Confusion with pin termination on BA183 vs B283???

Hey Guys,

I've posted this over at Geoff Tanner's place but thought I'd try here as well as someone is bound to know. I know that Joel (Rascal7) and TK off the top of my head have had experience with these cards... so here goes...

I'm currently in a refurb job for a client who had some old 1271 amps. They had the 31267's on inputs (I'm using a single primary and secondary to wire as a mic input) and LO 1166's on our with a B183, half stuffed, so B183AM (I've since made it an AV). I'm doing a custom job and racking them up as pres using the JLM Hot Rod Mod and Joe's Go Between kits for +48V, Polarity and a Pad.

I've worked on other modules before using the B283's, which to the best of my knowledge were the same as the B183's only smaller with a different component layout/overlay, and according to the documentation I have one or 2 minor differences, i.e bigger caps and one or 2 resistor changes and the Neve call sheets call for either one.

Here is the perplexing part...

If I look at the B183 boards Pin J is not connected to the 2N3055 Base as it is in the B283 cards. It does seem that there is provision for a jumper that could take the base of the 2N3055 to Pin J, bu on all 8 original cards I have there is no jumper and it looks like there never was one as there is no solder or flux residue and if I recall Pin J went to ground.

Here are pics of the cards:

B283



B183



Can anyone shed any light on this for me? Should there be a jumper on all 8 cards that has been omitted? Just confusing as these were apparently 'working' modules, though untested by me.

Thanks in advance

Cheers

Matt

Yes, pin J goes to ground, along with pins A and V. You can then use either the 183 or 283 for the circuit without any changes to the cards.

I'm not really sure what you mean about pin J touching the base of the 2N3055 on the 283... it doesn't. Only pins B, C and D (on the 283) touch any part of the 3055. Only pin B on the 183. This difference is fine, however, as none of the 1272 or 1290-type circuits connect anything to pins C and D, so the fact that these two pins connect with the 3055 on the 283 is irrelevant. Pin B is the only pin you directly connect that touches the 3055, and this is the same on both cards.

From a practical perspective the only 'real' difference between the two cards is the component layout, and therefore, the real estate required for the thing. Circuitwise they are the same, though the pinout does differ. Again, though, the differences in the pinout reflect only pins that aren't typically connected anyway (not in mic pre's anyway), and so the variance can be ignored -- the pins you will actually connect for use in a mic preamp are the same on both cards.

FWIW, just to make sure everyone knows what pin is what, pinout for both cards, starting at the far pin on the side of the 2N3055 transistor (the right side for both cards in your pictures above) is -- A B C D E F H J K L M N P R S T U V

I've built lots of pre's with both types of cards, and I don't do anything differently between them. In fact, when a BA283 failed in one of my 1084's, I popped a fully-populated 183 in there with no changes made to accomodate it, and it worked perfectly. It was a snug fit, however, so I ultimately repaired the 283 and put it back in.

JC

Hey Joel,

Thanks a lot for the info... I must have been drunk or something when I wrote that post because I see my problem and it stared me right in the face but my mind didn't click!!!!

In the old cartridges I took the cards out of they were mounted upside down, in my new rack I turned them over along with the Ampehnol edge connector, but in the recess of my mind I was counting the pins from the WRONG direction... so when looking at it I was seeing Pin T and wondering why it was connected as in my mind it was Pin C...

Anyways there is my stupid error for the day... I woke up this morning after sleeping on it and saw it straight away and I have wired them all correctly... but my mind kept telling me otherwise!!!

Cheers

Matt

Also, the JLM go-between kit you mentioned using above has a 20dB pad which is redundant in the class-A Neve stuff. I'd leave this function off for the circuits you're racking as Joe's Hot Rod Mod, like most every class-A Neve-type mic amp, incorporates a variable pad in the gain structure already.

Just a thought.

JC

Hi Joel,

Yeah I had thought of this, I left it in to keep symetery with with front panel layout, but yeah, it is redundant because of the adjustable Gain.

Cheers

Matt

Also, the JLM go-between kit you mentioned using above has a 20dB pad which is redundant in the class-A Neve stuff. I'd leave this function off for the circuits you're racking as Joe's Hot Rod Mod, like most every class-A Neve-type mic amp, incorporates a variable pad in the gain structure already.

Just a thought.

Click to expand...

The 20dB input pad is very useful and the best way to use the 1272 with or without hot rod mod as a unity gain audio warming device. Otherwise at pro line levels the 1272 input transformer distorts when it saturates at +7dBM. With the pad in the input can now take +27dBM which is perfect with HD protools systems and other D/A to A/D insert loops running at +18dBM to +24dBM in and out. Even on a loud kick drum into a condenser mic having the pad in and 1272 hot rods gain up usually sounds better to me.

Thanks for adding that Joe. I was wondering about that as I'm preparing to put together a 1272.

The complaint I've heard, particularly from those who worked in the era where many consoles were based around fixed gain blocks (or bloaks :wink, is that the sound of a gain block changes with gain setting. Thus, the "sweet spot" might be to far up the dial for the input level.

Excellent point, Joe. Interesting idea.

I'll have to try that sometime and compare the performance.

JC