More AMP10 problems

[paradox]

I'm back again, unfortunately.

My AMP10 now works, I'm getting from her but with an unbearable background hiss. It's the same on both channels, appears only when the amp unmutes, and is not affected by volume.

I've tried resoldering decoupling capacitors with no success. Is it possible that they have been heat damaged by the iron? One or two have gone a slight red colour where the iron has touched.

Also, my LM317 is too hot to touch during use, even with a small heatsink attached. Is this normal?

Thanks.

[thomaseliot]

Usually, if there is sound, the chip is OK.

More common is that hiss problems are related to bad solderings. A good method is to resolder everything: it takes less time than measuring the amp with a multimeter looking for strange things, with the risk to short pins and fry the chip.

Take care to signal path to the chip and from there to the coils (these last are really noisy if not perfectly soldered).

Remember that input and output binding posts must be isolated from chassis and PS ground.

[Scratchy]

There are many posts on this forum with hiss problems. (hint: search for hiss).

First thing to re-solder are the toroids. If they are not prepared cleanly before installation this can cause hiss.
The varnish on the copper wire ends must be completely cleaned off.
The ends must be completely tinned with solder before soldering the toroids into the PCB.

***If it was easy, everyone would be doing it***

[paradox]

Okay, I'll try resoldering the inductors (again!).

After that I guess I'll try replacing decoupling caps.

I'm also having trouble tracing the output path. It doesn't help that component names on the schematic and the assembly instructions don't match. I think what're labelled as L5 and L6 in the instructions are actually L1 and L2 in the schematic.

Thomas - when you say that the I/O binding posts need to be isolated, what do you mean? I'm simply wiring the ground from my inputs and outputs into the sockets. They have two sockets per channel, so I assume one of them is used for ground, right?

Many thanks

[Scratchy]

Hi Paradox.

Are you "grounding" one side of the speaker output?
If so, this is a no no.
The speaker outputs on these amps should never be "grounded".
Both + and - speaker outputs must be isolated from each other and ground.

The reason I am using quotes for grounded, is this term is often miss-used in place of "common conductor".
Grounded means connected to Earth, usually connected to the metal chassis or enclosure.
It is best to keep the PS center tap "common rail" connection isolated from the chassis ground or earth.
This is referred to as PGND in the AI.

***If it was easy, everyone would be doing it***

[thomaseliot]

I meant binding posts isolated from chassis.

[EmergencyDpt]

I used a torch to burn away the varnish, then used steel wool to remove the dust and baked varnish. After that I retrimmed the pots and everything worked out great. Don't forget to retrim the pots.

I also did the resolder trick. These guys won't steer you wrong on here. Very good advice.

[paradox]

quote:Originally posted by Scratchy

Hi Paradox.

Are you "grounding" one side of the speaker output?
If so, this is a no no.
The speaker outputs on these amps should never be "grounded".
Both + and - speaker outputs must be isolated from each other and ground.

The reason I am using quotes for grounded, is this term is often miss-used in place of "common conductor".
Grounded means connected to Earth, usually connected to the metal chassis or enclosure.
It is best to keep the PS center tap "common rail" connection isolated from the chassis ground or earth.
This is referred to as PGND in the AI.

***If it was easy, everyone would be doing it***

I'm not earthing anything at the moment. It's not in an enclosure yet. I was only going to earth the chassis for safety reasons. I can't see how you could practically earth the speaker connection anyway? Surely the fact that there are two screw terminals for each speaker suggest that you simply insert one wire into one, and the other wire into... the other? Or am I misunderstanding?

edit: maybe I really am misunderstanding. The speaker outputs share a "-" connection according to the schematic.They both go to the same GND point. How can I then isolate them from one another?

[thomaseliot]

Every Tripath amp has a "star ground" on the pcb. It is the ferrite bead, that connects AGND and PGND.

That point must be the reference ground potential for the chip, input and output grounds and power supplies grounds. This way all grounds have the same potential, the same reference, the same "zero" point.

If one or more of these grounds touch the chassis, or safety ground, or each other before star ground, you create other "zero" points, that not necessarely are the same "zero" of the star ground. This creates ground loops, because if two grounds are not at the same potential that means that a current will flow between these two points.

Safety earth must always be connected to chassis, but not to PS, input and output grounds. If you want to connect both, safety ground and chassis, to the amp, the right point is the star ground, the ferrite bead.

[Scratchy]

quote:Originally posted by paradox

edit: maybe I really am misunderstanding. The speaker outputs share a "-" connection according to the schematic.They both go to the same GND point. How can I then isolate them from one another?

The speakers outputs do not share a common connection.
The - is in reference to the polarity of the speaker ouput.
In this case - does not mean common or ground.

Have a look at the schematic on the ta2022.pdf datasheet on page 7.
http://www.support.41hz.com/showblob.asp?ID=12
It clearly shows each speaker output as a separate entity.
The fact that this chipset can be bridged means it cannot share a common connection between outputs.
PS. There is more valuable info regarding grounding in this datasheet as well.

***If it was easy, everyone would be doing it***