12V DC gainclone?

[wahab]

Originally Posted by irishpatrick33

I guess that transformer stuff makes sense since I was looking at a site that addressed typical gainclones... not this atypical approach.

So all grounds will go to the same place? Because the schematic for the 1558Q differentiates between two of the grounds: one goes to signal ground, one goes to power ground (substrate), and another is shown going to a non-specified ground.

And the TDA2040 just shows things going to ground without explanation.


I also read something somewhere which said any grounds coming on the amplification side need to be grounded closer than the signal grounds, so the signal doesn't get corrupted.

TDA1558 signal ground is simply connected to the others grounds,
only be cautious that the input cable shiled must be connected near the
signal ground pin, not near the point where all grounds are connected
together...

TDA2040 has the NEGATIVE supply to the case, so in the single supply
variant, it will be the ground...

anyway, keep the cases isolated if the heatspreaders are to be
in contact with a metallic casing....

[bosse]

check this
http://www.reber.si/TDA/TDA1562Q/e002044.pdf

[irishpatrick33]

Originally Posted by wahab

TDA1558 signal ground is simply connected to the others grounds,
only be cautious that the input cable shiled must be connected near the
signal ground pin, not near the point where all grounds are connected
together...

TDA2040 has the NEGATIVE supply to the case, so in the single supply
variant, it will be the ground...

Sorry I refer to things in household electric terms.

So to clarify:
On TDA1558, the shields from the input terminate at pin 3 on the chip. And the rest of the grounds all come together at the star ground, which then ties into the negative coming from the transformer.

On TDA2040, all grounds come to the star ground which then ties into the negative coming from the transformer.



And does the case get grounded also (assuming I use metal)? Thanks

[wahab]

Originally Posted by irishpatrick33

Sorry I refer to things in household electric terms.
And does the case get grounded also (assuming I use metal)? Thanks

in tda1558Q, the case is connected to the ground, anyway, so there s
no use to connect it to the star point, moreover, it s better to isolate it..

as already said, the case of the tda2004 isINTERNALLY connected to the
negative supply, not the ground..it happens that if the ic is used
with a single supply, the case will be ground connected, so
it s useless to connect this case to ground...
as i said, keep them isolated to prevent ground loops..

hope it helps..

[AndrewT]

Originally Posted by irishpatrick33

And does the case get grounded also (assuming I use metal)? Thanks

Hi,
no.
The case/chassis MUST be permanently connected to Safety Earth.

[irishpatrick33]

Originally Posted by wahab

in tda1558Q, the case is connected to the ground, anyway, so there s
no use to connect it to the star point, moreover, it s better to isolate it..

as already said, the case of the tda2004 isINTERNALLY connected to the
negative supply, not the ground..it happens that if the ic is used
with a single supply, the case will be ground connected, so
it s useless to connect this case to ground...
as i said, keep them isolated to prevent ground loops..

hope it helps..

I am familiar with ground loops, which is one reason why I am trying to make sure I get this right.


I need to clarify further. There will be two wires coming from the wall wart transformer - a positive and negative. So there's no ground coming from the transformer.

Beyond that I am more confused. It seems the grounding and neutral schemes are the most complicated part for me.

In TDA1558Q, I am confused. What am I doing with the ground coming from pins 14, 5,13? Also what am I connecting pins 7, 11 to? Are pins 7, 11 connecting to the neutral going back to the transformer?

In TDA2040, I think I am just as confused. Are all of the grounds going back to the negative of the transformer? Including the signal shielding? How do you isolate?


Thanks again, I am an idiot. Part of my problem is the fact I may use a non-metal case.

[irishpatrick33]

Originally Posted by AndrewT

Hi,
no.
The case/chassis MUST be permanently connected to Safety Earth.

Not sure how I would do that, as wall wart transformers do not even have an earth connection. At which point, I would probably have to run another wire from an outlet to the case.


So without plastic type enclosure this isn't a concern?

[AndrewT]

Originally Posted by irishpatrick33

Not sure how I would do that, as wall wart transformers do not even have an earth connection. At which point, I would probably have to run another wire from an outlet to the case.


So without plastic type enclosure this isn't a concern?

using an outboard Wall wart type supply that complies with the double insulation standard and has the two concentric squares effectively means you do not have a mains risk in your amplifier. You do not need to and cannot use a Safety Earth.

However, connecting another piece of mains connected equipment with a mains to earth fault will/could transmit the fault down the connecting cable to this piece of equipment and maybe on to the speaker leads. Make sure that all your other equipment fully complies with the Safety Earth requirement.

[irishpatrick33]

Alright, I have done a horrible job of explaining myself. Perhaps if I draw what I am thinking somebody can correct my errors.

I think it's safe to say I am 100% lost on the TDA2040.

[danielwritesbac]

Well, I bought this "significant wall wart plug" for $20.
Toshiba AC Power Adapter Cord for PA2521U-3ACA 15V 6A 9 - eBay (item 170421661028 end time Feb-16-10 02:34:36 PST)

The 15 x 6 = 90va, and that seems workable. Except, that is a switch mode, which is a frail technology, so a good size tank capacitor will be needed as a helper. Its a slightly dodgy prospect, but it was quite inexpensive.
Perhaps it will also be nicely clean power? We'll find out.

The voltage is too high for TDA1558Q; but I couldn't find 14.4v available. Almost all car amplifiers can run on 14.8 volts DC (a car actively trying to charge its battery), so I'm hoping at 15v regulated isn't too much for it.
I'm wondering if I can use diode drop or if that would make additional noise?

For durability purposes, I have 2 chips, so they can run 1 chip per speaker (parallel mode). I'd planned it this way because the thermal interface on that chip appears to be insufficient, due to its small size. This trouble is because I have 4 ohm speakers and have also selected too much voltage (for that size thermal interface).

If there happens to be DC offset variance (car amp chips are prone to it) then I'll just use the best channel on 1 chip for the right speaker And of course also use the best channel on the other chip for left speaker. This crude backup plan can also work to expand the thermal interface (to double), because either method is only 1 speaker per chip. The parallel mode plan is technically nicer, but either method can make a joyful noise.

No news yet on durability of the chip or power source.