exactly what I'm looking for. Right now I'm in California for another surgery within the next few days, so if you have some good vibes or prayers, pls pass them along. 
Nick

Hi Nick,

Thank you for your report and best wishes for a speedy recovery from your eye ailments. There are few things in life as important as maintaining good health and when things go wrong with that everything else takes a back seat.

I do appreciate your comments about the spartan aesthetics of the LDR1. We took a very simple approach with the enclosure on our first product and plan to using all the feedback we've accumulated to come up with something that I think you and others will like a lot better. We hope to release our LDR3B by late February which will be a 3 input, 2 output balanced (XLR) passive preamp. I believe it will be the first ever fully balanced passive preamp designed around LDRs. Sometime after the LDR3B, we'll be releasing the LDR3, a single-ended version also with 3 inputs and 2 outputs. The LDR3 will replace the the original LDR1/LDR6 line. A 3D Cad drawing of the LDR3B is included below.

All the best to your and your family and I hope all goes well with your next surgery.

Regards,
Morten

[Warpspeed CE]

I believe it will be the first ever fully balanced passive preamp designed around LDRs...

Sorry my prior art already precedes yours by about 3+ years...

[tortugaranger]

Sorry my prior art already precedes yours by about 3+ years...

I stand corrected.     I'd been given to believe that but did not know for sure. Thanks.