Need transistor source. sorting out Audix 35102 headroom

[q2audio]

Sorry Tillman, I didn't read all of your previous posts regarding modern replacements. Interesting that you have BC441 and 461 in place of the BC 413/415. The BC441/461 are rated at more Ic than the 2N3053/4037 but the 2N devices will work much of the time as a replacement, at least in my experience. Today, I replaced a 2N3053 and some SKxxxx device in a Neve BA438 op amp with the BC441/461 that belong in there. The 2N device had failed and was drawing a lot of current. I think the BC441 is rated at nearly 2A Ic, the 2N3053 is more like an amp.

I think that a discrete circuit is more fun than an op amp (well, more of a challenge) and will most likely have a more interesting clipping behavior. The op amp circuit is easier to layout and put together though. I'll bet that the modern equivalents of the BC413/415 will sound identical and the 40871/2 are just current amps, anything with similar ratings should work fine. The BC441/461 would be great if they were more readily available here in the US - Neve used them to do just what we are wanting and they rated them to drive a 50 ohm load, IIRC, in their BA440 op amp output stage. Come to think of it, a BA640 (IC version) would make a really simple solution to this problem. Easy to work with, you can get a bit of gain out of it if you want, and it will drive transformers all day - even if you short the output!

Thanks for posting the schemos!

 

[Greg]

I've got the 35102 and 35302 combo bench tested and working. Once Tillmann and I get it studio tested and we're satisfied, I'll post some PDFs of the wiring. I don't want to post anything yet until we're happy with the results.

 

[Tillmann]

So Greg and I put these through some varied tests on real instruments. We had a 35102 running into a 35302 pushing a big Sowter 4127 1:2 output transformer at 600 ohms. In all of an hour or two, we tracked a snare being hit pretty hard, some super loud and distorted electric guitars, a low level cleaner electric guitar, a large diaphragm tube mic on screaming vocals within 8-12 inches of the mic, and on a ribbon mic cutting screaming vocals from about two feet or more away (requiring 60 dB of gain). The idea- record some loud sources and some with high transients to try to make these units crap out. We also printed to Pro Tools quite hot- again to try to push the preamps and make them crap out. Normally I don't do this, but we thought it was best for the tests.

The result was as good as we could have hoped. With the 35302 modules they ran stellar. We never clipped them once and we never used a single input or output pad for some pretty hot sources. The only thing that we didn't do that I wish I would have done is just to feel the output transistors on the 35102 and the 35302, just to see how hot they were running. That said, most people I have been in contact with that have used the 35102's without some sort of mod on the back-end would have had major clipping under similar circumstances. These things have some really great headroom when they are setup properly, and I wouldn't be afraid of that 5534 on the input of the Revision 3 modules. These things sound great!

So we are going to go forward with the PCB's and try to get ahold of some modern transistor equivalents to the originals, just to test them for the forum. We are still going to use original vintage transistors if we can for our modules, but that's only because we've located some already.

So now all of you that have offered help, I would love to accept it. Mainly, the only thing that needs to be tested are the modern transistor equivalents. We've got all the schematics and the sort already. Anyone that is interested in doing that a bit more extensively after we get some PCB's, would be helping out anyone else that wants to use the pcb's in the future.


Cheers,

T

 

[Tillmann]

So it seems the suggested BD243D, BD543D and BD544D parts will be harder to find than the 40871 and 40872's. None of these are manufactured any longer, so finding equivalents for those 4087x transistors will be the main challenge that we could use help with. We will hopefully have some originals for our stuff, but probably not too many extra. I've searched Mouser, Digikey, and googled and came up with some sources that I've contacted, but I have the feeling most will not reply.

T

 

[guavatone]

wow, I missed come good progress on this thred. Are you making PCBs fot the 35102 output so u don't have to use the 35302? I'm just confused on including the extra Audix output module

 

[Tillmann]

[quote author="guavatone"]Are you making PCBs fot the 35102 output so u don't have to use the 35302? [/quote]

Yes. It's basically a portion of the 35302 circuit and will save space in a rack.

T

 

[guavatone]

Cool, I have 4 35102's that are almost working with UTC outputs. I was thinking about a Big FetBloak but I'll hold off to see hwta happens. BTW I don't mind if modern replacement Transistors are used. I don't think it will color the sound too much.

 

[Tillmann]

the trick is finding the modern transistor equivalents.

 

[Greg]

Yup what Tillmann said...

I should be able to finish the PCB design this week, and I'll send off to get some test PCBs made. Each PCB will contain two output stages since most people rack up a pair of 35102 per rack. I'll make sure to have headers or hardwired options. I still need to check if the replacement transistors are pin compatable, but if they aren't I'll make sure the PCB will have some type of jumper option.

I'm glad this project is moving forward... I really like these 35102s.

 

[Tillmann]

I'll be interested to see how these perform with 600:600 transformers. We used a 1:2 and liked the results of the extra gain.

 

[Greg]

yo Tilly... I placed a voltage divider before the 35302 as suggested by the datasheets, so the total gain of the output stage is unity.

 

[Tillmann]

I may have found all of the modern transitor replacements needed. I've ordered them and when the PCB's come in, I'll try them out.

T

 

[Greg]

I think I've got a test PCB ready to go. I'll check it one more time tonight then send off for the test boards.

It's a double-sided board... green is the bottom and red is the top. I used filled planes throughout the entire PCB.

 

[guavatone]

Greg, if you are planning on doing a bunch of these, try http://e-teknet.com/index.html

They are cheap but you need gerbers.

 

[Greg]

I got the line amps fired up this evening. My goal is unity gain, but as you can see, I've got a little extra. I'll work this out in the next day or two. Good news is they're passing audio just fine.

Enjoy.

 

[guavatone]

Great work Greg!

 

[guavatone]

Is there any news on this PCB folks? -Patiently waiting to fix my headroom woes.

 

[Greg]

Well I built another board last week with the replacement transistors instead of the originals, and it worked great as well. I've been extremely busy at work this week and haven't been posting much, but I'm going to take some better pictures and get something going in The Black Market to see if people are interested. So far it seems there won't be a lot of interest, but a small run is definitely in order.

Just let me know how many you want, and I'll make sure to get them for you. And your 35102 woes will finally be over ! :guinness:

 

[guavatone]

It would seem like audix modules don't change hands very often but your pcbs may be in short deman for a long(er) time since there are probably many modules out there that are wired wrong.

 

[Rob Flinn]

Tillman

Was it you that was mailing me about transistors ?? I've lost your addy so drop me a line !!