LDR Tube Preamp

0 Members and 1 Guest are viewing this topic. Read 725 times.

tortugaranger

  • Facilitator
  • Posts: 1423
  • Handcrafted high performance audio gear
    • Tortuga Audio
LDR Tube Preamp
« on: 20 May 2019, 04:14 pm »
Hi All,

After much flailing and gnashing of teeth the next Tortuga Audio product is coming out of hiding as it winds its way through the latter stages of development. This time I'm going to take a different approach insofar as I'm going to be sharing quite a lot of information early and often all the way up through release and early production. So get your popcorn out ...  :popcorn:

For now I'll be referring to this preamp as our LDR Tube Preamp. The official product name may differ.

This preamp is the culmination of several years of work on both our LDR based attenuator/preamp controller used in our passive preamps plus our hybrid tube buffer. The LDR Tube Preamp combines the most current/updated versions of these into a single integrated LDR preamp/enclosure. 

I'm unequivocal that this LDR attenuator/tube preamp marriage will sound outstanding because it already does sound outstanding as separate components linked together externally.

Here, in abbreviated form, are the highlights of this upcoming preamp:

1) LDR (light dependent resistor) based 100 step balanced attenuator - 60 dB range. Will probably use our existing V25 preamp controllers/attenuators but we'll move up to the V3 once it's available.
2) Unity gain hybrid preamp with a tube (6922 family) input stage and a discrete solid state JFET output buffer stage using an updated/improved version of our existing TPB.V1 tube preamp buffer
3) Flexible - handles both balanced (3) and single-ended (3) inputs in a single model so you don't have to choose between what signal type.
4) Rugged heavy-walled extruded aluminum casework/panels. Could probably run it over with a car and it would still keep going.
5) White on black 256x64 bit OLED graphical display for control located behind dark acrylic front panel lens - invisible when off.
6) Simple 7 button generic Apple remote
7) Powered via AC mains with toroidal transformer and linear supply into switching DC-DC regulated tube heater circuit and split voltage tube plate power circuit with very high PSRR
Eight) Approximate dimensions excluding knobs/jacks/feet etc. |  12 inch wide x 8 inch deep by 3 inch tall.  Knob and jacks will probably add no more than 2 more inches to the depth. Feet will probably add no more than 1 inch to the height.
9) Unit weight will likely be somewhere in the 10-15 pound range.

I'm not going to speculate on an availability date yet because I've always been wrong in the past but you'll know when I know if you follow this thread. But I'm committed to getting this done as soon as we can. Also not going to discuss final price yet but early adopters signing up for pre-orders will secure a substantial discount.

The pics below are 3D CAD screenshots. Final appearance and physical details are subject to change but I doubt it will look much different than depicted here.



« Last Edit: 22 May 2019, 02:46 pm by tortugaranger »

Chris Adams

Re: LDR Tube Preamp
« Reply #1 on: 20 May 2019, 06:32 pm »
Looks like a great product.

Will this be true balanced in and out? And if so, will you be able to mix say, single ended in and balanced out?

glynnw

  • Full Member
  • Posts: 708
  • I have tin ears.
Re: LDR Tube Preamp
« Reply #2 on: 20 May 2019, 06:39 pm »
Damn it man!  Now you are going to get rich with products like this and you'll forget all us little people.  This new product is the way to go.

tortugaranger

  • Facilitator
  • Posts: 1423
  • Handcrafted high performance audio gear
    • Tortuga Audio
Re: LDR Tube Preamp
« Reply #3 on: 20 May 2019, 07:16 pm »
Looks like a great product.

Will this be true balanced in and out? And if so, will you be able to mix say, single ended in and balanced out?

Yes....but.

Anything coming in balanced will be present on the RCA out but the RCA out will only carry one phase (pin #2) of the attenuated balanced signal.

Anything coming in on the RCA input will be present on the balanced output but ONLY on one phase (pin #2) of the balanced output.

Balanced inputs will be attenuated fully balanced meaning each phase signal is attenuated by itself (not converted to single ended first).

There's no bal->unbal or unbal->bal signal conversion in this preamp.

tortugaranger

  • Facilitator
  • Posts: 1423
  • Handcrafted high performance audio gear
    • Tortuga Audio
Re: LDR Tube Preamp
« Reply #4 on: 20 May 2019, 07:17 pm »
Damn it man!  Now you are going to get rich with products like this and you'll forget all us little people.  This new product is the way to go.


Little chance of that happening but nice thought.  :thumb:

paul79

  • Full Member
  • Posts: 862
Re: LDR Tube Preamp
« Reply #5 on: 20 May 2019, 09:54 pm »
 :popcorn:

tortugaranger

  • Facilitator
  • Posts: 1423
  • Handcrafted high performance audio gear
    • Tortuga Audio
Re: LDR Tube Preamp
« Reply #6 on: 21 May 2019, 01:58 pm »
Here we have what is hopefully the final prototype of the updated tube preamp buffer board for the LDR Tube Preamp. Unlike the previous design currently still in use in our TPB.V1 Tube Preamp Buffer, this "V2" version packs everything into only a single board that is also smaller overall.

We've eliminated one transformer from the design so now there's only one toroidal transformer. The tube heater and the tube plate voltages are each generated by its own dedicated switch mode DC-DC regulator. The plate switching regulator is split voltage and is followed by a second split voltage linear stage which will also accommodates optional Belleson SuperRegulators on both the positive and negative rails. The overall plate voltage potential  has been increased from +30 to 44 (+22/-22) volts (yes, it's THAT low!).

There are 4 separate circuits to handle the balanced stereo (2 phases per left/right sides). Each tube handles the +/- phases of the right and left channels. Each circuit has its own set of bypass caps for both power rails using high quality Vishay poly caps and Elna Silmac II silk electrolytics.

The V2 layout is designed to accommodate a wide array of high quality output coupling caps up to 1.25" in diameter and up to 2.5" in length. Enough room to handle most high end caps but probably not the biggest most costly available. We've standardized on V-Cap brand caps. Specifically their new line of oil damped advanced metalized (ODAM) audio caps which they will be announcing any day now and which we've been using pre-release versions of for some time now in our more recent V1 builds with really excellent results.

We'll probably know in about 2-3 weeks if this layout will be our final or not. If not, I'm confident it will only require some final parts realignment to arrive at the final/production PCB design. This is probably the 5th or 6th iteration on this V2 redesign and I've found that it usually takes that many iterations for most designs to get done. Which it were simpler/faster but there ya go.

Cheers,
Morten  :thumb:


rollo

  • Industry Participant
  • Posts: 4188
  • Rollo Audio Where Home demo rules
Re: LDR Tube Preamp
« Reply #7 on: 21 May 2019, 05:16 pm »
  Morten, an excellent move. LDR and tubes oh my !!! Sell tons.


charles

tortugaranger

  • Facilitator
  • Posts: 1423
  • Handcrafted high performance audio gear
    • Tortuga Audio
Re: LDR Tube Preamp
« Reply #8 on: 29 May 2019, 09:32 pm »
Today we ordered the next round of prototype boards for the LDR Tube Preamp. In about 2 weeks we should have a good sense of how close we are to completing the updated design of the tube board which includes the power supply except for the toroidal transformer itself which does not mount on the board. By the end of this week I expect we'll have the updated rear panel machined out so we can take the next step on the fit up of the IO board. We are telling ourselves that it's doable to have a fully functioning prototype in an unfinished enclosure by the end of June. Aggressive but doable. If we achieve that we should be able to hit a release date within the July/August timeframe. Much will depend on the outcome of testing when we get the new round of prototype boards back. Stay tuned!

LarryD56

  • Jr. Member
  • Posts: 53
Re: LDR Tube Preamp
« Reply #9 on: 29 May 2019, 11:28 pm »
I've been looking for something like this to step up from my Wyred 4 Sound STP-SE preamp. Looking forward to your evaluation....it should be good!

Larry D.

TX_Saint

  • Jr. Member
  • Posts: 7
Re: LDR Tube Preamp
« Reply #10 on: 11 Jun 2019, 12:56 am »
How is this product different than the LDR300.V25 Buffered Preamp that was recently discontinued?

TX_Saint

  • Jr. Member
  • Posts: 7
Re: LDR Tube Preamp
« Reply #11 on: 11 Jun 2019, 01:13 am »
Feature request: balance control. Many of us older folks have hearing loss in one ear that throws the imaging out of whack. Also some of us have one speaker in a corner that throws off the balance.

tortugaranger

  • Facilitator
  • Posts: 1423
  • Handcrafted high performance audio gear
    • Tortuga Audio
Re: LDR Tube Preamp
« Reply #12 on: 11 Jun 2019, 01:07 pm »
How is this product different than the LDR300.V25 Buffered Preamp that was recently discontinued?

The LDR300 employs a solid state buffer output stage. The LDR Tube Preamp uses almost an identical output stage but also employs a tube input/gain stage between the attenuator and buffer output. hence it's referred to as a hybrid tube/solid state preamp buffer. Some take exception to that terminology and want me to call that a linestage - toMAYto toMAUGHto. The gain is set by default at 1x (i.e. no gain).

In short, it uses a tube, while the LDR300 does not. Makes quite an overall difference in the performance - as in it sounds better with the tube.

tortugaranger

  • Facilitator
  • Posts: 1423
  • Handcrafted high performance audio gear
    • Tortuga Audio
Re: LDR Tube Preamp
« Reply #13 on: 11 Jun 2019, 01:08 pm »
Feature request: balance control. Many of us older folks have hearing loss in one ear that throws the imaging out of whack. Also some of us have one speaker in a corner that throws off the balance.

Done! All of our preamp products already have balance control as a standard feature.  :thumb:

TX_Saint

  • Jr. Member
  • Posts: 7
Re: LDR Tube Preamp
« Reply #14 on: 12 Jun 2019, 12:46 am »
Great to hear it has balance control. What is its output impedence?

tortugaranger

  • Facilitator
  • Posts: 1423
  • Handcrafted high performance audio gear
    • Tortuga Audio
Re: LDR Tube Preamp
« Reply #15 on: 14 Jun 2019, 08:00 pm »
6.14.19 Update

We've basically completed the design of the new tube/buffer board. Although I had high hopes for going with split voltage power supply I didn't like the performance as compared to prior single sided supply so after some quick mods to the board we tested it with +45 volts on the plate and it sounded quite sweet indeed. We also verified that there's no way around having to stay with our 50 VA shielded toroidal transformer which does make for a very tight cheek-to-jowl fit but so be it. I'd hoped to go with a slightly physically smaller transformer but dropping down to a smaller 25 VA will not cut it. Cheek-to-jowl it is.

Next week we plan on doing fit ups with the pcb/hardware in the new enclosure. That will allow us to settle on placement and dimensions of the input/output interface board using cardboard mock ups. If all goes well we're still on track to finalizing the tube/buffer/PS/enclosure/panels part of the design.

That leaves getting the new V3 preamp controller board over its final hump of development. Next week will tell the tale on where that stands. We've gone through a few iterations on a new LDR current control scheme and waiting to see if the new precision differential op amp closed loop current control scheme will behave well over the full range. Last iteration we got it work over 90% of the control range. All  most  there.

Once we have the new current control scheme nailed down there's a chunk of software work that remains. We are porting the software over to a bigger badder more powerful and more flexible software development tool chain that will give us new options for how to update firmware. We've already done the conversion work but need to do the fine turning on the new hardware. The interim plan is to be able to update the firmware by simply plugging  a thumb drive into the USB port. Longer term the firmware update will be over the air via WiFi.

If we see ourselves bogging down with the V3 development we may make the call to release the new LDR tube preamp with our current V25 controller which has the advantage of being a great performer and highly stable at this point.