matching...?

[MuBase]

Hiya to the beautiful people of E-M! Im in the assembly stage of building an sn voice module (SMS audio PCB..Thanks Bill!! ) which i intend to put in an old coco commotion serial flowol box ( http://electro-music.com/forum/topic-50071.html ) and am 90 % done. Just waiting for the 2 x 1k smd tempcos from magicsmoke and a socket for the 76477.
I wish to ask though....
Is it alright to use 2 x 2n3904 s instead of an lm394? I was thinking i could make the legs smaller and fit them into the 8 pin dil . Then placing the serially soldered smd 1k tempcos over the transistors with epoxy...
Does anyone know if this would be ok and not trubblesome?
Please help!
Thankx.
Steve.

[Mongo1]

Hi Mubase -

Yes - you absolutely can use 2 2n3904s for this. Just understand that if you want the thing to perform correctly, you will have to match the transistors. Otherwise the tracking will be a mess.

There are a ton of articles about how to match transistors around. Here's one from Ray Wilson at musicfromouterspace.com

http://www.musicfromouterspace.com/forums.html?CATPARTNO=&PROJARG=ELECTRONICS%2Ftroubleshooting.html&MAINTAB=SYNTHDIY&VPW=1277&VPH=579

There may be some problem with that link. If so, look for "Transistor Matching 101" in the index.

You can also look at Ian Fritz's matching scheme, which is much simpler.
http://home.comcast.net/~ijfritz/projects/transmat001.pdf

Gary

[MuBase]

Hi! Thanks for the reply. I will try this method today with the 2 2n3904s I have left from the 5 I ordered for the purpose of the SN voice. Something else to learn and add to my electronics knowledge repetoire!
Also I have just found a stockist in the UK of LM394's but not the DIP type. The can type. I assume these are good to use as long as you can fit the leads to the DIL socket??..
I will try the measurement method first though.
Thanks again!
Steve.

[Mongo1]

[MuBase]

OK Mongo, I get your drift...( no pun intended .) I did measure 2 simply just on a digital meter in the hFE socket and got 2 reading 175 and 179 but another reading 276?!?
Strange,
anyhow, I thought I'd have another try at finding the DIL type and found a Chinese Ebay source selling them for about $3.90 or something with $2.00 postage. It should take about 2-3 wks to get here but I think in the long run you are right. it will be worth it and it was relatively cheap! The cheapest deal I can find in the UK for DIL types is about £15.00 a pop!! Or I could get a canned version for £4.50 but the postage of £5.00 added would still make it more expensive than what I paid for the SN76477!!! Crazy.
Thanks again, will check in regularly with how the build is going. At the moment my main concern is with the layout on the box and how I will use the banana sockets to their best advantage...... :s
See Ya!!

[Danno Gee Ray]

Go for the ones in the UK.

[adambee7]

http://vintageplanet.nl/ have dils at a good price. cricklewood electronics are 18 pounds now for lm394s.

[MuBase]

Hi! I did actually this morning order the DIL version from China before I read the new posts from you guys...( apparently they only take 2 weeks to the UK so that's not so bad and I am trying to keep a tighter budget what with being one of the Ranks of Unemployed at the moment ...:s . ) But, have I done the wrong thing? I have read reports about some ics from China being dodgy...

[Mongo1]

[MuBase]

Hi Mongo. I think you're right. Highly variable. Anyhow we'll see... in the meantime I have just this minute recieved an SSM2044 through the post from UTsource ( another Chinese supplier of thousands of IC designs ) that I got for about £2.50! ( about $6.50.) I am planning on building a nice filter for SNv .Oh and thanks to "Magman." I managed to procure a 28pin SDIP socket from a 64pin having HACKsawed it down... . Great idea. Been having serious trouble sourcing an SDIP for the 76477 until now...see: http://electro-music.com/forum/topic-50758.html
The international joys of audio electronics....

[adambee7]

UTsource are very good. very eager to please.