[TMC]

I'm currently reading up on amps and right now I'm considering a Meta42 for a near future purchase/DIY. One thing I'm looking for is a flexible amp, that is with the possibility to change the amp itself for different sonic characteristics and changing the gain to be more suitable for the headphone in use. Is it possible to do both these things by using the same Meta42 circuit and just switch a socketed amp/a few socketed resistors? I'm also thinking about an amp that can be used with both wallmart and batteries. If I'm using for example a 9V battery, is there some kind of adapter that I can just plug in between the battery socket on the amp and the wallmart to use it with a wallmart? BTW approx. how long can a Meta42 run on one 9V?

 

[fiddler]

Well if you put a socket in the opamp slot, you can swap opamps to fairly drastically change the sound.

You can also make a low/high gain toggle switch, that maybe switches the resistor value for R4.

About switching from batteries to wall power... there are "closed circuit" DC jacks that have a built in switch, that automatically disconnects the battery circuit when you plug in the wall wart.

About battery life... it really depends on your configuration.

 

[TMC]

The possibility to just switch the op-amp when using a future pair of headphones with different sonical qualities certainly is in the back of my mind as that would be considerably cheaper than having to get a whole new amp. As for the resistor switch, if I'd simply make the R4 resistor a potentiometer, would that degrade the sound/stability of the amp in any way? That way I could finetune the gain and I wouldn't need to choose the 2nd gain now for a future pair of headphones. The DC jack with a switch sounds like a good solution for my needs. As for battery life, I'm going for a fairly basic config with a AD8620 to begin with. How many hours can you use your Meta42 with a standard alkaline 9V battery fiddler?

 

[usc goose]

mine goes about 7 or 8 maybe. (9v meta w/ 8620)

 

[TMC]

Quote:

Originally posted by usc goose mine goes about 7 or 8 maybe. (9v meta w/ 8620)

Ouch, that's considerably less than what I was hoping. With rechargables it would translate to about 5 hours. Maybe a portable Meta42 isn't that good an option after all, hmm. I think I'll need to ponder this some more, thanks for the info.

 

[fiddler]

Probably two gain settings will be sufficient for use with most headphones. Say have a low setting (3-4) for Grados, and high setting (7-10) for high impedance phones like Senn HD600. That should be MORE than enough. A single resistor will most probably sound better than using a pot. This is why people get stepped attenuators to upgrade from potentiometers.

I haven't tested with an alkaline 9V, so I can't tell you. My personal META42 runs on AA batteries, so it runs for a looooong time.

 

[fiddler]

Just how portable does it have to be? With AA's, you can aim for 50-100 hours easily.

 

[TMC]

Quote:

Originally posted by fiddler Probably two gain settings will be sufficient for use with most headphones. Say have a low setting (3-4) for Grados, and high setting (7-10) for high impedance phones like Senn HD600. That should be MORE than enough. A single resistor will most probably sound better than using a pot. This is why people get stepped attenuators to upgrade from potentiometers. I haven't tested with an alkaline 9V, so I can't tell you. My personal META42 runs on AA batteries, so it runs for a looooong time.

Yes I guess you're right, maybe I'm trying to be too flexible to ensure the amp will remain useful for as long as possible. Tell me more about the AAA setup, how many is it and are there any apparent weaknesses compared to a 9V, maybe the ability to drive high-impedance headphones well?

 

[fiddler]

With rechargeables, and the AD8620 opamp, you probably would want at least 8 AA or AAA batteries. This will give you about 9.6 V, a bit more on a fresh charge. The performance should be as good if not better than a 9.6 Plainview rechargeable, and it'll last a heckuva lot longer. If you use alkalines, you'll get about 12V with 8 batteries.

AA/AAA means having to use a larger case, or putting the batteries in a separate battery pack.

 

[tangent]

I wouldn't recommend changing out socketed components frequently. The contact strength will weaken, and the amp will eventually start misbehaving.

You'll either have to find a single amp config that meets most of your needs and desires, or make multiple amps and switch between them like you would different headphones.

 

[Knocturnal]

When I first read the subject of your post i was thinkinig why the hell would he want aflexible amp

. To answer your question you should get a META42 because you can modify it later or do whatever you wish to do to it. Hope this helps

 

[usc goose]

Quote:

Originally posted by TMC Ouch, that's considerably less than what I was hoping. With rechargables it would translate to about 5 hours. Maybe a portable Meta42 isn't that good an option after all, hmm. I think I'll need to ponder this some more, thanks for the info.

mine goes 7 or 8 with rechargable rayovac batteries actually. i think those plainview 9 volts are supposed to go longer. maybe 10 hours? i kind of doubt you're going to get much better than that though. i have 2 so i can keep a fresh one handy and i stash one or 2 extra standard 9 volts in my bag and my car. works fine for me.

 

[Mr.PD]

My META42 has been running for the last 6 months on 4 6volt lantern batteries. (24 volts)

It is kind of a bulky set up though. I can't remember the opamp that's in there, but it's not the 8620. The thing couldn't even go 12 hours on two 9volt batteries that it carries internally.

 

[TMC]

Quote:

Originally posted by fiddler With rechargeables, and the AD8620 opamp, you probably would want at least 8 AA or AAA batteries. This will give you about 9.6 V, a bit more on a fresh charge. The performance should be as good if not better than a 9.6 Plainview rechargeable, and it'll last a heckuva lot longer. If you use alkalines, you'll get about 12V with 8 batteries. AA/AAA means having to use a larger case, or putting the batteries in a separate battery pack.

That would be a bit too bulky for going portable for me. Maybe I'll just go with a stationary Meta42 instead.

 

[TMC]

Quote:

Originally posted by tangent I wouldn't recommend changing out socketed components frequently. The contact strength will weaken, and the amp will eventually start misbehaving. You'll either have to find a single amp config that meets most of your needs and desires, or make multiple amps and switch between them like you would different headphones.

Maybe I'm just hoping for too much here, but is there such a thing as a dual amp socket with a switch to change back and forth between these? I really want to keep it to one amp, so it would be great if you have any ideas how to do that. Because having 2 separate amps with only the op-amp and one or two resistors being different seems like a waste to me.