Thanks @luvdunhill! I'm using the buffer with the ubal/bal board which have a 1.3kohm resistor to ground on the output so i don't think an additional resistor is necessary. Plus I already have the PCBs and the pins match.

I am interested in buffers for another project though. Ill let you know.

cspirou: I would add an input resistor to ground as well. You can match Q1 to Q3 and Q5 to Q7, but I don’t think matching is all that useful here. If you want to try another small SMD buffer, let me know. I have just ordered some boards now that I have verified their performance versus sims.
 
I can include matched Toshiba JFETs and the other dual package BJTs are available at Mouser.
 

 

Those look pretty sweet Marc!


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what transistors are you using?

what transistors are you using?

I am using 2SJ106/2SK208, BCM61/BCM62, PHPT610030-series.

The 2SJ106 is the SMT version of the 2SJ103. The 2SK208 is the SMT version of 2SK246.

On 1/20/2017 at 9:59 AM, kevin gilmore said:

it had better look like this

the output impedance is about 1k, working on the diamond buffer output now

I'm going to order the transistors for this and the buffers. 

1. I know that I have to match for hfe and Vbe but do I match all the N together and the P together or do I match N to P?

2. The highest hfe is the BC546\556 C, this only comes with formed leads.  Will I need to straighten them out, and if so I'm guessing there's no issue with that?

What OPA is recommended? 

good question, it may say on the silkscreen.  I'll look at the board

Nope, I was hoping.  We'd have to ask kevin

Should be the same OP27 used in the Dynalo

In buffer and Un/bal board? 

The schematic I have says OP27.

diffinput3.PDF.pdf

Thanks Pars. On our boards we haven´t any reference. I guess that we can use the OP27 on the buffer too. 

So should we match P to P and N to N?  Or that plus P to N?

If nothing says otherwise, I will try to match as closed as possible P to P and N to N. 

That's what I was thinking

I ordered BC546B\556B  I couldn't find the C for both.  Anybody see a problem with the B?

2 hours ago, sbelyo said:

I ordered BC546B\556B  I couldn't find the C for both.  Anybody see a problem with the B?

C has the highest hFe. B might be okay if you measure a bunch and take the highest measuring ones. It seems to be in stock here:

https://www.tme.eu/en/details/bc556c-dio/pnp-tht-transistors/diotec-semiconductor/bc556c/?utm_source=octopart.com&utm_medium=cpc&utm_campaign=compare-2018-01
https://www.rocelec.com/part/FAIFSCBC556CBU

I haven't ordered from either place so I don't know what they are like.

That first place had them both...  Darn, guess I didn't search hard enough.  I ordered 250 each of the B from arrow and a transistor tester off ebay.  We'll see what kind of numbers I get.  

the transistor tester measures hFE and Vf.  What's are acceptable values for this circuit?  How closely should I match the devices? 

 

I’d match for hFE, but also try to get Vf (also known as Vbe) as close as possible as well. I’d shoot for 5% if possible. Matching the N and P is often nigh impossible depending on device type. You just have to do the best you can.


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Got it...  Is an hFE of 300 good enough for this circuit?

The majority of what I'm seeing is 315 hFE after measuring 34 devices.  Is 315 good enough?

I would think so. That is in the upper half at least of the range for B devices.

cool...  I should be able to get them all tightly matched then.

Finally, can BTAs work?

 

BTA is the newer B designation.

Just wondering if MPSA06/56 could be used in place of these? Pinout is backwards (EBC vs. CBE for BCs).