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Topic: re:LTD 400 distorted sound... |
Mike Kowalik
From:
San Antonio,Texas
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Posted 24 Dec 2003 12:54 pm |
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| I have a LTD 400 that just doesn't sound right to my ear.....I hear a bit of distortion or overdrive when I play thru it....could the speaker be damaged or can this be due to improper setting of the sensitivity knob? |
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Ken Fox
From:
Nashville GA USA
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Posted 24 Dec 2003 5:08 pm
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Mike, I am having the exact problem on an older Session 400. Fortunately I have 2 Sessions and could verify the speaker was OK. I have just ordered new power supply filters (a common cause for this buzz). I should have them in after the first of the year and will let you know if that fixed it. I am getting distortion on single notes and worse for 2 or 3 notes.
My filters had a spike that exceeded 1/4 of the saw tooth waveform height. According to what I was reading on the Peavey Forum, that is a sign they need replacing.
Your speaker could be suspect as well. The older BW tend to have a problem with the foam insert in the back rotting away and falling into the voice coil and gap area. You can press the speaker evenly and push it in to check for drag. If so, remove the magnet and clean the gap (blow it out first with compressed air, a lot of loose material will come out). Clean the gap with packing tape (I wrap a business card with the tape to help get it in the gap). Clean it and use denatured alcohol to clean the residue off of the bobbin (if any is there). There are other solvents that will work; perhaps someone else can shed some expertise on this.
[This message was edited by Ken Fox on 24 December 2003 at 05:10 PM.] |
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jim milewski
From:
stowe, vermont
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Posted 24 Dec 2003 5:12 pm
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| same problem with one of mine, yet to look at it, Ken, if I have no ripple on my DC, the caps would be good...right? |
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Ken Fox
From:
Nashville GA USA
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Posted 24 Dec 2003 6:24 pm
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You should see a bit of ripple with a scope, very little wuth an AC meter.
A while back I had an LTD 400 with a buzz only in the reverb! It was the 5000uf filters causing that one. If one filter is not filtering as well as the other, a problem is created. These filters are for the plus and minus 50 VDC supplys (they connect directly to the reverb drive transistor pair). If filtering is equal, any ripple will be equal and opposite in polarity, hense self-cancelling. If their is a difference in the amplitudes of the two ripple voltages, the difference gets amplified.
I had this same problem on an old Standel amp once, drove me nuts, but I figured it out. Someone had replaced filters and the values were not the same for the plus and minus rails, the difference was pure hum in the output!
I am hoping this is the problem with this amp. I jsut order my parts from Mouser tonight, I should get them in just after the first of the year.
The speakers are always worth looking at. The last two Sessions I got in had foam rubber in the gaps. A just got in an Artist VT, with the older style Black Widow (Spider on the back). It was so bad , the voice coil was seized. I had to carefully twist the magnet to loosen it. It took half an hour to clean up, but worked just perfect. It also had two dead 6L6GC tubes, a bad fuse holder and the wire to the fuse holder was unsoldered! Of course it had the standard issue, 20 amp auto fuse in it! Tough old amp! It came out working perfect. |
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Gary Walker
From:
Morro Bay, CA
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Posted 24 Dec 2003 11:30 pm
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| One of my old LTD 400s developed a distortion and it was in the reverb section. When I cut the verb down, the fuzzies disappeared. The Tech that fixed it said that was common. |
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Brad Sarno
From:
St. Louis, MO USA
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Posted 27 Dec 2003 5:17 pm
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These amps respond real well to new power supply filter caps. I recommend also bypassing those filter caps with small film caps. Try .47uF/100v mylar or poly caps. This will really clean up and quiet down the amp.
Brad Sarno
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Ken Fox
From:
Nashville GA USA
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Posted 9 Jan 2004 7:16 pm
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I got the new power supply filters in and also Brad Sarnos tone cap mod. The buzzing is gone, that was caused by the filters. The tone mod is great. I am still getting intermodulation distortion. I have two amps, so I put them both on the bench for comparison. The good amp will get around 40 volts peak with a 1000 hertz signal loaded at 4 ohms or unloaded. The bad amp will get the same unloaded only! When I load it the bottom half of the signal squares off! I have to lower to 20 volts to get a clean wave.
According to Peavey techs they suspect the diff pair of transistors at the very front end of the power amp. I have these in stock and all the drivers as well. Hopefully I will nail it down tonight .
[This message was edited by Ken Fox on 10 January 2004 at 08:22 AM.] |
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