The ask dsavitsk thread

[luvdunhill]

Now that this thread is thoroughly off topic ... do you have any thoughts on where to get a quad, or even a pair, of unmatched LU1014D's?.

Source on hard to find parts? That's my specialty

Two sources, both very reliable.

Search Results

LU1014D N-Channel POWERJFET Lovoltech 2pcs - eBay (item 220338538567 end time Jul-01-09 12:29:33 PDT)

Also, I'd suggest trying the IXYS DMOS devices if you want to go back to that plan

Edited June 11, 2009 by luvdunhill

[Dusty Chalk]

I think you need your own thread around here, many people enjoy picking your brain about things

How about I just rename this thread, since the OP's original question was answered?

[postjack]

How about I just rename this thread, since the OP's original question was answered?

dew eet.

[Dusty Chalk]

(I was asking for verification, thanks for reading my intentions.)

Done.

[luvdunhill]

cool!

So, since you have your own thread, Pars mentioned something about you saying that replacing a plate resistor in his Counterpoint preamp with a DMOS type CCS was a bad idea. I was wondering, why would something like this ever be a bad idea? I don't really know the circuit, but the question was asked in the general and this specific example was brought up as a counterpoint (heh) to why replacing a plate resistor with a solid state CCS wouldn't always be a good idea...

[Pars]

Actually I had been talking to Doug in a thread over on hf regarding that. I think it was nikongod in chat a couple of weeks ago here who said he thought it would be a bad idea after looking at the schematic.

[luvdunhill]

ok, I apologize, my facts are wrong, but the question still exists

[nikongod]

I thought it was a bad idea because the rest of the pre has gone to such great lengths to use no SS parts anywhere. Tube rectifier, pentode voltage regulator,, the whole thing is grid biased (even the phono-stage). The only silicon is in the heater & biassing supply.

For sure the CCS would improve PSRR/SNR, linearity, and bump the gain, but I think its cool having an amp with no SS parts anywhere.

I guess my opinion is more philosophical than scientific.

[Pars]

I thought it was a bad idea because the rest of the pre has gone to such great lengths to use no SS parts anywhere. Tube rectifier, pentode voltage regulator,, the whole thing is grid biased (even the phono-stage). The only silicon is in the heater & biassing supply.

For sure the CCS would improve PSRR/SNR, linearity, and bump the gain, but I think its cool having an amp with no SS parts anywhere.

I guess my opinion is more philosophical than scientific.

Ahh, gotcha. When you said that about the ccs, I either missed why or whatnot. There is another ss piece in here:

SA-5/5.1 Level I Power Supply Upgrade. As in the audio stage, I install far better resistors and film capacitors, and upgrade the aluminum electrolytic capacitors, using Black Gate Powdered Graphite capacitors. The solid-state constant-current source for the error amplifier tube is eliminated, removing the final source of "transistory" colorations.

Price for SA-5/5.1 Level I Power Supply Upgrade: $1150

Add $110 setup fee to this price if not done with an "LSP" upgrade.)

A Siliconix CR160 CRD is used here, protected by a 91V zener from getting over-voltaged. I was thinking about replacing this with an IXYS DNR2450 (PN off the top of my head, bought one but haven't tried it yet) so I could get rid of the zener, etc.

[luvdunhill]

I thought it was a bad idea because the rest of the pre has gone to such great lengths to use no SS parts anywhere. Tube rectifier, pentode voltage regulator,, the whole thing is grid biased (even the phono-stage). The only silicon is in the heater & biassing supply.

For sure the CCS would improve PSRR/SNR, linearity, and bump the gain, but I think its cool having an amp with no SS parts anywhere.

I guess my opinion is more philosophical than scientific.

ok, thanks Maybe Chris needs to see if he has enough heater and real estate for a pentode CCS then!

[Pars]

Nah, this is one of thos '80s slim designs made to appeal to the SS peeps looking at Levinson, etc., so it is very space challenged. I don't want to destroy the resale value, so if I want better I'll just get rid of it and buy something else (or build it). I do have an Aleph P1.7 partially done (and languishing)

[dsavitsk]

I'm late to my own party

removing the final source of "transistory" colorations.

More marketing than reality. A CCS, if it's any good, should not add any "transistory" colorations, but instead just keeps the power supply caps out of the signal loop, thus removing "capacitory" colorations which are far worse offenders.

replacing this with an IXYS DNR2450

The IXYS parts are the 10M45 and the 10M90 for higher voltage. The DN2540 is a Supertex part. They are essentially the same, though the biasing resistor values will differ.

[falkon]

good thread rename

[Smeggy]

awesome transmogrification!

I just wish I knew what the hell you're all jabbering about

[voodoochile]

This is cool, congratulations, Doug!

Suppose I should include something electrical-

"Still have not done anything with my D3As."

[luvdunhill]

The IXYS parts are the 10M45 and the 10M90 for higher voltage.

Doug, for your original question, how about a 1000V 10A 400W DMOS device?

http://ixdev.ixys.com/DataSheet/DS99529A(IXTH-TT10N100D).pdf

[dsavitsk]

"Still have not done anything with my D3As."

Me either. I made up those boards and then got swamped with work. The intention has been to use it as a driver with a phase splitting choke for a PP amp. I have the tubes, the OPTs, the chokes, and just about everything else necessary for the project except for the time to do it. Maybe this summer ...

For those who have not seen it (it isn't linked from my site for some reason), the D3a project is an experimental breadboard for experimenting with lots of different circuits. Details are at ecp.cc

[dsavitsk]

Doug, for your original question, how about a 1000V 10A 400W DMOS device?

http://ixdev.ixys.com/DataSheet/DS99529A(IXTH-TT10N100D).pdf

Look at that -- it's hard to tell just how much voltage it needs across it at 250mA, but it looks promising.

I am, for now, just using LM317 based CCSes (this is for the L'espressivo 3 filament supply). I had a trimmer in there for adjusting current, but the heat was causing the resistance to change, and they were turning themselves off after about 20 minutes of use. The build is such that adjusting them while on was problematic.

I tried this circuit diyAudio Forums but it ended up not working at all, or rather, not working as expected -- which I am still a bit confused about. Colin thinks, I think, that the transistor cannot drive the mosfet properly as the circuit simmed properly. I replaced the trimmers in the originals (LM317 based) with some fixed resistors and all seems OK now -- but a better CCS would certainly be a good thing.

[pabbi1]

If you need a few of these devices to play with, I have, oh, 90 or so. Just ping, and I'lll send.

[recstar24]

I just wanted to chime in and say how excellent Doug is. II emailed him a while back about my amp and seeked his opinion on what he saw with the schematic and my description. The man seems to have a very thorough understanding of tube circuits and maximising performance. We got together for him to check out and implement some of the things he felt needed addressing. This included bypassing the cathode bypass caps which were electrolytics with some obbligato films. Doug measured voltage levels and made sure that generally speaking things were running to spec as I had concerns of resistors and caps drifting a bit and whatnot.

Doug saw the biggest improvement in my amp to be the input stage, and I agree. I have always thought that Craig with his designs could have delved more into maximising the input stage. The majority of his amps lean on using the 6SN7/6Sl7 resistor plate loaded into the output stage, sometimes with a cap sometimes DC coupled. In my case with the 6J5 though the amp has never disappointed me I always felt and heard that the tube was not running optimally, and never was truly driving the 2a3 or 45 as well as it could. After almost a year with the amp the sound manifested itself simply as a traditional, SE DHT type of sound, a slight softness to tone and just a lack of pop for lack of a better word.

Doug sent me some info and links as well as his own experience with using an active load CCS for the plate of the input tube 6J5 (specifically a depletion mode cascoded CCS I believe). I felt this would be a step in the right direction. An led bias was also put in, and current was doubled running through the tube to operate it in a more linear part of its curve. Other than cool red LED lights popping through the hood and portholes I am pretty giddy and startled at the results. More gain for one thing, which was very noticeable on speakers, and a sense of more focus and definitely more clarity. The proverbial "wiping another layer" of grunge that exists in our audio path. The amp was quiet before but I do notice that there is a sense of vividness and contrast that I don't think was there before. I am looking forward to living with the tweaks a bit and just soaking it in and enjoying the music.

Doug was really nice and gracious with his time and thoughts, and he is just a super nice laid back guy. In fact we have other ideas and thoughts for the next time we get together, he truly is a perfectionist and he seems to be able to see lots of different angles on how to approach things. The amps that he built, especially his espressivo, are fantastic. That little balanced mosfet follower he has sounded great.

[dsavitsk]

I'll add a little clarification to Ryan's post. His amp is a Moth 2A3/45 with a 6J5 driver (the 6J5 being 1/2 of a 6SN7). The driver is direct coupled to the output tube meaning that the voltage on the plate of the driver sets the grid bias for the output tube. This isn't necessarilly my favorite topology (every design has trade offs, but some of the trade offs in this direct coupled design are ones I wouldn't necessarilly make), but rather than tear it all up we decided to try to get as much out of it as possible.

As Ryan said, most of the work was on the drivers. On Ryan's, the drivers were biased at ~-3.5V and ran at ~4mA which put the plates at about 115V. The current seemed low to me as I think the 6J5 needs a bit more current to sound its best, and rp drops a bunch with just a few more mA. But, increasing the current changes the plate voltage which changes the output tube bias which all has to be accounted for. So, we also lowered the bias on the driver. By lowering this to 1.8V and increasing the current to ~7mA, we got the plate at about the same spot. Also, 1.8V is conveniently the voltage dropped by a red LED which we used for bias replacing the resistor and cap which is a good thing. The LED provides more or less fixed bias, very low impedance, and lower distortion than a standard capacitor. We also used a CCS to set the current.

For a parts outlay of about $15, these two changes effectively get 2 (electrolytic) capacitors out of the signal path and increase how linearly the tube performs. The downside is that since the bias on the driver is lower, it probably can't drive the output tube to full output, but this is hardly an issue with headphones.

For now, we added some bypasses to the output tube's cathode bypass caps. We are talking about maybe changing to ultrapaths at some point, or something else, but it is a weak part of the amp. There are also a few other modifications such as snubbers to the filament supplies, etc.

[recstar24]

Just a quick update. Snubber caps were placed across the diodes in the power supply to block out any switching hash that might be getting into the filament supplies. Heat sinks were "creatively" attached to the cascode mosfet in the CCS for the input/driver tubes to help dissipate heat. As an extra precaution fuses were placed in series with the plates of the output tubes - if the driver stage fails or something happens to make the bias run away on the output tubes the fuses will trigger saving not only the tubes but also the output transformers as well.

Only sonic thing I can add is how dead silent in terms of noise and has the amp is. With my shure se530's plugged in and the volume pot maxed, there is not noise or hash whatsoever. Before there was tube hiss around 12 but nothing serious and definitely not part of my listening volume, but considering the IEM's are pretty sensitive is even more impressive than before.

[luvdunhill]

yay, I knew this thread would come in handy.

So, my question is regarding pin 9 on 6dj8, 6kn8, 6922, 7308, etc (i.e. the shield). I also want to be able to use 12.6v tubes that use pin 9 as a CT, like 12AT7, Ecc99 (I'm not sure if there are any 12.6v only tubes of this ilk, but if so maybe support them as well).

What's the best way to handle this pin on a PCB? I have an earth connection that connects to the XLR shields as well as the shields on my input transformers, as well as a circuit ground. Also, what to do with the CT when it's not being used, in the case of 12.6v operation of the 12AT7/ECC99, ground it? Is there some configuration that will work well for all the above tubes?

Thanks!

[dsavitsk]

For shielded tubes, you can AC or DC couple the shield to ground. I've done both, and both seem to work OK. So, you could just AC couple it (100n is fine) and then it should be fine with CT or not CT tubes.

For a more complicated solution, use an 18.9V supply and a 42R resistor in series with the heater. Then, 12.6V/150mA tubes (12**7) will drop 6.3V across the resistor while 6.3V/300mA tubes will drop 12.6V across it. You could add a relay, as well, that would connect the CT to ground in the event that it is supplied with 12.6V. The drawback here is that you are limited to 12.6/150 and 6.3/300 tubes, which may be a limitation you are unwilling to make.

There is only one 12V non-ct only tube that I know of, but it is a secret. Send me a PM and I'll tell you about it.

[luvdunhill]

Thanks Doug!

Currently, I'm using a pair of 100R 0.5W resistors to create an artificial center tap and then this feeds into a voltage divider, where the bottom resistor is bypassed with a 100uF cap and the top resistor is connected to B+. The values are configured to raise the potential around 60V. Then at the tube pins I'm using a pair of 100nF ceramic caps to filter out common mode garbage and RF that can couple to the cathodes. The center of the two ceramic caps is connected to earth. For reference, earth is connected to ground via a pair of diodes and a capacitor.

Now, the above arrangement works well and is dead quiet. I'm using the two 0-6.3VAC windings, one for each tube. I've left the shield unconnected, because I didn't know if there would be an issue tying the shield to ground (or earth) if the heater is floated above ground (by ~ 60V). So, I suppose this is my first question, is this okay?

Now, lets say I want to use a ECC99 or 12AT7, in which pin 9 is a center tap, not a shield. To do this, I swap out my 0-6.3V heater winding with a 0-12.6V windings as well. Can I really connect this to ground (or, is earth more appropriate) since the heater is raised? Reason says that this needs to be tied to the voltage divider instead.

Finally, does any of this change (100R false center tap, raising said center tap up 60V, pair of ceramic caps at socket pins, and whatever arragement you propose for the shield/CT) if this 0-6.3VAC and 0-12.6VAC winding becomes a DC heater? I agree that a +-3.15VDC and +-6.3VDC bipolar DC supply would be better since it takes care of common-mode noise, not just differential mode... but assuming I don't have that luxury, does the above arrangement still work well?