Matching Transistors - How and Why?

bluesky · « **on:** 13 Dec 2003, 10:23 pm »

This is a just a question that has been at the back of my mind for a while and I thought if I don't ask I'll never know.

The Aksa amp kit set has some matched transistors, at least the 55 watt kit set does. I am wondering why we need them and how is it done?

Does Hugh sit up until midnight every night with an electron miscroscope measuring atoms or some such thing? It is just that I thought transistors would be pretty standard things (but all products are manufactured to be within predetermined tolerances) but obviously not and it must be important to the sonics otherwise it wouldn't be done. I assume it must be the same as for the matched sets of tubes I often see advertised on various forums.

Cheers

Bluesky

PSP · « **Reply #1 on:** 14 Dec 2003, 12:03 am »

It's gotta be hell... I think he counts the number of angels on the tips each of the three leads for each device. It's a good thing he's so dedicated!

EchiDna · « **Reply #2 on:** 14 Dec 2003, 12:13 am »

counting atoms?

counting Angels?

try this instead:

http://sound.westhost.com/transistor-matching.htm

cheers,

AKSA · « **Reply #3 on:** 14 Dec 2003, 03:28 am »

Hi Ian, Peter and Glen,

Ah, if only I did count the angels - perhaps they could teach me a few things??

Matching of transistors is only required with the 100W AKSA; both output NPNs are matched, and both output PNPs are matched. This ensure that like devices switch on and off at precisely the same instant, as well as passing identical currents.

To achieve this, the matching is performed on both base/emitter voltage, the point at which the transistor begins to turn on, and on the beta, the gain of the device. I designed a special jig using a high accuracy Fluke DMM to do this; as far as I know very few amp makes match on both characteristics because it is time consuming and expensive.

My jig is very simple, but very effective, and as long as I buy my devices by the thousand I can be sure to have plenty of matches within the one large batch. But this sort of matching is probably out of the reach of the small constructor; one more reason to have the kit, where bulk purchases make this possible I guess. Matching is absolutely pivotal to good sonics.

Cheers,

Hugh

Propstuff · « **Reply #4 on:** 15 Dec 2003, 08:23 pm »

Actually, I counted the Angels on the pins of my transistors and there WERE more on one side than the other.
Could this be why my balance is a little off-centre? :-O

N.

AKSA · « **Reply #5 on:** 15 Dec 2003, 08:40 pm »

Nicholas,

No, no no!! You are not off-center, Sire, you are Left of center!!

This is perfectly normal, and is the mark of a deep thinker. In time you will get over it. You will, over time, drift back to a balanced position, but this often takes decades of erosion by the worldly travail which changes us all...

Cheers,

Hugh

SamL · « **Reply #6 on:** 15 Dec 2003, 10:02 pm »

Hi Hugh.

I have mixed up my transistors while unpacking my aksa100n kit. Can I send them back so that you can rematch them for me?

Sam

AKSA · « **Reply #7 on:** 15 Dec 2003, 10:17 pm »

Sam,

Set a DMM to diode test, and perform the following small test:

1. NPNs (5200).
Red to base (left side, metal face down, leads towards you)
Black to emitter (right side, metal face down).

Ignore the collector (center).

Take down the reading, in mV. Should be around 550-620 mV.
Match the two which are the same.

2. PNPs (1943).

Red to emitter.
Black to base.

Same test as above. Match the two which are within one mV of each other.

Simple!!

Cheers,

Hugh

SamL · « **Reply #8 on:** 15 Dec 2003, 10:45 pm »

Thanks!

Will check if my dmm got diode test, if not will borrow from someone.

Sam