MODS For Soundcraft 400b Input Modules

[The Convicted]

Originally Posted by living sounds

Thanks Jim. I replaced the transistors with 2N1085, matched them all for hFE as closely as possible, but some are not as well matched as they should, and this seems indeed to relate to difference in maximum gain before breakup for the channels. Will have to test it some more. Panasonic FM 1000 uf 10V was what I had in there before (with added bypass caps), but there is a very audible difference, it just sounds way better without any cap.

Are you using the AD8512 in the mic, and eq sections. And the AD 8510 in the the driver as well?

[living sounds]

Originally Posted by The Convicted

Are you using the AD8512 in the mic, and eq sections. And the AD 8510 in the the driver as well?

Only at the input and for the high pass (two first op amps). I like other op amps better for the EQ, the AD8512 sounds kinda weak in the EQ. For The TL071 I use an OPA827.

[Jim Williams]

If the gain blocking cap is removed, you will need to use a matched transistor pair like the AD MAT03. Otherwise, transistor mismatch will increase the DC to saturate the transistors.

[living sounds]

Originally Posted by Jim Williams

If the gain blocking cap is removed, you will need to use a matched transistor pair like the AD MAT03. Otherwise, transistor mismatch will increase the DC to saturate the transistors.

So matching transistors like the 2N10803/4/5 for hFE is not enough? I've found that mismatches of 3-4 points (like 204 / 208 on the hFE) meter to be insufficient to be able to use the full gain range, but matching is difficult because of temperature sensitivity.
BTW, it was a big surprise to me how much better the 1085 sounds compared to the stock transistor. I was expecting less noise, but it turned out to be a lot less grainy, better bass, sweeter high end etc. Would the AD MAT03 sound as good?

Thanks!

[Matt Syson]

Hi
You could go for matching, then glue them together as a start. Then either fit a method of DC correction (pot and large value resistor suitably placed) or a DC servo. See also Jensen mic amp suggestions for servos.
Matt S

[living sounds]

Originally Posted by Matt Syson

Hi
You could go for matching, then glue them together as a start. Then either fit a method of DC correction (pot and large value resistor suitably placed) or a DC servo. See also Jensen mic amp suggestions for servos.
Matt S

Thanks Matt! I think they heat very similarly, at least in some cases, since there is no DC on certain channels. But I'll look into it.

[The Convicted]

Originally Posted by living sounds

Only at the input and for the high pass (two first op amps). I like other op amps better for the EQ, the AD8512 sounds kinda weak in the EQ. For The TL071 I use an OPA827.

Im going to order the OPA1611 for the EQ sections, but Im going to keep the AD8510 for the drivers.
I also installed Machined IC sockets too.

[living sounds]

Originally Posted by The Convicted

Im going to order the OPA1611 for the EQ sections, but Im going to keep the AD8510 for the drivers.
I also installed Machined IC sockets too.

Make sure you've got single-to-dual adapters then, the OPA1611 is a single op amp, the TL072 a dual.

[The Convicted]

Originally Posted by living sounds

Make sure you've got single-to-dual adapters then, the OPA1611 is a single op amp, the TL072 a dual.

So Ineed to purchase 2 qty OPA1611 per channel with a single to dual adapter?
I see Brown Dog has them, are the ICs soldered on both sides of the adapter and then installed into the socket?

[The Convicted]

Originally Posted by The Convicted

So Ineed to purchase 2 qty OPA1611 per channel with a single to dual adapter?
I see Brown Dog has them, are the ICs soldered on both sides of the adapter and then installed into the socket?

Also, I know you've been pulling out your caps lately, but how did you like the sound of your mods before cap removal?
Im really hoping these will sound awesome..........

[living sounds]

Originally Posted by The Convicted

So Ineed to purchase 2 qty OPA1611 per channel with a single to dual adapter?
I see Brown Dog has them, are the ICs soldered on both sides of the adapter and then installed into the socket?

Yes. But you could also just get the OPA1612. Two OPA1611 obviously also consume a lot more power than a 1612.

[The Convicted]

Originally Posted by living sounds

Yes. But you could also just get the OPA1612. Two OPA1611 obviously also consume a lot more power than a 1612.

Then THe OPA1612 it is, how come you didnt use that?

[living sounds]

Originally Posted by The Convicted

Also, I know you've been pulling out your caps lately, but how did you like the sound of your mods before cap removal?
Im really hoping these will sound awesome..........

It sounds just way better without the caps. Even a single electrolytic cap with additional bypass polypropylene cap takes away definition and details and makes the sound of the console less natural.

With all the mods in place (except for the class A bias via a resistor, which was a dead end and actually worsened the overall sound significantly) it now sounds truly awesome. I'm not lusting after a discrete transformer-coupled console anymore. It's completely transparent, so you can add whatever color you want via outboard, tape etc.

[living sounds]

Originally Posted by The Convicted

Then THe OPA1612 it is, how come you didnt use that?

I tried many different op amps in the EQ, and to my ears the LME49723 sounds just perfect for that position. I had a lot of them lying around, too. The OPA1612 is a much better part on paper, but it might not necessarily sound better in the EQ circuit. I would have to test it, but again, I really like it the way it is now. The LME49723 easily beat several other higher performance parts I had here in sufficient quantity in the EQ.

[living sounds]

Just shot out the LME49723 vs. AD8512 and OPA1612 (+ a passive EQ for Reference) in the Souncraft EQ. I still prefer the LME part in that position. Simply put, it's got more balls, more definition, the other op amps sound weaker and somewhat artificial in the high end. The passive EQ is a little sweeter in the high end, I prefer it for certain sources and for the master bus.

[living sounds]

Just shot out the LME49723 vs. AD8512 and OPA1612 (+ a passive EQ for Reference) in the Souncraft EQ. I still prefer the LME part in that position. Simply put, it's got more balls, more definition, the other op amps sound weaker and somewhat artificial in the high end. The passive EQ is a little sweeter in the high end, I prefer it for certain sources and for the master bus.

[The Convicted]

Originally Posted by living sounds

Just shot out the LME49723 vs. AD8512 and OPA1612 (+ a passive EQ for Reference) in the Souncraft EQ. I still prefer the LME part in that position. Simply put, it's got more balls, more definition, the other op amps sound weaker and somewhat artificial in the high end. The passive EQ is a little sweeter in the high end, I prefer it for certain sources and for the master bus.

Thats sounds cool, I ordered the OPA1612 last night, later on Ill try the LME49723 on your suggestion. Thanx for all your help on this thead, youve been so informative!

[The Convicted]

What would happen if your orientation of the transistor pins were wrong?

The pinout diagram for PN4355 is C-B-E
The pinout diagram for the 2sa1084 is B-C-E

I know I did not account for this.

[Matt Syson]

Hi
It won't work and there is a small possibility you will damage other parts but there should be enough resistance around the circuit to make this unlikely.
By the way, 'pulling' the output stage 'up' or 'down' to make it more 'class A' you need to know whether the particular chip wants to go up OR down as they are not all the same. If it sounded worse or no better then you probably got it the 'wrong way'.
Matt S

[The Convicted]

Thanx matt, I havent gotten as far to even hear them yet. But was curious to see if that would have affected the low output problem I was having

[Aerophone]

i'm also interested in removing gain cap and a pair of interstage decoupling cap after the mic amp input transistor pair.
Mat03's are too expensive and dificult to obtain.
Is ssm2220 a good choice? because it fits like a glove in my d&r pcb layout (CBE pinout), also the mat03's for that matter.

thanks!

[ramjac]

Great project and thread guys. How about an update?

[hymenoptera]

yes, update plz