You can see the photos of the reverb cable and missing ferrite here:

http://www.guitarkitbuilder.com/content/mailbag-marshall-valvestate-vs265-repair

Thanks JM - he's already noticed a higher level of hum when he turns up the reverb so he'll want to fix it in this particular case. 

Now that I have a photo of the whole chassis I can see that the cable that was using the ferrite ring is the audio cable for the reverb tank. 

A reader of ours wrote me to ask about a ferrite ring that broke while he was opening up his Marshall VS 265 amp.  I have no idea how it broke, but he was replacing potentiometers when it happened.  Does anyone know which wires/cable (AC mains?) go through the ferrite ring , and if it's just straight through or wrapped or what? 

Quote from: gbono on April 16, 2011, 07:54:48 PM
They use a potentiometer in that application? Why not and RPG or optical encoder - opps I forgot keep it cheap and cheerful. What about the Spider IV's? Same issue?

I can see the merits of a potentiometer approach, in that it allows you to load amp presets electronically, without having to have a servo or similar mechanism on the switches.  I just think they didn't engineer enough noise rejection into the control logic.  I don't know about the Spider IVs.

QuoteDo you have a schematic for this amp?

No.  Line 6 is notoriously unhelpful about providing schematics, and due to all the control switching, LSI chips, etc., it's not an amp that many would attempt to repair. 

In my music schools we use a number of Line 6 Spider III 150 watt amplifiers, and the controls on them have always been a bit screwy.  The controls, such as a six position effects selector, use potentiometers which I assume go to some sort of A/D converter with triggers for when each switch "position" has been reached.  There are small LEDs around the perimeter to indicate which effect is selected.  However sometimes these LEDs will dance around a bit (change on their own, without the knob being touched), and clearly the amp is confused about which effect is selected.  This is at best disconcerting and at worst prevents you from selecting something.  And worst of all, it's intermittent - comes and goes, and we've never been able to correlate it with any other activity or location. 

My assumption further has been that this is due to some sort of power line noise or poor power supply regulation or noise filtering.  We have six of these amps and they all do it from time to time at all locations.  While I haven't asked them in a couple of years since we bought them, the retailer and manufacturer have both answered along the lines of "check your power," ignoring the fact that this happens in all three commercial buildings we lease, as well as in my home, as well as in several different clubs where we've used them to gig.  Their answer might as well be "upgrade the mid-atlantic power grid" as far as I'm concerned, but I digress.

I've got one of these amps on my bench right now to fix an input jack.  I thought I might also try to address the noise problem.  I'm soliciting the forums suggestions for 1) your agreement or alternative theory on what the cause might be and 2) if you think it's a power noise issue, where would you attempt to improve the power conditioning and how?  For example, I might try a ferrite core on the power cord, or something in the filter section, or perhaps something at the potentiometers?  I'm really looking for practical experience here on suppressing transients that might confuse switching logic.

thanks

Teemuk,

I should have clarified that my question concerned SS amps, even though the scope photo is of a tube amp.  Is your answer the same for SS, with the exception of grids?

Quote from: teemuk on April 07, 2011, 08:39:27 AM

And before anyone even says "soft clipping" this is a typical output of a clipping tube power amp running to a resistive load:
Trainwreck:

Teemuk,

Would you characterize the crossover distortion in this oscilloscope image as "typical" or "severe"?  Do you find the crossover distortion is more pronounced in the oscilloscope view with a resistive load?  I was recently looking at an amp that looked just like this in the scope and my thought was that I needed to make some adjustment to smooth out the crossover, but I'm not sure what normal should look like.

I'd be interested to hear what methods/procedures other repairers recommend or follow to test an amplifier after its been repaired.  I've generally used a 1kHz tone and run the amp into a dummy load for 8 hours or so to see how it handles getting hot, but someone's probably got a better procedure.  What do you do?

JM, I'd love to get it for $10.  We'll see what happens when we negotiate. 

I have an opportunity to buy a non-working Kasino Snake Eyes bass amp for $50.  I've read a little bit of the background of these amps and their connection to Kustom.  Anyone ever worked on one or know anything about them?

I just picked up a Peavey Supreme TransTube head, and unusual for me, it works without my needing to repair it.  I really was just in need of an empty 4x12 cabinet for use in a music school as a room divider, and saw this Peavey half stack advertised for $300.  The cabinet has 4 Eminence G12K85 speakers in it that I'll sell.  Between the head and the individual speakers I think I can get my $300 back and get the cabinet for free.  I'm really impressed with the head though - very nice tube sound, nice features and construction.  This is my first experience with the TransTube technology and I have to say I'm impressed by it.  It also looks like it would be very straightforward to work on if needed.  The opamps are socketed, which is nice, and the rest of the layout is very clean and open. 

Thanks to Teemu for his book and direction to the Peavey Papers on TransTube - an interesting read.  Anyone else have any experience with this amp?  Does anyone want one or more of the speakers - I'll let them go for below the price I see quoted in eBay, as thanks for the assistance I've gotten through this forum.  Let me know.

Regarding Teemu's book - is there any reason I shouldn't link to it from GuitarKitBuilder.com?  I think our readers would want to know about it.

FYI, I found a bad op amp that was causing the problem with the clean channel.  In case anyone else is working on one of these, the current nomenclature is for channel 1/2 while mine uses channel A/B.  The schematics shown on the Carvin site are very different than my model, and it wasn't until I took a look at the SX100 schematic that I saw that the drawing was labeled SX100/SX200.  This was the correct schematic version for mine, at least for the preamp board.

The bad op amp is on the channel B input, which was passing DC voltage to the volume pot and causing the noise/hum among other problems.  I should have this amp ready to go once the part arrives. 

What's the fair market value of this amp, with no footswitch, given it's got the Eminence speakers?

JM, thanks for letting me know, I'll up the price when I sell it.  I found this item confirming it as well based on the part number 381208  http://www.carvinmuseum.com/forums/viewtopic.php?p=121073&sid=96c34ddb7cfde035211e19bf3d10820d .

Yes the amp has digital effects, and thanks on the tantalum call.

Bry, thanks also for the help and looking up the part.  I'll get to work on fixing the amp today.  Channel 1 works fine, but channel 2 makes a lot of noise as soon as the volume pot is raised above 0.

Also, if you know, what type of capacitor are the yellow ones, eg C24 in the center of the 4th photo?