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Post new topic LTD 400 with a hiss
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Author Topic:  LTD 400 with a hiss
Dale McPherson


From:
Morristown, Tennessee, USA
Post  Posted 28 Sep 2019 7:16 am    
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I just bought a Peavey LTD 400 with the BW spider speaker. The amp sounds great but the higher I turn the reverb......the more hiss I get. Reverb works good. It is not real bad but I can't stand an amp with a hum or hiss. When the amp has the reverb turned all the way down.....the noise goes away. The higher the setting, the more hiss. Any ideas? I am considering sending the amp back to Peavey for updates but don't know exactly what to tell them to look for. My new Session 115 makes no noise, can't remember if this was normal on the older ones.
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Willie Sims


From:
PADUCAH, KY, USA
Post  Posted 28 Sep 2019 1:13 pm    
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The LTD amp is the same chassis as the session 400 amp. There are two small transistors inthe reverb section that control the reverb. These are small transistors, you can replace or have a electronic technician replace them. The transistors or matching transistors, very cheap they are side-by-side on the circuit board. Take the chassis out, spray the two transistors with freezon, with the amplifier on. If the hiss go away replace the two transistors.

I repaired my session 400 this way
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Steven Paris


From:
Los Angeles
Post  Posted 28 Sep 2019 9:30 pm    
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Willie Sims wrote:
The LTD amp is the same chassis as the session 400 amp. There are two small transistors inthe reverb section that control the reverb. These are small transistors, you can replace or have a electronic technician replace them. The transistors or matching transistors, very cheap they are side-by-side on the circuit board. Take the chassis out, spray the two transistors with freezon, with the amplifier on. If the hiss go away replace the two transistors. I repaired my session 400 this way

What ARE the two transistors?
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Jack Stoner


From:
Inverness, Fl
Post  Posted 29 Sep 2019 1:55 am    
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There were two models of the Session 400. The original model was discrete components and the later LTD model is solid state. Which do you have?
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Dale McPherson


From:
Morristown, Tennessee, USA
Post  Posted 29 Sep 2019 3:35 am    
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Jack, I have no idea. How can I tell?
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Ken Fox


From:
Nashville GA USA
Post  Posted 29 Sep 2019 5:29 am    
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The Peavey LTD 400 has a small cabinet like the Nashville 400
The later Session 400 LTD is a larger cabinet like the older Session 400 or Session 500

On the original Session 400 and it companion amp the LTD 400 the reverb tank plugs into the chassis with RCA male cables. It is possible to get those reversed. The reverb will still work but will have hum and or hiss in the reverb signal
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Last edited by Ken Fox on 29 Sep 2019 6:33 am; edited 1 time in total
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Ken Fox


From:
Nashville GA USA
Post  Posted 29 Sep 2019 5:32 am    
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Equally important is the direction the tank is installed in the amp. It must have the reverb can connectors facing the front of the amp.
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Ken Fox


From:
Nashville GA USA
Post  Posted 29 Sep 2019 5:34 am    
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https://bb.steelguitarforum.com/viewtopic.php?t=348363&highlight=
Good post here for you
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Dale McPherson


From:
Morristown, Tennessee, USA
Post  Posted 29 Sep 2019 8:27 am    
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Here is what I found when I open the back and took the reverb unit out of its covering. It appears there are 2 units screwed together. Only one is wired up. Ken, I switched the wires and it was worse. When I unplugged the reverb unit.... I could turn the reverb knob wide open without any noise or hiss. . Makes me think the amp unit is ok and a problem in the reverb tank. But then I am not smart about electronics. I think ordering a new reverb tank is a step in the right direction. Does anybody know the correct unit number? I like this amp and want to keep it. It is the small cabinet LTD400. Thanks


Last edited by Dale McPherson on 29 Sep 2019 10:12 am; edited 2 times in total
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Ken Fox


From:
Nashville GA USA
Post  Posted 29 Sep 2019 9:17 am    
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Follow the post above. It will have a drawing that will help. Same reverb model numbers apply to your amp
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Dale McPherson


From:
Morristown, Tennessee, USA
Post  Posted 29 Sep 2019 10:19 am    
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Thanks Ken. Your advice and help is always appreciated. Thanks, Dale
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Ken Fox


From:
Nashville GA USA
Post  Posted 29 Sep 2019 1:23 pm    
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The two transistors mentioned above could be also be a potential cause. They are in the reverb send circuit With the tank out you are only getting the reverb return part of the circuit.

Try another tank for sure to check it. If you have another Peavey amp around you use the tank from it

The other original is a 4EB2C21B


Just saw the picture you posted. Two tanks face to face. Very odd. Check both as maybe one will work. Install per my drawing with the RCA jacks to the front of the amp
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Willie Sims


From:
PADUCAH, KY, USA
Post  Posted 30 Sep 2019 9:24 am    
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Steven
you asked what kind of transistors. I referred to in my post a bout the hissing reverb. The number of the transistors is SPS953 they are MATChing transistors on the circuit board just behind the reverb control. my session 400 was a 1972 model, the schematic and owner manual was for a session 400 and LTD amplifier with the JBL speaker.
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Steven Paris


From:
Los Angeles
Post  Posted 1 Oct 2019 9:46 pm    
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I believe a good substitute for the PV SPS953 transistors used would be a ZTX851 (https://www.mouser.com/ProductDetail/Diodes-Incorporated/ZTX851?qs=sGAEpiMZZMshyDBzk1%2FWizF0eVyYE44ZFkAmH18RRwk%3D) ---these have just about the lowest noise figure for any BP NPN transistor, and they also have very high voltage and current maximums. This, in combination with replacing the caps with polypropylene ones, will probably make a noticeable improvement in the reverb circuit performance.
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George Kimery


From:
Limestone, TN, USA
Post  Posted 2 Oct 2019 1:57 pm     LTD 400 with a hiss
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If you decide to replace the reverb tanks I would suggest you replace them with Mod tanks. It improved my Nashville 112. I don't like Peavey amp reverb. If it were mine I would use my Wet Reverb pedaI and not even fix the reverb.









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Dale McPherson


From:
Morristown, Tennessee, USA
Post  Posted 2 Oct 2019 2:14 pm    
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Update. I received my new Mod reverb tank this evening and made the exchange. Sure sounds better. Still have a little bit of hiss. I did notice some faint crackling coming from the speaker so it is probably time for an overhaul. I am appreciative of all the help and replies. That is what the forum is all about.
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Jack Stoner


From:
Inverness, Fl
Post  Posted 3 Oct 2019 2:17 am    
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I installed a John Lemay "mod" to a friends original model Session 400 (discrete components). The mod replaced all the capacitors on the preamp board. Quieted down the "noise" in the amp.

I don't know if John Lemay still sells a kit or if Ken Fox has one. But that would be my recommendation.
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Steven Paris


From:
Los Angeles
Post  Posted 3 Oct 2019 4:00 pm    
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I thought that the Session/LTD mod of replacing the caps was from Brad Sarno---??? I think the LeMay mods were for NV400s.
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Last edited by Steven Paris on 3 Oct 2019 10:48 pm; edited 1 time in total
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Dale McPherson


From:
Morristown, Tennessee, USA
Post  Posted 3 Oct 2019 4:21 pm    
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I have the chassis out. Can anyone tell me how to tell if it has been modified?
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Steven Paris


From:
Los Angeles
Post  Posted 3 Oct 2019 10:28 pm    
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Here's the original Sarno mod page, with photos:
https://web.archive.org/web/20180214233657/http://home.earthlink.net/~bradsarno/session_400page.html
That should help identity mods made(or not).
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Jack Stoner


From:
Inverness, Fl
Post  Posted 4 Oct 2019 2:16 am    
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The Lemay mods were many years before Brad came on the scene.

Brad, or even Ken Fox may have or did Session 400 mods but they are different than the original Lemay mod. John Lemay was the first with the Nashville 400 mod, too. Ken Fox had an "intensive" mod for the Nashville 400 but much different and more involved than the Lemay mod (which Peavey copied).
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