Atlas DCA55 good enough for transistor matching?

[robomatique]

Hello!

I have some transistors to match for opamps (quite a few) and I wonder if this would be good enough for measuring:

http://www.peakelec.co.uk/content/products/atlasca.html

According to the specs, it will do:

Transistor gain accuracy -3%-5 HFE +3%+5 HFE
Transistor VBE accuracy -2%-20mV +2%+20mV

Would this be ok for matching 550's for the melcors and 2520's?

Thanks

Robert

 

[PRR]

> Transistor VBE accuracy -2%-20mV +2%+20mV

+/-20mV Vbe accuracy is useless. Any two transistors from the same bag will be +/-20mV, probably +/-5mV. And for opamps, +/-5mV is not very good matching, you want more like 1mV.

As for gain-match: in most audio, this is utterly pointless. We have better things to do in audio than worry about the base path resistance matching. There is usually a 3:1 difference in the resistance seen by two bases of a pair, so typical Beta mis-match is a very small added error. It typically has little to no effect on audio performance.

You can select high Beta and same-Vbe pairs with a battery, a couple resistors, and a voltmeter. Heck, you can select matched pairs in-circuit by putting sockets on one opamp board and measuring the output error.

> matching 550's for the melcors and 2520's?

However, are you sure you want to match? The Melcor may have been assembled from run-of-the-mill transistors, without any pretense (or need) of high DC accuracy. IIRC: Even a perfectly matched pair will be unbalanced in that design. And that is part of the charming sound of the older less sophisticated designs.

 

[robomatique]

Thanks PRR!!! :grin:

[quote author="PRR"]
However, are you sure you want to match? The Melcor may have been assembled from run-of-the-mill transistors, without any pretense (or need) of high DC accuracy. IIRC: Even a perfectly matched pair will be unbalanced in that design. And that is part of the charming sound of the older less sophisticated designs.[/quote]

If you don't think matching is necessary I won't do it, I'd rather not... I just thought it was more or less necessary.

Thanks again, this forum is the best (or the people in here...)

Robert

 

[Category 5]

...maybe not for the Melcors, but what about the 2520s? The 550s should be matched for that right?

robo...do a search for "match transistors" and you'll dig up my old thread on this. there is a very simple circuit floating around that can be used for matching vbe on pnp or npn transistors (2 different configs)

You need a couple of resistors, an op amp, and a socket.

The test warns against touching the transistors with your fingers when inserting them into the sockets. Heed this! Touching the transistor for less than a second will drop the vbe my 20mv or more!

If my BC550s ever arrive (backorder) I am planning on just pluggin them all into my breadboard, waiting for them to stabilize (temp) and then thest them in the breadboard.

I am ordering 100 so if I get more pairs than I need I'll be glad to give them up to others in the group.

Shane

 

[robomatique]

If you can spare 31 pairs (62 550's) and you want to match them for me... I would be in :wink:

 

[Category 5]

:shock:

What are you going to do with 31 op-amps! I doubt I'll get that many extra pairs, but we'll see!

Shane

 

[Guest]

Atlas currently have a little special offer
http://www.peakelec.co.uk/acatalog/jz_special_offers.html?sfgdata=4

£130 (incl VAT and delivery) for Atlas LCR Passive Component Analyser and the Atlas DCA Semiconductor Analyser.

For those wanting to seriously measure their caps for EQs and make sure their trannies for a BA283 are over 600hfe
(and don't want to build there own test rigs)

 

[Guest]

Word of warning - do not do what I did
Put the DCA semi conductor leads into a circuit that is switched on or filter caps are still discharging
Result = Error 2 - return to base for fix - out of warranty
£30 fee
Nice..