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the venerable acoustic 370

Discussion in 'Amps and Cabs [BG]' started by nonsqtr, Nov 25, 2003.


  1. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Just had a chance to play through this excellent 70's head again recently. What a great bass amp! It's amazingly fat for a solid state amp, sounds thunderous through a set of big speakers. Unfortunately it's starting to distort a little at higher volumes, don't know what that's all about but it might be starting to get flaky. Maybe it needs a cap job or something. Anyone know about servicing these things?
     
  2. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    You can find a schematic for your 370 at http://www.acoustic360.com

    It has a big power supply cap (or two) and a big output cap. Some of the transistors may be a bit hard to find...

    Good luck!!!!
     
  3. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Schematics are good. How about a service manual? "Will work for JPG's"!
     
  4. ihixulu

    ihixulu Supporting Member

    Mar 31, 2000
    getting warmer
    What cabs are you putting it through? The 370 has pretty high distortion characteristics at close to full output which is 230W into 4 ohms or 365 into 2 ohms. You use a Walter Woods head right? Maybe you're expecting a cleaner sound out of it than it is designed to deliver? Just asking, not implying anything.
     
  5. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    I'll bring the 370's service manual to work on Monday and scan it...

    Actually I have a bunch of Acoustic stuff that I can share with the web site...360 service manual, stuff on the 220, old catalogs, etc.

    Grexa ain't going to be happy when that stuff hits www.Acoustic360.com...
     
  6. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    ihixulu is right...the 370's power ratings were generated at 5% and 10% THD.

    My Acoustic 450 head is a little grindy compared to my Pearce/AMP/QSC rack setup...
     
  7. user

    user

    Oct 26, 2003
    Chicago
    BillyB are you in Lake Zurich?
     
  8. Rickenbackerman

    Rickenbackerman

    Apr 17, 2001
    Laurel MD
    I've got a 370 too... doesn't seem very loud to me. Maybe it needs new caps and power transistors?
     
  9. user

    user

    Oct 26, 2003
    Chicago
    What is the recommended service for an old Acoustic head? I have a 450 and have never had it serviced? What is the procedure and cost?
     
  10. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Thanks BillyB_from_LZ! E-mail me if there's any way I can assist. I'll be happy to trade for whatever I have, mostly pro audio stuff like mic pres, mics, and compressors. And plenty of odds 'n' ends! Yes, the distortion I'm hearing is not the "natural" distortion of a 370. That's a nice fat bottomy distortion that's also there. What I'm hearing is something else, it sounds like a component's fried. Could be bias related, maybe one of the diodes went, that seems to be pretty common. It starts happening at about half volume, when the amp is still pretty clean, and it gets really bad a high volumes. Another suspect might be the compressor circuit, the 370 has this little FET-based thing that they call "AGC" but it's really just a limiter.
     
  11. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    Oh yeah, I have some big speakers to run this amp with. Big 18's, probably not as thunderous as a pair of 301's but they'll do. I thought at first it might have been an impedance related thing, so I tried the head with 8 ohms, 4 ohms, and 2 ohms load. The crackling distortion happens earlier with a 2 ohm load. I have to raise the volume to almost the clean limit with a 4 ohm load before it kicks in. The amp has a wonderful fat sound, it would sound really good without the crackling!
     
  12. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    I've heard that the small caps in the preamp have a bad habit for not aging well.

    When I owned a dead 370, I asked a service tech what it would cost to go through it, he said "too much" and suggested that I simply replace all of the small signal transistors in the power amp.

    I never did get around to trying before I got tired of looking at it and raised it up the eBay flag pole to see who would salute...that they did.

    User...I suppose any 40 something tech would have Acoustic experience. The guy I spoke with works at Accutrack on Algonquin (near Elmhurst)in Arlington Heights/Elk Grove Village.
     
  13. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    Oy!!!!

    I have scanned the 370's service manual...as a single document it's 27 MB (that's at 200 dpi). I tried making each page a pdf...but I can't post pdfs...

    I'll have to figure out how to upload stuff to my web space at home.
     
  14. Rockbobmel

    Rockbobmel Supporting Member

    I just missed one for $160. I had one once. It got stolen. I used it with the Acoustic 18 and a modded Traynor cab with 2-15" SROs. That amp made me very happy. The only improvement I would have made was to get another one. It sounded best when pushed to the distortion point. I think Dan Elliot from G-K calls this "riding the rails" I'm into tube amps now, but I would pick one up if the price was right.
     
  15. Chasarms

    Chasarms Casual Observer

    May 24, 2001
    Bettendorf, IA USA
    370s are a little deceptive in their loudness. I have used one with the original folded cabinet. On stage it was hardly audible and 30 ft out in the club, it was flapping pants.

    Personally, I like the 360 much better as far as tone.
     
  16. Rockbobmel

    Rockbobmel Supporting Member

    Thanks Guys,
    This sparked me to look again, and there was one for $149. I put a deposit on it. It will be here next week. I hope it don't need work.
     
  17. nonsqtr

    nonsqtr The emperor has no clothes!

    Aug 29, 2003
    Burbank CA USA
    BillyB, do you still have the individual pages? Any chance we can do a sequence of partial transfers or does it have to be the whole file all at once?
     
  18. ihixulu

    ihixulu Supporting Member

    Mar 31, 2000
    getting warmer
    BillyB, I've sent you a PM.
     
  19. BillyB_from_LZ

    BillyB_from_LZ Supporting Member

    Sep 7, 2000
    Chicago
    I still have the manual with me at work. I'll play with it at lunch-time and see what I can do...