Lectrosonics Voice Projector 28 strange problem

turisz

turisz

New Member
I just got a Lectrosonics Voice Projector 28 (rebadged as Lindaco Voice Projector 2529 made in switzerland, but it is obviously made in the USA, I do not understand why they did that).

So my problem is, when the device is powered via the AC adaptor, there's a disgusting distorted sound on the speaker with a 50 Hz like hum, but it also amplifies. But if I give it 12 volts DC via the battery cables, it works flawlessly, there's no slight humming, it just doing what it supposed to do.

The hum is not really related to the input or output volume, it is present even when everything is on the lowest level possible.

The biggest problem is that there's no manual for this thing on the internet, I've sent an email to Lectrosonics but they have not responded yet.

I guess the problem is somehow related to the voltage regulator part, but I am not really an expert in electronics, but I've worked on a few electrical things.
 

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turisz said:
So my problem is, when the device is powered via the AC adaptor, there's a disgusting distorted sound on the speaker with a 50 Hz like hum, but it also amplifies. But if I give it 12 volts DC via the battery cables, it works flawlessly, there's no slight humming, it just doing what it supposed to do.
Click to expand...

greetings;
So? you solved the issue.. perhaps a bad cord? may be rig a new cable via the battery connection?
 
Binkman said:
greetings;
So? you solved the issue.. perhaps a bad cord? may be rig a new cable via the battery connection?
Click to expand...
Um, no I have not solved it, because the adaptor which came with it is an AC-AC adaptor, so I can not use it to power this thing up via the battery cables, plus if I rewire it, it can not be used from batteries (it does not really matter because these 40 years old batteries are obviously dead anyway). But I thought about that earlier what you just said.
Thanks for the reply!
 
Without a schematic.. Nobody here would know even DIY.. you might post it there.

You said feeding 12vdc it works.. So these are old batteries recharge type? So a new wall rat wouldn't work?
 
Yes the biggest problem is that I do not have a schematic and Lectrosonics have not responded to my email. I do not really wanted to rewire things, just to keep it as it was. The old batteries were rechargeable and built into this thing. A new adaptor would do the trick with the rewiring of the battery cables to the charger port, but that's the last thing I want to do, maybe it is just some old resistor which is fooling me. Thanks for the tip I'll post it in the DIY section!
 
Hiya 0- welcome to AudioKarma!

Please - only post your problem once, in a single thread.
I just deleted the Duplicate post in the DIY thread.
 
for it to run off AC it must have a rectifier and smoothing capacitor and maybe a regulator . fact of it running off battery power suggests fault is around the 3 things i mentioned .
 
petehall347 said:
for it to run off AC it must have a rectifier and smoothing capacitor and maybe a regulator . fact of it running off battery power suggests fault is around the 3 things i mentioned .
Click to expand...
Luckily, it is a very basic circuit (but complex enough to fool me heh)
I searched for the components:
- 2 diodes (a diode coupled with a capacitor can act as a rectifier right?)
- 2 MPS6521 NPN transistors
- TIP42A complementary PNP transistor
- CA2002M audio amplifier IC
- the others are just capacitors, resistors, led's and potentiometers
 
turisz said:
there's a disgusting distorted sound on the speaker with a 50 Hz like hum,
Click to expand...

Sounds like the classic symptom of a power supply filter (smoothing) capacitor gone dry, causing a huge ripple on the rectified AC supply. A DC supply has no ripple (and has its own rectifier and filter capacitor).
 
cpt_paranoia said:
Sounds like the classic symptom of a power supply filter (smoothing) capacitor gone dry, causing a huge ripple on the rectified AC supply. A DC supply has no ripple (and has its own rectifier and filter capacitor).
Click to expand...
Well, I just replaced all of the electrolytic capacitors to new ones, but there's no change, it still does that.

Oh, and I opened up the power supply and theres nothing else inside just a transformer.
 
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