modding AMP300

[amo]

I want to start modding my the AMP300 (I have several) from Audiosource, this is already a very good amp for a loughable price! There are many items i can change, but i want to begin with the variable gain resistors, as these seem the easiest. They are simply two tiny variable film pots on the rear, and I am wandering if taking them out and replacing them with a couple of decent single value resistors will make a difference. If so, what are the best types of resistors? Whats the best way to choose at what level to fix these? I want to run the device in bridged mode, and will not need even close to the 475W @ 8 Ohms promised. So will fixing these at a lower level result in higher quality output from the bridged circuit?

Stupid question: the manual dictates that for the bridged circuit to function properly both the left and right input chanels must be connected and the summed output will be amped (as in a .1 LFE sub ch). Whats the correct way to wire this thing if i want to use it as a monoblock driving a single channel? By the way, I have access to ballanced outputs. Can I use this to my advantage when driving the bridged circuit?

This is a 100% discrete amp with an ample torroidal tran, and I believe, 4 output transistors per channel. (next step will be replacing the white "sand" resistors next to each of the output transistors, as i believe this will make the biggest sonic difference, from the reading I recall on this forum. after that will be the reservor caps, if i have enough patience)

[scaramoucheii]

Hey AMO

I recently picked up 2 of these AUDIOSOURCE PHEONIX GOLD AMP300 's at Fry's in LA for 149.95 US $ .... After looking inside one and seeing the Toshiba output transistors and large Toroidal transformer I though it could be worth at least 150 bucks. The chassis and PSU are worth way more than the 150$ I paid.

After some listining I was not overly impressed, but considering the usless circuitry in the signal path, and the fact that the amps were quiet and fairly dynamic, considered that some modding would make these into decent amps for 150 $

Therefore .....I also will be putting these amps under the soldering iron and removing all the crap from the circuit path.

I will start by:

1: measuring the trim pots resistance, and then replacing them. But I would assume, (Wrong or right) that replacing them with a piece of straight wire would be a good place to start.

2: I'm also interested in removing the front panel trip pot and "balance" control.

Once I get in there with a scope and trance the signal path around i will have a better Idea. I may be able to just move the "input" past all the crap to the input of the first stage . Alnother idea may be to just use the chassis and power supply and rip out the power boards and replace them with the LYNX,

http://audio-innovation.eu/shop/prod...1e41b9b6635e07

Simon

[amo]

I have posted the schematics for this amp here on the site. They make it soo easy to remove the needless stuff. The entire input section, including all the stuff in the rear and the detached boards at the front, are connected to the amp via a cable. I simply disconnected it and connected directly to the source, with 22K resistors in series to compensate. I also rerouted the output wires, getting rid of the "A/B" switches. The sound is improved 1000%.

At this price, the best performance gained out of these amps, I believe, is going active, considering the heatsinks stay ice cold under 2 ohm loads....

Have fun, and let me know if you think of something else. I evaluated this for an active project I am doing, but in the end, I think I am too lazy to swap out all the crappy caps in the signal path, so I will leave this for a smaller project, and go with nice chip amps for the bigger project...

[scaramoucheii]

Hey Amo ....

Where did you post the schematic ? That would certainly help me out a lot.

I once had a old NAD218THX that I repaired and improved using schematics from this forum .....

I agree about your comments on the speaker switching circuit also. Cleaning this amp up with these simple improvements easily makes my 150 $ investment a nice little bargain.

Simon

[scaramoucheii]

Hi Amo

So I found the other thread on this topic.

Please explain what I did

However I could not download the schematics, Perhaps you could e-mail them to me directly ?

Thanks

Simon

[scaramoucheii]

OK, So I used a different browser and was able to successfully download the prints. Very nice and detailed. So you don't need to try and e-mail them .......

Thanks.

[nigelwright7557]

Originally posted by scaramoucheii
Hey AMO

1: measuring the trim pots resistance, and then replacing them. But I would assume, (Wrong or right) that replacing them with a piece of straight wire would be a good place to start.

Simon

For goodness sake dont replace the bias pot with a short cct !!!
On my amp that would put enough volts across the MOSFETS to short the power supply !

[Stormrider]

I believe he's talking about volume level controls.

[scaramoucheii]

Correct ... These are not bias pots.

I have the prints now from AMO so I will go through the amp next week when i have some time.

I have 2 of these amps so i can do some critical listining and compare the mods one at a time against the non modified referance !

Simon