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September 23, 2021, 10:53:37 AM

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1
The Newcomer's Forum / Re: Orange Crush 12L (No Sound)
« Last post by flester on Today at 07:41:14 AM »
I had this model and got a tech to successfully repair it by changing the Opamp. If you have the skills it might be worth replacing it, using a socket so that it would be easier to repair again.

But then some pots and PCB traces failed and I made it worse while trying to fix it. I decided to gut it and made it into a hybrid head, plus a handy, bright orange,  1x6" cab for other projects. The power supply section is still useable, I think.

A pity in a way because it is probably one of the better small amps in that price range.
2
Amplifier Discussion / I would like to build an audio signal detector
« Last post by yeto on Today at 06:50:08 AM »
I am new at this but I want to build a 9V guitar amp. Would the following device work for tracing my progress as I build the amp so I don't have to plug in a guitar every time I want to input a signal to check progress and if this device will work can someone show me how I would wire it up and use?

https://www.aliexpress.com/item/33050874674.html?spm=a2g0o.productlist.0.0.78fa7326adjujo&algo_pvid=3f9a222e-9837-46ee-af4d-d25ef3e4aac7&algo_exp_id=3f9a222e-9837-46ee-af4d-d25ef3e4aac7-1&pdp_ext_f=%7B%22sku_id%22%3A%2267382343472%22%7D

Thank you in advance for any help,
yeto
3
The Newcomer's Forum / Re: Orange Crush 12L (No Sound)
« Last post by Mark N on Today at 01:55:14 AM »
Thanks for giving it a look, Willpirkle. Unfortunately, the 20L schematic is a whole different design. I did try to look for a schematic, but I don't believe anyone traced it. There aren't any diodes near the input. Audio signal goes through a capacitor, then resistor to ground before going into pin 5 of the IC chip. Pin 3 appears to just go to ground.

I didn't know over-voltage protection was a thing, but now I do. So that was helpful.
4
The Newcomer's Forum / Re: Orange Crush 12L (No Sound)
« Last post by willpirkle on September 22, 2021, 07:01:02 PM »
Yep, pin 7 is an output, and should be ~0VDC so that IC is definitely toasted (yes, same pin out as the TL072). You could socket it, if you’d like to experiment with other op-amps, or make changing it simple in the future if it fails again. I couldn’t find the schematic for the 12L, but I did find the 20L which includes over-voltage protection diodes on the input. Assuming those are also there on the 12L (2 diodes connected to pin 3), then changing the op-amp should do the trick. But Enzo may have something else to check - he’s a super-boss around here!
5
The Newcomer's Forum / Orange Crush 12L (No Sound)
« Last post by Mark N on September 21, 2021, 11:21:22 PM »
I have an Orange Crush 12L practice amp that suddenly stopped working around the same time my Danelectro Nifty Fifty (which I made another thread about) started malfunctioning. I get no sound through speaker or headphone jack.

This one has a 4558 as IC1 so I reused the trouble shooting from the Danelectro Amp (which uses an TL072, but I believe they have the same pin out) Using Enzo's helpful advice from the other thread I tested the DC Voltage on the pins and got

Pin 1: 0
Pin 4: -14
Pin 7: 13
Pin 8: 13

So I assume this IC has gone bad, correct? My understanding is that Pin 7 should read around zero. I tested the sound using an audio probe as well, I was able to trace sound from the input jack to a capacitor but then the signal goes to IC1. Testing the other leg of the capacitor I got no sound. I pulled the capacitor and was able to run a signal through it fine.

I plan on ordering another 4558 IC chip, but is there anything else I should be checking?
6
The Newcomer's Forum / Re: Basic testing of non-functional equipment w/multimeter?
« Last post by SwamiRob on September 20, 2021, 03:45:28 AM »
Thanks for the help! It's been so long since I've really used one that I forgot that they can be used with an active circuit (of non-lethal power ratings that also won't destroy the thing obviously haha). The supply was dead so got a new one, simple enough. All the wiring & fuse seemed fine, so I can only assume that the actual transformer had died maybe? Way above my level of understanding to mess with that anyway.
7
Amplifier Discussion / Re: Roland Jazz Chorus 50 troubleshooting
« Last post by Enzo on September 17, 2021, 11:01:46 PM »
And without looking at a schematic, I'd ask:  are the power supplies right?  I expect the op amps run on a pair of 15v supplies or similar.  f they are lopsided or have poor filtration, you can get distortion.   And certainly FX circuits need quality power.  Within a channel, I will take the mere moments it requires to go down the ICs and check their output pins for unwanted DC offset.  it is possible your signal runs into that DC offset and clips extra early.  Like that.
8
Amplifier Discussion / Re: Roland Jazz Chorus 50 troubleshooting
« Last post by joecool85 on September 17, 2021, 09:00:25 PM »
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 : https://www.synthxl.com/wp-content/uploads/2020/01/Roland-JC-50-SERVICE-NOTES-2nd.pdf

Here is a little video of the amp, showing the distorted sound.
https://photos.app.goo.gl/zvWB812VUS7bAtHz6

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?

Any update on this amp?  Curious if you got it sorted.

Also, welcome back!
9
The Newcomer's Forum / Re: Hello
« Last post by joecool85 on September 17, 2021, 08:58:03 PM »
Welcome aboard!  I'd love to see pictures or video of some of your past projects!
10
Amplifier Discussion / Re: Fender London Reverb
« Last post by GOR3 on September 17, 2021, 02:32:15 PM »
Yes and no.  By which I mean, that is the fault that caused me to open up the amp, but it's not the reason for my post.  The reason for my post was to see if the low supply voltages were "normal."  That is, were the voltages I measured the same as others who had had this amp on the bench.  I'm confident (perhaps foolishly) that I can remedy the intermittent channel.
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