Hi all,
I'm pretty new to working on amps and on this forum.
I acquired a "DragenAudio" GA45-R with Spring reverb that sounds quite nice for next to nothing...
Only thing is: It has a hum that I don't understand:
- It's only in the clean channel and completely (!) disappears in Gain channel
- It's independant of any volume control
- It's independant of a guitar plugged in (tried multiple cables and guitars that work well on my other amp.
Any ideas where to start the search would be appreciated...
Jake
I'm pretty new to working on amps and on this forum.
I acquired a "DragenAudio" GA45-R with Spring reverb that sounds quite nice for next to nothing...
Only thing is: It has a hum that I don't understand:
- It's only in the clean channel and completely (!) disappears in Gain channel
- It's independant of any volume control
- It's independant of a guitar plugged in (tried multiple cables and guitars that work well on my other amp.
Any ideas where to start the search would be appreciated...
Jake
Google found nothing relevant when I searched for "Dragen", "Dragen Audio", "Dragon Audio", and several variations on "Dragen" plus "GA 45".
I'd suggest that a good starting point is to post a photo or two, so that we can at least see what you're dealing with. Right now, we have no clue at all. Is it solid state? Valve? New production from China? Vintage equipment from somebody's attic? Tiny little toy amp? Big old classic valve amp? I have no idea.
The next thing to try to locate is a schematic diagram (aka circuit diagram.) If this is a small obscure brand, this may prove to be very difficult or impossible.
If you cannot find a circuit diagram, a distant second-best is a set of detailed photos of the internals. If there are circuit boards, try to get clear photos which show all the components (including IC part numbers if solid-state.) Perhaps someone will recognize the general design of the amp, and that might yield some clues as to how to proceed.
Good luck!
-Gnobuddy
Hi Gnobuddy,
you are right, and that's my problem, too. There is literally nothing to be found on the internet.
Nevertheless:
- it's a solid state amp
- I'll add pictures the next time I'm in my workshop (assuming you mean pictures from the inside...)
- It is rather new, but/and made in China (so no vintage equipment)
- It's a 1x12 Combo:
Jake
you are right, and that's my problem, too. There is literally nothing to be found on the internet.
Nevertheless:
- it's a solid state amp
- I'll add pictures the next time I'm in my workshop (assuming you mean pictures from the inside...)
- It is rather new, but/and made in China (so no vintage equipment)
- It's a 1x12 Combo:
Jake
Thanks for posting the external pic!
Yes, I did mean pictures of the inside. It's a long shot - but there is a tiny chance that the pictures will show something (like bad wiring) that might cause your hum. Or somebody might recognize the circuit boards - perhaps they are used in similar amps carrying more recognizable brand names - and the circuit diagram for that other brand might be known.
As I said, it's a long shot!
-Gnobuddy
Cute little amp. I dug around and found the completed ebay listing for this unit:
Gitarren Verstarker - Dragon Audio - GA 45 R -mit eingeb.Lautsprecher- zum 2.Mal | eBay
The closeup photo of the controls shown in the listing reminds me of a old Peavey Rage but with a reverb knob added. It would not surprise me if you opened this up and found a 4558 opamp pair in the preamp driving an ST TDA2040 power amplifier loaded with a 3 or 4 ohm speaker.
Stph
Gitarren Verstarker - Dragon Audio - GA 45 R -mit eingeb.Lautsprecher- zum 2.Mal | eBay
The closeup photo of the controls shown in the listing reminds me of a old Peavey Rage but with a reverb knob added. It would not surprise me if you opened this up and found a 4558 opamp pair in the preamp driving an ST TDA2040 power amplifier loaded with a 3 or 4 ohm speaker.
Stph
There are several photos, and they are much bigger than the one the OP posted (mouse over to zoom in.)
I found contact details for the manufacturer (or maybe only the reverb tank manufacturer?) on one of the images - phone numbers and an email address (see attached image). I would suggest following up on these, see if you can get a schematic or any other useful information.
Stephen Keller's input is very interesting too. Nice detective work!
-Gnobuddy
Attachments
Judging from the description about the hum in the clean channel, I'm guessing it is the very amp that JakeBlues "acquired ... for next to nothing."
Could be a cold solder joint or broken connection somewhere in a "ground" or "shield" circuit. If the volume controls have no effect on the hum level; this tells you the problem is likely after the first pre-amplifier stages. Instrument amps get dropped and banged around all the time; get a good light source and magnifying glass and look over the copper side of the circuit board very closely for loose or broken joints and connections. Look over the component side closely as well for loose wires, especially shielded cables and connectors. If you have connector, switch, potentiometer, etc. corrosion; Caig De-Oxit works great; it is expensive but worth every penny.
Apparently this amp is also sold under the Yiwei brand name. I doubt contacting any of the folks will yield a schematic, but figured I'd pass along what I found:
China Guitar Amplifier (GA-45R) - China Guitar Amplifier, Bass Amplifier
YueSen Musical Instrument Factory China --Products
Quality GUITAR AMPLIFIERS GA-45R of 34731702
It is also available under the brand name "E-WAVE." It is possible various forum searches might turn up something more.
Stph
China Guitar Amplifier (GA-45R) - China Guitar Amplifier, Bass Amplifier
YueSen Musical Instrument Factory China --Products
Quality GUITAR AMPLIFIERS GA-45R of 34731702
It is also available under the brand name "E-WAVE." It is possible various forum searches might turn up something more.
Stph
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I notice some of the electrolytic capacitors are lying almost on their sides, instead of standing vertical.
They may simply have been installed like this at the factory, in which case there should be no problem.
But if they were installed vertically and later pushed over by some clumsy person working inside the amp, there is a chance that one of the wire leads underneath the capacitor broke. Depending on the function of that capacitor in the circuit, this could cause hum (if it is a filter cap that normally removes hum from the power supply lines.)
So there's a small chance that your mysterious clean-channel hum is caused by one of these capacitors having been damaged by mis-handling.
I suggest carefully looking at the leads under each of the capacitors that is bent heavily to one side. Don't move the capacitor unless you have to, as you don't want to break leads yourself! Just check and verify that there are two unbroken wires running from each capacitor into the little holes in the PCB.
-Gnobuddy
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