B1 Buffer Preamp

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B

BFNY

Member
Joined 2004
dviswa said:
Dear Mr. Pass, ZM,

I know B4 is coming, but I have a Full range OB with Woofer assist project going, so perhaps with a little help from you I can do a P-P protoboard version. Here are a couple of questions:

In post #161 ZM posted one of your drawings. That drawing did not identify the 3 Rs and 3 Cs, but ZM did in his hand drawn picture in post #153, so I will use the same. What is the formula for computing R1, R2, R3 and C1, C2, C3 in ZM's HP filter. I am assuming the same formula can be used to compute the values for the LP filter as well. ZM presented some values which are good for crossing over into a tweeter not into a full range.

What is the insertion loss of this configuration? that might determine if I will need a gain stage.

What is the slope of this filter?

ZM, I did not understand why you tied the outputs of the 2 filters together with 10K at point 6. Please explain.

Thanks a lot,
Dinesh
Click to expand...

This is my favorite active filter calculator program, Filter Pro from TI, but there are many others. "If it's free, it's for me" applies here.

http://focus.ti.com/docs/toolsw/folders/print/filterpro.html

As you can see, the posts 153,161 show a 3 pole (nominal 18dB octave) filter. Most programs only suggest 2 poles per buffer stage, and that's what you'll see in the TI Filter Pro Sallen-Key calculations. Of course, instead of op-amps, you would use B1 buffers without input pots. ;)

Bob
 
D

dviswa

Member
Joined 2004
BFNY said:


This is my favorite active filter calculator program, Filter Pro from TI, but there are many others. "If it's free, it's for me" applies here.

http://focus.ti.com/docs/toolsw/folders/print/filterpro.html

As you can see, the posts 153,161 show a 3 pole (nominal 18dB octave) filter. Most programs only suggest 2 poles per buffer stage, and that's what you'll see in the TI Filter Pro Sallen-Key calculations. Of course, instead of op-amps, you would use B1 buffers without input pots. ;)

Bob
Click to expand...


Bob,

Thanks a lot. I downloaded the program and as you said the program only seem to compute 2 pole filters instead of 3 pole filters. This will be a great start.

Thanks again,
Dinesh
 
B

BFNY

Member
Joined 2004
dviswa said:



Bob,

Thanks a lot. I downloaded the program and as you said the program only seem to compute 2 pole filters instead of 3 pole filters. This will be a great start.

Thanks again,
Dinesh
Click to expand...

I think you can make it 3 stage by adding the components from the first stage to the 2nd stage, in front. A quick check using PSPICE would confirm it, or maybe someone else already knows the answer.
I always end up in PSPICE as I use passive components (Ls and Cs) for most line stage filters. Especially for things like notches which are more efficient that way. You still need a buffer at the output though. And I'd rather have a current sourced JFET buffer than an op-amp for that buffer by a long shot. My 200 2sk170's from a group buy just arrived :D

Bob
 
P

pchw

Member
Joined 2006
This must be answered before, but for some reasons, I couldn't find the answer.

First, when we talk about match jfets or fets in that matter, is there any rule of thumb of the definition of "match", for example, 1%, 2%, 5%, or 0.1V, 0.01V (FETS), or 1ma, 0.5ma,0.1ma (jfets).

Another question is for jets, the specs call for idss of V(DS) 10V, if I use a 9V battery, do you need to multiply the number by 0.9? Also, if 2 jfets match very closely (let say, within 0.2ma) with the 9V battery, can I assume they are just as close with 10V?

FWIW, I was matching 50 Toshiba 2SK170BL for the Pearl phono yesterday. I need 2 match quads, and they spread from high 6ma to low 10ma rather evenly :bawling: and they have the same date code ..... Now, you know why I asked such the above questions :)

Thanks,
 
Nelson Pass

Nelson Pass

The one and only
Joined 2001
Paid Member
First off, matching is less critical for a B1 than most other circuits.

9V matching is just fine - just try to have all the devices under the
same conditions, including ambient temperature.

We test for current 1-20ma, and match to about .1 mA. In your case,
just group them as closely as you can and be happy.
 
A

AndrewT

R.I.P.
Joined 2004
udailey said:
I heard that you should either pick them up with tweezers or not test them for a few minutes after you place them in your testing circuit. Because your body temp from your fingers on the 2SK170 will change the reading.
Click to expand...
Yes, the temperature is important.
But the BL have a zero tempco at a similar current to (high) Idss. You will find that they change little and slowly and stabilise fairly quickly, even between fingers gripping and fingers off.
The V grade Idss falls slightly as temperature rises.
The GR grades rise fast and far with temperature. They are VERY sensitive to temperature.
 
V

vonfilm

Member
Joined 2006
On the Pass DIY B1 board what are the holes marked CCW, W, and CW ? Is this where P100 and P200 hook up?

What are the unmarked holes between L1 and L2, and R1 and R2?

Is there an easy way to use this board with more than 2 sources?

Would this Parts Express 18VDC 600ma wallwort work as the B1 power supply?

http://www.parts-express.com/pe/pshowdetl.cfm?Partnumber=120-1165&CFID=892944&CFTOKEN=72610757

I guess everyone thought my parts choices were perfect since there were no comments. My order has arrived from DigiKey and I will begin stuffing soon.

A little while back Mr. Pass wrote that he would be stuffing one of these boards. I would really like to see an overhead photo of the B1 board stuffed by the master. :cool:
 
Nelson Pass

Nelson Pass

The one and only
Joined 2001
Paid Member
V

vonfilm

Member
Joined 2006
Thank you Mr. Pass. I did not notice that the voltage could go up to 50% higher at less than maximum load. I may try changing that resistor if I cannot find another power supply.

Does anyone know of a regulated wall wart or power supply that would work well in this application?
 
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