Vox Escort Mains/Battery Powered Amp Humming help.

[Steve Conner]

I've alredy checked this with my stabilized power unit, the noise was still there.

Try it with an actual battery, not a power supply plugged into the mains. I'm wondering if the unit is picking up noise from mains wiring. If you take it outdoors with a battery, there's no mains wiring anywhere near it.

[J M Fahey]

Hi benilo.
To start with something, the full answer is much longer but i'm busy now (2 anxious Musicians picking 2 100W heads and 1 2x12" cabinet tonight) but to begin with your sound sample (posting it was a smart move):
1) The hiss from 0-6 and after 15 is *too much*, it must come from the TBA810 itself because volume on "0" kills the single transistor preamp.
You may have a bad 810 or some *very* leaky capacitor is injecting that hiss and the poor 810 just amplifies it.
The input pin that Jazz P Bass refers to is nº 8 on TBA810.
First suspect is the 0.1uF capacitor there, just replace it .
Also short the 220K resistor from pin 8 to ground.
Hiss still there?
Replace the 100uF caps from pins 6 (gain), 7 (bypass) and 12 (bootstrap).
The first two have the + sign pointing to the IC ; the last one has the + pointing away.
Also check that the 1000 uf output one is not leaky, you should measure no DC on the hot speaker pin.
Add a 0.1uF ceramic cap from pin1 to pin 10.
Replace the 220uF filter cap with a 2200uF x 25V one.
2) The noise from 6 to 15 is neither hiss (waterfall type) nor 50Hz or 100Hz hum (deep low steady note) but "mains buzz", high frequency components of the AC signal which usually come "through the air", being inductive or capacitive in nature.
That's why they are the high frequency part, they "transmit long distances".
I *strongly* suspect poor wiring and layout, in this case to and from volume pot, plus you having a strong interference source close by, very probably a CFL ("high efficiency") lamp or a fluorescent tube.
"Modern" electronic ballast ones are greatest offenders; old iron ballast less so.
That's why Steve suggests you try your amplifier in the garden, away from house wiring.
You don't need exact 18V to test it, if you have a 12V battery (¿your car?) or a couple rechargeable packs will do. Use at least 12V.
If not available, carry your regulated power supply outside with an extension cord *and* put the amplifier at least 1 meter from it, preferably 2 m. .
The buzzy noise should dissappear.
I made and sold a ton of "similar-to-Pignose" battery powered amplifiers, but mine were high gain, were used in some classic Argentine Rock albums, and were carried everywhere by top musicians to "warm up" when on the road.
I distinctly remember my surprise when touching the tip of a plug with my finger to make the classic buzz to test whether said cable was working, and only getting a soft click and no hum, buzz, nothing. Eerie !!!
This happened , literally, in the middle of a road between cities, even in the inside of a rolling, Diesel powered Tour Bus !!!
In any spark fired car you get spark noise.
Oh well, I got carried away, my clients will kill me.
PS: I forgot: very good pictures and beautiful amplifier. Congratulations.

[Jazz P Bass]

Quote"You *may* use a TDA2030 there, after some brain surgery.
What do You mean withbrain surgery?
As I wrote above, I'm from germany and therefor I'm not a native english speaker."
I believe the reply was meant to indicate that a circuit modification would be required to use a TDA2030.
Hense the "brain surgery".
Circuit board surgery?

[benilo]

Hi benilo.

Hi "J M Fahey"
first of all thanks a lot for Your long post.
I appreciate very much all Your suggestions, but
it will take some time to try out everything, because the times when there was an
"electronic shop" in every city seem to be over, even in Germany.

But, be sure I'll try out every hint You provided.

I hope You could satisfy your customers in the meantime.

Best regards
benilo

[benilo]

Hi benilo.

Hi "J M Fahey",
during the weekend I found the time to do some tests You suggested.

To start with something, the full answer is much longer but i'm busy now (2 anxious Musicians picking 2 100W heads and 1 2x12" cabinet tonight) but to begin with your sound sample (posting it was a smart move):
1) The hiss from 0-6 and after 15 is *too much*, it must come from the TBA810 itself because volume on "0" kills the single transistor preamp.
You may have a bad 810 or some *very* leaky capacitor is injecting that hiss and the poor 810 just amplifies it.
The input pin that Jazz P Bass refers to is nº 8 on TBA810.
First suspect is the 0.1uF capacitor there, just replace it .

As I was trying to check your proposal, I found out that there ist no 0.1uF cap at this place.
Seems the Schematic is not very accurate at all.
See the little Schematic I've attached below.
There is no cap, there is only on Resistor with 300K.
Do I need the capacitor there?
Maybe the missing cap ist the cause of the noise?

Also short the 220K resistor from pin 8 to ground.
Hiss still there?

Doing this, the hiss vanishes, nothing comes out of the speaker.
But, if I short the resistor on the other side of the 300K Resistor, (the side of the poti),
the noise ist still there. (This seems clear, because this should be the sams as Volume=0 with the poti.)

I hope, I could give You some more useful hints.
With best regards, benilo.

[J M Fahey]

Ok Benilo, just what I needed.
Pull that stupid 330K resistor from there , and replace it with a nice .1uF x 50V ceramic, noise should dissappear.
Just to be safe, follow the path from pin 8 to pot cursor, you *might* have some bad/cracked solder, cracked track, etc.
Also confirm that Vol. potentiometer center lug really reaches ground when on "0".
Anyway, "if" you still have hiss after all this, you should replace the TBA810; its input transistor might have become leaky/degraded, of which the noise might be just the symptom.
I mention this only to cover all bases; 90% that you already repaired it.

[benilo]

Ok Benilo, just what I needed.

Hello J M Fahey,

Pull that stupid 330K resistor from there , and replace it with a nice .1uF x 50V ceramic, noise should dissappear.

Unfortunately, that didn't work.
But to clarify Your proposal:
I replaced the 300K Resistor with the 0.1 uF cap, so that between pin 8 and the poti there was
only the 0,1 uF cap.
With this configuration no signal at all came out of the speaker.
Which means also: no noise.
Does that mean, that the TBA810 ist OK?
When I use the same parts like in the schematic (0.1 uF cap and a 220K Resistor)
the noise is just the same as before.

Just to be safe, follow the path from pin 8 to pot cursor, you *might* have some bad/cracked solder,
cracked track, etc. Also confirm that Vol. potentiometer center lug really reaches ground when on "0".

I have to try this once more.

Anyway, "if" you still have hiss after all this, you should replace the TBA810; its input transistor might have become leaky/degraded, of which the noise might be just the symptom.
I mention this only to cover all bases; 90% that you already repaired it.

I'll be back here when I know more.
Best regards
benilo

[JohnnyGiant]

Hello, I've got the same amp and I've got no hum problems.
Because I've got no sound at all and I'd like to repair it.