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Post subject: Ultra Chorus distortion on clean channel
Posted: Thu Nov 03, 2011 4:26 pm
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I picked up a "As-Is" Ultra chorus for $100.

The owner said it made internittant strange sounds so bought a replacement amp since he was gigging.

Short story, replaced the left channel output paired tranisitors and fixed a cold solder joint on C41 cap.

The unit seems to be working to specs, but I notice on both inputs using the clean channel a bit of distortion when the guitar volume is set to 10. My question is, is it normal for this unit to have a little distortion or do I have a possible pre-amp problem that needs to be fixed? It almost sounds like a tube being over driven...I may have to make a short video and post. Hard to explain what I'm hearing. I do not hear it on a London Reverb Showman.


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Post subject: Re: Ultra Chorus distortion on clean channel
Posted: Thu Nov 03, 2011 6:03 pm
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What type of pickups does your guitar have?

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Ultra Chorus distortion on clean channel
Posted: Thu Nov 03, 2011 9:00 pm
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Not sure...will check, but they are single coil stock. I have a London Reverb Showman sitting right next to it. It sounds clear on the showman. Since this post, I replaced the (2) TL072 IC's in the pre-amp but same thing. I suspect a cap in the clean channel has gone soft causing signal clipping. Now I know what the previous owner was saying when he stated he didn't like the sound...


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Post subject: Re: Ultra Chorus distortion on clean channel
Posted: Thu Nov 03, 2011 10:26 pm
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Got it. My thinking was, the symptom might have been the result of hot humbuckers which tend to drive a pre-amp harder and more quickly into saturation. I think you're on the right track about a coupling cap somewhere in the signal chain. Every Ultra Chorus I've ever heard sounded squeaky clean on the clean channel even when the volume control reached the threshold of aural pain.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: Ultra Chorus distortion on clean channel
Posted: Thu Nov 03, 2011 11:40 pm
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Thanks, that's what I wanted to hear. Squeaky clean...


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Post subject: Re: Ultra Chorus distortion on clean channel Sovled
Posted: Fri Nov 04, 2011 7:33 pm
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CR34 and CR35 were shorted. The amp was sending good signal out of the right channel but the left channel had a problem so the over all sound was degraded. I found a few caps that were going soft so changed them out.
Also, one .47 ohm 5 watt (r-112) was open.
This is a really nice little amp.


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Post subject: Re: Ultra Chorus distortion on clean channel
Posted: Sat Nov 05, 2011 12:31 am
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The Ultra Chorus did huge production numbers for FMIC -- at one time, it was their most popular amp.

Arjay

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