"WHAMMY" Pass DIY headphone amp guide

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That worked, thanks so much 6L6. Project done, and it sounds great. I increased the gain by substituting 10k for 4.75k resistors at R4 and R8 (or was it R10). Now it really works like I would expect a preamp to work.

Thanks Wayne, 6L6 and all the contributors to the thread. Without assistance from the DIYaudio community I'd wouldn't have a working project.

Always good to see another successful build and happy DIYer.
 
Hey there. I just got the PCB and the parts kit from The diyaudiostore. The IEC receptacle they shipped is huge! Including the solder lugs, it will intrude 2 1/8 inch into the enclosure. If I put the IEC in the middle of the rear of the enclosure, the rca inputs will be way over one side. Not pretty at all. Anyone know what diyaudiostore was thinking when they selected this ginormous receptacle?
9939402_l.jpg
 
Ok, so... with everyone talking about DC offset... I have 12mV in one channel and 63mV on the other.

The value is not that high (i hope?), but will the difference between one channel and the other (4x higher on one) have any impact with sound?

More importantly, with this scenario, is there actually any way to change and level the offset?

Thanks for any feedback,
Rafa.
 
Answer to RAFA

Hello Rafa,


63mV offset in one channel seems a little bit high to me?
I am not an electronic engineer.
What I know is that it should not be higher than 50mV.
Perhaps one of the profis can answer this.


In my Whammy I have offsets of 1.2mV and 0.8mV.
I think it can also depend on the Opamp you are using. But I am not sure.



Greets
Dirk
 

6L6

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Anyone know what diyaudiostore was thinking when they selected this ginormous receptacle?

Yes, I do.

It’s internally wired, has only one fuse drawer, is switched, filtered, and, the most important, has 3 clearly labeled tabs on the exterior for Live, Neutral and Earth. It covers all the requirements for most countries mains wiring, and happens to be a really nice IEC. :D

Of course, if it doesn’t fit the enclosure, save it for another project and use something that works better for your build. This is DIY after all.
 
Last edited:
Yes, I do.

It’s internally wired, has only one fuse drawer, is switched, filtered, and, the most important, has 3 clearly labeled tabs on the exterior for Live, Neutral and Earth. It covers all the requirements for most countries mains wiring, and happens to be a really nice IEC. :D

Of course, if it doesn’t fit the enclosure, save it for another project and use something that works better for your build. This is DIY after all.

Thanks for the explanation. I really appreciate the response.

I think I will get it to work. It does look like a very good quality receptacle.
 
Connect your RCA ground buss to the output ground. As far as I can tell, your inputs are not connected to ground except through the capacitor...

Thanks @6L6!!! I know this was meant for @Hook, but it worked for me as well!

To summarize my earlier post, my symptoms were:

- loud hum/buzz in left ear
- amp was silent with AD opamp wasn't working at all, TI opamp at least produced music but also the loud buzz. At first I thought I had fried the AD opamp somehow.
- Additional discoveries from last night: music was actually coming through in both ears, but the buzz was overwhelming it in the left. There was a quieter buzz in the right ear, so it was easier to hear the music.

Fix:

I took the RCA ground wire out of the hole behind the Alps pot and touched it directly to the output ground. Eureka, the buzz disappeared! I reconnected the AD opamp, and it was also working fine once the ground connection was fixed.

When the RCA ground wire is not connected to anything, the buzz is equally loud in both ears. When it's connected to the ground hole behind the Alps pot, it's much louder in the left ear. Does anyone know what would explain these symptoms? I did cut out a corner of the PCB near the C28 capacitor, and it looks like a trace connecting the PCB grounds was running along that corner. Would that explain the problem?

Is it ok if I keep the RCA ground connected to the output ground near R24? Would that cause any ground loop problems?
 
So I took away the input capacitors!

For both channels, the input DC offset(at input RCA jack) is less than 0.5mV; while the output DC offset(at headphone jack) is less than 1mV, depending on the op amp I use.
I tried different op amps and the worst DC offset in one channel is only 2.xmV. The best is 0.0mV.
(by accident, I turned on the amp once without an op amp installed. DC offset at output went up to 56mV!)

The SQ does improve compared to my vintage oil caps:
More clarity, more bass; treble is rendered more naturally.
Vocal is more upfront and everything has an extra layer of realism.

I believe "around 1mV" DC offset is a very good value?