[flavo]

I made a thread recently about the mismatching of my Rogue super 99 pre and my Nu-Force STA200.
I'm enjoying the sound they produce through the Dali Helicon 800s so I wasn't looking to mix things up.

https://www.optoma.com/ap-nuforce/product/sta200/
http://www.rogueaudio.com/Products_99.htm
https://www.dali-speakers.com/discontinued/helicon-mk1/dali-helicon-800/

But I think I'd like to try out a near zero gain preamp.
I'm looking at several passives right now. I don't know much about them, but I'm hearing things about impedance matching I think?
If I get one from a US producer I suppose it wouldn't be an issue if I had to send it back for a change if I changed amps to something drastically different.
Am I getting that completely wrong?
I think I read that the Tortuga self regulates that feature so I wouldn't have to worry about that with them?

On my short list are these:
Tortuga - https://www.tortugaaudio.com/products/passive-preamps/ldr3-v25-passive-preamp/
Khozmo - https://khozmo.com/stereo_selector.html
Hattor - http://www.hattor.com/mini_preamp.html
Axiom w/ Walker mod - https://luminousaudio.com/collections/axiom-ii-passive-preamp

What ever you recommend must have a remote and be in the $1K range or less.

What is it that I don't know that will help me pick the right pre so I don't end up in this mess again?

Thanks folks

Mike

[Jon L]

I have/had many passive and active preamps, including LDR opto-couplers, Transformer Volume Control, simple volume pot, one-resistor in path (EVS attenuators), etc, but if one requires remote control, the most pure-sounding passive is still Placette remote volume control.
https://www.stereophile.com/solidpreamps/604placette/index.html

If one does not need remote control and is willing to manually turn the knob behind the amp at RCA inputs, then EVS Ultimate attenuators.

[glynnw]

I have a pair of Ultimate Attenuators and had a Placette 20 some odd years ago, but since encountering Tortuga a few years back I have quit looking around.  I was using a TVC at the time and immediately the Tortuga trounced it, especially in the treble.  Add a remote with both volume and balance, multiple inputs and adjustable input impedance and great support - I am on my 3rd unit.  Wish I could afford their new full preamp, but not in the picture at this time.

[JackD]

flavo

This will do everything you need and more.  I have used it with both the Nuforce and the Job 225 as well as close to a dozen other amps. You also have the option later to send it back to EJ for the Stage 2 upgrade.  Full function remote included.

https://www.usaudiomart.com/details/649598426-wyred4sound-stp-se/

[TJHUB]

I tried a couple of passive technologies and good attenuators prior to trying a Tortuga LDR.  The Tortuga is absolutely transparent, has great features, and is sold and supported by a great guy.  I have not even considered replacing it.

[ssglx]

I tried several passives in my system and settled on a Tortuga. It's awesome and pleases me completely. I've noted its sonic characteristics in previous posts.

[JLM]

Use of a passive preamp requires use of the correct (short/low capacitance) interconnects and compatible source(s) to power amp.  Back in my purist days tried a passive with high capacitance interconnects and the highs were definitely muted, so switched to stepped attenuators (at the power amp) to correct the problem.  Here's a good read:

https://www.monoandstereo.com/2016/02/is-passive-preamplifier-right-for-you.html

[flavo]

Use of a passive preamp requires use of the correct (short/low capacitance) interconnects and compatible source(s) to power amp.  Back in my purist days tried a passive with high capacitance interconnects and the highs were definitely muted, so switched to stepped attenuators (at the power amp) to correct the problem.  Here's a good read:

https://www.monoandstereo.com/2016/02/is-passive-preamplifier-right-for-you.html

Thanks for that info. Its sounds like with the Tortuga, as long as you keep the cables short it shouldn't matter?
I was bit confused on the impedance input and output.
I have a Bluesound Node 2i and the output is 2.1 VRMS, and supports connection to a minimum load impedance of 5kΩ
My STA200 has an Input impedance of 51k ohms

Copied from the article JLM linked:
 "An impedance ratio of 100:1 or greater is almost certain to work well with passives.
For example, a DAC with a 500 ohm output impedance and a SS amp with a 50K ohm input impedance
is all but certain to be a good match for a passive pre."

[ssglx]

Maybe I'm just lucky, but I've had great results with the Tortuga and interconnects from Morrow and Audience. My DAC outputs 2v and my Monarchy amp has an input impedance of 100K, and (as modified) requires ~1v for full output.

Morten at Tortuga can address the impedance issue, but my results were great out of the box. Full, rich and transparent sonics.

[Tomy2Tone]

Flavo, did you used to have a Truth preamp at one time? I know it’s not passive but is zero gain from what I understand. Just curious why it didn’t work for you, or has your system changed since then.

[Mike-48]

Use of a passive preamp requires use of the correct (short/low capacitance) interconnects and compatible source(s) to power amp.  Back in my purist days tried a passive with high capacitance interconnects and the highs were definitely muted, so switched to stepped attenuators (at the power amp) to correct the problem.  Here's a good read:

https://www.monoandstereo.com/2016/02/is-passive-preamplifier-right-for-you.html

The post by JLM is an important one. I tried a passive for a short time, but in my setup (long, low-capacitance balanced interconnects), the frequency response changed measurably (by up to 6 dB in the low bass) as the volume was changed. Nothing special about my gear: a solid-state pre and solid-state amp. So make sure you can return any unit you buy if you find the same thing.

[flavo]

Flavo, did you used to have a Truth preamp at one time? I know it’s not passive but is zero gain from what I understand. Just curious why it didn’t work for you, or has your system changed since then.

Wow! Great memory.
I did indeed have a Truth pre. Every single component of my system has changed since then. And it's not that the Truth didn't work for me. It just wasn't a miracle worker and had no remote.
I've come to realize that no remote for me, equals a death sentence to any component  that come's through my front door.

The post by JLM is an important one. I tried a passive for a short time, but in my setup (long, low-capacitance balanced interconnects), the frequency response changed measurably (by up to 6 dB in the low bass) as the volume was changed. Nothing special about my gear: a solid-state pre and solid-state amp. So make sure you can return any unit you buy if you find the same thing.

But your saying you had a long run of interconnects? I think my longest interconnect will be around 3' or less.
Great point though. I have a cheapo Nobsound on the way.
I'm pretty close to getting a Tortuga preamp now.

[fredgarvin]

Thanks for that info. Its sounds like with the Tortuga, as long as you keep the cables short it shouldn't matter?
I was bit confused on the impedance input and output.
I have a Bluesound Node 2i and the output is 2.1 VRMS, and supports connection to a minimum load impedance of 5kΩ
My STA200 has an Input impedance of 51k ohms

Copied from the article JLM linked:
 "An impedance ratio of 100:1 or greater is almost certain to work well with passives.
For example, a DAC with a 500 ohm output impedance and a SS amp with a 50K ohm input impedance
is all but certain to be a good match for a passive pre."

I may be remembering wrong, but the input impedance of your amp is only in the 20's, which might lead one to think that choosing the right passive will take some consideration.

[mresseguie]

Hello, Mike.

I have never heard one, so I have no idea of its sound or reliability. That said, have you considered CIAudio's PLC-1 MKII Remote Passive Preamp for $1095 new?

https://ciaudio.com/product/plc%E2%80%A21-mkii-remote-passive-line-controller

Enjoy your journey.

Michael

[kernelbob]

Hi flavo.

I'll add my recommendation for the Tortuga controller, joining glynnw, THJUB, and ssglx.  I'm using a Tortuga in my bi-amplified system with a pair of Lampizator True Balanced 211 amps on the mid/treble and a pair of Spectrons as monoblocks on the bass.  The 211 amps present 200k input impedance.  The Spectrons present 25k so I use a Tortuga Tube Buffer ahead of the Spectron so the Tortuga controller sees 200k impedance also.

A key feature of the Tortuga is that there are no switches, potentiometers, switched resistor attenuators, jumpers, etc. in the signal path... none from the input to the output.  If you view the interfaces of those physical attenuation devices under magnification, you'll see that what appear to the naked eye as smooth surfaces are actually a series of peaks and valleys.  This means that the actual contact area between the surfaces is rough.  This forces the flow of the signal to jump across those connections.  Not good eats.

When you turn the control on the front ofOT the Tortuga, you are not directly altering inline or shunt impedances.  You are only sending an instruction to the control software that you want to change the attenuation of the signal by a specific amount.  The software matches the desired attenuation value with an internal table that maps the necessary illumination of a pair of inline series and shunt light dependent diodes (LDRs) to accomplish the desired attenuation.

You can of course make that same attenuation change using the provided remote from you listening position.  (for Jon L) There is no difference in how you tell the software that you want to change the attenuation level-- whether using the control knob on the Tortuga or using the remote control.  So it is not the case that "if one requires remote control, the most pure sounding passive is still (a) Placette remote volume control".

There is a comprehensive set of controls available via the remote, all of which have no degradation of the signal since they also are instructions to the control software such as:

1)  You can change the left/right balance and switch between stereo or mono.

2)  Instruct the software to re-calibrate the LDRs for a specific input impedance setting.  This can be done anytime, but my Tortuga's LDRs are extremely stable.  That calibration takes place whenever you specify a change in a saved impedance setting.

3)  Change the input impedance presented to the source.  On a single ended unit, you can select any input impedance between 1k and 99k in 1k steps.  On my balanced unit, that's per phase, so the net impedance between the plus and minus phase is 2k to 198k.  By the way, you can save nine specific impedance settings.  For my Lampizator Pacific DAC using a vacuum tube balance output stage, it likes to see high impedances.  I normally use "97k" (i.e. 194k balanced).  I have nine values saved between "91" and "99".  A tenth setting of "20k" is fixed as a default in the software.  All you have to do is select which of the nine custom settings to change, set the value you want and press a button have the control software define the values needed in the corresponding lookup table.  Oh, and you can switch between any of the saved input impedance settings from your listening position.  That makes it simple to hear the difference.

4)  There's a variety of user preference settings.  For example you can specify how many of the available inputs are selectable.  The attenuation setting can be set to display steps from 0 to 99 or in -dB values.  Display brightness is selectable.  You can set the display to go dark after a number of seconds (you can select the delay seconds before going dark).

5)  You can switch between inputs and disable inputs to only make the inputs you want to be available for selection.

6)  Since I use the balanced version, I requested the available absolute phase selection.  This lets me switch between the "normal" to "inverted" from my listening position. 

All of these controls are performed without adding any of those nasty switches, potentiometers, attenuators, etc. in the signal path.

One last point, if you get a Tortuga controller, using battery power provide a significant performance improvement.  Morten makes a companion battery unit.  I'm using an Optima deep cycle marine battery and a very small trickle charger to keep it topped off.

Hope this helps.  Feel free to PM me if you have questions on all this.

Best,
Robert

[Rusty Jefferson]

Consider the Sonic Euphoria PLC passive preamp. The autoformers eliminate the need to carefully impedance match. They generally go for about $750-$1k these dsys.
https://www.stereophile.com/solidpreamps/106sonic/index.html

[glynnw]

And don't forget that Absolute Sound loves the Tortuga.  On their list of recommended components.

[MttBsh]

I too own a Tortuga passive and love it. Morten plans to release updated, lower cost modular versions of his preamp later this month https://www.audiocircle.com/index.php?topic=168215.0

[rollo]

  A passive preamp is noy a one size fit all. Ones amp must have a very low input sensitivity for starters. Second ones source requires a 3V output for BEST results. Cables as well require low cap. Have fun trying. Autoformer based passives or transformer based are my favorites. Most others I have found to be thin sounding.


charles

[ssglx]

YMMV..., the LDAR sounded nothing like the other passives including a K&K TVC (which was amazing in its own right - transparency).

With a satisfaction guarantee from the vendor, anyone wanting to check out passives in their system should not hesitate to; regardless of the potential issues noted in this thread.