Show posts

This section allows you to view all posts made by this member. Note that you can only see posts made in areas you currently have access to.

Show posts Menu

Topics - 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..
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!
Tubes and Hybrids / First tube amp.
December 03, 2008, 03:13:06 AM
Not exactly a hybrid, but I like to show off.  ;) Here is my first venture into high-voltage tube stuff. High Octane from AX84.

Pretty happy with the externals. Got to find some miniature chickenheads, though.

Messy, as always.....
The Newcomer's Forum / Reposting my encyclopedalia
February 27, 2008, 06:20:06 AM
I have had quite a few requests for this lately, so I thought I should repost it her. Quite a usefull tool for beginners and transistor swappers....
It is still a work in progress, and any tips on other stuff to be in here is welcome. I'm working on transelating the mm drill sizes to inches for you weird Americans.
Admins, feel free to add a link to the FAQ if you feel like it.
Amplifier Discussion / Good source for transformers?
September 12, 2007, 05:06:12 AM
I'm looking for a 2x24V secondary, 230V Pirmary transformer with a rating of 300VA, and I can't seem to find anyone else than who will ship internationaly. On elfa, the trafo costs around 100$ without shipping, wich I find a little to expensive. Anyone know of a good source for cheap trafos? I used the last time, and they were great, but I don't think they have what I'm looking for this time. The trafo will be used for a AMP5.
Amplifier Discussion / Using car HiFi amps
June 18, 2007, 10:00:05 AM
Would it be possible to use something like this with guitar?

Distortion:                            <0,08 % THD at 2ohm
                                          <0,1 % THD at 4ohm
Frequenzies                           20 Hz -20kHz +/-0,5dB
Dampening                            >95dB
bass boost                            +8dB, centered around 45hZ
Input impedance                     20kOhm
Input sensitivity                      150mV - 8V
Output impedance                   Stereo: 2-8 ohm
                                           Bridged: 4-8 ohm
Dc input                                10-16 V

RMS                                     2 x 50W at 4 ohm and 14,4 V
                                           2 x 75W at 2 ohm and 14,4 V
                                           150W bridged at 4 ohm
Max power                             200w bridged at 4 ohm
Fuse                                     20A

Protected aginst shorts, to high dc and overheating.

Looks like a typical poweramp to me, and the chassis is made of tinned aluminium. Would it be suiteable with guitar ,bridged for mono and high power with the right preamp?
I have sent my girlfriend and daughter home to my mother in law for about a week, wich has given me time to finnish of my stereo LM 1875 amp. I'we done all the offboard wiring now, and everything should be ok. I'we added a volume pot at the input, and it works ok when it comes to control volume. However, when I turn it down, my chips start to clip, like it does when it's getting to hot. Sort of like a hard tremolo. when playing above half the volume, I don't have this problem, and I don't have it when I use the volume controll on my Behringer gdi21, wich I use as a preamp.

The amp sound fantastic, anyway, but it would be great to be able to controll the volume, as it is plenty loud. Could it be low freequenzy oscilaion? Ground loops?

Some pics, just for fun. The pics are taken with a cell phone-camera, so this hing looks a lot better in real life.

Gutshot. Wiring looks messy here, but is in fact pretty neat.

Another gut shot

The fan and led controlling circuit

The volume pot in question

The input and outputs

Power switch, fan and led

Amplifier Discussion / Drill sizes
May 09, 2007, 09:38:28 AM
Might be usefull here too....
Drill sizes for common components, like leds, pots etc....
I lost one of those little plastic isolators that you use to isolate the chip from the chassis when you mount it, and I don't have anyone in spear. Is there anything else that can be used? Anyone have any good ideas?
Schematics and Layouts / TDA2005 amp
March 16, 2007, 03:55:39 AM

A little down on this page you'll find schematic and layout for a TDA2005 amp.
Look on the middle of the page for where it says :

"Een warme avond verder:
Schema in pdf
Layout in pdf
Componentenopstelling in pdf
Schema/layout voor Ulticap/Ultiboard in zip"
Just to be absoloutly sure, I wanna check with you guys (once again...) that I'm ordering the right transformator for my stereo LM1875 kit. Don't want to buy a trafo for $100, and find it's not suiteable for the job.

This is what I'm looking at:
Would this be good for my purpose?

Looking at the prices, I see that transformersare way cheaper over at parts express than here in Norway. Unfortunatly they wanted to charge me $79 for shipping it via USP Express. That got me thinking about ordering it to one of you guys, and having you to ship it with USPS to me for way cheaper. If anyone feel like helping me out with this, please let me know.
Amplifier Discussion / Has anyone seen this?
February 05, 2007, 12:28:11 PM
Amplifier Discussion / Class T-amps
January 04, 2007, 08:37:51 AM
Have any of you guys tried a class-t amp for guitar. I got my SI T-amp from think geek today, and it gets great rewievs from the hifi-people. it cost 29$, wich is next to nothing. The circuit seems super simple, it recuires 12 v dc, and the chip don't need heatsinking. It is based on a Tripat 2024, wich is awaileable from PartExpress. Anyone tried one of theese with guitar? Looks like an easy buid, or an easy rehouse if you buy the SI version.
Amplifier Discussion / RobertT.....
November 28, 2006, 06:15:21 AM
Seems like Harrison Ford from diystompboxes has found this forum too. I say one of you admins ban RobertT emediatly.
Amplifier Discussion / Pictures
November 19, 2006, 09:52:46 AM
We need a picture-thread for the amps, too! Post your DIY-amps here!!
My little gem:

My stereo ruby:
Amplifier Discussion / The nelson 6W miracle (?)
October 03, 2006, 03:32:16 PM
I decided to do a little soldering again, and had a shot at this one:

I etched the pcb, wired it up, and no  sound at all. Only thing that happens is that the chip gets hot. Realy hot!! So I checked the pcb for shorts, checked the orientation of caps and chip and checked the PS. Same problem, so I checked it all again. I guess I have checked everything a thousand times now, and I still get nothing.

I was therefor wondering if anyone have built this, and if it worked. I've checked it against the datasheet, and it seems to be ok. Any idea what I can have done wrong?
I don't think I'we gotten the part about grounding or the way to wire up a center taped transformer right. Since English is not my main language, I have a little trouble understanding how to propperly ground the Pcbs and transformer. I therefor drew up a quick schem of how I think the offboard wiring should be done, and would love if anyone would care to comment any mistakes. I was also wondering if it is important to have insulated jacks? I forgot to add a fuse on the drawing, by the way.

In the Manual for the Lm1875 amp, it says thet Chassis-ground(CHG) should be connected to a point on the chassis.  I can't, however, find a hole named chg on my pcb's. Any help is appriciated.

Quick drawing of how I think it should be done:
My guess on the offboard wiring
Amplifier Discussion / Volume controls!
August 20, 2006, 05:27:13 PM
I have seen other places that people use atenuators as volumecontrols on the Gainclones. Is it possible to use a standard pot before the amp, like used on gain-controls on stompboxes? If so, what value should the pot be?
Schematics and Layouts / Joe Davisson's new Guitar amp
August 10, 2006, 02:25:45 AM
Joe just posted this over at
if it's anything like his other circuits, it's deffinitly worth checking out!