DGE transistors, 2SB737?

DLJ

Member
2009-11-05 12:48 am
I have been looking for more 2SB737s and have been making the rounds of the chip brokers who claim to have some in stock. They are offering "DGE" 2SB737s at about $2.50 each with 35,000 available. They claim they are "made to Rohm specs" but I can find no information on this company. Anyone with any experience? Who is DGE?
 

DLJ

Member
2009-11-05 12:48 am
Hi,
I would definitely stick to original parts.
Have you checked this site for instance: 2SB737S current availability from distributor 1-Source Electronic Components
You should also consider 2SC2545 (2SC2546-2SC2547) from Hitachi that has even lower noise, wider operating frequency range and is better sounding, or 2SC3329 from Toshiba.

Yes, in fact 1-Source are the people who offered to get Rohm, but later offered only DGE parts. I can find no information on DGE. I'm not going to buy 10,000 parts (minimum, at USD 2.50 each!) from a company I have never heard of. I guess no one else here has heard of DGE either.

The transistors you mention are NPN, we need PNP for emitter-follower output stages. Now we use Hitachi (Renesas) 2SA1084/1085 in new designs, which is the complement to the C2545 you mention, and it's OK but B737 has a different character that works well with one of our older designs. The complement of the 2SC3329 is 2SA1316 and those are as difficult to find as 2SB737.
 

WuYit

Banned
2010-10-17 3:07 pm
WuYit, Hiraga set the current low. This simply does not get you the best noise performance with low ohmic resistance cartridges that are the current state of the art not to mention output impedance and gain. No, i am not in the game to "improve" Hiraga. I could show you a way to get at least 6dB better noise performance and a 100 times better distortion performance ( numerically, i do not talk about sound here, this is subjective ) but after 2000 posts on my MPP thread i get a bit tyred to defend my aproach. Hiraga has his place in history and i whould be the last one to negate the influence he had on me 25 years ago. Anyway, this is not about phonostages and way off topic. You can still buy original ROHM transistors but you have to know and trust your sources. Buy some, measure them ( i can show you how ) and nobody can cheat you.
 

WuYit

Banned
2010-10-17 3:07 pm
Joachim,
sorry for the misunderstanding, I did not oppose the increased current. The 2SB737 was meant to be and should be biased at high currents for both (subjective) linearity and noise. DC offset at the input could be a problem for Hiraga, however, when it comes to MC amps, common base topology and battery supply are essential.
I have some 2SB737 and 2SD786.
 
No problem. I have enough low noise bipolars too. The ROHM, the Toshibas and the Hitachi-Renesas but i have not directly compared the performance yet. I design with Fets in the input most of the time now because of the offset problem you mentioned. That problem can be solved with trimming or a floating PSU and you are right, a common base stage has a special magic about it although i am able to get a very similiar subjective results ones i had the sound of a common base stage in my ears with other topologies. It´s all about dynamics and that special slamm in the bass i think.
 

DLJ

Member
2009-11-05 12:48 am
WuYit, indeed the problem is current. Noise spectrum vs. current is not shown on datasheets and we still must characterize each part, or at least each production run. We have fairly good correlation between fft spectra (looking at maximum peak values over a few minutes) with perceived noise character. Tonal balance is another question and we are still working on analytical methods for that. A typical microphone output stage (one emitter follower for each side of the line) has no more than 3.5 mA from phantom power so this is our limit. Some parts we have tried, like the THAT arrays, are very quiet at 20 mA but much noisier at 3. We have seen huge differences also from different foundries of the same maker -- Fairchild 2N5087 from one plant are entirely different from those from another.

Joachim, thanks, I will go look up your MPP thread, we are always interested in new topologies. We are concerned with the mic output stage and the mic preamp stage too, try to get as much transparency as possible so that the mic capsule's character is fully available to the a/d converter. It's that pesky path in between that we have to take care about...

On a related note, I learned that Renesas 2SA1084/1085 is now end-of-life, last buy from the factory is in December. They are still available for about 15 cents, we'll be buying a good stock of them. The NPN is on "no promotion" so it will soon be EOL as well, I think.
 

DLJ

Member
2009-11-05 12:48 am
Joachim, I use them for condenser mic output stages. Years ago, the front-end FET was the limiting noise source, with the output stage being several dB lower. Now we have better FETs and for the moment, the limiting noise source is the acoustic damping resistance around the microphone diaphragm, but the FET and output stage contribute too. So we chip away at the noise wherever we can and try to make the system as robust as possible (good matching to avoid killing the CMRR of the preamp, enough current to drive long cables, etc.)

The mic preamp stage is more generic. When it's working with a mic having emitter-follower outputs and high sensitivity, good bipolar or FET designs are fine. But when using good ribbon mics, for instance, the transistors are once again the dominant noise source. We still need a transformer (usually two, one in the mic and one at the preamp) to get well above the voltage noise of the input devices.