Finding PM1000 transistors - master module noise

[rockprocess]

I'm looking to replace the original transistors in the master modules of my PM1000 to reduce noise.  Jim Williams and others recommend going with the 2SC2545 NPN and 2SA1083 PNP.  However, I can't find these anywhere and I'm under the impression that what's on Ebay is counterfeit. 

Does anybody have any sources for PM1000 transistors?  Thanks!

 

[scott2000]

I usually take a chance on the bay if the seller has excellent feedback..... Unfortunately counterfeits can probably be good enough to work and you'll never be the wiser unless they are real bad so, I understand the apprehension.

I remember getting some op amps from a reputable seller and after a/b ing for a while with an original I had, I swear I could hear a weird sound quality about them....they worked fine with no issues but still.............. after the seller couldn't really give me any background on where they originated, I sent them back.

I've had some luck looking at other schematics from gear that have had the same components used and bought a part from them.

Maybe Jim Williams might have some ideas where to look?

Good Luck!

 

[abbey road d enfer]

I'm looking to replace the original transistors in the master modules of my PM1000 to reduce noise.  Jim Williams and others recommend going with the 2SC2545 NPN and 2SA1083 PNP. 

I don't think you could expect much improvement by just changing the transistors. In fact, if you want to go this route, you need to change only Q1 in the master module, the other transistors have no effect on noise.
The biggest issue IMO is that the input transistor in the summing amp runs with too small collector current, about 200uA, which suggests optimization for sources of about 5 kohms. The bus impedance is about 900 ohms for the 24 channel frame, which would require running the input transistor at about 0.5 to 1mA. In addition, the 470 ohms resistor at the input of the summing amp (probably there to solve an unstability issue) increases noise by about 1.5 dB.
Remember, the PM1000 was the first attempt of Yamaha at entering the pro audio market; their engineers had a consumer background, and it shows in every detail of the design, like single rail, all-discrete, running input transistors at too low current (as they did in HiFi, where the typical MM cartridge has an impedance of a few kohms). It didn't matter much considering the typical use in PA, but including them in studios revealed some of their performance limits.

 

[rockprocess]

Thanks for the feedback and thoughts!  I had never noticed the small collector current on Q1 before. 

I have a 16 channel board and my master 1 is pretty dead quiet, that's even with the original 2SC1000 transistors.  My master channels 2-4 are from a larger board and have the 16 - 24/36 switch at the top - the transistors are not the 2SC1000, etc.  I'm puzzled why I have no noise on master 1 but do have noise on the other 3.  I've recapped all four of them identically.  The only difference is the transistors that I can tell.

Any ideas on any tweaks to the collector current that might impact the noise?

 

[abbey road d enfer]

Thanks for the feedback and thoughts!  I had never noticed the small collector current on Q1 before. 

I have a 16 channel board and my master 1 is pretty dead quiet, that's even with the original 2SC1000 transistors.  My master channels 2-4 are from a larger board and have the 16 - 24/36 switch at the top - the transistors are not the 2SC1000, etc.  I'm puzzled why I have no noise on master 1 but do have noise on the other 3.  I've recapped all four of them identically.  The only difference is the transistors that I can tell.

Any ideas on any tweaks to the collector current that might impact the noise?

In series 2, transistors are supposed to be 2SC1681. They are supposed to be slightly better than 2SC1000, but nothing really significant.
Datasheet suggests running them at about 500 uA. It can be done by replacing the collector resistor with 80-100k. That would involve changing the emitter resistor for about 1k.

 

[rockprocess]

I've got my master module noise issue solved and wanted to follow up for those that may run into this problem.  Apparently my board has a mix of different era master modules.  My master channel 1 is a series 1 module (2sc1000 transistors and no 16/24/32 switch).  My master channels 2,3 &4 are series 2 (2SC1681 transistors with the gain switch).

Turns out my problem was a capacitor loaded in the wrong way by a previous tech.  When I did the 2nd recap, I followed his/her cap orientation.  I can see how it'd be an easy mistake.  The issue is with C3.  The negative side is oriented to the left on Series 1.  The negative side is oriented to the right on Series 2, when facing the board with the output transformers away from you. 

I got cap 3 oriented the right way and all the hum and noise went away.  I went a head and replaced Q1 with a 2SC2547 for good measure.  Sounds great.  Thanks to all for the great input!

 

[JW]

Bumping this one from way back. Attached the schematic for the master module.

Abbey or anyone else, just to confirm, we're talking about the collector resistor for Q1, which would be 220K? And the emitter resistor for the same, which would be 3.3K? No change to Q2?

And easy enough change that I might try with my console.

 

[abbey road d enfer]

Bumping this one from way back. Attached the schematic for the master module.

Abbey or anyone else, just to confirm, we're talking about the collector resistor for Q1, which would be 220K? And the emitter resistor for the same, which would be 3.3K? No change to Q2?

And easy enough change that I might try with my console.

There is another thread where the subject has been discussed somewhat deeper.
https://groupdiy.com/index.php?topic=66874.0
The topology chosen by Yamaha is far from optimum and very difficult to mod, particularly with smaller frames.

 

[JW]

Abbey,

What do you mean by "smaller frames?"

And your link is to this thread.

So, swapping those resistors out isn't a good idea?

 

[abbey road d enfer]

Abbey,

What do you mean by "smaller frames?"

16channel

And your link is to this thread.

Doh! I'll try to find the other thread.

So, swapping those resistors out isn't a good idea?

It takes changing several things to get a noticeable improvement.