[jackox]

Hi Dan

IMO real balanced can also be used as a real SE.
The use of transformers is an OK solution but defeat real balanced design.

Yes I'd need XLR and real balanced (2 pair of tubes) as I would use the buffer in a real balanced path.
From DAC to amps.

[RDavidson]

Use of transformers is "real balanced."
What you're referring to is dual differential balanced, which is double the circuitry and ~double the $. Dual differential is not some sort of panacea at the end of the day either. In fact it can introduce other issues.

[RonP]

Hey Dan,

I know this isn't highest priority, but I hope you are still working on this.

On memorial day I picked up a Tube PreAmp. Man oh Man!! I spent decades listening to solid state only. I was missing out.  I'm never going back to a tubeless system if I can help it. I even ordered a integrated tube setup for the home office.

This is the kinda product that would really be transformational to those with run all sold state. So please keep plugging away! I think this product could really spread some audio joy!   

[modwright]

Hi guys, finally caught up and back on this design!

Putting pen to paper and laying out PCBs to decide on options.

Base model will be a VERY wide BW, very low THD (< .003%) buffer.
Stock design will likely have 2 inputs and a toggle to select between them.
Tube type: 6922.

Now for options:

1. Balanced inputs and outputs. I have to disagree that transformer coupling is not a true balanced design. Pro Audio has been using line matching transformers forever and they are the ideal way to couple signals! Using 2 x the tubes for a 'true balanced' design means that you have twice the circuitry and twice the tubes to match. I believe there is the misconception that a transformer is 'adding' something to the signal path that will only color the sound. Experience has taught me that transformer coupling IMPROVES the sound, by nature of how it handles signal.

So, what I am saying is that the balanced option will be transformer coupled in to out. This means that a balanced input signal will see a balanced load and the output will be fully balanced. There will be no SE wired XLR's.

2. Volume control w/remote is the other option. This will require a PIC and controls and will likely use an Alps motorized VC or similar. I know that there are better volume controls out there, but including them would drive the price of this product up too high. Plus, there are so many options that I would be asked to use custom and specific steppers, etc. and this product does not lend itself to this. This is not a modification product, but a production product. In order to keep prices reasonable, I have to standardize some things.

3. I am looking to offer a way to customize the sound. Offering different tube options is one way, but often this means that the design is not really optimized for any one of the tubes, but compromised to allow all of them to operate. The other way to go would be to use a pair of 9-pin sockets and a pair of Octal sockets, each biased specifically for a different tube. I am thinking 6922 and 6SN7. Each would be a separate circuit with its own specific bias, etc.  The other way to go would be to offer the same tube but different bias points.  Different bias for a tube can add warmth or detail and allow for a way to change the tone of the sound.

4. I will review this thread to see what other options we discussed.

Thanks,

Dan Wright

[I.Greyhound Fan]

Sounds like a useful product.  I would prefer the 6SN7 tubes. Also, what about tone controls that you can bypass?

[modwright]

OK, I just reviewed the entire thread...I am embarrassed that this started in 2018 and it has been so long. So much has happened since then! I'm glad my son and I made the trip to Europe in 2019,  because we all pretty much burned the calendar in 2020! Anyhow, I am still very much moving ahead with this product and now I have the time and momentum to take it to the finish line!

The options that I feel should be included in the base model:

1. Two RCA inputs, toggle to select.
2. Two pairs of RCA outputs, to allow connection to amp and SW's.
3. When powered off, it will default to a bypass mode. I.e. if you don't want it on when watching movies or whatever, just power it off and the unit will act as a straight wire bypass.
4. I think that 9-pin and octal sockets to allow two different and fully optimized tube types is the way to go. Rather than bias one tube circuit for multiple tubes, I will simply have two sets of sockets, each optimized for its own tube. Likely 6922 (9-pin) and 6SN7 (Octal).
5. I am not sure about tube rectification. This may be a add-cost option.
6. Volume control will be an add cost option that can be bypassed.
7. Volume control option will include remote: Power, mute, input select and volume.
8. Balanced inputs and outputs will be an add-cost option, including four Lundahl transformers for input and output coupling for truly balanced inputs and outputs.

I think this about covers it!

I am looking at a modular design, that will allow you to add the upgrade options and install them easily yourself. This will not be hard for the balanced option. The R/C volume option may be a bit more tricky. Perhaps we offer it from the factory w/or without VC. This would involve several changes.

Another thought on the subject of volume control! We could offer remote power, mute and input select. Those of you who want the best possible attenuator, could then use a separate passive attenuator. There area  number of very good and custom designs available. It could sit beside the Analog Bridge and connect via short interconnects. This is the solution for those who want the BEST attenuator and the best buffer!

I will share images of the front and rear layout and overall chassis design soon.

Thanks!

Dan Wright

[modwright]

I have decided the following:

I am going to forego the volume control entirely. Not even as an option. Those who want a high quality VC, can use a high end stepper or other passive.

There will be no tone controls. The 'tone control' if you will, will be the choice of 6SN7 vs. 6922 and tube rolling. Because, these two tube families have a different tone.

I have also decided there will be no R/C at all. The design will be kept simple, and as something that can be added to any system, not as a preamp replacement.

XLR inputs and outputs may be standard, but wired SE. As an add cost option, there will be a user-installable PCB with four expensive Lundahl transformers to fully couple inputs and outputs for fully balanced I/O.

Front panel controls will be simple, clean and symmetrical:

Power, Mute -- Tube Select and input as four small buttons, two left and two right.
Center will be MWI logo and graphics.
Tubes will be exposed through lid for easy tube swapping.
Tube rectification may be standard.
HT/BP will be integral with the unit defaulting to bypass when turned off.

At this point, the overall dim's of the unit look to be: 10"W x 3.5"H x 12"D.

That is where I am at now. It is decision time and I am moving forward!

Thanks,

Dan W.

[GregC]

Hi Dan, if tube rectified does that mean the power supply will be linear and not a switching supply?  Will the power supply be external?

[I.Greyhound Fan]

Good choice to keep it as simple as possible Dan.  It will keep the price down and probably sell better.

[modwright]

That is the intent. This product needs to be market specific, VERY good and priced reasonably.

Thanks,

Dan

[modwright]

FWIW Specs:

The optimized 6922 circuit measures as follows:

Frequency response: Flat 20Hz - 100Khz
Noise: -110dB
THD: < .003%

Thanks,

Dan

[GregC]

Hi Dan,

Your description make sense for a simple and well executed design.

Just so I can understand how the HT bypass will be implemented, would one of the inputs be connected to the HT processor outputs, so if the buffer is turned off the HT processor is routed to the output of the buffer?  If so would a preamp be connected to the other input so if the buffer is turned on then the preamp can be ran through the active circuit?    Would the input selector need to be set to the HT input for the bypass to work when the buffer is turned off?

Thanks,
Greg   

[modwright]

RE HTBP, the intent would be, that either the last input used or a fixed input used, would be the default input when the unit is powered off. Normally Closed (NC) relays would default to a bypass configuration when the unit is powered off, as a straight wire bypass. There may not be a bypass button, rather, just the fact that you power it off. This is the most elegant way to handle it.

Because there is no volume control, the volume would be entirely dependent on the VC in your source, preamp or integrated amp as when you normally use it.  There is no danger of risking high outputs because the design does not attenuate the signal when operating.

Thanks,

Dan

[modwright]

Another option that I considered at the onset of this product, was to include a modular linear power supply, to power the DAC that the unit is connected to.

I used the inexpensive Pro-Ject DAC to design the prototype. It relied on a wallwart for 5VDC supply to power the DAC. The DAC did amazing things in a compact package, but a phone charger as supply was not ideal! I built a dedicated 5V DC linear supply into the prototype to power the Pro-Ject DAC and also of course fed the signal into the tube buffer stage. The combination of power supply and tube buffer were nothing short of incredible in terms of the boost in performance.

Now, some DACs have good supplies, some use wall warts and they operate from different voltages.

The digital LPS supply design would be modular and could be designed for different voltages: 5V, 8V, 9V, 12VDC, etc.

The other thing to consider is what the power connector type is on different DACs.-

If this option interests you, please tell me which DACs, what voltages and what the power connector type is.

I envision a PCB that could be user installable and a port on the back of the unit with cover plate unless the option is ordered. You would have to order the supply with the right voltage and specify power connector type. I can envision a standard connector on the end of our product, that is perhaps custom on the other end, provided there are only a handful of different connectors used. I think most use a simple mini-jack 2-conductor design.

Thanks,

Dan

[rfluongo]

I just stumbled across this thread and am very interested to see what product comes out of it. I have used a Bent Audio AVC-1 for years with a horn/SET system but recently reconfigured to Spatial Audio X3/SS amp and am thinking about how to reintroduce some tubes into the system.

My initial thought was a tube preamp but I really don't need gain. I'm already at the low end of the VC with the X3s.

[modwright]

Your situation is exactly the need that I am trying to meet!

Adding tubes in the right (Wright?) way! Very low distortion, low noise and wide bandwidth. We are adding the holography and 3-D soundstage of tubes without the overly warm distortion and poor frequency response of common tube buffer designs.

Please stay tuned as I will be wanting Beta testers when we make the first short run.

Thanks,

Dan

[RonP]

Dan,

Clean power is a godsend. People underestimate what results it can yield. Your unit having a flexible and clean power supply for itself and to "rescue" other components, only adds value. Having it as an option, even better. Someone can get in the door first and then come back later when funds permit to upgrade the power supply.

Do it! please 

[modwright]

I will certainly add the option.

My intent with this product is for it to be versatile, high value and allow an attractive and highly productive upgrade path.

Thanks,

Dan

[The Rang]

I might as well just give you my VISA card now

[modwright]

It sounds like this product is in demand? 😁

Thank you! I am moving full speed ahead on this.

I am currently working out the 6922 and 6SN7 tube option circuit and layout. Work is going well!

Thanks,

Dan