[goofytwoshoes]

I've been happier than the proverbial pig with the LDR3.V25 (impedance at 20K ohms) connected to a First Watt F5 (input impedance 100K).  A pair of Aleph 2 mono amps will arrive soon.  Their input impedance is 10K ohms.  Main source is a Korg DS DAC 10R.  Korg doesn't publish output impedance; they suggest that load impedance should be at least 10K ohms.

What impedance setting should I try first?

[tortugaranger]

I've been happier than the proverbial pig with the LDR3.V25 (impedance at 20K ohms) connected to a First Watt F5 (input impedance 100K).  A pair of Aleph 2 mono amps will arrive soon.  Their input impedance is 10K ohms.  Main source is a Korg DS DAC 10R.  Korg doesn't publish output impedance; they suggest that load impedance should be at least 10K ohms.

What impedance setting should I try first?

The First Watt 100k input impedance is ideal for a passive while the Aleph's at 10k is on the low end. When you combine the 20k default Tortuga passive with the 10k Alephs the Alephs set the upper limit of impedance where you get  10*20/(10+20) = 6.7k. Even if you raised the Tortuga impedance to say 50k it won't move the needle all that much 10*50/(10+50) = 8.3k  It's probably a fair assumption the Korg output impedance is fairly low are are most contemporary sources so if it's say 100R then you'll have a bridging ratio of 8300/100 = 83:1 which is plenty good enough. Much will depend on the strength of the Korg DAC output stage. I would leave the impedance at 20k and see how it sounds. If disappointed you can then try 99k on the Tortuga and see if that gets you into the land of good and if so consider dropping it to 50k since less is generally better. If not then the Alephs may not be a good fit or you can consider adding a buffer.

[goofytwoshoes]

Thanks for the quick reply!

Should be interesting to set several impedance choices and switch between them.  Buying the Aleph amps would have been a tougher decision if I didn't have the options available with the 3.V25.  And I'm hoping that you'll eventually offer a buffer upgrade kit for those of us that have the kit version of the preamp.

Also have a Bride-of-Son-of-Zen preamp coming with the amps.  Will be fun to compare single-ended passive LDR preamp to balanced active Nelson Pass design.  While I have the utmost respect for Nelson Pass' work, I doubt that the BOSOZ will be equal to the Tortuga.  Bought the BOSOZ because it was an incredible deal, and because that clinched the incredible deal on the Aleph amps.

I'm hoping  that some participants in the upcoming tour of the buffered preamp will have amps with similar low input impedance, and can offer a comparison of buffered to unbuffered sound quality.  I would have joined the tour, but I'm in Canada.

[goofytwoshoes]

The Aleph amps arrived about 6 weeks ago.  The sound quality is SO good with the Tortuga, that I left the impedance at 20K and never thought any more about it.  Yesterday, I upgraded the Tortuga firmware, and then programmed two more impedance settings - 50K and 99K.  The only difference that I can hear between the 3 impedance choices, is that I lose a wee bit of volume (at my normal listening level of 50 to 60 on the Tortuga's scale of 0 to 99) when I switch from 20K to 50K, and then lose a wee bit more when switching from 50K to 99K.  At "bother the neighbours" volume setting of 85, the difference is much more pronounced. 

I'm back to the 20K impedance for all listening, as this seems to be totally compatible with the Korg 10R DAC (and also an ifi Nano DSD DAC) and the Aleph 2 amps.  I needn't have worried about the Aleph amps (10K input impedance) not playing nice with the Tortuga. 

The Tortuga has been in-house for about a year.  Other than my son almost refusing to give it back after I loaned it to him, there's been zero issues with it. And I'm still totally in love with it.

[kernelbob]

I'm using an LDRxB just back from the v25 and OLED upgrade.  Low amplifier input impedance is of course relevant, but my experience is that the input impedance setting of the Tortugas is very important to the voicing of your source equipment.  I've been using the Lampizator Golden Gate DAC and recently upgraded to their Pacific DAC.  These are both vacuum tube designs, using a tube rectified power supply and a quad of tubes for the output (one per each phase of each channel) using balanced output.

Both of these DACs benefit from seeing a high input impedance controller/preamp.  These are the impedance settings on my Tortuga:  20, 65, 75, 78, 81, 84, 88, 91, 93, 95.  I stay in the 80's and 90's range.  The steps may seem small, but each has subtle effects on the DAC's sound.

At higher values bass is tighter, soundstage more focused.  Treble begins to be a bit subdued at the highest settings which can be beneficial with bright or hard sounding recordings. 

Lower values in can have more bloom and can open up the soundstage when called for.  At the low end of the range (in the 70's for my system), the frequency balance can begin to tilt upward.  Sometimes this is just what a particular recording likes.

This optimization of source equipment performance is just one of the great features of the Tortugas.  It lets me optimize the sonic signature of my system, all from the listening position with the remote.  I have yet to find any other controller/preamp that provides that degree of control over my system.

By the way, the improvements with the v25 upgrade are well worth it.  I was able to compare my Tortuga before ordering the upgrade with a friend's Tortuga that had the upgrade.  The v25 was more dynamic and transparent.  The OLED upgrade adds a lot of functionality and ease of use.

Best,
Robert