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Messages - syndromet

Hi, guys.

It's been a few years since my last visit, and I'm happy to see the forum thriving.

A few weeks ago I was lucky enough to catch a guy in the act of throwing a pristine looking 1981 Roland Jazz Chorus 50 in the dumpster. I managed to stop him, and brought the amp home with me. However, not all is well inside this thing. The JC-series is known for their clean sound. This one will break into some nasty sounding distortion, even when playing soft with weak single coils. If I turn the guitar volume down to almost zero it does not distort, so it does react to dynamics. Also, the chorus effect and the reverb is not working. The Vibrato works as it should. Plucking the springs in the reverb pan comes thru loud and clear. All other controls seem to do what they are supposed to to.

The amp uses the same circuit as described in the second half of the service manual found here :

Here is a little video of the amp, showing the distorted sound.

There is no sign of bad solder joints, burnt components or bulging caps. I will recap this thing, but I want it up and running first. I don't think the problems are caused by gone electrolytic caps.
As far as I can see from the schematic, there is no logic in that both the reverb and chorus not working. Can anybody take a look at the schematic and help me with where I should start troubleshooting?
Hi guys, long time no see!

I've been playing around with tube stuff for the last few years, but I figured it was time to have some fun with SS again. I'm planning a pedal sized amp based on the TPA3116 driven by a MI Crunchbox. I'm using one of these boards for the power amp:

When I hook the pedal straight into the power amp board I get sound, and it's nice and loud. I can hear the potensial, but the sound gets way to bassy. The crunchbox is usually a pretty trbley pedal, but when hooked up to the TPA3116 I need to turn the tone controll all the way up, and I still feel I miss a little too much treble.

The pedal has an output impedance at around 1 Kohm, and the amp board has an input imedance of 10 Kohm. Ofcource, the pedal is made to see impedances a lot higher than this, and I suspect that is why I get a lot of treble loss. What is the best way to fix this? I can't change the input impedance on the power amp without affecting the gain of the amplifier, right? And since the output of the pedal is 1 Kohm, I don't really see how a buffer can make things better?

Any Ideas to how I can make this combo work? I can already hear that it has a lot of potential..
The honeymoon is over, and I still love this little amp. It compliments my Hiwatt clone wonderfully, and records really, really well. She's definitively a keeper! Thanks for all the help along the way, guys!
So many cool guitars! Great looking amp too...
Amplifier Discussion / Re: I think I want a Pignose.
December 07, 2012, 08:04:38 AM
Quote from: Enzo on December 05, 2012, 07:08:41 PM
The transformer after the preamp is not there just to isolate the stages.  Look again.  The output stage is push pull, the format very similar to a tube power stage.  The transformer acts as a phase inverter or splitter.

Could this be the reason why these amps sound somewhat tube-like? I don't think I've seen this configuration with transformers in bigger SS amps? Why not?
Amplifier Discussion / Re: I think I want a Pignose.
December 07, 2012, 08:03:16 AM
Lots of great info here, guys!  :dbtu:
I noticed that the amp is actually very similar to Brian Mays Deacy-amp, which in my opinion is one of the coolest sounding rock amps ever. I think I'm shifting my focus from the Pignose to a Deacy, for this build, and then maybe build a Pignose later. I also have a speaker somewhere that looks a lot like the original Deacy, and if memory serves me right, it has a 6,5" dual core speaker like the original.

Thanks for the link to those transformers. Looks like the right stuff for a deacy-build. I don't mind if I reduce the wattage, as I'm looking for an amp that will record great at low volumes.

I see that the Deacy use one AC125, one AC126 and two AC128 for transistors. I have a bunch og russian GT308's. Would it be any problem replacing the 125 and the 128s with these? I don't know the spec of the AC126, but from the schematic I'm thinking this transistor have a lot more gain than AC125 and AC128, so I'll probably just buy an AC128 for this position.
Amplifier Discussion / I think I want a Pignose.
December 04, 2012, 02:32:21 PM
Hi, guys! It's been a while since last I contributed with anything here, as I've been busy getting kids, building a house, building a career and playing with tubes. I finally have some spare time again, so my interest in building guitar related gadgets have come back. I'm currently building a Hiwatt DR504, fixing an Ampeg SVT 6 pro and producing a small run of guitar pedals for sale.  :dbtu:

After seeing this video, I think I'm falling in love with the pignose 7-100, and I'd love to build a high quality version of this wonderful amp. I see the amp already have been discussed on this forum a few times before, but I can't find any info on the transformers used in it. I was wondering if any of you guys who actually understand this kind of stuff knew what impedances the transformers are? If not, I'm hoping some of the experts here can make an educated guess.

I'm guessing the transformer between the preamp and the power section is has a 1:1 ratio, and that it's function is purely to isolate the two stages from each other. When it comes to the transformer on the output section, I  guess it's there to match the impedance to the speaker load. What would be the primary impedance on something like this? Is there anyway to calculate this stuff?

Pignose video:


It's good to be back.
Thanks in advance!
Amplifier Discussion / Re: Can anyone identify this Amp?
December 04, 2012, 02:10:28 PM
I would really, really love to get my hands on that speaker! I think this amp is worth buying just for the speaker.
The Newcomer's Forum / Re: books on amp building
March 05, 2009, 01:46:45 PM
Teemu, I don't see your book in that list?!? To me that is the most important book on guitar solid state amps. Learned a LOT from reading it. I'm actually reading it for the second time now.

Thank you for the list above, and thank you for your book. You should recieve some kind of medal...

Updated, if someone cares.  ;)
Thats just sick! Looks like a complicated build. Gut shots, please?
Preamps and Effects / Re: Pictures
February 26, 2009, 06:57:02 AM

You're welcome. And you should deffinitivly listen to J M Fahey. That schem looked great and easy enough to build.
Amplifier Discussion / Re: Pics of my last build
February 24, 2009, 08:09:12 AM
That looks wonderful. :tu: