[tortugaranger]

hi , i have plan to put a volume control in my dac ,   i have swap the active stage and run direct from the chip with a 3.9uf coupling cap , Z out is 10K  1,5V   do you think the new 20K board will work ?

I'm no expert on DACs but I'm curious how you came up with an output impedance of 10k? The output stage of most DACs is a current signal that can be converted into voltage using various I/V options most of which have relatively low impedance (usually well under 1k).

If we apply the recommended guidance of a 10:1 ratio for impedance bridging then a 10k source should be mated with an amp having at least a 100k input impedance. I confess we're in somewhat uncharted waters here and while the 20k board would work, the question is would it work really well? I have my doubts.

Can anything be done to reduce 10k output impedance? Is that the real value?

Any thoughts on this from the peanut gallery out there in AC land?

Best,
Morten

[juanitox]

thanks,  in fact it is a kind of discrete dac call the TOTALDAC ( like lavry gold ) but i have removed the  OP AMP at the output ( sounds better like this) .   i'm not really sure about the 10K  as it is just words about the manufacturer .  do you have a method  to mesure the output impedance ?

anyway i 'm using a 25K shunt pot right now so just tell me when the new revised board will be available to order

[doctorcilantro]

If you ordered 2 days ago then your ordered hasn't shipped yet. If you can give us a week or so I'm reasonably sure we can include the upgraded software in your order. Let me know.

Regardless, you should be in good shape with your tube amp. Have had very good feedback from customers running CD/DACs into tube amps.

Cheers,
Morten

Thanks, and to verify if I'm running DAC single-ended output at 50ohm>LDR>100K input tube amp...should I wait for updated chip? I probably should to have the flexibility. 20K is more compatible overall I take it.

[tortugaranger]

Thanks, and to verify if I'm running DAC single-ended output at 50ohm>LDR>100K input tube amp...should I wait for updated chip? I probably should to have the flexibility. 20K is more compatible overall I take it.

Since we're almost ready to ship units with the HiZ software, I'd definitely wait regardless of your rig. The benefits are too good to not wait.

[doctorcilantro]

Ok, Trung and I are waiting 

[tortugaranger]

We start shipping LDR passive preamps with the new HiZ (high impedance) software this week. 

Here's a link to the announcement we put out over the weekend: http://www.tortugaaudio.com/hiz-controlsoftware-improves-ldr-passive-preamps/

Cheers,
Morten

[tortugaranger]

We start shipping LDR passive preamps with the new HiZ (high impedance) software this week. 

Well, that turned out be a bit premature. Still had some more development work to grind through. It took another whole week before we started to ship with the high impedance software.

I'll share a little of the "sausage making". When we build and test a LDRx board (with pres-matched LDRs installed) we end up with 245 resistance data samples for both the series and shunt LDR for both the left and right channels. This is roughly the same type of data you'd get if you controlled the board with a linear stereo pot - the all analog approach. Which is more or less how our original design worked only it was implemented digitally.

But with our new HiZ approach things get a lot more complicated. We take each of those series/shunt data sets for each side and create 245x245 data matrix which is roughly 60,000 data points of series vs. shunt resistance in all combinations. Times 2 for left/right channels = 120,000. Time 2 for master/slave - balanced = 240,000. Lots of data. Then we run all that through a computer program to optimally match up the best series & shunt resistance values that yields both a smoothly matched left/right (master/slave)  -60 to 0 dB attenuation curve while also maintaining an input impedance of 50k +/- 10% and then distill all that down into a matched  70 step series/shunt resistance schedule that gets programmed into the final software build for that specific board. And then we do the same thing for the next board we build and so on. It would be insanely time consuming and costly to do this any way other than to almost fully automate it so that's where a LOT of the development time went. To figuring this out and writing/debugging the software to do reliably in very little time.  Thankfully, that's now done.  And it's all mo' betta.

And now we ARE shipping!

Cheers,
Morten

[tl1000sv]

I hope you are patenting your process.  The OEM market seems like it would be very promising.

But with our new HiZ approach things get a lot more complicated. We take each of those series/shunt data sets for each side and create 245x245 data matrix which is roughly 60,000 data points of series vs. shunt resistance in all combinations. Times 2 for left/right channels = 120,000. Time 2 for master/slave - balanced = 240,000. Lots of data. Then we run all that through a computer program to optimally match up the best series & shunt resistance values that yields both a smoothly matched left/right (master/slave)  -60 to 0 dB attenuation curve while also maintaining an input impedance of 50k +/- 10% and then distill all that down into a matched  70 step series/shunt resistance schedule that gets programmed into the final software build for that specific board. And then we do the same thing for the next board we build and so on. It would be insanely time consuming and costly to do this any way other than to almost fully automate it so that's where a LOT of the development time went. To figuring this out and writing/debugging the software to do reliably in very little time.  Thankfully, that's now done.  And it's all mo' betta.

[tortugaranger]

I thought I'd post some subjective thoughts on the performance improvement as a result of the higher impedance (HiZ) control software algorithm.

After a few weeks of nose-to-grindstone work on getting this upgrade polished and out the door I finally took time last night to do some critical listening on my main rig, not just the small test rig I use in the lab/office for development/testing. I realize that anything I say here will be viewed as self-serving and thus heavily discounted but if you can't blow your own horn then who will!

I'm really impressed by the improved audio quality. And I don't impress all that easily. There's now a more relaxed fullness that was missing. A more lush sound with a more natural tonal balance. And yes the dynamics are noticeably improved as well. The percussive pluck, pop and slam from strings to drum heads are now more clearly evident. What I wasn't expecting was the improved sound stage. It seems wider and more even. Love that. Overall, a very satisfying sound!

While the importance of impedance (matching) has long been recognized, conventional implementations of LDR based passive preamps have fallen short on optimizing impedance. I'm quite pleased to report that we've broken past that barrier and have set the bar at a much higher level. This has only been possible through software based digital control of an analog system. This hybrid approach has allowed us to free LDRs from the limitations of analog control and implement a programmed impedance and attenuation schedule that more closely emulates the voltage divider characteristics of conventional attenuation methods while retaining all of the wonderful audio characteristics of LDRs.

Whether you're a DIY tinkerer or an seasoned aficionado of audiophile gear, I invite you to give us a try. Especially if you were holding back, not quite convinced that passives, and especially LDR based passives, was a wise choice for you.

When it all comes together, this obsession with audio can be a thing of beauty!

Cheers!
Morten

[konut]

What does the main rig consist of?

[tortugaranger]

What does the main rig consist of?

Current main rig is all composed of versions of internal prototypes except for my current DAC which is a Schiitt Bifrost with all the currently available upgrades. The DAC was a recent addition. It's ok for the money. Amps are a pair of prototype mono LM4780 chipamps with nominal 100-120 watt output (a pair of LM4780's are used in each mono configured in parallel mode which doubles their output). These are each powered with oversized 400 VA toroidal linear power supplies which are also internal prototypes. Speakers are prototype ported cabinets utilizing the 8 inch Audio Nirvana full range drivers with optional baffle step compensators which I sometimes kick in but of late leave bypassed. Source is dedicated PC laptop with a 1TB external drive dedicated to music only running JRiver controlled via JRemote (excellent!!! ) app on an iPad. The music PC laptop is kept current with a mirror image of all the music files kept on my main PC desktop using GoodSync (great piece of software!!). The desktop in turn gets backed up on a network attached server that runs on FreeNAS. I have over 900 GB of music files most of which is FLAC.

I'm of the view that your preamp (attenuation throttle point) and speakers are the 2 most critical pieces of kit in terms of influencing overall listening satisfaction. You can add DACs etc. in with preamps. Amps are a distant 3rd and then comes everything else way behind the amp that are the subject of endless arguments among audiophiles that will never ever be resolved.

Full range speakers have their own unique issues but I've become a huge fan of the Audio Nirvana drivers. Single point sound source with no crossovers and thus no phase shifting etc. I'm definitely in the "less is more" camp these days.

I go to audio shows and listen to rigs costing many 10's of $thousands and then get home and listen to my rig described above and frankly I'm not missing much. In my view it's possible to have a phenomenal high end system today for well under $10k all in. But I'd spend my big money on preamps/DACs and speakers first. If you don't get those right, the rest doesn't help much.

Wrote way more than I'd intended. 

[konut]

Thanks for the thorough reply. Just the kind of details us audio geeks relish! A passive preamp is the very definition of the "less is more" philosophy. Thanks for perfecting this critical piece of the puzzle.

[MikeLdiy]

Received the new HiZ chip today.  What Konut said.  Seems a bit more cohesive.  Sounded really good before too though.  The status LED now flashes at lowest volume setting and when changing the volume.

[glynnw]

Received latest 10K chip yesterday and have put a few hours on it.  While nothing gives me an Aha! moment (other than that great flashing light during volume changes) everything just seems to flow a bit easier with better tonality.  The few recordings that were harsh before now seem less so.  Overall a good improvement.

[stellavox]

Hi Morten,

I and a few others have had a chance to listen to my LDR3X versus a few other "competing" LDR units.  One prototype, in addition to a switchable output buffer, has the ability to "tune" the input impedance of each source.

Our "listening results" indicate that this is a HUGE feature.  The only two impedance values we could "choose from" at the time were 10K and 20K.  With two different systems the effect on the high frequencies was obvious.  On one "bright" system, switching from 20 to 10K seemed to roll off the highs in a pleasing manner.  In the other system, the lower impedance "dulled" the highs.  SO, I'm experiencing that the varying impedance capability acts as a sort of "treble control" (I'm an old fart and can remember these things).  Of course now you will also be competing with interconnect manufacturers!!!/???.

I believe that your customers will find this capability VERY worthwhile.  Don't know if a 1K "vernier" is necessary - maybe 5K steps is more "reasonable" - easier to implement; and "tune"?

Keep up the good work1

Charles

[stellavox]

O yeah,

Should have also mentioned - The switchable buffer on one pre sounded "better" on the system we tried it on - better control of the lows.  My experimentation indicates that the lower output impedance also mitigates a LOT of differences between pre/amp interconnects.

Then add switchable 6/12/18db gain and you are REALLY home - with the "Ultimate Line Stage!

Charles

[tortugaranger]

I believe that your customers will find this capability VERY worthwhile.  Don't know if a 1K "vernier" is necessary - maybe 5K steps is more "reasonable" - easier to implement; and "tune"?

Yes, adjustable input impedance is on the front burner of "new features". Owners of our LDR3x.V2 board or our newest LDRx/LDRxB preamps will be able to update their firmware once this has been tested and released. Ultimately I hope to make it possible to run/store attenuation tables for multiple impedance settings and then be able to switch  back/forth between them to determine which is optimal for your rig. Results from that should prove very interesting.

I will likely roll out a Beta version of this to a few customers to try it out first and refine it before making it available to everyone.

No promises on timing but I'm hoping to have this available for Beta test before the end of the year.

[tortugaranger]

O yeah,

Should have also mentioned - The switchable buffer on one pre sounded "better" on the system we tried it on - better control of the lows.  My experimentation indicates that the lower output impedance also mitigates a LOT of differences between pre/amp interconnects.

Then add switchable 6/12/18db gain and you are REALLY home - with the "Ultimate Line Stage!

Charles

You do realize that the inclusion of a buffer stage together with adjustable gain (along with volume control & input switching) is the very definition of an active preamp/line-stage.

As it turns out we've had a buffer on the drawing board for some time now. In all likelihood it will end up being a symmetrical cathode follower tube design using a split voltage power supply such that the output is essentially at zero volts DC (although it will have an AC coupling cap). This topology should yield excellent PSRR and result in a dead quiet tube buffer. I'll only release this if/when it's clear  that it will add rather than take away from the benefits of the LDR preamp design. However, I will likely stop short of adding a gain stage. Philosophically, this runs against may grain. If one needs more power/volume far better to either get a bigger amp or even better yet more efficient speakers.

[ClefChef]

I built several preamps with Tortuga board as a volume adjusting unit - Aikido tube preamp, also ACF-2 Aikido tube buffer (the above mentioned "symmetrical cathode follower with split voltage power supply"). In my opinion Tortuga is fine as is - it serves specific "purist" market needs. Adding Tortuga to preamp with gain does not work well due to certain characteristics of LDR that get exaggerated in the gain stage. Tube buffer adds complexity, complicated power supplies, etc.

I like Tortuga as it represents "lightweight" audio component in terms of power consumption and, therefore, efficiency - it fits well with modern digital amps. It also works very well with tube power amps without buffers.

[tortugaranger]

In my opinion Tortuga is fine as is - it serves specific "purist" market needs.

Any buffer would be a stand alone product and would not become a required part of or in any way change our basic LDR passive preamp controller design. We get numerous inquiries regarding the addition of an output buffer. Again, if I can't convince myself it adds value then we ultimately won't offer it. And a gain stage isn't in the cards for many reasons.

And yes, the Tortuga is fine as is.