"WHAMMY" Pass DIY headphone amp guide

Wayne, just wanted to send out a big THANKS for this headphone amp!!

Having read this entire thread, watched the keynote at BAF and gone through most of the 'other' Whammy thread, I must say its a beautiful design and, in true 'Pass' style, very generous of you to share this with the community!

Not only a fantastic Headphone amp, but one that can be 'tailored' by DIYers with different op-amps. That is just fantastic.

Really looking forward to building this great AMP, with (hopefully) a minor mod to include RCA outs to double as PRE for the ACA.

Thanks again! Best regards,
Rafa.
 
Hi Budweiser,

I was surprised you got 0.1mV DC offset with an LM833 and 100K R3 and R5.

I get a no load DC offset of -0.1mV with 5.1K R3 and R5, and an OnSemi LM833N, and I get the following voltages on the opamp pins :

1 O/P1 -0.29
2 I/P 0.0
3 I/P 0.0
4 VEE -16.66
5 I/P 0.0
6 I/P 0.0
7 O/P2 -0.27
8 VCC 16.36

Could you kindly post the voltages you have on the pins of your LM833 ?

Ok, rookie mistake on my part.

Pin
1. -.11
2. 0.0
3. 0.0
4. 16.47
5. 0.0
6. 0.0
7. -.17
8. 16.32

Now for the rookie part.... Measured wrong connections on headphone plug. When I did the correct ones I came in at 31.2 mV. Ok time to switch out 100k. Sorry for the mistake.
 
Ok, rookie mistake on my part.

Pin
1. -.11
2. 0.0
3. 0.0
4. 16.47
5. 0.0
6. 0.0
7. -.17
8. 16.32

Now for the rookie part.... Measured wrong connections on headphone plug. When I did the correct ones I came in at 31.2 mV. Ok time to switch out 100k. Sorry for the mistake.

Switched out 100k with a 10k. Offset is now 1.3mV with pin 1 and 7 changing to -.17 and -.23
 
After turning off power one of the LEDs (D6) still glows slightly, when I pull the power plug, it goes completely out. Any ideas? It was not doing this prior to the R3and R5 switch to 10k.

Mine does the same. My build is stock to the BoM.

I've uploaded a YouTube video of it, on/off/on/off. There is a bright flash from the left hand LED on turn off.

DIY Audio Whammy Turn on and off - YouTube
 
LM833 DC Offset

Ok, rookie mistake on my part.

Pin
1. -.11
2. 0.0
3. 0.0
4. 16.47
5. 0.0
6. 0.0
7. -.17
8. 16.32

Now for the rookie part.... Measured wrong connections on headphone plug. When I did the correct ones I came in at 31.2 mV. Ok time to switch out 100k. Sorry for the mistake.

budwiser,

Thanks for the explanation. I can sleep easier now :)

I zeroed the DC offset of my LM833 at 6.1k using a trimmer. The nearest I had in the box was 5.1k which gave me -0.1mV.
 
Strange LED behaviour

After turning off power one of the LEDs (D6) still glows slightly, when I pull the power plug, it goes completely out. Any ideas? It was not doing this prior to the R3and R5 switch to 10k.

Hi budwiser & chiily,

I also have some strange LED behaviour after unplugging it that I didn't have until I had to replace the LEDs diodes and regulators : one LED goes out in about 17 seconds the other takes more then 2 minutes. As the left and right channels are identical I can't see how one side would take longer to discharge than the other - unless I have damaged something.
 
0.3v difference is fine.

Don't worry about the LEDs extinguishing. Many circuits have different current draws on the rails. Plus, if you are looking at this under no load, it's essentially meaningless.

Carry on.

:D

To the LEDboyz. :D Mine do that as well. I thought it was strange at first too. But, they were discussed a few pages back. Nothing to worry about apparently.
 
LED Extinguishing Time

To the LEDboyz. :D Mine do that as well. I thought it was strange at first too. But, they were discussed a few pages back. Nothing to worry about apparently.

I have seen the posts telling me it's not a problem, but I haven't seen an explanation why one side of the Whammy will draw a significantly larger current than the other, when both sides have essentially the same capacitor and resistor values (ignoring tolerances) arranged in an identical way :)

When you pull the power plug the energy stored in the capacitors dissipates through the LEDs. The stored energy is a function of the voltage applied. As both sides get the same voltage, and both sides have the same capacitance and resistance, then both sides should have the same amount of stored energy, so surely the length of time the LEDs take to extinguish should be approximately the same ?

What am I missing please ?
 
Have finished mine now, initially it was very quiet and hugely distorted, checked everything for dry joints and polarity, all good. Swapped the IC and everything is sweet.
1 DOA 833, swapped it for an OPA2134 I had.

I have added a pair of RCSa on the back panel and will hook them up to the output at some stage as Pre amp outs.
 
Asymmetric current draw from a symmetrical amplifier ?

I think he means that the circuit as a whole does not draw equal amounts of current from both + and - rails, so one will drop in voltage quicker than the other when the power is cut.

If what Silasmellor says is correct, can someone explain how one half of an apparently symmetrical amplifier i.e. identical component values arranged in an identical way can draw a significantly different current to the other half ? (one channel of my Whammy takes over 7x longer to discharge than the other)