2 channel and 4 channel operation

[gnome]

Hello, I just finished putting together an Amp9 low, haven't tested it yet, but I want to use it with a battery in either two or 4 channel mode, how do I wire up the inputs and outputs so I can easily switch between them?

[Scratchy]

This is easier said than done.
The AMP9 output cannot be run "open circuit" (no load).
So you have 2 options:

1) Use 2 load resistors on the two unused outputs when in 2 channel mode and remove them in 4 channel mode.
2) Parallel the 2 unused outputs with the 2 active outputs in 2 channel mode.

Both solutions also require switching the inputs appropriately.
Inputs should also never be left "floating" (open circuit).
Unused inputs are normally shorted to ground.

There are a few posts regarding this in this forum - search for "parallel output"

***It's so easy, everyone should be doing it***

[gnome]

Thanks Scratchy for your reply
So to ground the inputs and put a dummy load on the outputs I could use a jack with a switch like this?
http://www.futurlec.com/Pictures/P065STSCK04.jpg

[dvenardos]

I got information from an experienced builder that it is recommended that all channels be loaded on the amp9 but not required.

[Scratchy]

quote:Originally posted by dvenardos

I got information from an experienced builder that it is recommended that all channels be loaded on the amp9 but not required.

You mean someone more experienced than V-Bro?


What members built what amps and how many?

quote:Originally posted by V-bro

20 more AMP32, two more AMP6-B, ten more AMP11 and six more AMP9-B...

Four more AMP4, four AMP15, one AMP7, one more Truepath, AMP6, two more AMP32...

An AMP6, two AMP15, AMP6-B, four AMP32, Truepath, three AMP7....


------X-max. can be several meters on any driver, too bad it can be done only once...------

So here V-bro recommends not to leave any open circuit outputs.
http://www.41hz.com/Forums/topic.asp?TOPIC_ID=2369

Finally, I suggest you have a look at the Datasheet:
http://www.support.41hz.com/showblob.asp?ID=48

Tripath also recommends that an RC damper be used after the LC low-pass filter. No-load operation of a
TAA4100A amplifier can create significant peaking in the LC filter, which produces strong resonant
currents that can overheat the integrated MOSFETs and/or other components. The RC dampens the
peaking and prevents problems.

***It's so easy, everyone should be doing it***

[col_s]

the Amp9 circuit already has a 10R resistor and 220nF cap in parallel with the output after the LC filter, a.k.a "zobel"

i've run my amp9 without load on a few channels for days and it was fine and didn't get hot, but i've got a relatively large heatsink and it's probably better to be safe than sorry and just add a load on the outputs

[dweekie]

You will find the same statement in all the Tripath datasheets. The Amp9 (and all other 41hz amps) already have that RC damper across the outputs in the output filter, so I think that specific point is addressed. That doesn't necessarily mean it's best for the amp to run without a speaker or resistor, but that protection is there for those circumstances.

I have run the Amp9 without load on 2 of the channels, and I have run other models on a single channel without issues. I would agree that all unused channels should have a resistor, but I don't think you will find any broken amplifiers due to turning on the amplifier without a resistor. I also don't think you will find anybody who's built and played with as many Tripath amps as V-bro; he's a human soldering machine! [)]

BTW, Scratcy, I didn't post that board yet; next week for sure, I promise!

EDIT - col_s basically said the same thing 33 seconds before me in just two sentences. Now I just look like a wordy copycat [xx(]

[V-bro]

Hi guys and thanks

there is indeed the R/C zobel damper, when the inputs are not connected to any signal this will sure hold up. I would still use a load as the filter wants to see a speaker-like impedance to operate correctly.

Will it not damage the amp it might emit more switching frequency noise. I just always add the resistor to be safe.... But even though I've built loads of amps I still do stuff out of habit rather then thorough investigation, maybe I'm too precautious after all?[:I]

------X-max. can be several meters on any driver, too bad it can be done only once...------

[Scratchy]

quote:Originally posted by dweekie


BTW, Scratcy, I didn't post that board yet; next week for sure, I promise!

NP Dweekie, I have a few unfinshed kits to build yet, as well as repairing Prezden's AMP6-basic (I got a replacement chip for him).

***It's so easy, everyone should be doing it***

[gnome]

okay so I have tested it,and I was more than pleased that it worked, considering that I haven't done any kit building in 15 years and it has been so long because most projects were dismal failures, I am super super happy, and then I measured the current draw and was blown away, at 100-200mA (at 12V) the volume was amazing, this is into a pair of 8ohm speakers, quite stunning. I will be able to bang out music with a 10W solar panel all day!
However I am getting a very unsubtle'hizz', not concerned for the moment because I haven't boxed I up yet, and I was testing it next to a desktop computer, so I'll look at that again when I have mounted it properly.
now just a few more questions:

what sort of dummy load is appropriate? I have searched but haven't found anything specific

can I skip the sleep switch, and just go with a "mains" and mute switch? having three "on" buttons seems exessive to me

what is AM mode?