[tortugaranger]

After 3+ years of iterative development of our LDR passive preamp technology and related preamp models, it's time to make some decisions on what to focus on next. To that end, I would welcome your feedback, thoughts, suggestions etc. While I have my own product ideas and preferences, what matters in the end is what are YOU interested in seeing and what are your friends interested in and what do you think everyone else might be interested in. So consider this a wish list request. Opine and wish away!

I'll seed this with a few thoughts:

1) Version V3 of the LDR3x Preamp Controller Board. - This would involve a complete hardware redesign utilizing surface mount components resulting in a much smaller board. One possibility is the complete separation of the digital controller from the analog wherein a single digital controller board would interface with multiple LDR boards with each LDR board providing a stereo channel. For example, a typical singled ended stereo preamp would have 1 controller board and 2 LDR boards. A 2x5 ribbon cable would connect from the controller to each LDR boards. For a balanced system you would have 4 LDR boards. You could just keep adding channels to get a 7.1 systems. The V3 might also have a new companion display module with would be LCD screen rather than 7 segment numerals. The V3 or close variant would likely be a candidate for OEM version for use by other manufacturers.

2) Buffered LDR Preamp - Technically this would not be a "passive" preamp since the output of the LDR attenuator would feed into high impedance buffer stage which could have unity gain or perhaps optional gain boost. The presumptive benefit of a buffer would be improved dynamics for those systems where a passive isn't the best fit. More than likely this would be a solid state buffer with a high current delivery capacity. We've been noodling on this for quite some time and are currently favoring TI's LME49600 buffer chip. This buffer would be an optional add-on to the existing line of preamps, possibly also a retrofit option, and could also be a true stand alone buffer product without a front-end LDR attenuator.

3) Integrated Headphone Amp - Turns out that the buffer design we're pursuing is also an excellent candidate for a headphone amp with the addition of appropriate gain plus an output disconnect safety circuit to prevent feeding excess DC offset into the headphones (due to excess external offset from source or internally generated offset from power supply failure/imbalance etc. ).  While headphone amps is a crowded market, we would have the key differentiator of being the ONLY one with an LDR front end with all the commensurate sonic benefits relative to all the others with volume pots. Also, our headphone preamp will a true balanced design with a pair of amps driving each channel for a total of 4 amps per headphone. Of course it would also have a conventional single-ended output.

4) Phono stage/preamp - I have a working prototype that I've listening to for the past few weeks connected with a high output (2.5 mv)  moving coil cartridge with excellent results - to my ears at least. Just like the buffer option, the phono stage could be an option for out existing LDR preamp product line that would allow direct connection of turntables to our preamps without the need for a separate phono stage. This would probably start off as being compatible only with MM and high output MC cartridges. Low output MC cartridges require additional design considerations we've yet to tackle. I'm of the opinion that most audiophiles find the "phono stage" to be a bit mysterious but it's actually quite a straight forward device. It's basically an active filter (with gain) to correct for the RIAA standard frequency bias baked into all vinyl records starting way back in the 50's or thereabouts. And of course it has to also boost the low millivolt level output of the phono cartridge to typical line level voltage (~2 volt RMS) needed by downstream premaps/amps.

5) Fully integrated amp - Here we'd marry the existing LDR preamp plus buffer plus phono stage with our own amp which might be chip-amp variant of the LM4780 run in parallel for somewhere around an 80-100 watt output. Of all the above ideas, this is my least favorite since it goes against my audiophile grain of separate components. Yet I've had a few inquiries asking for this so I could be totally wrong about this from a marketing standpoint. Noticeably absent from this list of features is an integrated DAC. A DAC is one thing we will not seek to develop in-house. But licensing an existing DAC design/board is always a possibility.

Thanks for reading all this and double thanks for offering your input.

Cheers,
Morten

[craig sawyers]

I think that where you started - with the benefits of a passive unit using LDR's is where to stick.  As soon as you add active circuitry you have moved away from that "keep it simple" philosophy.  But it does have the advantage if the output cable runs are long, and cable capacitance loading is an issue.

I like the first option a lot - it changes the architecture only, with potential benefits of simplicity and flexibility.

A further option that might be worth adding to balanced units is phase invert.

Cheers

Craig

[poseidonsvoice]

I like all your ideas, but I like Option 1 the most especially if we can design a 7.1 or 7.2 LDR based attenuator without fancy digital manipulation that is  common in high end AVP's. Just a simple volume control. The ability to trim each channel (+/- 10 dB in 1 dB steps) would be awesome. Buffer stages can be added if needed of course.

Regarding Option 4, I've sent you a PM.

Best,
Anand.

[JohnR]

Since you asked

I don't think you should obsolete your V2 board already, it's less than year since it came out.

I do think multichannel would be interesting. I don't think you should be thinking "7.1" but "any number." The trim idea from Anand would also be very interesting, but I think you can do "-" only. I think this would also need a way to program in the impedance of the output device, so that channels stay matched across the range. (i.e. you can't assume that all channels are driving the same impedance if you really want this to work well.)

I think that an inter-chassis solution would be very interesting. That way attenuators could be built into amps, and all controlled from the... er controler.

A single front panel rather than bits and pieces seems like a logical thing to do.

[tortugaranger]

I think that where you started - with the benefits of a passive unit using LDR's is where to stick.  As soon as you add active circuitry you have moved away from that "keep it simple" philosophy.  But it does have the advantage if the output cable runs are long, and cable capacitance loading is an issue.

I like the first option a lot - it changes the architecture only, with potential benefits of simplicity and flexibility.

A further option that might be worth adding to balanced units is phase invert.

Cheers

Craig

Thanks Craig. I agree with you as a technical matter but as a commercial/marketing matter I suspect there's a hard core faction of audiophiles who view passives as inherently less good than an active premap. It's an undeniable part of being human that our strongly held views are often the very thing that prevents us from trying alternatives that may challenge those views. Any active preamp (or any audio unit with a volume control) could benefit from LDR attenuation. The question comes down to this. As an audio company should we continue to solely promote our core LDR passives or also offer a buffered (a.k.a. active) version of  same product for those who wouldn't touch a passive with a 10 foot pole?

Best,
Morten

[tortugaranger]

I like all your ideas, but I like Option 1 the most especially if we can design a 7.1 or 7.2 LDR based attenuator without fancy digital manipulation that is  common in high end AVP's. Just a simple volume control. The ability to trim each channel (+/- 10 dB in 1 dB steps) would be awesome. Buffer stages can be added if needed of course.

Regarding Option 4, I've sent you a PM.

Best,
Anand.

Thanks Anand. Your insights are welcomed and valuable as always. Done properly a single controller board would interface with any number of LDR board/channels. With a 7.2 system you're looking at possibly 9 channels which if each LDR board is a 2 channel unit this would require 5 boards each with either a 10 or 14 pin ribbon cable connector back to the controller board. All doable with enough controller board real estate and header pins.

Your PM suggestion regarding amp options is well taken. Less reinventing of the wheel thank you.

Best,
Morten

[tortugaranger]

Since you asked

I don't think you should obsolete your V2 board already, it's less than year since it came out.

As a practical matter I don't think we'll be ready with a V3 for another year or so. Also, I don't expect any future iteration of our LDR preamp boards to have materially improved sound over our existing designs - but of course I could be wrong about that.     I view it as a design refinement based on everything we've learned to date that will broaden its potential application.

I do think multichannel would be interesting. I don't think you should be thinking "7.1" but "any number." The trim idea from Anand would also be very interesting, but I think you can do "-" only. I think this would also need a way to program in the impedance of the output device, so that channels stay matched across the range. (i.e. you can't assume that all channels are driving the same impedance if you really want this to work well.)

The multi-channel is quite doable. Achieving uniform output impedance from multiple passive L-pad attenuators would be truly challenging if not impossible without using output buffers.

I think that an inter-chassis solution would be very interesting. That way attenuators could be built into amps, and all controlled from the... er controler.

Eventually we hope to have a suitable OEM version that could work well anywhere an attenuator is needed along with input switching and remote control. We welcome inquiries and I'm sure this will end up involving a bit of collaboration before it becomes a reality.

A single front panel rather than bits and pieces seems like a logical thing to do.

Yes, the control features/options have outgrown a simple remote and a 2/4 digit display.

Best,
Morten

[RDavidson]

I really like option 2, primarily for the impedance matching it would provide.

Wyred 4 Sound makes, essentially, what you're considering (with the exception of the type of attenuation used) with their STP-SE.
What I'd personally like to see is a tube buffer option. The only preamps / buffers I've seen with this configuration are those by Gary Dodd and one of the selectable configurations in Red Wine's new LIO.

Could you offer both a tube buffer and SS buffer, perhaps in the same unit so the user can select per their preference? What'd be killer is if the buffer(s) could also be bypassed entirely. This would be a game changing 3-in-1 design.

[33na3rd]

Everyone seems to want something a little different than each other. Perhaps a modular architecture could make everyone happy, including Morten? 

I think a phono stage with high enough gain to drive most amps would be a fine idea. If you do build a phono unit, please include a mono switch!

[rollo]

  Melos comes to mind. Using your excellent LDR volume controls with a tubed linestage would be inviting. For the SS crowd no tube just linestage.


charles

[tortugaranger]

What I'd personally like to see is a tube buffer option.

We've been working a 6SN7/6CG7 tube buffer design for a while now. The  trick is getting them to be stone cold quiet which I believe we've accomplished. The SS vs. Tube buffer comes down to cost vs. value with tubes always costing more due to power supply requirements and DC offset protection.

Could you offer both a tube buffer and SS buffer, perhaps in the same unit so the user can select per their preference? What'd be killer is if the buffer(s) could also be bypassed entirely. This would be a game changing 3-in-1 design.

While this would make for an interesting demo unit I believe it presents an awkward choice commercially and may ultimately confuse most buyers. And it would definitely drive up the cost. Offering both flavors separately is a possibility.

[tortugaranger]

I think a phono stage with high enough gain to drive most amps would be a fine idea.

I'm not sure a "one gain fits all" approach would work since there's a fairly wide range of output voltages depending on make, model, type of cartridge. Just maxing out the gain for all possibilities will likely disappoint. The higher the gain the higher the signal to noise ratio. Then there's special design considerations for MC (moving coil) cartridges which tend to have very low output of only a few tenth's of a millivolt vs. MM (moving magnet) cartridges with up to 5 millivolt of output. Over a an order of magnitude range.

If you do build a phono unit, please include a mono switch!

Easy enough to do but I'd like to understand better why you'd find this desireable.

[JohnR]

Eventually we hope to have a suitable OEM version that could work well anywhere an attenuator is needed along with input switching and remote control. We welcome inquiries and I'm sure this will end up involving a bit of collaboration before it becomes a reality.

I guess I didn't explain my suggestion very well. I was thinking about DIY boards, where the attenuator modules could be built into amps. Then several amps could be controlled from the one controller.

Just an idea

[33na3rd]

I'm not sure a "one gain fits all" approach would work since there's a fairly wide range of output voltages depending on make, model, type of cartridge. Just maxing out the gain for all possibilities will likely disappoint. The higher the gain the higher the signal to noise ratio. Then there's special design considerations for MC (moving coil) cartridges which tend to have very low output of only a few tenth's of a millivolt vs. MM (moving magnet) cartridges with up to 5 millivolt of output. Over a an order of magnitude range.

Easy enough to do but I'd like to understand better why you'd find this desireable.

No, you would have to have some gain choices to be sure. My current phono unit has choices between 48, 60, & 70dB. Even though the 70 setting is enough gain for my Denon DL-103 at .003 mV, it still sounds better at 48dB with a 23dB step up transformer. I don't know why this would be, but I know I'm not the only one that prefers a lower gain phono setting with a SUT.

The reason for including a mono switch, is mono LP's! Mono LP's sound better played summed, even with a stereo cartridge. Playing summed lowers the surface noise dramatically, and renders a smoother top end. A simple  double Y connector/adapter can show you the difference easily, even with all those extra connections. It is most effective between the phono unit & preamp. Placing the summing cord before the phono unit can/will change the cartridge load, which is not advisable.

Many of the classic jazz albums were cut in mono. And don't forget the recent Beatles mono box set! Ortofon came out with the 2M White mono cartridge just for that release!

[Ric Schultz]

I would do an active solid state buffer and and active tube stage with gain.  The National part is great but sonically even better is a Lsk170 biased via another LSK170 acting as current source.  You can match them to get zero offset or use a lower IDSS part as the buffer and a higher IDSS part as the current source and trim the current source to get zero offset.  You could also try paralleling them for more drive.  A single jfet has 50 ohm output impedance so two in parallel would get you 25 ohm.  The fet is slightly more lucid and real than the National buffer.  I use the jfets in my Oppo mods on the output of the ESS DACs.  For best sound the National buffer needs to be biased for maximum speed and I use .15 modified Wima bypass caps right on the pins to keep them stable.

An active tube line stage would give added gain and give the liquid and palpable sound some people crave.  The tube stage would have to have great regulators, resistors, power supply caps and output caps.....much more expensive.

[tortugaranger]

I would do an active solid state buffer and and active tube stage with gain.  The National part is great but sonically even better is a Lsk170 biased via another LSK170 acting as current source.  You can match them to get zero offset or use a lower IDSS part as the buffer and a higher IDSS part as the current source and trim the current source to get zero offset.  You could also try paralleling them for more drive.  A single jfet has 50 ohm output impedance so two in parallel would get you 25 ohm.  The fet is slightly more lucid and real than the National buffer.  I use the jfets in my Oppo mods on the output of the ESS DACs.  For best sound the National buffer needs to be biased for maximum speed and I use .15 modified Wima bypass caps right on the pins to keep them stable.

An active tube line stage would give added gain and give the liquid and palpable sound some people crave.  The tube stage would have to have great regulators, resistors, power supply caps and output caps.....much more expensive.

Thanks for the input Ric. I've not worked with the lsk170's but I've heard they are popular. I ran a few sims of this with a split voltage supply and also used an op amp servo to null out any output offset (regardless of IDSS mismatch) by feeding the servo out back into the gate to trim things out. This could potentially eliminate the big output coupling cap which I would think is big plus sonically. With this approach I'd probably also want to have DC offset safety disconnect relay just in case things went wacky upstream with the power supply, jfets etc.

Curious why you'd want to add gain with the tube stage at all...or...why with tubes and not SS? I reread your note and realize you were suggesting putting the fet buffer TOGETHER with a tube stage with gain as a package. 

[gregfisk]

I think a popular product would be a simple volume control in its own enclosure with a remote. I believe there are many people that won't buy a preamp if it doesn't have a remote for volume, me included. The manufacturers of these preamps choose for whatever reason, may it be cost or sound quality not to add a remote.

This would simply be an additional product in your line up prebuilt or DIY but one that I believe would be a good seller and capture the market that you're otherwise not tapping, which of course are people that don't want a passive preamp.

Just my .02 cents.

Greg

[RDavidson]

I think a popular product would be a simple volume control in its own enclosure with a remote. I believe there are many people that won't buy a preamp if it doesn't have a remote for volume, me included. The manufacturers of these preamps choose for whatever reason, may it be cost or sound quality not to add a remote.

This would simply be an additional product in your line up prebuilt or DIY but one that I believe would be a good seller and capture the market that you're otherwise not tapping, which of course are people that don't want a passive preamp.

Just my .02 cents.

Greg

You should probably read the first post of the thread (re: buffered preamp).

[Ric Schultz]

You don't need any coupling caps with the jfet buffers.   Please see this thread:   http://www.diyaudio.com/forums/pass-labs/145201-building-symmetrical-psu-b1-buffer.html    for info on the circuit and using shunt regulators.  You don't need an output resistor either.

No, I was not suggesting using a solid state buffer with a tube line stage....but two separate products....a solid state buffered unit for lower output impedance and a separate tube output stage version (offering gain and buffering and the highly desired tubey sound).

[gregfisk]

You should probably read the first post of the thread (re: buffered preamp).

 This is not what I was talking about. When I had the original LDR3 in my system while it was on tour I was able to test it with an amp that had a volume control. Whether I listened to the amp with the LDR in the system or out of the system I couldn't here a difference. That's why I think using an LDR as a volume control only would be a great product, no gain, just a remote volume control for any active preamp that doesn't have one.