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Cigar box Apheared 47 - Page 4

post #46 of 58


OPA4132 is the signal channel amp.

 

But it's all relative...you could you whatever your favorite jfet single, dual or quad op amps are...

A couple of OPA1642 would sound pretty good as would AD8620.

 

The ground driver is an OPA551 high current op amp.

 

Quote:
Originally Posted by sandbasser View Post

Avro-Arrow -

 

A question for you...

 

What is the OpAmp in the schematic in Post #36???

 

Thanks,

post #47 of 58

Those voltages are way off...you blew the TLE2426.

 

For 15 volt input, if your negative probe is on the TLE output pin (virtual ground),

you should have +7.5 it you touch the positive probe to the V+

and -7.5 volts if you touch the probe to the V-.

The LED should have no influence on the circuit.

I'm not sure what "Diode" you mean?
 

Quote:
Originally Posted by T.B.N. View Post


DOH! it was the LED. I soldered in the LED and there's no smoke. Live and learn. If you don't mind I'll share what my measurements are:

 

V- to V+: ~15.50V

 

Vground to V- ~16.25V

 

Vground to V+ .625V (I got a negative number when I had the positive end matched up with V+ for some reason, so I switched it around.

 

How are these voltages? Close enough?

 

 

Quote:
Originally Posted by T.B.N. View Post

I checked the connector. The extra pin is a switch; it is connected to the negative side when not plugged in, and unconnected when the plug is in. 

 

Could the smoking problem be that the LED or Diode weren't connected when I plugged it in?


 
post #48 of 58

I checked the construction page again...the Diode is for reverse voltage protection.

If your power supply is hooked up backwards, the diode conducts and shorts

out the power supply.

If your power supply is hooked up properly, the diode is not conducting and has

no influence of the circuit.

post #49 of 58
Thread Starter 
Quote:
Originally Posted by Avro_Arrow View Post

Those voltages are way off...you blew the TLE2426.

 

For 15 volt input, if your negative probe is on the TLE output pin (virtual ground),

you should have +7.5 it you touch the positive probe to the V+

and -7.5 volts if you touch the probe to the V-.

The LED should have no influence on the circuit.

I'm not sure what "Diode" you mean?
 

Crap, I don't know what I did wrong at all. The diode and the LED aren't the problem, then something I did is way off... Hopefully the BUF634 is ok, the TLE is cheap and I have a couple. Back to the drawing board, so to speak...
 

post #50 of 58


Probably wired the TLE2426 wrong.

I've done it myself.

Quote:
Originally Posted by T.B.N. View Post



Quote:
Originally Posted by Avro_Arrow View Post

Those voltages are way off...you blew the TLE2426.

 

For 15 volt input, if your negative probe is on the TLE output pin (virtual ground),

you should have +7.5 it you touch the positive probe to the V+

and -7.5 volts if you touch the probe to the V-.

The LED should have no influence on the circuit.

I'm not sure what "Diode" you mean?
 

Crap, I don't know what I did wrong at all. The diode and the LED aren't the problem, then something I did is way off... Hopefully the BUF634 is ok, the TLE is cheap and I have a couple. Back to the drawing board, so to speak...
 

post #51 of 58
Thread Starter 

Yep, I think I put it in upside down, wired one of the pins wrong, or both. I fixed it and put a new chip in and it works fine now. ~9.8V on each side from the ~20V from the power supply. I should have been more careful. Now I'll be extra careful when I do the more expensive opamps.

post #52 of 58


That sounds much better.

Good job.

 

Quote:
Originally Posted by T.B.N. View Post

Yep, I think I put it in upside down, wired one of the pins wrong, or both. I fixed it and put a new chip in and it works fine now. ~9.8V on each side from the ~20V from the power supply. I should have been more careful. Now I'll be extra careful when I do the more expensive opamps.

post #53 of 58
Thread Starter 

So I've got new problems...

 

I had a lot of things going on and wasn't able to work on the amp for a while. I finally got it all wired up and I'm measuring ~10 VDC on the headphone jack. I tried some old ipod earbuds and all I hear is a low hum... Any ideas? The voltage doesn't change at all by changing the volume.

post #54 of 58
Quote:
Originally Posted by Avro_Arrow View Post

FWIW, Here is my version of the Apheared 47.

 

I'll draw up a board for it some other time.

 

A47.png

 

What's the point of the 499R resistor in the signal path? Is it simply some from of protection in case someone turns on the amp while the volume pot is turned fully to the right (i.e., shorted)?

post #55 of 58

It helps to balance the impedance seen by the inputs on the op amp.

In reality it's almost impossible to balance as the volume pot presents

a variable impedance to the + input of the op amp.

It's really an optional part.

post #56 of 58
With no caps on the output, would this amp not take out a set of headphones very quickly if something were to pack in with one of the opamps or the PS circuit? Or am I confused... wink.gif

Sent from my HTC Desire HD A9191 using Tapatalk 2
post #57 of 58
Quote:
Originally Posted by TrollDragon View Post

With no caps on the output, would this amp not take out a set of headphones very quickly if something were to pack in with one of the opamps or the PS circuit? Or am I confused... wink.gif

Sent from my HTC Desire HD A9191 using Tapatalk 2


Yes, you could.

Many other DIY amps (and probably many commercial amps) also run the rick of destroying your beloved headphones due to circuit failure.

post #58 of 58

... speaking of which, I'm running a configuration similar to yours (with 0.22uF input caps, though) and getting about 30mV DC offset on the headphone jacks. Is that still kind of okay, or should I think about output caps instead of/in addition to the input caps?

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