1176 Plosives: looking for Rev A schematic or high res internal shots

[Neeno]

Hi Rob !
That means you still have the plosives problem.
Try this:

Remove the 130k resistor from your ratio board and put a 68K instead.
If you used Hairball's ratio board, remove the jumper and put a 47k instead.

Let me know if this solves the problem.

I've been comparing the diagrams & noticed that on the original R46 is 22k & on rev A it's 8k2,c ompared to Mnats 47k.   It strikes me that tese values would reduce the gain of the s/c amp significantly !

I just swapped out R46 for the 8k2 that is used in the REV A version.  It makes quite a difference to the operating range.   If using the 47k or 22K in the other versions it goes from nothing to -20db GR at about 10 o'clock input pots rotation.   With an 8K2 in this position -20db happens at about 12 o'clock on the input control.  The threshold point stays the same.

Basically it's more controllable.

 

[mnats]

Neeno, I got your PM asking me to look at this thread, but I'm not sure if I understand what you would like me to contribute.

The boards I designed were made to encourage the DIY of the 1176 with the FET in the pre and line amp. The values I ended up with are an amalgam of the various schematics that are circulating on the 'net but there is no suggestion that I am trying to prevent anyone from using other values or say that the ones I ended up with are "best". I have always been ambivalent about putting component values on boards as there is obviously some ambiguity about some of the components in a design as old as this one - though the R46 value that Rob found was obviously a mistake!

According to the JBL document serials 101-216 are all Revision A. The circuit is very similar between the earlier serial numbers and later ones and each should require only the smallest of modifications to implement. Since the rarest ones seem to be the most coveted I decided to base the audio path on the earlier schematic.

If the Rev A worked just like the Rev D in the all buttons mode would mean that they were more similar than not and to me defeats that would the purpose of offering a Rev A. If you want the all buttons mode sound that we know, build a Rev D. The Rev A does other things well as some have already discovered.

Hope that clears a few things up. I'm happy to see that you are experimenting with your build and sharing it here. That's the DIY spirit!

 

[Neeno]

Thank you very much Mako !
I did some confusion.
Today I checked the UAUDIO website and they state that the FIRST 1176 was called 1176A wich means rev A.
That sound strange, but probably it was the first revision after the first prototype.
After the first 24 pieces Mr.Putnam revised it and they built the AB version (which in the JBL document is called Rev A), this is what I understand looking at the serial number logs.

Now, I tried to populate another board following the JBL REV A schematic (which in reality should be the REV AB) and that solved the brit mode behaviour. No plosives and no unexpected distortion.

Thank you again to give us the rev A board !
The layout is just great to experiment, and well, I'm really learning something this time !

 

[Neeno]

I just checked, but on the rev A schematic I see 47k, on the original 1176 is 22k but I can't find where you got the 8.2k value.
The sidechain used by Mako is more similar to the sidechain used on the Rev D, but I think that it doesn't make much difference.
As you can see the 10k resistor connected to the Q Biad trim pot was implemented only from rev B and it is not present in the original nor rev A schematic.

I've been comparing the diagrams & noticed that on the original R46 is 22k & on rev A it's 8k2,c ompared to Mnats 47k.   It strikes me that tese values would reduce the gain of the s/c amp significantly !

I just swapped out R46 for the 8k2 that is used in the REV A version.  It makes quite a difference to the operating range.   If using the 47k or 22K in the other versions it goes from nothing to -20db GR at about 10 o'clock input pots rotation.   With an 8K2 in this position -20db happens at about 12 o'clock on the input control.  The threshold point stays the same.

Basically it's more controllable.

 

[Rob Flinn]

Hmmmmm,

Maybe I should use my reading glasses more often !!  Anyway it much more controllable with an 8k2 ;-)

I'll try you mods tomorrow.

I just checked, but on the rev A schematic I see 47k, on the original 1176 is 22k but I can't find where you got the 8.2k value.
The sidechain used by Mako is more similar to the sidechain used on the Rev D, but I think that it doesn't make much difference.
As you can see the 10k resistor connected to the Q Biad trim pot was implemented only from rev B and it is not present in the original nor rev A schematic.

I've been comparing the diagrams & noticed that on the original R46 is 22k & on rev A it's 8k2,c ompared to Mnats 47k.   It strikes me that tese values would reduce the gain of the s/c amp significantly !

I just swapped out R46 for the 8k2 that is used in the REV A version.  It makes quite a difference to the operating range.   If using the 47k or 22K in the other versions it goes from nothing to -20db GR at about 10 o'clock input pots rotation.   With an 8K2 in this position -20db happens at about 12 o'clock on the input control.  The threshold point stays the same.

Basically it's more controllable.

 

[edanderson]

rob, i think you may have mixed up the values for R46 (47k or 22k) and R48 (8.2k). 

ed

 

[martthie_08]

here some more inside photos of a blue stripe 1176:

these have been completely recapped, it seems...

 

[Rob Flinn]

rob, i think you may have mixed up the values for R46 (47k or 22k) and R48 (8.2k). 

ed

Ed, i think your right !!

I just performed the mods that Neeno documented, but haven't listened to them yet.  However, certainly in conjunction with swapping R46 to a 22k they soften the action of the blue stripe very significantly, when I test  them with an ac millivolt meter & scope on the bench.

I will do some audio tests later this afternoon.

 

[Rob Flinn]

Having had a brief play with it, that seems to sort the problem out a bit, & makes the i/p control not as fierce.

I'm not convinced that the problem has completely gone though.  When used on all buttons in, you still have to be very gentle with the input & attack controls to eliminate the initial click when the compression kicks in. 

So in a nutshell I'm not sure if that has completely eliminated the problem.  What do you think Neeno ?

 

[Neeno]

Hey Rob !
Good news !
Well, actually I have mine built like a rev AB.
I did more than the mod on the ratio board.
Tomorrow I'll make a list of all the parts values I've used.

Pick a sample groove from your collection, squash it in brit mode and record the results.
Send me the unprocessed sample, tell me the setting you've used and I'll do the same and report back.

 

[Rob Flinn]

I took the modded Blue Stripe to a friends studio this afternoon, where we had a bit more of a play with it, & the general opinion was that it worked very well in all different ratio combinations on voice & drums.  We didn't notice any popping etc

 

[Neeno]

Great !
If anyone is interested I'll post the list with the values of the Rev AB.
It should be more stable than the rev A.
The values are what I was able to read from the fuzzy schematic and are not checked.

I'm still looking for someone with a real Rev AB to compare them, please.

Cheers

I took the modded Blue Stripe to a friends studio this afternoon, where we had a bit more of a play with it, & the general opinion was that it worked very well in all different ratio combinations on voice & drums.  We didn't notice any popping etc

 

[Rob Flinn]

Would be interested to see the AB mods you have performed.

Have you tried it yourself ?    Does it stop the meter action from being sloppy ?

 

[Neeno]

What do you mean with "Sloppy" ???
What I've learned is that with the discrete meter circuit, you must use a real ANSI VU-Meter.
Sifams works great and they are faster compared to the original UA meters I have here.
Probably the fastest of the bunch I have here are the good old Triplett.

Would be interested to see the AB mods you have performed.

Have you tried it yourself ?    Does it stop the meter action from being sloppy ?

 

[Rob Flinn]

By sloppy I mean they have overshoot.  i.e if you switch from say +4 to GR the meter bounces around the zero mark before it settles. I'm using modutec meters.

 

[cannikin]

Great !
If anyone is interested I'll post the list with the values of the Rev AB.
Cheers

Neeno, please post your findings,  I have been watching this thread because I'm about to build two RevA

 

[Stagefright13]

Well been using Mako's original rev A for a long time now. It's on 4 CD's now. Never had a need to change it. I'm really really picky on sound. And it is working for me. Not much worried about the all buttons in. I don't even use that on my rev D's. I guess that sound would be cool here and there as an effect.

I am actually afraid to change it cause it is working so well. For me it would be like upgrading protools in the middle of a gig lol!

Thanks Mako my stuff is running daily!

John

 

[Rob Flinn]

John I don't use "all in" mode much, but the mods make the input control less of an on/off switch, & give you smooth control.  So in my opinion they are worthwhile to do.

 

[Stagefright13]

Thanks Rob I may try that. Right now I have promised myself to finish my dual rev D. Just needs a wiring job and Cal. Been so busy but I could really use it lol. It's SO close.

John

 

[ilfungo]

sorry  but I am a beginner...


the mod are:

1  - R46=47K or 22K instead 8.2k

Ratio board:

2 - 68k instead 130

3 - 47k instead the jumper

is it correct?

Thanks