Well, getting back to this, thanks to Brad Smalling (aka lunatic) that sold me his 4 output
trafos!! :D
They are smaller than I thought which makes me wanna have them on the PCB also.

Just trying to make my mind between GO FOR SPLE or GO FOR OPTION. OPTIONS are winning today but need a little advice here. Going to have 3 switches: POLARITY, C/LINE INPUT, 48V ON/OFF.

Doubt is: for LINE INPUT, I'm going to use a pad like Jakob did on G9. Do you guys think it's ok to use it as DI also? Good thing is the input TX will be on the circuit this way, no additional cct needed...

Other than that it'll be 2 with Melcor 1731 and 2 with 2520 original, the one we have today.

Gonna include options for Jensen, OEP and Lundahl input TX, all on board.

I think all of those options sound fine and should be easy to acheive without over-complicating things.

I've found that the biggest difference in sound was acheived by using different output trafos. I went through 4 or 5 inputs, from hammond to jensen to utc, and similarly, I went through 4 or 5 different output trafos. The color, sound and performance was greatly changed with every output trafo used whereas little change occured at the front end. Same for the opamps, I have 2 with Melcors and 2 with 2520's. IMO, you'd be very hard pressed to tell the difference.
I also added line input and DI on all 4 of mine. I used a simple H pad for the line input and a switch (as Fabio is thinking of) and for the DI, I used a switching 1/4" jack after the input trafo straight into the opamp. Both work great and the DI sounds excellent.

Originally posted by Tommytones:

I also added line input and DI on all 4 of mine. I used a simple H pad for the line input and a switch (as Fabio is thinking of) and for the DI, I used a switching 1/4" jack after the input trafo straight into the opamp. Both work great and the DI sounds excellent.

So you didn't find that you needed a separate line input transformer to keep the quality of the sound high? I was thinking of using a 1/4" switching jack as well, but thought the sound quality would'nt quite be as good without some kind of input transformer ... maybe a 1:1.

Steve

It sounded great to me so I left well enough alone. I would imagine that if you would design an entirely seperate line input stage with transformer that it would delivery very interesting results but I feel that it may be a bit overkill in this situation.

Originally posted by Tommytones:
I've found that the biggest difference in sound was acheived by using different output trafos. I went through 4 or 5 inputs, from hammond to jensen to utc, and similarly, I went through 4 or 5 different output trafos. The color, sound and performance was greatly changed with every output trafo used whereas little change occured at the front end.

Hey, can yo list the transformers used both on inputs and outputs?

Maybe with some impressions descriptions...

Thanks a lot!

bump!

Sorry Raf ... I can't promise that I will BUT I will try to find a few moments to put something simple together. Actually, very fast ...

Input
Hammond 812
Jensen 115KE
UTC A24
and a couple of old no name things I had laying around

Output
Hammond 106863 (custom output)
AP2503
RCA (forget the number) custom made-came from the api console at RCA-very big hunk of iron
UTC (forget the number) again, some old custom jobber-again, BIG

Inputs were very similar. Hammond, Jensen and UTC were the best. UTC was slightly smoother but overall there was very little difference in sound.

Outputs varied a lot. All primary impedences ranged between 25 and 75 ohms. The Hammond was very mid-range present with tight (almost rolled off) bottom (a bit agressive). Very nice on guitar cabs actually. The AP2503 was similar but much smoother overall (very nice as we know). The utc was quite colored. Big bottom end and smooth over all but lacked in the middle. The RCA is my fav. Huge bottom end but still tight. Great open high and mid range. The top is very very smooth. Lots of space around your sound with this one. This trafo is also colored but it works very well. Not surprising as it was designed to work in this circuit. They just seem to compliment whatever you put through them in the right way. Cuts where you want and bumps where you want. Amazing on bass and snare! I was lucky enough to score 2 more of them on ebay. I ended up with 2 channels using the RCA's and 2 channels using AP2503's. All 4 channels are using Hammond 812's at the input (just because I had them). Once I get my trafos from James, I'm gonna repeat the same although I will try out some of the newer trafos I have aquired since at the input.

I guess that pretty much explains it.

Hey Tom, thanks, nice info.

Do you think you can do some measurements (dimentional and eletrical) on those RCA bigboys when you got time?? That would be great!

almost there!!!

API312

[ November 17, 2003, 06:10 PM: Message edited by: Fabio Bauman ]

Tommytones, post: 323330 wrote: Sorry Raf ... I can't promise that I will BUT I will try to find a few moments to put something simple together. Actually, very fast ...

Input
Hammond 812
Jensen 115KE
UTC A24
and a couple of old no name things I had laying around

Output
Hammond 106863 (custom output)
AP2503
RCA (forget the number) custom made-came from the api console at RCA-very big hunk of iron
UTC (forget the number) again, some old custom jobber-again, BIG

Inputs were very similar. Hammond, Jensen and UTC were the best. UTC was slightly smoother but overall there was very little difference in sound.

Outputs varied a lot. All primary impedences ranged between 25 and 75 ohms. The Hammond was very mid-range present with tight (almost rolled off) bottom (a bit agressive). Very nice on guitar cabs actually. The AP2503 was similar but much smoother overall (very nice as we know). The utc was quite colored. Big bottom end and smooth over all but lacked in the middle. The RCA is my fav. Huge bottom end but still tight. Great open high and mid range. The top is very very smooth. Lots of space around your sound with this one. This trafo is also colored but it works very well. Not surprising as it was designed to work in this circuit. They just seem to compliment whatever you put through them in the right way. Cuts where you want and bumps where you want. Amazing on bass and snare! I was lucky enough to score 2 more of them on ebay. I ended up with 2 channels using the RCA's and 2 channels using AP2503's. All 4 channels are using Hammond 812's at the input (just because I had them). Once I get my trafos from James, I'm gonna repeat the same although I will try out some of the newer trafos I have aquired since at the input.

I guess that pretty much explains it.

HI, I'm in Montreal and and some Hammond 106863 (8) to sold tell me if some on interested

cordialy

Nomademix

I just built a couple of the classicapi vp26's with the gar2520. They've come a long way since this thread was started, but since it's still active, i just wanted to say I highly recommend it. If anyone in the NYC area needs help building them let me know.

Nick Vivid's
166 Orchard St.
New York NY 10002
646-397-6251

Jeez, this thread is ten years old!

If you want to get a full +24 dBu while still running at 15 volts, use the Jensen JT-123-BMCF transformer, it sounds great and it'll give you a 1:2 step-up at the output.

The most important issue on the input side is NOISE, and with an ordinary JT-110 or JT-115 your noise floor is somewhere around -118 dB (just due to the winding resistance of the transformer). However with the lower-impedance JT-16A (like John Hardy uses) your noise floor drops a full 11 dB to -129, and that is definitely noticeable, and it's even more noticeable after 20 passes with an EQ plug-in.

However with a low impedance input transformer you should NOT be using 7815/7915 regulators, you'll even the tiniest bit of power supply noise and the PSRR of most of the op-amps (including the discrete ones) is not all that great. You can't just buy a low-impedance transformer and expect it to work, when using low impedances you have to pay CAREFUL attention to the audio grounding.

Most of the discrete op amps still aren't spec'd very well. For instance you can't see a simple curve of distortion versus output level. But you can sure hear that relationship when you crank the volume control.

hangtogether, post: 405881 wrote: Most of the discrete op amps still aren't spec'd very well. For instance you can't see a simple curve of distortion versus output level. But you can sure hear that relationship when you crank the volume control.

That may have applied in the days when the thread was started, but nowadays manufacturers are keen to specify certain of their devices as audio products, and for those parts are a lot more sensitive to giving audio designers more of what they need to know in their data sheets. As an example, [[url=http://[/URL]="http://www.ti.com/l…"]here [/]="http://www.ti.com/l…"]here [/]is the data sheet for the TI INA103, in which page 7 is almost entirely devoted to curves showing noise + distortion against load, frequency, output level, closed-loop gain etc.

Boswell, post: 405891 wrote: That may have applied in the days when the thread was started, but nowadays manufacturers are keen to specify certain of their devices as audio products, and for those parts are a lot more sensitive to giving audio designers more of what they need to know in their data sheets. As an example, [[url=http://[/URL]="http://www.ti.com/l…"]here [/]="http://www.ti.com/l…"]here [/]is the data sheet for the TI INA103, in which page 7 is almost entirely devoted to curves showing noise + distortion against load, frequency, output level, closed-loop gain etc.

Yes, the "chips" are fairly well spec'd.

I was talking about the "discrete" op amps, like the 990c and etc. All the API-2520 "variants". Most of 'em just aren't spec'd at the same level that the chips are. You can't see the curves we're talking about, for say, a 990c. They don't exist.

Which is a shame, because the 990c offers much better performance than most of the "chips", at or near the point where distortion begins. If you take an OPA-627 and massively over-drive it, you'll get a HORRIBLE sound that's completely unusable for recording.

However, if you take a 990c and overdrive it, it actually sounds "good". :)