Pro Audio Design Forum

I drew C11 as 10 uF. You may be seeing the "u" as an "n."

Your 159 Hz is correct for 10 nF.
The desired 10 uF value is 1.6 Hz.

Great, that makes more sense. I thought 160Hz high pass was eliminating too much low bass.
This is my schematic for now. I will add on the volume-knob and variable voltage resistor like you have drawn.

Will report back soon.

OK, looks much better.

You might want the option to add a compensation capacitor between pins 5 and 8 of the NE5534.

If you wind up not adding input pots, then you might put a 100K from the input capacitor (+ side of C connected to input jack) to ground to bleed off any stored DC.

I suggest that you route this manually because you will wind up with a better layout and learn in the process.

Thank you very much for the feedback again!

I added 100k ohm at the input (between the +ve side of the cap. and GND). I am figuring out what exactly are the PIN 5 and 8.
TI's datasheet explains it's to compensate for the input offset voltage arising from mismatch from input stage. Unfortunately this does not make a whole lot of sense to me yet.

In the meanwhile, can you recommend a potentiometer for this purpose? I briefly looked at your store, and I found http://www.ebay.com/itm/ReAn-Control-Kn ... 1c56b2beb2. Seems rather big for my small amplifier, but would this work?

Thank you!

TI's datasheet explains it's to compensate for the input offset voltage arising from mismatch from input stage. Unfortunately this does not make a whole lot of sense to me yet.

It is pins 5 and pin 8.
Pin 8 does double-duty including offset.

You do not need an offset trim between pins 1 and 8.

You might want to have the ability to add a compensation capacitor (typ. 10-22 pF) between pin 5 and pin 8.
For the gain that you show you do not need it.
But the NE5534 is not unity gain stable.
If you ever needed to lower the gain you might need the capacitor.

Thanks for looking at the store!

I have some 10K and 100K Alps linear pots.
The knobs only fit the 100K because the shafts are different on the 10K.
You could use either value in the circuit.

So one way of understanding the offset compensator is that the op-amp can output a voltage even if both input are tied to GND.
To compensate for this drift, we use the compensator pin. Cool!

I ended up attaching a generic 0805 capacitor to the pin 8 and 5. And I marked them as DNP.
It is a good time to do the PCB layout now I think. Thank you for your help thus far .

Btw, I sent you a message through eBay regarding combined shipping. Check your inbox!

Thank you

b1gtuna wrote:So one way of understanding the offset compensator is that the op-amp can output a voltage even if both input are tied to GND.

I can't speak for Wayne but I suspect his question was not what but "why". We can now buy off the shelf op amps with very good DC performance.

To compensate for this drift, we use the compensator pin. Cool!

Drift (over time?) or error due to device tolerances.

Since your schematic shows a DC blocking cap, output DC apparently is not even a concern.

I ended up attaching a generic 0805 capacitor to the pin 8 and 5. And I marked them as DNP.

As i recall the 5534 is stable for noise gains above 10dB so your design looks just about there.

A small feedback cap across R5 is sometimes useful to swap out package input capacitance and/or layout stray capacitance. While I wouldn't expect much phase lag for pF level strays with the modest (low) impedances you are using.

It is a good time to do the PCB layout now I think. Thank you for your help thus far .

Btw, I sent you a message through eBay regarding combined shipping. Check your inbox!

Thank you

Since you have included voltage gain in your path I might be temped to add another resistor to make the gain stage differential between input ground and output ground, while a circuit this small may not make much difference.

JR

I can't think of a single audio application where I've seen the offset trim on a 5534 used.
Or for that matter any 5534 circuit.

As JR points out a capacitor across the feedback resistor might be good to have on the board as a "DNP."
With a 2K Rfb you won't need it but if you decide to scale it later on to a significantly higher value you might need it.

Thank you both Wayne and JR for the inputs. I have added a capacitor across the feedback resistor, and marked as DNP.

I haven't had the time to sit down and layout the board yet. Will be back shortly!

Hello everyone, I am back with another question. I appreciate all your guidance!
The short-circuit maximum current of NE5534 is 38mA (as per the datasheet). Can I assume that I can power 2 X NE5534 with an 80mA boost circuit?

I have tried calculating the power requirement. So far I got only this far:

A pair of Sennheiser HD449 has 38ohm impedance. The gain of my design is 3.2 ((2.2k + 1k)/1k). So I don't think the output will ever reach the 12V r.m.s as long as I feed a sane input audio signal.
I read somewhere that iPod's have output voltage of 1.1v r.m.s. With the gain of 3.2, the output from the amp is 3.52v (1.1v * 3.2 gain).

Hence the power output from the amp is about 0.1 watt (3.2v * 38mA). Can I assume that an output voltage based on 0.1watt and the impedance of my headphones (38ohm)?