Building first amp - Pass A40

[jkomp316]

Hello everyone;

Awesome community, I've gotten lost in all this info the past few days. I've decided to build a Pass A40 amplifier. I found an old Signal 88-6 transformer and will probably use TIP142/147s. My only point of reference in audio is an Onkyo 8511...

I do have a question regarding preamp though. I know many of you will probably cringe at this, but I'd like to drive the amp from the headphone out of any portable device.

Would it be beneficial to lower the input impedance of the amplifier? I am concerned a headphone amp will lack proper gain at a 40k load. How would the pro's on here attempt this without disrupting the harmony of the circuit?

edit: I'm looking at 30mW per channel and around 1.10v across both channels.

Thanks in advance
Jake

[Zen Mod]

you can drive it with chicken , if you wish - that's your amp ;

any (usual) gain stage will maximize swing working in lighter load

you'll later reach harmony ( if ever ) with some other preamp

[jkomp316]

So this isn't possible without an additional gain stage? The values posted are <RMS levels for most integrated headphone amps. I know there is impedance mismatch, I thought I could modify the amp somehow to help this. I'm new to this audiophile stuff, I stumbled into all this looking at power supplies for stepper motors. Anyone ever hear of a RepRap?

[jkomp316]

Could I choke the input by reducing amperage and increasing voltage? I don't know the math regarding frequency response.

[dyrevennen]

Originally Posted by jkomp316

Hello everyone;

Awesome community, I've gotten lost in all this info the past few days. I've decided to build a Pass A40 amplifier. I found an old Signal 88-6 transformer and will probably use TIP142/147s. My only point of reference in audio is an Onkyo 8511...

I do have a question regarding preamp though. I know many of you will probably cringe at this, but I'd like to drive the amp from the headphone out of any portable device.

Would it be beneficial to lower the input impedance of the amplifier? I am concerned a headphone amp will lack proper gain at a 40k load. How would the pro's on here attempt this without disrupting the harmony of the circuit?

edit: I'm looking at 30mW per channel and around 1.10v across both channels.

Thanks in advance
Jake

Hi,

and welcome to the community. I am kind of a newbie here myself and I agree that the community is great :-)

I have an old A40 running steadily for many years already. I usually use a preamp (Tandberg), but just made a test driving the A40 from the headphone out on my iPod (It plays Bach organ music as I type this). It works great, but cannot play very loud. It seems like the the output voltage from the ipod is too low. Loud enough for Bach on a Sunday afternoon (and then some). Too low for a proper party. But it sounds as well as you would expect from an ipod, and there seems to be no impedance issues.

Hope this helps. Goos luck with your project.

Dyrevennen.

ps. Sure I know the RepRap project. Considering buying an ultimaker myself. I even met Adrian (The inventor of RepRap) at a public talk about reprap at Bath university a few years back. It is cool technology :-)

[jkomp316]

HeadWize: DIY Workshop > Need cost effective build for ipod preamp to home stereo

-have a look at the post by PRR

he suggests a passive gain amplifier using half of a center tapped transformer.