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Best transistors for audio front ends.
Old 28th June 2005
  #1
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Best transistors for audio front ends.

I'm curious what everyone feels are the best transistors for audio front ends like mic pre's/line inputs etc. ive used MAT quite a bit. The reason i ask is ....someone mentioned to me Rb spread is very important and 2n4401's are pretty good because of Rb. Also MAT is quite expensive. So - anyone got any better alternatives ? ie....their favorites for front ends that sound good ? As there are so many transistors - it would help for me to narrow the field down - so to speak.
Also - one other thing i would like some detailed info on is - i'm aware the SM57 mic is very sensitive to loading. If someone could go into some tech details on this point - i would be appreciative. And any ideas on which transistors might match well with this mic's needs. Thanks.
Old 28th June 2005
  #2
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brianroth's Avatar
 

It all depends on how any transistor is applied in a circuit...no hard and fast answers.

The LM394 is still available (dual "super match") and is very quiet.

Bri
Old 28th June 2005
  #3
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Tim Farrant's Avatar
 

It depends a little on the source impedance. In a transformerless mic pre input stage, the transistors need to have a good noise spec at low (150ohm) source. If the input is transformer coupled with a step up ratio, then more common garden transistors or opamp inputs are OK.

With the new "anti heavy metal" laws that take effect in Europe this time next year, a lot of the devices with good low source impedance specs are becoming obsolete. This is a problem our company is facing right now, having used Hitachi devices for this function for some time - but manufacturing of them has ceased/will cease.

The MAT's have really poor DC performance last time I fiddled with them - supposed to be a matched pair but did not seem to be very well matched at all!

Cheers
Tim.
Old 28th June 2005
  #4
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tim.
interesting comment about metal.
i wasnt aware. sounds like some turmoils coming in the transistor market.
brian...thanks
Old 29th June 2005
  #5
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Turmoil in any specialized electronics market.

It's driven by idiot zealots in the anti-pollution circle of politicians.

Disposable TV's, Cell phones and computers are the issue, but the penalties
are affecting every manufacturer.

How many hi-end products in any field litter the landfills? It's the consumer crap.

I'm not for improper disposal of stuff by any stretch, but this is a nasty issue for
lots of people.

Thanks EC
Old 29th June 2005
  #6
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vince @ speck's Avatar
 

Quote:
Originally Posted by Dan Kennedy
Turmoil in any specialized electronics market.

It's driven by idiot zealots in the anti-pollution circle of politicians.

Disposable TV's, Cell phones and computers are the issue, but the penalties
are affecting every manufacturer.

How many hi-end products in any field litter the landfills? It's the consumer crap.

I'm not for improper disposal of stuff by any stretch, but this is a nasty issue for
lots of people.

Thanks EC
Hey Dan,

Nice reply.... I guess!

Did this response get posted to the wrong thread, or did you just have a really, really bad day at a Circuit City store.
Old 29th June 2005
  #7
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brianroth's Avatar
 

One hideous aspect is the lead-free solder. It takes a blowtorch to get it flowing, compared to eutectic tin/lead/(and often silver) solder, and every joint looks positively terrible...like my first grade-school attempts at making cold solder joints.

When the "walls start closing in", I'll stock up on plenty of eutectic tin/lead Kester. I wish I had done the same thing when the "nannies" banned automotive R-12 freon...

Bri
Old 29th June 2005
  #8
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I think it must be the Circuit City thing, Vince.

When I look around at the sheer number of disposable electronics being
sold in such incredible numbers and how that driving force is causing the
decimation in the availablility of smaller market parts it pisses me off.

You buy Analog Devices parts, notice how the actual "analog" catalog
is shrinking? They're eyeballing the Cell/picture phone market, to hell
with us guys that need 44 volt parts.

Or good FET's. Or thru hole parts. Or tape even.

Go I-Pod, yeah right.


Thanks for letting me grumble,

The old curmudgeon
Old 30th June 2005
  #9


As far as the Lead-free stuff goes - The EU is pretty selfish in that they don't care how many liters more of toxic chemicals have to be used in Asia to keep a gram of lead out of Gemany. Europe can go to hell (and will, when the Islamic fundamentalists take over, if not before).

As to front-end transistors - you generally use them in a differential pair, so having them on the same substrate is a good thing. the LM394, as mentioned before, is a good choice for BJT front ends.



-tINY

Old 30th June 2005
  #10
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brianroth's Avatar
 

This part, a second-source for the discontinued 2SK170, has caught my attention:

http://www.linearsystems.com/datasheets/LSK170.pdf

I need to order some and play with them!

Bri
Old 30th June 2005
  #11
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The Linear Systems parts are pretty good. The first batches were a little iffy, they seem to have gotten their act together now tho.

But I'm only using them in a little FET/BJT follower for a DI, not a mic impedance converter, which would be way more critical.
Old 30th June 2005
  #12
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brianroth's Avatar
 

Yes, I was thinking more along the lines of High-Z inputs as well, although I am curious how they might perform in a grounded gate configuration in lower Z circuits. Just a curiosity thing for me....

Bri
Old 30th June 2005
  #13
Gear Head
 
Hayman's Avatar
 

Quote:
Originally Posted by Dan Kennedy
But I'm only using them in a little FET/BJT follower for a DI, not a mic impedance converter, which would be way more critical.

Hi Dan,

Is that the one you are using (K170) in the DI-section of your MP2NV?


Richard Hjemmen
Old 30th June 2005
  #14
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pulsar modular's Avatar
 

Quote:
Originally Posted by tINY


As far as the Lead-free stuff goes - The EU is pretty selfish in that they don't care how many liters more of toxic chemicals have to be used in Asia to keep a gram of lead out of Gemany. Europe can go to hell (and will, when the Islamic fundamentalists take over, if not before).

As to front-end transistors - you generally use them in a differential pair, so having them on the same substrate is a good thing. the LM394, as mentioned before, is a good choice for BJT front ends.



-tINY

I think you forgot about those fumes coming out of your gas guzzling SUV. I guess it works fine for you to crank up your air condinioner, and to hell with everyone else on this planet.
Old 1st July 2005
  #15
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Yeah, it's the 2SK-170 and 2N4403 in a little tightly fedback arrangement.

Works pretty well, gets funky driving the input tranny, sounds good until you
really slam it, but it was something I whipped up in a couple of hours and it seemed
to work so that's where it stayed.
Old 1st July 2005
  #16
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Geoff_T's Avatar
 

Quote:
Originally Posted by pendejo
I think you forgot about those fumes coming out of your gas guzzling SUV. I guess it works fine for you to crank up your air condinioner, and to hell with everyone else on this planet.
Hi

An oddly bitter post in the middle of a useful technical one?

I recall looking at a representation of the worse global polluters and it's not the CA region by any means. More likely the South American rain forests burning and third world factories and refineries whose staff probably haven't seen an air polution regulation.

I don't know if tINY drives an SUV but I drive a 1991 SAAB 900S convertible that does over 30mpg on the freeway.

I'm doing my bit.

Old 1st July 2005
  #17
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pulsar modular's Avatar
 

Quote:
Originally Posted by Geoff_T
Hi

An oddly bitter post in the middle of a useful technical one?

I recall looking at a representation of the worse global polluters and it's not the CA region by any means. More likely the South American rain forests burning and third world factories and refineries whose staff probably haven't seen an air polution regulation.

I don't know if tINY drives an SUV but I drive a 1991 SAAB 900S convertible that does over 30mpg on the freeway.

I'm doing my bit.

Well, I happen to think that I had all the justification I needed for my response to tiny brain's offensive comments.
Old 1st July 2005
  #18
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Geoff_T's Avatar
 

Quote:
Originally Posted by pendejo
Well, I happen to think that I had all the justification I needed for my response to tiny brain's offensive comments.
Hi

As you live in CA I presume your comments re polluters also apply to you?

I'm originally from Europe and feel that much of their laws and regulations are at the expense of others. tINY expressed an opinion that you poorly countered.

Now what this has to do with transistors I leave up to you....

Old 1st July 2005
  #19
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pulsar modular's Avatar
 

Quote:
Originally Posted by Geoff_T
Hi

As you live in CA I presume your comments re polluters also apply to you?

I'm originally from Europe and feel that much of their laws and regulations are at the expense of others. tINY expressed an opinion that you poorly countered.

Now what this has to do with transistors I leave up to you....

Yes, I use public transport when I can.

I am also originally from Europe and I think its strict environmental laws is a great achievement. It's one of the few areas where its ahead of the US. Many stinking, polluted lakes and rivers from my childhood are now clean enough to swim in. A lot of money is spent on this, and rightly so in my opinion. I find it pretty rich to call that hypocritical, coming from someone living in a country who is the largest emitter of greenhouse gases and whose government has consistently refused to do anything about it.
Old 1st July 2005
  #20
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brianroth's Avatar
 

Hmmmmmm.....while I absolutely recognize the need to be good stewards of this Earth, I am slightly confused about why this conversation about pollution, etc has been dropped into the middle of a discussion of transistors for preamps.

Perhaps I roiled the waters with my comments about pending lead-free solder, and if that's why we are no longer discussing the original topic, perhaps I should remove my comments and set them into the "bar and grill" section of this board.

( I did not intend for my disdain of lead-free solder to cause this discussion of new transistors to become a reason for the good folks here to begin a political shouting match!).

There's plenty of that on Cable TV....! <g>

Bri
Old 1st July 2005
  #21


For your information, my large vehicle does not burn gasoline. (Though my small car and motorcyle do).

I think Pendejo's comments are typical of a lot of "environmentally concerned" people: Keep the perceived polution out of my backyard. It doesn't matter if that action causes more polution somewhere else.

Mainly, this move by the EU will cause reliablity issues for s while until the new technology forced on manufactures is better understood. The other side effect of this European manuver is that many of the less used items will not be availible in Europe (like descrete transistors).

I'm always concerned when politicians start playing scientist or engineer....



-tINY

Old 2nd July 2005
  #22
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there are many extremely bright people on here.
and i was hoping for particularly the sm57 loading discussion.
ive heard this mic - and the old 545 thru' good pre's.
and always been curious from a technical sense why the 57 has this property of loading.
Old 2nd July 2005
  #23
Good low impedance input transistors usually need very low E/B resistance. I use Hitachi 2SA1084 pnp's and 2SC2546 for npn's. These are rated at .5 nv/hz squared, a very good spec. They are also the faster species than the slow 2SB and 2SD transistors. I stopped using the LM394 back in the 80's as it sounds like crap.

For slightly higher input Z, the obsolete Motorola MPSA18 is good. I use obsolete Motorola MRF radio frequency transistors for more critical work, these are 1.6 gig ft's with a noise spec of .3 nv/hz squared.

Even if these other transistors are discontinued, plenty were made and are available through the NOS resellers. Be prepared to pay a bit more for them.

BTW, I'm doing my part in the war against excess, I'm buying a Hummer to go with my Jeep Wrangler!

Before ya'll blow an earth day gasket, my sacrafice was the decision to not have children, so I feel I have the duty to waste as much as my phantom family would.

Got sand?


Jim Williams
Audio Upgrades
Old 3rd July 2005
  #24
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jim...
thanks for the info. funny you should mention the mpsa18.
i have quite a few and found their sound... recording wise quite pleasant.
on this point about E/B resistance. when i look at transistor specs i dont see this ever mentioned in like the digikey catlgs. how does one find this out ?
i dont even see it mentioned on detailed transistor spec sheets.
I have a motorola transistor spec sheet book here. unless i'm missing something.
thanks for your kind help.
Old 4th July 2005
  #25
Sometimes the manufacturer shows this spec, sometimes they don't. It's not the only important spec as the noise spectrum can vary and still average out in measurement. So sometimes the hiss is more noticeable for similar spec'ed parts. Other noise sources can pop up from passive resistors which load and bias the transistor. It's a bag of snakes to work out besides transistor selection.

If I need more detailed info on a part, a call to the manufacturers applications engineer will usually do the trick. A great way to get info overload is to attend an electronics manufacturers trade show. Having several Motorola EE's conferencing together about a part can be enlightening.

Oh, the Hummer should be arriving in a few weeks just in time for mud season.

Jim Williams
Audio Upgrades
Jim Williams
Old 4th July 2005
  #26
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jim.
Thanks. I'll try contacting some manufacturers.
Actually - i just want a nice porsche.
but i dont think i'll ever get it.
as i have elderly family to worry about in their final years.
best car i ever drove was a friends aston martin vantage. scary machine. peace.
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