• TalkBass has been independent since 1998. Add your voice.
    Create a free account to reply to discussions, view embedded media, and browse with fewer display ads.
    Join free Log in
    Want zero display ads or expanded classifieds tools? Compare plans.

Need Micro-Tech 1200 Help

Vic Winters

Vic Winters

Apr 20, 2006
4,057
398
Western NY
#1
I picked this amp up via trade a few weeks ago. My problem is that Channel 2 puts out a stronger, cleaner signal than Channel 1. I still get sound from Channel 1, but it's no where near as loud, plus it also produces more distortion in the form of hum and speaker movement even when the preamp is muted. I A/B tested both channels with the same cab, same cables, same gain and volume levels on both the preamp and power amp. I tried posting the question on the Crown forums and have not recieved a reply. I contacted Crown via email (very quick responses from them), nearest Crown service station is an hour and a half away, shipping directly to Crown one way is $22, and costs $70/hour to fix.

This weekend, I opened it up and took an ohm meter to just about everything inside, I thought it might be able to find a discrepancy somewhere between Channel 1 and 2, but all measurements came out the same on both sides.

I know it's not something easy to diagnose without having it in front of you, but some ideas would be nice. I can send it in at anytime, but if I can save myself the minimal $114, that would be nice.
 
#2
Dumb question, but this is happening when you're in stereo mode (not bridge mono or parallel mono)?

If you need a manual and it's not on the Crown site, send me a PM with your email and I'll get a .pdf to you. I also have a service manual, but it's for the 2400, which I own.

Marshall
 
#3
In stereo Channel 1 is doing what I described in my first post. When I bridged it into an 8 ohm 4x10, performance suffered there as well. There was no way it was putting out the 970 watts it should have been. The 310 watts from Channel 2 by itself into the same cab seemed louder. I didn't try parallel mono.

They have the service manual on the website which I plan on checking out tonight, but thank you.
 
#6
If there's a good place near you, then let them work on it. What you describe could be as simple as a bad op-amp, or it could also be some instability causing high frequency oscillation in the output section. A good tech will be able to find the problem and fix it.
 
#10
There's very little you can do with just a multimeter, then, to test a channel that works but not well.

If the channel were completely dead you might be able to find where the fault is. Without also having an oscilloscope (about 100 MHz bandwidth), you can't really verify whether the channel has an oscillation problem. Without a signal generator, you can't check the signal flow through the channel. The $60 bench test looks like your best next step.
 
#13
Sound Source is VERY reputable. They will give you an honest quote. Robb Storms and Chuck are very good techs. You may also want to call Nau Engineering in Chili. (He's in the phone book white pages) John Nau is also a very reputable man and a great amp builder. He's actually the authorized GK service center in the area. PM me when you narrow it down and I'll see if I can help you out. If you call John, tell him I recommended him. You don't need to ship the amp. You can get the same service locally. Just for the heck of it, call Beau at Brighton Sound. He was a Crown dealer, but I'm not sure if he is any longer.
 
#15
Have you tried to play with the 3 way sensitivity switch, located behind the screwed plate on the back panel. Also, when changing from stereo to bridge or parallel, turn the amp off a few seconds while you change settings. Have you tried if just the rear pots are OK. The manual is available on the crown site, that's where I got mine.
 
#16
I don't unserstand what the senstivity switch would have to do with anything. One channel is working perfectly fine, and one is having problems. If they were both lacking, then I could see that being a possibility.

I always turn the amp off before making any changes to any settings, the only exception to this would be adjusting the gain pots.

Both pots seem fine. Lower output with more distortion and speaker movement even when the preamp is muted leads me to believe that it's more than just a pot.

I printed out the operation manual, and I've looked at the service manual online.
 
#17
A friend of mine, a 3rd year electrical engineering student at RIT can get me access to an oscilloscope and signal generator. Any tips so I'm not going in there blind? He knows how to used the equipment, but I'd like to know exactly what I should be looking for.
 
#18
The first thing is to look at the output with the scope and no signal. If there's a HF oscillation (and it may be in the tens of megahertz), you'll see it.

Then put a signal into it. The output should look just like the input signal, only bigger (according to the gain setting). If it looks distorted, noisy, etc., then you or a qualified tech have to dig deeper.
 

Latest posts

Top Bottom
Back