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transistor pair in input module delta dlx Studio Headphones
Old 26th December 2010
  #1
Gear Maniac
 

transistor pair in input module delta dlx

merry christmas and a happy ending!

hope you all didnt choke on any turkey bones this year


i have a service and upgrade coming up with my soundcraft delta dlx rack mount 8-4-2 desk.

ill have the ic´s left alone, will change every el cap with panasonic fc and add some wima and ceramics.

but i was thinking about the matched trnsistor pair in the pre circuit. think they are a1316 or something, ive lost my schems in some way a whiled ago... read somewhere that thoose are good to replace with better once.

so whats better?

and how does a proffesional tech match transistors? i just have a chineese copy of a fluke meter that has got hfe measuring. would this be enough?



take care!
Old 21st June 2011
  #2
Gear Maniac
 

i searched the net on this question instead. and i got at least some info about it.

so the input transistor pair is a impedance stage making the op happy.

2sa1084/2sa1085 seemd like a popular swap and just the other day i recieved 100 x 2sa1085 from germany.

still no idea what is crusial when selecting pairs.

would a diode test be good when matching except for hfe measuring?

i even took a pair of transistors out of a module and hfe measured them. one showed 164 the other 441..!
Old 22nd June 2011
  #3
They came with 2SB737's and some with 2SA1316BL's. Both are very low noise, the 2SA a faster part. 2SA1083/4/5 all are similar in noise.
Generally, hfe match is good enough to get decent CMRR specs. If you want to get anal, get a curve tracer and match them that way. Keep in mind local thermal drift will cause matched transistors to drift apart. The only way to prevent that is to encapsulate the pair for thermal matching, not going to happen.

The opamps are the bigger sonic problem there.
Old 23rd June 2011
  #4
Gear Maniac
 

thanks for the advice.

when matching hfe i noticed that the temp drift was much lower with the 1085.

i was thinking about squeezing them together with some white paste and a plastic stripe.

hope my op swap will work aswell.
Old 14th August 2011
  #5
Lives for gear
 
dysenterygary's Avatar
 

Quote:
Originally Posted by 5.333V View Post
i searched the net on this question instead. and i got at least some info about it.

so the input transistor pair is a impedance stage making the op happy.

2sa1084/2sa1085 seemd like a popular swap and just the other day i recieved 100 x 2sa1085 from germany.

still no idea what is crusial when selecting pairs.

would a diode test be good when matching except for hfe measuring?

i even took a pair of transistors out of a module and hfe measured them. one showed 164 the other 441..!
Where did you order them? And how was the improvement over the stock transistors?
Old 14th August 2011
  #6
Gear Maniac
 

reichelt elektroniks - germany.

still waiting for better resistors and some electrolyts before the first channel strip is reassembled again. cant say what i hear(experience) yet.

hopefully less noise and sweeter highs.
Old 31st August 2011
  #7
Gear Nut
 

5.333v, how's it coming along...?

im entertaining the idea of upgrading a couple sc delta's, was wondering how yours was going? I had JW do my master section, im starting on the psu's next.....currently deciphering digikey part #'s......
Old 9th December 2011
  #8
Gear Maniac
 

i just noticed that my 2sa1085 from reichelt are marked hfe class E, but they dont measure that way.

either they are incorrectly marked and should be class D, or they are something else...
Old 9th December 2011
  #9
I stopped buying NOS transistors, too many fakes out there these days. I have bags of mismarked transistors, counterfits, some with remarked numbers, etc.

I buy them new these days, Renesas makes the 2SA1084 and the 2SC2545, Toshiba makes the 2SC3329BL. Unfortunately, you need to buy a reel of 2500.
Old 9th December 2011
  #10
Gear Maniac
 

what a pain in the grass with the fake parts market...

i made an order for 100 pcs of renesas 2sa1085(e) from allied electronics just now.

rs electronic sweden have them aswell but they do not state what hfe range. i asked, but they were not interested in finding out for me..!

ill prob think of the other ones i have as useless... :(


recently i got some 2sc2247 from bdent to go together with the 2sa1085 in other projekts. thoose seemd correct.
Old 6th September 2013
  #11
Gear Maniac
 

first 4 channels are remade and tested quickly.

1085 transistors matched on the hfe.

every signal path and feedback resistor are dale/vishay.

all feedback caps are mica.

all opamps are swapped.

all interstage caps are removed exept the one in the gainstage and efter the eq. thoose are bypassed with wima 10nf.

i got a bunch of edac transformers from a allen&heath mod3 for free. i inserted them instead of thoose phantom blocking caps. they doesnt seem to add any gain but they sound quite transparent and add some sweet harmonic bass.

so far everything sounds more hifi, relaxed and more clear.

i wonder if the micpreamp can be tweeked more. like removing resistors/caps/diodes before the input transistors to get more high band and less noise...
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