LSK Line Stage Original Schematic BAF 2013

[vdi_nenna]

Where can I find the LSK Line Stage schematic? I see variations, but not the original.
Saw it in the BAF video.

 

[Zen Mod]

freeze the veedeeo

 

[vdi_nenna]

Thanks ZM. I was hoping someone already started a dialog on this preamp, but this is a good a place as any. 🙂

Thx

Vince

 

[Botte]

http://www.diyaudio.com/forums/pass-labs/244106-lsk-pre-baf-2013-a.html

🙂

 

[vdi_nenna]

Bottle, I know about that version. 🙂

Interested in the original only. 😉

 

[Zen Mod]

isn't 'nuff said in Papa's veedeeo ?

😉

 

[vdi_nenna]

Will this work for DC and bias adjustment?

Does the circuit call for 45V rails, like the veedeeo says? 😉
I suppose there's a voltage drop across R4 and R5? It doesn't appear to drop with 1 resistor.

Thanks,

Vince

 

[Zen Mod]

I can't see that you really changed anything ;

clarify what you mean with "1 resistor"

 

[vdi_nenna]

I can't see that you really changed anything ;

Added the 5K pot and changed the 1k 3w to 1.5k...for DC and Bias adjustment.
Copied the placement from the F5. Nelson said it could be tweaked from almost anywhere in the circuit, so I chose there. Is it wrong?

clarify what you mean with "1 resistor"

I was wondering if there was a voltage drop because the max voltage for the jfets is ~40v. I figured there needs to be a voltage drop.
Not that I would change the voltage but that it was already designed that way by Mr. Pass.

 

[vdi_nenna]

Do you think the sk170 and sj74 pair need to be matched or all 4 jfets need to be matched?

 

[Botte]

Will this work for DC and bias adjustment?

Does the circuit call for 45V rails, like the veedeeo says? 😉
I suppose there's a voltage drop across R4 and R5? It doesn't appear to drop with 1 resistor.

Thanks,

Vince

I didn't need a 20V swing on the output, so I cut my power supply to 34 volts and I used adjustable voltage regulars to balance out the DC on the output.

 

[vdi_nenna]

Thanks Botte. That's a good idea.

Did the DC vary much for you? Did you have to make great adjustments or were they minor?

How was your matching of jfets? Did you match all 4, the front pair or back pair?
I want to use the LSK fets to show some support. At $45 for 8 j74s, it could get costly.

Thanks,

Vince

 

[Botte]

Thanks Botte. That's a good idea.

Did the DC vary much for you? Did you have to make great adjustments or were they minor?

How was your matching of jfets? Did you match all 4, the front pair or back pair?
I want to use the LSK fets to show some support. At $45 for 8 j74s, it could get costly.

Thanks,

Vince

I didn't get to hung-up on matching because they are not parallel devices and having them in the same ball park always helps. Both channels turned out with similar distortion characteristics. As for the adjustments, only relatively minor adjustments were requited. Hope this helps 🙂

 

[vdi_nenna]

Hope this helps

Yes it does! Will get started in a week or two.

Thanks,

Vince

 

[vdi_nenna]

Buffer Stage

Would like to add a simple buffer on the output of the LSK. Would I need to add offset adjustment to the front of the LSK circuit as well as the buffer section? The buffer section I'm looking at has offset adjustment. It's part of the Xen-over crossover.

 

[Zen Mod]

offset thingie just on Curl/Borbely buffer

 

[vdi_nenna]

So no offset adjustment on buffer. Adjust offset only a trails.

 

[Zen Mod]

I wouldn't do that

 

[EUVL]

Ah, a single-ended Blowtorch with JFETs. 😉

For line level output (2Vrms), you can easily get it to work with +/-15V supplies.
I used voltage (LM329) and current (E202) sources in Spice for maximum PSRR, but easy enough to change back to resistors.

Bandwidth > 2MHz / -3dB
Gain = -6 (inverting)

Distortion at 2Vrms output see attached. Not bad.
Balanced (complementary differential input stage) would be better.
(See our HAGS for the DAO headphone amp.)


Patrick

.

 

[vdi_nenna]

offset thingie just on Curl/Borbely buffer

I'm sorry. I got it backwards. Offset only at buffer.