Legend Model A30

[OMguy]

Hi everyone, I have a Legend Model A30 that starts crackling loud after about 10 min. The back of the amp says Model A series II. I have tried two different 12ax7's and did not solve the problem! Thanks to anyone that could post a schematic for me! Thanks ----------------------OMguy

[Enzo]

Well, did you try different power tubes?

[OMguy]

Hi ENZO, this amp only has two tubes in the front end. Everything is solid state after that. The noise can be turned down by the volume control. Would you happened to have a schematic? Thanks --------------------OMguy.

[Enzo]

Not that I know of or I would have posted it. I guess that makes it hard to change power tubes if it has none.

SO your preamp has the noise, since the volume control will kill it. You have swappeed the tubes, so eliminate them. Next suspect on my list is a noisy resistor, probably a plate load.

But your problem takes 10 minutes to build in, so it sounds like something warming up and failing noisy. That is what freeze spray is for. Once the trouble starts, spray freeze-it on components looking for one that goes back to quiet when frozen.

[OMguy]

Thanks for the advice on the freeze spray Enzo. I will try that! It is going to take me some time to get it back on the work bench and maybe someone might post a drawing! Thank you ----------------------OMguy.

[52 Bill]

This is a different model, but I would assume that it may help some.

Legend Amp Doc Page

[OMguy]

Hi 52 Bill, I have seen that schematic posted. There was also another post about board numbers. The number on my Legend board is printed (Legend 009-5007-00). It is all one board with only two tubes off board. What has me wondering is all the transistors and ic's that control the signal. I had it on the bench tonight and it took 1 hour to start to slightly thunder. I could get rid of the noise by turning down the ModeB 1'st stage preamp volume. Thanks for your help -----------------------OMguy

[Mark Black]

These are all I have (pretty poor quality on the schematic)

[OMguy]

Hi Mark Black, The schematic and layout looks a lot like the board I have,and I did not realize there must have been several different circuit arrangements! I started to try to plot out the front end (not getting very far), but on the board I have the 1/4 inch input jacks go through a resistor (22k) then to a small shielded cable to pin 7 of the 1st 12ax7. I noticed on the drawing you posted it goes through an IC (op-amp) first! Interesting the different arrangements! I may have stumbled across a bad .1 cap (after replacing 3 other caps and 1 4558 ic). I have not heard the noise after that for one hour tonight! I will let it sit until tomorrow and report back if that was it or not. Intermittents the fun ones!!! Thank you for the drawings -----------------------OMguy

[OMguy]

Hi to all, I ran the amp for 4 hours and no noise!!! While I was testing it I took some images of my board. The big cap hanging off the solder side was the cap I subbed for testing.

[soundguruman]

It's usually the solder connections, most frequently on the controls, that fail.
unsolder the controls...
Carefully clean the lugs of the controls, because they were oxidized when they were "soldered" onto the board.
Then solder them back in.
The failure of the factory to use clean components, resulted in cold connections, and solder joint failures.
Test all the tone controls, volume controls, they may not work... this is a sign that the connections are bad.

[ceebee]

Life Saver......thanks Bill

These are all I have (pretty poor quality on the schematic)

I have searched far and wide for the A30 schem-layouts for more than four months. The 1982 version in the shop matched dead on with your attachments. A BIG Thank You!!!!!

Anyone with words of wisdom on chasing a reverb squeal, always there and gets louder only if the verb is "turned up" Bad cap or connections? Thanks again......

[ceebee]

Sorry MARK.... I called you Bill...

[soundguruman]

I have searched far and wide for the A30 schem-layouts for more than four months. The 1982 version in the shop matched dead on with your attachments. A BIG Thank You!!!!!

Anyone with words of wisdom on chasing a reverb squeal, always there and gets louder only if the verb is "turned up" Bad cap or connections? Thanks again......

Reverb is hooked up backwards?
There is a broken wire in the reverb tank? A bad coil.
The controls inside the chassis have broken solder connections, re-solder board. Especially where controls and jacks are soldered in.
The legs of the controls were too dirty to solder in. Cold connections resulted. Remove the controls, clean the legs, solder back in.
the control is cracked?
send return jack is dirty or has patch-cord inserted. Gain knob for effects loop is turned too high.
When send is connected to return w/ a patch cord, it adds a gain stage. The gain can be too high and cause squealing.

[ceebee]

Dirty legs.... hehehe.... and that was the problem..... thanks.