B1 Buffer Preamp

[Babowana]

Hahahahaha . . .

 

[Tea-Bag]

Here is another pic.

MashBill,
It looks very nice.
The little case looks like it was made for the job, and tidy wiring of course!

 

[okapi]

Manhattan style B1:

An externally hosted image should be here but it was not working when we last tested it.

at Vcc's from 10 to 32V

An externally hosted image should be here but it was not working when we last tested it.

thanks for the great post. would you mind also commenting/posting data on the ratio of the second to the third harmonic as you drive down THD by increasing supply voltage? I am guessing that since the reduced distortion is not the result of increased feedback that ratio should remain the same?

Also did you happen to look at intermodulation distortion?

happy new year

Tim

 

[labjr]

Has anyone compared linear taper vs audio taper pots? I noticed that some are using stepped attenuators which are mostly designed with an audio taper.

I would think you want a linear taper pot for this application since the B1 has unity gain when fully turned up. Thus it would have a similar volume at a given setting as a preamp with gain using an audio taper pot.

I'm guessing this is the reason Nelson chose the linear pot.

 

[MashBill]

Has anyone compared linear taper vs audio taper pots? I noticed that some are using stepped attenuators which are mostly designed with an audio taper.

I would think you want a linear taper pot for this application since the B1 has unity gain when fully turned up. Thus it would have a similar volume at a given setting as a preamp with gain using an audio taper pot.

I'm guessing this is the reason Nelson chose the linear pot.

I used a dual gang audio taper pot. I'm glad I did. It works just like every other volume control that I've used. My sources have too much gain already. I use the B1 to bring them down. It would be rare for me to use the B1 wide open. I'm a creature of habit and the audio taper "feels" right.

Bill

 

[labjr]

I used a dual gang audio taper pot. I'm glad I did. It works just like every other volume control that I've used. My sources have too much gain already. I use the B1 to bring them down. It would be rare for me to use the B1 wide open. I'm a creature of habit and the audio taper "feels" right.

Bill

That makes sense. I guess it depends on the source doesn't it.

Thanks

 

[MashBill]

MashBill,
It looks very nice.
The little case looks like it was made for the job, and tidy wiring of course!

Thanks! I respect Nelson too much to throw his circuit into a tuna tin or other such enclosure. It's no Pass Labs product, but it turned out better than I expected.

I've received several emails inquiring about the case, so I will provide the info here for everyone's benefit. The enclosure is a
Lansing Instrument GrayBox series. The part number for this configuration is P2H08-VB3B. It is much nicer than I expected and the photos do not do it justice. I will definitely use them again on future projects.

Also, FYI they offer a 15% discount and "No-Risk Sample Offer" on your first purchase. If you receive it and are not happy, return it (unmodified) for a full refund.

Bill

 

[vdi_nenna]

Pot too big?

Is a 250k Ohm log taper too big for the B1?
Is 10k too low? This is what I have on hand.

Thanks.

V~

 

[Johnloudb]

I think 250K would be too much series resistance with the gate. 10K is good, it's not too low.

 

[labjr]

Can someone point me to the procedure for matching the 2SK170s. I was thinking of buying 100 pieces in that group buy and I wanted to know how hard it is to match them. Or if I will get many matched pairs out of 100 pieces.

Thanks

 

[Babowana]

If you are thinking of the matching for B1, what about this way?


Cheers,

>><<

 

[okapi]

hi bobwana,


thanks for that helpful post.

when did you take your measurement? did you wait for the voltage to settle or take the measurement right away or something else?

thanks,
Tim

 

[Babowana]

when did you take your measurement? did you wait for the voltage to settle or take the measurement right away or something else?

Mmm . . . 13 Dec 2008.
I was waiting for the voltage to settle (about 20-30 sec?).

Cheers,

>><<

 

[jameshillj]

... and suggest using a ZIF socket and cotton gloves - saves any mistakes handling the components.

 

[labjr]

If you are thinking of the matching for B1, what about this way?


Cheers,

>><<

The article says apply 10 volts or so to the drain. 19v isn't too much? I guess the resistor has to be 1K ?

By the looks of the results on the paper, it doesn't look like I'll get a lot of matched pairs out of 100 pieces. I wonder if I'm better off just buying matched pairs.

 

[AndrewT]

100 off will give you a variety of matches. Expect a yield of >50% with Idss pairs closer than 2%.
The B1 does not require matched pairs. It requires devices with a similar Idss selected from BL grade. Two sets of 2 could be got from about 25off.

I would reduce the resistor to 100r0 and reduce the voltage to ~11V.
This will get you close to Vce=10V that is in the specification.

 

[Babowana]

The article says apply 10 volts or so to the drain. 19v isn't too much? I guess the resistor has to be 1K ?

So, the 10V is Vds, isn't it?
When I do the test as shown, a voltage drop will happen across 1K resistor, and it will be about 8V (with 2sk170 "BL"). Then Vds will be about 19-8=11V. It looks not bad method . . .

Cheers,

>><<

 

[AndrewT]

and when Idss = 6mA and when Idss=12mA. What Vds then?

 

[Babowana]

and when Idss = 6mA and when Idss=12mA.

I will pick up abt-8mA stones only,
and will throw away all others into garbage bin

My boys will go to dig out the bin and use them matching 6mA-6mA or 12mA-12mA . . .

Your method is better.

I just wanted to use the voltage supply (19V) from the computer ac adaptor which was only available for me . . .

Cheers,

>><<

 

[udailey]

I think I remember Papa saying that it didnt matter which grade you use. He said you could even go use the V grade and it wouldnt matter.
Uriah