Yet another 12B4 line stage, or is the 12B4 better than the Grounded Grid.....

[apassgear]

Originally posted by Mark A. Gulbrandsen
Ok, this Glassware article on a H-V regulator is very interesting to say the least and it might be the cats meow for use with the 12B4. It features low output impedance over a very wide range and it could easily be setup to deliver the 320 volts thats required by Brian's 12B4 line stage. Any input on using this circuit would be appreciated.... I was thinking of an IRF740A as the pass device, but any other suggestions for a similar but higher voltage device would be appreciated as the 740 is rated right at 400 volts.

Thanks,
Mark

Mark.

I have used IRF840 for simillar aplication good to 500V with good results

[mach1]

Voltage and current capacity aside, the key parameter for mosfet selection in this application is low output capacitance.

The IRF710 is champion in this area with a low 34pF. If you need >400V I recommend the 2SK1119. This can handle 1000V and has roughly half the output capacitance of the IRF840 (100pF v 190pF).

have fun

[Looneytunes]

Dave & Sherman, thanks for the tips. I'll add a load of clip leads to the list. And, a remote power switch too. I hadn't considered the possibility of blowing out the windows, but...

I've also been following everyone's posts on the power supply. Being a NewB, I need to keep it simple. Can anyone recommend a simple power supply design to get me started? Considering where I'm at, an unregulated supply might be best for now. It doesn't have to be great; I can always improve it (or replace it) later.

Thanks everyone. And, I second Evan... this site is the best.

[bordins]

Hi apassgear, thanks for putting my comments about 12B4 at AV forum here.

Please forgive me for my poor EE knowledge. I'm still confused what you're talking about. I'm not sure you guys are trying different ways to supply power to 12B4, in order to make the "best" sonics out of it ?

What're sonic differences between different types of power supplies ? Diode, bridge, diode tube, regulated (LM), ... Mine just got diode tube PS which is in between full bridge and full tube. Another friend told me regulated PS is the best. I'm still not sure what best means ?

One observation from my friends about a 12B4 preamp (I borrowed) is that it sounded so fantastic, but forwarded ! The sound stage is very wide, but imaging is forwarded. I think it is because of too high B+.

My current build sounds not forwarded, but a bit less airy than the other one.

Any suggestion would be greatly appreciated.

Cheers.

BTW, I ordered Oritek X-2 interconnect. Hopefully, it'll put my 12B4 preamp to the next level.

[Mark A. Gulbrandsen]

What're sonic differences between different types of power supplies ? Diode, bridge, diode tube, regulated (LM), ... Mine just got diode tube PS which is in between full bridge and full tube. Another friend told me regulated PS is the best. I'm still not sure what best means ?

Well, I don't think there IS a best power supply per say. Some claim that alot of iron sounds best while others say regulated is best. Both have just about as many advantages and disadvantages as the other. I have tended to favor regulated over the years but I am getting itchy to try an iron based supply and listen to hear which is better at least on my 12B4 line stage. Since it is so revealing it should be easy to hear the effects of different supplies.

Supplies fdefinately do affect how a unit sounds to some degree but in the end its still a matter of taste. Since I'm powering my 12B4 from a regulated H-V bench supply for now I at least have something to compare it to.

Personally I feel there are some important advantages to regulated supplies over heavy iron type. It isn't necessarily cost... a properly designed regulated power supply is also not going to be inexpensive to build. Regulated supplies can also be noisy and their output impedance can vary over the frequency range we deal with. However a good supply such as in the link below that has fairly flat output impedance, low noise, and very tight regulation should sound very good. It also takes up a heck of alot LESS space. This allows for incorporating the regulators right into the line stage itself... keeping the regulator very close to the actual operating circuit and keeping noise levels on the dc line down. I would however definately keep the raw power source out of it and locate that elsewhere.

I believe I've located a good regulator here. Its claims are for use on MC preamps so it has to be a quiet one. Since the 12B4 has poor PSRR this sort of regulator ought to work really well. Am planning on building it next week if time permits so we'll see.

One observation from my friends about a 12B4 preamp (I borrowed) is that it sounded so fantastic, but forwarded ! The sound stage is very wide, but imaging is forwarded. I think it is because of too high B+.

I don't experience that forwordness that you experienced with your borrowed 12B4. There can be a closeness unlike anything I've heard when the recording is mic'd that way but otherwise what I've experienced is massively more detail much better imaging and a wider deeper sound stage over my Grounded Grid line stage. Vocals that are close mic'd are as though they are right in the room with you. Those that have been over to hear it agree its pretty incredible.

If you build your own you might want to build it similar to Brian Becks diagram that uses the CSS to bias the tube, his diagram is posted a few pages back in this thread. His circuit is definately a large improvement over the original circuit and it only costs a few dollars more to implement. Just be sure to bypass those electrolytics with a really good quality film cap... Multicap, Wonder-
Cap, Auracap, Whatevercap or something equivelent. Then you can sit back and marvel at all the stuff you were missing in all your recordings.

Mark

[Ed LaFontaine]

Hey guys, my lurking took me into T3h Geek Zone, where I found this power supply. Just trying to increase the options without being redundant.

http://geek.scorpiorising.ca/circuit...pplySCHEMA.png

"The pass BU806 should be mounted on an adequate heatsink - a 5W one is good for most preamp apps. The error-amplifier too, should be heatsinked, a 2W is good for all apps.

Circuit protection is the underrated 1/8W, 470 ohm resistor on the pass transistor's emitter - it's a "fusable" link ;-) "

[kooltubes]

Originally posted by bordins

One observation from my friends about a 12B4 preamp (I borrowed) is that it sounded so fantastic, but forwarded ! The sound stage is very wide, but imaging is forwarded. I think it is because of too high B+.

My current build sounds not forwarded, but a bit less airy than the other one.

Hi Bordins,
I have experienced the same thing before and I came to the conclusion that the sound is affected by the operating point and the PSU!
There are those who prefer running the 12B4 at high current, while other will be happy running them at lower current. You can voice your preamp by altering the cathode resistor in order to find the sweet spot, but you may need to fine tune your psu each time you do so; it's a long but rewarding process

My PSU is simple: 2x 6CJ3+10H+25mf (oil)+10H+25mf (oil) then for each channel: 20H+50mf (oil)
The 12B4 is resistor loaded (7K5) and 390R at the cathode //330mf
The soundstage is huge
I am waiting for some 12A4 to experiment.
I am wondering if there would be any further benefit using a parallel feed output à la Magnaquest?

[Mark A. Gulbrandsen]

Thanks for that link Ed. I just happen to have a couple of BU806's in my junk box. So I will also build this one and see......

Mark

[Zen Mod]

Originally posted by Ed Lafontaine
Hey guys, my lurking took me into T3h Geek Zone, where I found this power supply. Just trying to increase the options without being redundant.

http://geek.scorpiorising.ca/circuit...pplySCHEMA.png

"The pass BU806 should be mounted on an adequate heatsink - a 5W one is good for most preamp apps. The error-amplifier too, should be heatsinked, a 2W is good for all apps.

Circuit protection is the underrated 1/8W, 470 ohm resistor on the pass transistor's emitter - it's a "fusable" link ;-) "

Originally posted by Mark A. Gulbrandsen
Thanks for that link Ed. I just happen to have a couple of BU806's in my junk box. So I will also build this one and see......

Mark

that's my bunch of mates

[planet10]

Originally posted by Mark A. Gulbrandsen .. a properly designed regulated power supply is also not going to be inexpensive to build. Regulated supplies can also be noisy and their output impedance can vary over the frequency range we deal with. However a good supply such as in the link below that has fairly flat output impedance, low noise, and very tight regulation should sound very good.

PSU is VERY important. The whole purpose of a linestage or a poweramp is to regulate how much of the power supply rail(s) gets sent out the output.

A passive supply has the advantage of not adding a whole lot of grunge to the rails & the ability to supply & sink current.

A regulated supply is another circuit and it needs to have a smooth & very low impedance with wide bandwidth. Most regulated supplies tend to be series regs (because they are easier to build and less wasteful of energy). They can't sink current very well thou. A good shunt reg. like a passive PS, can source & sink current, but are less efficient. The Broskie reg linked above is a shunt reg. A well worked out shunt reg with exceedingly good performance is Allen Wright's Super Reg (<0.005 ohms output impedance with low noise & very wide bandwidth). You can buy the book (Preamp Cookbook -- one of my top 3 recommended tube books) and diy it or you can be lazy & buy the kit. Even wit this subperb reg in the circuit he still recommends a choke load supply for its superior regulation.

A good shunt reg will have much wider bandwidth & much lower impedance than is possible from any passive supply, but getting a good one from scrtach is a real challenge (just a little off and they make a real good oscillator)

dave