Acoustic 150 - Hat in Hand

[numpsha]

  I own a generation 2 ('72-'76) Acoustic Control 150 head -- love their amps. I want to give it a general housecleaning (recap, check voltages, clean pots, etc.) but, (re inspired by Teemu's book!) I'm also considering some minor mods like inserting an fx loop, tweaks to the tone stack and small improvements to the power amp. Thanks to the folks at the Unofficial Acoustic Control site I have access to the owners and service manuals, with schematics and signal+dc parameters, for the pre-'72 150 head. Problem is, the newer ones (at least the 17-11 preamp board) were revised. The only info I've been able to scrounge off the 'net about the revision is: the rated power output went from 110rms to 125rms and the tremolo circuit dropped the optocoupler for a FET component. Suppose I could trace the pcb's and hack a schematic, but my eyes and head for the maths to calculate voltages and freq's are kinda shaky lately.

I feel pretty cheesy asking, but I really can't afford $20 just now to buy a scan of the service manual/schematic and wonder if anyone here could email (or provide a link to) a copy relating to this revision for me? (Hangs head, shuffles feet)

Thanks!
Rob

[GaryM]

On my 150, I lowered the tone stack cap values and it made huge improvement. I changed the .01 mfd treble boost switch cap to a .001 mfd and changed the treble control cap from .1 mfd to a .01 mfd. Looking through my drawings, it appears I have the same schematic set as you. Does your PCB look like this one?

[numpsha]

Thanks for the tip, Gary.

That board is likely the same 17-11 rev. I have. Problem is, I'm temporarily in an assisted living home and the amp is at home. I'll bring it up here next week and check it out.

Interesting thread you have going with Teemu about your Road head.

rob

[GaryM]

Rob, I found the schematic! The Acoustic 134 is the 4X10 combo version of the 150 head. Over on the Acoustic WIKI, download the schematics for the 134 and it has what you need. I just verified the schematic with my 150, which is a later model like yours. It is accurate and free of charge.

Best regards,

Gary

[numpsha]

Thanks, Gary! Dunno how I missed that.

Never did get that head opened up; it's in a snowbound storage trailer (record 100+ inches up here in NH). Soon though --- gives me time to beef up my rusty and lacking skills. Like SPICE. Just checked and I downloaded it exactly eight years ago yesterday. Got lazy and started using those little freeware calculators instead. Having been away from this hobby for several years, I'm finding more fun in "learning how to fish" anyway. Such as modeling an active eq for those cap changes you suggested.

BTW -- have you lit up that Road yet?

best,
Rob

[GaryM]

You'll have fun digging into that 150, Rob. The effects channel always sounded weird in mine. I dug out my scope and signal generator and found asymmetrical clipping in the preamp. It is related to biasing of the stages after the EQ. I'll report back later as it is my project for today.

That Road amp is on the back burner since I've blown two sets of outputs trying to fire the darned thing up. 

Is the SPICE program a freeware program? I've heard about it but have never used it. I'd like to check it out.

Gary

[teemuk]

SPICE is just an abbreviation for "Simulation Program with Integrated Circuit Emphasis". So, basically it's just a common name for software-based circuit simulators and like with any software, some are free and some are not. You can read more from: http://en.wikipedia.org/wiki/SPICE

If you want to try, I kindly recommend LTspice/SwitcherCAD III: http://www.linear.com/designtools/software/#Spice

It's absolutely greatest freeware SPICE software I know. Has an easy GUI, tons of features and no restrictions for number of imported models or component count (which is a problem that bothers many other freeware SPICE software).

[numpsha]

I took your advice, Teemu, and have been playing around with LTspice for a couple of hours. Looks like the opamp library features their proprietary chips but gives you the ability to "roll your own" and, as you say, unlimited model imports and component counts. Lots of neat features to check out. They even have a user group with additional tutorials and libraries. I downloaded the quickstart and help pdf's, too.

Thanks -- this a heck of an improvement over the old Orcad Pspice I have. Check this one out, Gary.

Rob

[GaryM]

 :tu: Thanks, gents! I downloaded it and will check it out tomorrow at work. During breaks that is...  8|

[JackSpratt]

Rob, I found the schematic! The Acoustic 134 is the 4X10 combo version of the 150 head. Over on the Acoustic WIKI, download the schematics for the 134 and it has what you need. I just verified the schematic with my 150, which is a later model like yours. It is accurate and free of charge.

Best regards,

Gary

Hey guys, anybody still here? I realize this discussion is almost 10 years old but I need the schematic for the that later revision of the 7-11 board. I'm not sure if anything called Acoustic WIKI still exists. If anybody can share the schematic with me or show me where I can get it I would be eternally grateful!

- Jack

[DrGonz78]

Here is the service manual and the 17-11 board is pg18-19. Not sure this the one you are searching for...??

Edit: Well looking closer this one says 1971 and the one I think your looking for is for 1972 and later generation 2 or something. I will keep a look out for anything on the matter.

[JackSpratt]

Here is the service manual and the 17-11 board is pg18-19. Not sure this the one you are searching for...??

Edit: Well looking closer this one says 1971 and the one I think your looking for is for 1972 and later generation 2 or something. I will keep a look out for anything on the matter.

Yeah, sorry but this schematic is ubiquitous and not the one I need. This one has the LDR component for tremolo, the later revision(s) used FETs per this discussion.

[JackSpratt]

Here is the service manual and the 17-11 board is pg18-19. Not sure this the one you are searching for...??

Edit: Well looking closer this one says 1971 and the one I think your looking for is for 1972 and later generation 2 or something. I will keep a look out for anything on the matter.

Yeah, sorry but this schematic is ubiquitous and not the one I need. This one has the LDR component for tremolo, the later revision(s) used FETs per this discussion.

Found it, finally. Page 22 if anyone needs it.