NYD-1B (one-Bottle) FINISHED!

[emrr]

You find the FET necessary to drive the DRV134 correctly?  The stated DRV134 input Z is fine on paper, but maybe it's not a happy sonic situation. 

For those wondering, the MILA-1 does the same thing while keeping it all tube using 2 bottles. 

 

[OneRoomStudio]

According to the DRV134 datasheet it likes to see a low impedance source and I think the plate of a triode is a little too high to drive it properly (the input of the DRV134 is the equivalent of a 10K load). By putting a source-follower FET in front of it, I can keep the load off the plate and drive the DRV134 with a nice low impedance. As an added benefit, I get the soft clipping of the FET before the hard clipping of the opamp.

The MILA is certainly a good all-tube solution, but this way I only need a bottle per channel and can keep the power transformers much smaller (and cheaper). The 12AV7's draw significantly more current than their 12A_7 brethren, so two triodes per channel already presents more of a current draw that "typical" dual triode circuits.

 

[lassoharp]

Looks interesting.  Just curious - how much does the total solid state rig + it's PS add to the cost?  Using a custom PCB?  I've never tried the DRV134 before.

 

[shabtek]

I am curious how this works.
Re: efficiency/power draw,
1 bottle is set up/biased  to drive lowish Z--I think 10k load is fine.
If permanently driving very hiZ than idle current of 2nd stage is higher than needed.

 

[Kingston]

Interesting idea if you can deal with the tradeoff in sound with DRV134 vs. a good transformer. That simple FET stage "has no sound".

What I find highly inefficient is the fact the design requires +24V, +12V and -12V (or similar) extra rails. Even if they need very little current that's a lot of extra parts compared to something like MILA-1, or and extra SRPP stage or similar, which just needs 250-300V and heaters for barebones setup.

+24V, +12V, -12V, +300V, heaters and possible phantom. That's quite the Frankenstein PSU.

Go for it, of course!

 

[JTraverse]

Very nice, retro look to this piece. I like how you used another piece of chassis to mount your valves.

 

[emrr]

If permanently driving very hiZ than idle current of 2nd stage is higher than needed.

True, with your redesign you are apt to want more voltage versus current output.  You have more voltage with your R14 2M2 load, so you should look into reducing any unnecessary current and evaluate how the additional voltage affects the feedback loop.  I'd also try feedback loop from various places and with whatever different appropriate values; after C3, Q1, C4 and see if you find something you like better.  Lose C6, etc.  Of course, after Q1 you'd lose it's overload characteristic, but you might gain something too.   

 

[OneRoomStudio]

I am curious how this works.
Re: efficiency/power draw,
1 bottle is set up/biased  to drive lowish Z--I think 10k load is fine.
If permanently driving very hiZ than idle current of 2nd stage is higher than needed.

You're right. I'll have to change the cathode resistor of the second stage to something more like 750Ω. The original design ran a little more current through the plate, but also seemed to load the plate unnecessarily. With a 10K load in parallel with the 22K plate resistor, the load is 6K8 (and actually lower if you take the feedback path into consideration). Seems to me like that would start to affect high frequencies.


As for the power supply - it's not as difficult as one would think. I can create all the voltages with two 24V transformers and a handful of other parts. The first (higher current) transformer creates the 24VDC, voltage doubler for phantom, and bipolar 12VDC. The second transformer steps the 24VAC back up to 240VAC, which give me my B+. I could run the filaments off of the +12VDC or create 6.3V from the 24V....

 

[lassoharp]

I am curious how this works.
Re: efficiency/power draw,
1 bottle is set up/biased  to drive lowish Z--I think 10k load is fine.
If permanently driving very hiZ than idle current of 2nd stage is higher than needed.

You're right. I'll have to change the cathode resistor of the second stage to something more like 750Ω. The original design ran a little more current through the plate, but also seemed to load the plate unnecessarily. With a 10K load in parallel with the 22K plate resistor, the load is 6K8 (and actually lower if you take the feedback path into consideration). Seems to me like that would start to affect high frequencies.


As for the power supply - it's not as difficult as one would think. I can create all the voltages with two 24V transformers and a handful of other parts. The first (higher current) transformer creates the 24VDC, voltage doubler for phantom, and bipolar 12VDC. The second transformer steps the 24VAC back up to 240VAC, which give me my B+. I could run the filaments off of the +12VDC or create 6.3V from the 24V....

http://frank.pocnet.net/sheets/093/1/12AV7.pdf

Look at nominal rp under typical circuit conditions and compare.  Also consider effects of FB.  Looks to be a good load to me. 

 

[ilfungo]

sorry
There is a layout as LA2A?
Thanks