Easy electronics trouble on a 78 Super-Axe

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Easy electronics trouble on a 78 Super-Axe

Postby denis » Mon Oct 20, 2014 1:44 pm

Hello,

After helping me saving my "fleur de lys", i now have another challenge for you :
I also have a trouble on my 1978 Super-Axe : the guitar sounds very dark and bassy, whatever i do, and the tone pot seems to have very few effect.
Appart from that, everything works, including the phaser and the compressor, but it makes it almost unplayable.

Does anybody knows where i could fin a schematics for the wiring ? Or knows where i should look at ?

Thansk once again for the help !

Regards,

DENIS (France)
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Re: Easy electronics trouble on a 78 Super-Axe

Postby RPVogh3 » Tue Oct 21, 2014 3:51 am

Here are some Super Axe pictures and schematics I have collected in past years. Unfortunately, some are such low resolution that they have to be interpreted with a bit of imagination.

I have not had a Super Axe guitar, so I'm guessing at what some of this is.

The controls:
Separate from the control panel there is a single pickup switch. No pickup volume controls.
Image

Controls in the control panel:
Image

The modules. Control panel and two black box modules.
The larger black box module seems to be the phaser, the smaller black box module seems to be the compressor.
Image

Control panel sketch:
Image

Inside the phaser module:
Image

Schematic including pickups and pickup switch (or switches)
It seems to show some complex switching of the pickups, perhaps phase reversal switching.
Most of that witching seems not to be present in the single pickup switch models.
The schematic is hard to read. It says FRONT PICKUP and BACK PICKUP at the left side.
Image

Schematic omitting the pickups:
Image

Schematic of phaser:
Image

Schematic of compressor:
Image


As to what is making the tone very dark and bassy, I'm not sure. Here are a few things to try.

It appears the two modules have plugs on them. If so, Unplug one at a time, carefully. Suggest the compressor first. The pickups go to the compressor all the time, even when the compressor switch is set to off. and it something in it is loading down the tone, then unplugging that module may let the rest work. Perhaps its input section has a problem and is letting its input capacitor act as a tone capacitor loading down the treble. If there are no plugs on the modules, then you may have to disconnect the wire to the input of the compressor module.

The tone control is near the output. The tone control pot has three terminals. Two are connected together. If somehow the third terminal of the tone control pot has become shorted (connected) to the other two terminals, or to ground, then it will be like the tone control is turned for minimum treble all the time.

If none of that works, you may need to disconnect the wire from the pickup switch where it goes into the control panel, and temporarily connect it straight to an amplifier, bypassing all the electronics in the Super Axe. That will give a test of whether the problem is in the pickups (if the tone is still dark and bassy) or in the Super Axe electronics.

...Richard
Last edited by RPVogh3 on Tue Oct 21, 2014 9:30 pm, edited 1 time in total.
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Re: Easy electronics trouble on a 78 Super-Axe

Postby Norm » Tue Oct 21, 2014 7:53 pm

This is all I can find

Gretsch Guitars
17600 N. Perimeter Drive, Suite 100
Scottsdale, AZ 85255
Phone: 480-596-9690
Email: consumerrelations@gretschguitars.com

Let us know if contacting them this way works or not and maybe we can suggest something else...
...that's how it looks to me...The opinion expressed above is my own and does not necessarily reflect the views of this station. Your mileage may vary...

Audio samples: http://www.youtube.com/user/acountrygent/videos
That should do it.
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Re: Easy electronics trouble on a 78 Super-Axe

Postby denis » Wed Oct 22, 2014 3:22 am

Hello,

Thanks for the help.

I found a part of the solution. First, looking at the schematics, i realized that the "blend" pot of the phaser has an effect on the sound, even when it's off. On my guitar, i almost always let it on 10, i just put the phaser on or off with the switch.
Phaser switch off, i turned down this pot and indeed i gain a lot of dynamics !
I also noticed that i've got a residual resistance on the tone and volume pot, even when there are on 10. i cleaned them with lubrificant and not only they turn now way easier but i gained even more dynamics.
It's still a bit dark on the neck pickup but it's quite normal on the bridge one. I don't think the guitar has a problem anymore, i begin to think that i just don't like the sound of these pickups... And i find them very microphonic.
I'm now thinking about replacing them with Classic 57 ones...

Regards,

DENIS
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Re: Easy electronics trouble on a 78 Super-Axe

Postby David Elliott » Wed Oct 22, 2014 10:31 am

This site may be of some help:

http://www.tdl-tech.com/superaxe.htm

David
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Re: Easy electronics trouble on a 78 Super-Axe

Postby David Elliott » Wed Oct 22, 2014 10:41 am

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Re: Easy electronics trouble on a 78 Super-Axe

Postby denis » Thu Oct 23, 2014 12:18 pm

Thanks David and Richard.
That is a lot of help.
In fact, i already did everything you suggest, Richard.
Unplugging both modules, i still have a bassy sound.
I'm now thinking about connecting the pickups directly to an amplifier but the pickup switch can't be reached without unmounting the pickups.
That will be some hard work, i guess... but i'll do it.

Like i said in another post, i just wonder if it doesn't comme from the pickups themselves. Maybe i just don't like the way they sound... And they also are very microphonic.
I've got a replacement pair of Seymour Duncan, i think i'm going to try to put them on the guitar, just to know if the problem comes from the pickups or from the electronics.
If it comes from the pickups, i'll consider replacing them with a pair of Gibson Classic 57.
This guitar deserves to sound better than it does for the moment.

DENIS
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Re: Easy electronics trouble on a 78 Super-Axe

Postby RPVogh3 » Fri Oct 24, 2014 2:37 pm

Denis...

I think you can leave the pickups mounted and not have to get directly to the pickup switch, in order to test only the pickups. Looks to me like you can remove the control panel and connect to the signal from the pickup switch (and thus to either or both pickups) at the control panel.

I think you don't need to reach the pickup switch in order to test just the pickups connected to an amplifier.

The signal from the pickup switch goes (per the schematic) to both the compressor module and to the compressor switch, probably the contact of that switch closest to the center of the control panel.

You probably don't even need to disconnect the pickup switch wire from the control panel, though you could do that. TRY THIS FIRST: To disconnect the pickups and the pickup switch from all else, without cutting a wire or un-soldering anything, set the compressor switch to ON and unplug the compressor module. Now the pickups go nowhere into the Super Axe electronics.

You should be able to amplify only the pickups without disconnecting anything, and by only removing the control panel and letting it dangle by the wires. You might need a couple of short clip leads to make the connection from the Super Axe control panel to a guitar cord going to your amp.

...Richard
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Re: Easy electronics trouble on a 78 Super-Axe

Postby denis » Sat Oct 25, 2014 4:10 am

Thanks for the help !
RPVogh3 wrote:To disconnect the pickups and the pickup switch from all else, without cutting a wire or un-soldering anything, set the compressor switch to ON and unplug the compressor module.

Sorry but i don't understand this part. How can i disconnect the pickup switch without cutting or unsoldering a wire ?
The wire that comes from the pickup switch is directly soldered to the circuit board il the control panel (where everything else, including the pots) are soldered too.

DENIS
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Re: Easy electronics trouble on a 78 Super-Axe

Postby denis » Sat Oct 25, 2014 7:30 am

YES !!!
Solved !
I spent 5 more hour on it but it was worth it ! First il did connect the pickup switch directly to the a jack and to an amp and the sound was great ! The pickup are not the responsibles...

I also noticed that the output impedance of the pickups were 8.5K, but at the output jack, i had only 4.2K left.
I followed the track with an ohmeter and found a trouble near the compressor trimpot. Just after it, the impedance was divided by 2. I turned it and found that it was modifying the output impedance ! At 10, i had 8.5K at the ouput, compressor off and compressor module unplugged, and a normal sound (not dark) !

Then i noticed that the input of the the compressor trimpot was soldered on 2 of the 3 posts of the compressor switch (left and center). Looking on the schematics, it shouldn't. i Unsoldered it and resoldered it only on the left post.and.... VIctory ! The guitar sound great, no more bassy sound !

I fact i noticed a bit of wire left on the switch after a previous fix. The wire should have broke sometime and someone resoldered if at the wrong place. So the compressor trimpot was always in the circuitry, even compressor off, and was sucking the tone.

Thanks for the help !
Here is my second guitar saved this week, with a great help from you !

DENIS
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