Hi, since this forum offered such great advice on my last project I am turning to you again in hope for some help.
I had this amp for a year now and I am rather satisfied with it.
Joyo AC-40 - Google Photos
There is only one problem: A permanent background hiss as soon as I turn it on at around 30db (background at 20db). I usually play this amp at volume 2, so its no biggy. But I would like to understand and fix if possible.
IF I turn up the volume of the MIC channel, the hiss increases a bit (about 7db at max volume). That seems to be expected.
But hear comes the funny thing and that I REALLY would like to get rid of.
IF I turn up the guitar volume at 5 a zing (or beep) is added that changes frequency as I go further. It peeks (frequency and volume wise) at 7 at 42db and is gone back to the "normal" background noise at 9. It sounds a bit like tuning an old radio.
I tried to record it with my phone. CAREFUL LOUD!
Any help on diagnosing/fixing this is greatly appreciated!
I am sufficient with a soldering iron and a multimeter, if that is of any help.
I had this amp for a year now and I am rather satisfied with it.
Joyo AC-40 - Google Photos
There is only one problem: A permanent background hiss as soon as I turn it on at around 30db (background at 20db). I usually play this amp at volume 2, so its no biggy. But I would like to understand and fix if possible.
IF I turn up the volume of the MIC channel, the hiss increases a bit (about 7db at max volume). That seems to be expected.
But hear comes the funny thing and that I REALLY would like to get rid of.
IF I turn up the guitar volume at 5 a zing (or beep) is added that changes frequency as I go further. It peeks (frequency and volume wise) at 7 at 42db and is gone back to the "normal" background noise at 9. It sounds a bit like tuning an old radio.
I tried to record it with my phone. CAREFUL LOUD!
Any help on diagnosing/fixing this is greatly appreciated!
I am sufficient with a soldering iron and a multimeter, if that is of any help.
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> IF I turn up the guitar volume at 5 a zing (or beep) is added that changes frequency as I go further.
It is oscillating. Have you made ANY changes inside?
It is oscillating. Have you made ANY changes inside?
No, it did this from the start.
I mean yes I have made changes (changed the battery, added a power output). But the symptoms were there before.
Still, I could disconnect all that stuff and power it externally if that would help.
I mean yes I have made changes (changed the battery, added a power output). But the symptoms were there before.
Still, I could disconnect all that stuff and power it externally if that would help.
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Googled for some user reviews. On the site of Thomann/Uk you find exact the same complaints from 2 customer reviews. This al cheapo with its heavy SLA looks like a poor design to me.
The hiss is noted on the Australian distributor site and claimed to be "normal".
BUT I see in your pictures a massive power converter, and I doubt it is Joyo stock. Or silent in the audio band. It is normal for a volume control to be most sensitive to electric waves in the air around half volume, which fits your "volume at 5 a zing ...changes frequency ... back to the "normal" background noise at 9".
BUT I see in your pictures a massive power converter, and I doubt it is Joyo stock. Or silent in the audio band. It is normal for a volume control to be most sensitive to electric waves in the air around half volume, which fits your "volume at 5 a zing ...changes frequency ... back to the "normal" background noise at 9".
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@bucks bunny & PRR: You are right. It is all true.
The Joyo is not the best design there is, one of the reviews at Thomann is from me. ;-) I can accept the background hiss, it is actually quieter than my laptops fan in my studio. I just want to get rid of the high pitch zing, if at all possible.
Yes, there is a power converter in the amp converting 12V to 9V for pedals. It is mounted on the power side of the amp as far away from anything as possible. But it is not powered when this happens and even if it is that does not change the symptoms experienced.
I have disconnected the mods from the board and powered it directly via the original battery and the new LiFePo4 battery (at the 12V IN terminal of the amp) and with the power supply (at the 15V IN terminal of the amp) alternatively. The symptoms stay the same.
If I cannot fix it, I would like to understand it. So, the original power section of the amp might be at fault here?
The Joyo is not the best design there is, one of the reviews at Thomann is from me. ;-) I can accept the background hiss, it is actually quieter than my laptops fan in my studio. I just want to get rid of the high pitch zing, if at all possible.
Yes, there is a power converter in the amp converting 12V to 9V for pedals. It is mounted on the power side of the amp as far away from anything as possible. But it is not powered when this happens and even if it is that does not change the symptoms experienced.
I have disconnected the mods from the board and powered it directly via the original battery and the new LiFePo4 battery (at the 12V IN terminal of the amp) and with the power supply (at the 15V IN terminal of the amp) alternatively. The symptoms stay the same.
If I cannot fix it, I would like to understand it. So, the original power section of the amp might be at fault here?
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There is no "fault".
It's just a poorly designed, and as mentioned before, "cheapo" amp.
You get what you pay for.
OK, let's call it that. Poor design. And yes, its a cheap amp for sure.
How would I avoid it if designing an amp? It seems to be a well known issue if i judge PRRs post correctly.
How would I avoid it if designing an amp? It seems to be a well known issue if i judge PRRs post correctly.
After a bit more testing I found out that the TREBLE control is introducing the oscillation. It starts just before 5 and is gone at 6,5. So very specifc value. The VOLUME control does just amplify that.
I can live with that or work around it. Thx to PRR for pointing me in the right direction (again).
I can live with that or work around it. Thx to PRR for pointing me in the right direction (again).
