Allen And Heath System 8 Modifications

[The Convicted]

Looks like there are 4 ztx214 transistors in the input channels

the 2sa1084-85 have different pin orientation.

[The Convicted]

is there anyway to modify the power supply I already have?

This is a 16-16-2 layout, the power supply, supplies one amp. Can I boost this some how?

I plan on changining the ICs to AD8512s on 6 channels and possibly the master section.

[The Convicted]

Anybody want to add some input?

[2N1305]

Yesterday, I tried answering to the post. I pressed "Post response" or whatever the buttons' called, and the fec#$ng thing lost what I wrote.
So, in an nutshell this is what it was:
The only way you can upgrade the power supply is by changing the power transformer, and that is by far the most expensive thing in the power supply. If you can get a power transformer with the same voltage outputs with higher current, it will cost you upwards of 75$, I believe. The amount by which the current draw went up with the modifications/add-ons you described are not sufficinet, in my opinion, to necessitate upgrading the power supply. If you want, you can change the output transistors, the electrolytic capacitors, that will most probably need to be done as they are getting leaky.

As I recall the original power supply for this A&H board was "wimpy" if I remember someone's quote on GS. As far as I can tell, it does the job, but if all the channels are going at 0dB mean level, outputting into a load (whether it's a recorder or an A/D converter), and you're running al lot of condenser mics, then yeah, the supply's probably gonna bust a fuse.

It's your choice. spend 100$ or more upgrading that, you might not really need it, or save money on mods that will be more apparent(sonically).

Cheers!

[2N1305]

Originally Posted by The Convicted

Electrolytics- Larger Values, what to increase to? With poly bypass. Or could I remove the elctrolytics ith these newer opamps?

You most surely cannot. that's like removing the water tank from your home and relaacing it with a half gallon tank. sort of. I think you know waht I mean. You cannot expect a small value cap, especially a ceramic or mylar (you can't even get mylar caps over 0,1uF I think) to store energy like an electrolytic, even a 1uF.

Originally Posted by The Convicted

Im setting up a little test station to try each strip out, I have a scope, tone generator, power supply for +/- rails. Need to learn how to use them though.

Bussing and master section?

Anyone can offer suggestions or help, I sure could use it....Thanx James

Scematics Posted as well

Nice. I love it when gearslutz become geekslutz... e!

[2N1305]

Look at that... it put a smiley where I tried to write "he he"

I wonder what happens when I write Feck or "gaerls" does Father Jack appear?

[The Convicted]

Originally Posted by 2N1305

You most surely cannot. that's like removing the water tank from your home and relaacing it with a half gallon tank. sort of. I think you know waht I mean. You cannot expect a small value cap, especially a ceramic or mylar (you can't even get mylar caps over 0,1uF I think) to store energy like an electrolytic, even a 1uF.



Nice. I love it when gearslutz become geekslutz... e!

I only meant pulling caps when using these new opamps. I talked to J Williams yesterday on the phone and he set me straight about the issue.
I replaced the caps
Phantom Blocking cAPS WERE 47/50, now 100/63 .1uf poly bypass

Line Input Caps 10uf/16 , now 47/50 with bypass

mic near the transistors was 220/10 now 1000/10v with bypass

All three ICs AD8512 on Brown Dog Headers

Power Supply rails 100uf/25 now 1000/25 with .1uf mono ceramic bypass

transistors Im going to change to 2sa1084

Now I need to set it up and test.

The other OPamp Im looking at is the LME49720, because its a 8 pin DIP and there is no need for adapters other than machined sockets.

[The Convicted]

Originally Posted by 2N1305

Yesterday, I tried answering to the post. I pressed "Post response" or whatever the buttons' called, and the fec#$ng thing lost what I wrote.
So, in an nutshell this is what it was:
The only way you can upgrade the power supply is by changing the power transformer, and that is by far the most expensive thing in the power supply. If you can get a power transformer with the same voltage outputs with higher current, it will cost you upwards of 75$, I believe. The amount by which the current draw went up with the modifications/add-ons you described are not sufficinet, in my opinion, to necessitate upgrading the power supply. If you want, you can change the output transistors, the electrolytic capacitors, that will most probably need to be done as they are getting leaky.

As I recall the original power supply for this A&H board was "wimpy" if I remember someone's quote on GS. As far as I can tell, it does the job, but if all the channels are going at 0dB mean level, outputting into a load (whether it's a recorder or an A/D converter), and you're running al lot of condenser mics, then yeah, the supply's probably gonna bust a fuse.

It's your choice. spend 100$ or more upgrading that, you might not really need it, or save money on mods that will be more apparent(sonically).

Cheers!

Ill try it as is then, if I need to upgrade, Ill build a power one 3 amp supply

[Remeniz]

Keep us updated with this and how it sounds with replacement caps.

I'm about to start replacing the caps on my mixer. It's interesting that you go for higher rated caps. Does that increase the low end response?

[The Convicted]

Originally Posted by Remeniz

Keep us updated with this and how it sounds with replacement caps.

I'm about to start replacing the caps on my mixer. It's interesting that you go for higher rated caps. Does that increase the low end response?

from what Ive read in other posts , it does.............

[2N1305]

Originally Posted by The Convicted

All three ICs AD8512 on Brown Dog Headers
.

Brown dog headers? what?

[oxide54]

Originally Posted by 2N1305

Brown dog headers? what?

MSOP-8/SOT-23-8 to 8-pin DIP adapter (p/n 030502)

[dysenterygary]

Hey convicted, where are you getting your 2sa1084's from? And are you replacing the complement transistors also? With what?

[The Convicted]

Hitachi 2sa1084 transistors

Out of production but you can find them here
http://www.cpcares.com/BipolarTransistor/2SA1084.html

I found another place where you can get 2sa1085 trannies for 1.07 a piece.. Ill try to find that store and post it.

All 4 transistors in the system 8 input modules are the same, so I was going to replace them with the 2sa1084 or 85

[2N1305]

Originally Posted by The Convicted

Hitachi 2sa1084 transistors

Out of production but you can find them here
http://www.cpcares.com/BipolarTransistor/2SA1084.html

I found another place where you can get 2sa1085 trannies for 1.07 a piece.. Ill try to find that store and post it.

All 4 transistors in the system 8 input modules are the same, so I was going to replace them with the 2sa1084 or 85

Trannies or tranny is a term for transformer, not transistor.

but seriously, why change them? do the 2SA1084 have better noise charateristics? That would be the only valid, worthwhile reason.., I think.

[The Convicted]

I know they are low noise, transistors recommended by Jim Williams for his 200b mods but, what they will do for me...I dont know. Im just trying to put better components in and try to hear a difference.

[2N1305]

Well, supposing these transistors are about 1$ each, it's definitely worth a try. It's swapping them out that takes time.
But you seem to have more experience with a System 8 here than anyone else!

[The Convicted]

Originally Posted by 2N1305

Well, supposing these transistors are about 1$ each, it's definitely worth a try. It's swapping them out that takes time.
But you seem to have more experience with a System 8 here than anyone else!

Its more impulsiveness than any thig else!

I have three different opamps to try out.

-AD8512 on an adapter enough to do 4 channels
-OPA1612 on an adapter enough to do 2 channels
-LME49720 in 8pin DIP enough to do 2 channels

The AD8512 and the opa1612 are from my soundcraft 400b project I abandoned.
If these opamps are stable, I think this is gonna be a nice sounding rig.

[The Convicted]

And I will post sound examples and pics when its done!

[The Convicted]

Heres some pics of The mods to the input modules. Have to find time to run it through the scope

[2N1305]

Great pictures!

say, is that an HP 204D to the right of the o'scope? I have one just like it except I have to run it off an external +/-13V power supply because it was the Battery-powered option model...

[The Convicted]

Originally Posted by 2N1305

Great pictures!

say, is that an HP 204D to the right of the o'scope? I have one just like it except I have to run it off an external +/-13V power supply because it was the Battery-powered option model...

It sure is friend

[2N1305]

Hey, what are those two diodes in pic 8 of 9? looks like you're adding some kind of clipping circuit, or you're protecting the input of some sensitive opamp or transistor base...

[The Convicted]

Originally Posted by 2N1305

Hey, what are those two diodes in pic 8 of 9? looks like you're adding some kind of clipping circuit, or you're protecting the input of some sensitive opamp or transistor base...

it is .1uf mono ceramic capacitors on pins 4 & 8 or the power rails to the nearest ground, that is what they call "local bypass" to stabilize the new low offset opamp.

[neil.johnson]

Hi all,

Interesting thread - and prompted me to sign-up!
Picked up a Mk II 2416 last night courtesy of the bay of E. Needs a new PSU, and something this vintage is definitely due a rebuild/recap.

I've gone over the schematics of this beast for a while now. Got a growing list of mods and tweaks to make. If anyone has any questions about the electronics side I'd be happy to help out when I can.

Cheers,
Neil

[MrMegaEli]

I have one without a power supply, and I'll try doing mods when I do that. How much current does the board draw?

[neil.johnson]

Originally Posted by MrMegaEli

I have one without a power supply, and I'll try doing mods when I do that. How much current does the board draw?

Well, the original MPS8P power supply has 1A regulators, but the general opinion seems to be that it is not enough. So I'm designing a 3A power supply with a few extra features. I think that should be sufficient, even with op-amp upgrades etc.

Cheers,
Neil

[MrMegaEli]

Also, could you use discrete op amps on the input modules?

[MrMegaEli]

Ok cool, I know some who has a psu already designed, for plus minus 15 volts and 48 volts, I'll see what the current rating is