Post #38 here:
3 stage LIN topology - NFB tappings?
The high current speaker return must not be able to influence the inputs to the chip.
hello everyone, forgive me mooly I still haven't understood correctly: at what point of the power supply should I connect it?
You return the speaker back to the power supplies zero volt line (ground) directly and not via any of the wiring/pcb print that would allow the speakers high current to cause problems by it modulating the voltages around the chip.
Look at the diagram I linked to.
It doesn't matter how much current flows in the speaker, that current can no affect anything around the amplifier connected to the blue wire.
We have to do this because all wiring and PCB print has resistance, and that resistance develops a volt drop as current flows through it. That can cause instability and oscillation as it turns the normally negative feedback around the chip into positive feedback.
Look at the diagram I linked to.
It doesn't matter how much current flows in the speaker, that current can no affect anything around the amplifier connected to the blue wire.
We have to do this because all wiring and PCB print has resistance, and that resistance develops a volt drop as current flows through it. That can cause instability and oscillation as it turns the normally negative feedback around the chip into positive feedback.
hello everyone, I reassembled a circuit with lm1875, and I always have the same problem, first a strong continuous noise to the speakers, then when I connect the source the noise disappears and the sound is heard very very distorted, I think I always make the same mistake but I can't figure out which one, it would seem a mass problem, I took pictures, if anyone wants to try to understand where I'm wrong I would thank him very much.
Pictures might help but no guarantees.
How to attach images to your posts.
When you connect the source and the noise disappears are you able to measure correct voltages on the chip?
For a dual rail supply all pins should be zero apart from the supply pins.
How to attach images to your posts.
When you connect the source and the noise disappears are you able to measure correct voltages on the chip?
For a dual rail supply all pins should be zero apart from the supply pins.
ok controllero',intanto ti mando qualche foto,sono un po disordinate penso,abbi pazienza
claudio dematteis has shared 1 photo with you! | Flickr
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claudio dematteis has shared 3 photos with you! | Flickr
dimmi se riesci a vederle
An externally hosted image should be here but it was not working when we last tested it.
claudio dematteis has shared 1 photo with you! | Flickr
https://www.flickr.com/photos/189679288@N05/shares/136AU9
claudio dematteis has shared 3 photos with you! | Flickr
dimmi se riesci a vederle
Well you have done a very neat job with those boards but unfortunately it is not easy to trace out from a picture to see whether any major layout problems exist.
You must also have the chips mounted on a heatsink at all times.
Why don't you try and make just one channel work first of all. The circuit is simple enough to build 'dead bug style' without using a board. If you do this you can be certain to get the wiring correct.
You must also have the chips mounted on a heatsink at all times.
Why don't you try and make just one channel work first of all. The circuit is simple enough to build 'dead bug style' without using a board. If you do this you can be certain to get the wiring correct.
si i dissipatori li ho montati dopo, prima di provarlo,vuuoi che ti mando delle foto piu definite?ho fatto cosi ho fatto funzionare solo un canale,certo è quello che non capisco ,è cosi semplice!! si potrei usare delle pcb gia fatte ma a quel punto non c'è piu' divertimento,ma la cosa strana è che gia' le ho assemblate in passato e funzionavano correttamente,ho anche assemblato un 3886 e funzionava benissimo ,dopo un po che sono andato a riprenderlo non funzionava piu',è un mistero.
but thanks for confirming it