AMP4 Setup help for 4ohm

[nightanole]

This will be My very first power amplifier, ever. Ive built several headphone amps and run the smt lab at my work so soldering is not a problem.
However after i bought the thing i now have access to the build procedure and there are options. I dont know how to set the gain since it doesnt make sense. How a gain of 1 creates a 20v signal from a 1v source I cant comprehend.

Anyway heres my specs and any help and build advise would be welcome:
PS= dell 160watt 19.5 notebook switching supply
speakers= 4 ohm pioneer rev's in free air baffle
source= 2vrms usb dac (gona have to tone is down to get to the 1.41vrms limit)
power switch= Do i need one with this setup?
volume pot= 10k alps, It does have a switch, should i wire that to the mute circuit?
Soft start= Do i need this and how to i do it?
heatsink= would an alum case the size of 2 packs of cigarettes be good enough?
gain= ??? Im using a 1vrms-2vrms dac or a mp3 headphone out.

[krilli]

There are two gain stages in these amps: First is the input stage, which really acts as a kind of buffer and should emit a line-level signal. This signal goes to the power stage, which handles the gain from the line-level signal to the actual amplified 20V signal. Hope that helps.

[PedalPower]

If by "soft start" you mean muting for long enough to prevent thumps, then see http://www.41hz.com/forums/topic.asp?TOPIC_ID=2639

You will need a power switch if you want to be able to switch it off! The power supply will constantly consume a small amount of energy if that power switch is on its output.

Don't see what advantage wiring the pot switch to the muting circuit will give you.

I'm not sure that the PCB will fit into the size of case you specify (esp given the height of the capacitors); I have an aluminium case big enough for the PCB and the innards of a 60W Dell laptop power supply, and it's big enough to keep both cool. But then that's less than half the theoretical power.

I have found that the surge current to charge the reservoir capacitors can cause laptop power supplies to register a short circuit, and if they're not self-resetting they won't power the amp, so you'll have to remove one or both of them.

[nightanole]

Since the amp is so efficient I wasnt sure if i needed a power switch Since i wasnt planning on unpluging the power brick everyday. If the thing only sucks 30-50ma at idle Id rather omit the switch and just unplug from the wall durring the weeks it wont be in use (its going to be a portable boom box sort of deal).

Here is my extra case:

http://www.drillspot.com/products/39...80BK_Enclosure


I mainly need help in choosing the optional parts of the board. Rail resistors, mute jumper, gain, output relay.

[pepolman]

See Jan's explanation about signal levels in the first posting of this thread.

http://www.41hz.com/forums/topic.asp?TOPIC_ID=600

As far as the rest of it goes, do you not have the assembly instructions? Most of these things are covered by Jan in the notes.

From what I've read you should be okay on the relay (should work as low as 18V with a wire jumper for R100) and rail resistors as supplied (200K for R54/R52)will be okay down to 17V.

If you don't really need the mute function you can permanently close the jumper.

[nightanole]

Ok things i think i know:
1. install mute jumper
2. R52 and R54 should be 200k (19.5v supply)
3. wire install for relay since im below 25v
4. input will be 5.64vpp, so i should set the gain for 28.7k/20k for a gain of .697 which would knock me down to about 3.93vpp

Does that sound like all i need to know for parts other then the varied turn on thump/soft start implementations?

[pepolman]

Looks like you've got the idea!

With the gain you don't need to be exact. I would err on the side of a little higher gain, but as long as you're reasonably close it won't be critical.

[nightanole]

Well shes soldered together...

150ma idle current sound about right? 9v regulator is warm to touch, control chip (i think) is slightly above room temp. Tripath is about 40c without heatsink. I havent hooked up speaker nor sound to it, but i did adjust the trim pots for a .5ma dc offset.

[krilli]

I think my Amp4 consumed a little less current when idle, 50-100mA, but this is from memory. Also, I omitted the output relays and transistors which surely suck some juice. Is 150mA when unmuted and awake, so on but simply not producing sound? Is it the same when you put the amp to sleep?

[nightanole]

full build with relays, unmuted and awake, no inputs or outputs connected. I cant put her to sleep since mute is jumpered