Headphone amp / mixer

[GrooveChampion]

Maybe I'll upload some pics over there, but so far I just ordered some PCB's out of sheer frustration.

[bones79]

Mao, just checking... Is z1 still 9.1v zener 1N4739?
Thanks!

[MAO]

Yes sorry, but It can be higher depending on the charge pump you use.

Check out madbean's build notes for the road rage regarding the charge pump zeners.

There's no need for a LT1054, the layout will work for all the other charge pumps listed in the road rage. You would need to lift pin 1 if using the LT1054.

I prefer the ICL7660SCPA which can take a 12v zener. (9.1 is ok too)

I can send you my JamMan if you want to check it out before building it. Let me know.

[bones79]

Thanks, I have some 9.1v in stock so that's fine. Just need to source a decent switched stereo jack socked for the aux in... Any recommendations there?

[MAO]

I'm sure there are better ones, but originally I used these 3.5mm jacks from Tayda.

Not fun to work with but did the trick. If you download the datasheet, you connect B and E to the headphones out, A, C and D to ground.

I used a meter to figure out which pin was which.

If I were to do it again for myself, I'd probably go with stereo 1/4 inch jacks and use an adapter for the 3.5 mm audio in cable and headphone out. Already had the adapter for my headphones so I'm now using a 1/4 inch there.

[bones79]

Hi Mao!

I'm afraid I need your help again, if you have time. I built and housed the layout, and the aux audio input and headphones output seem to work nicely - mp3s played on my phone sound great through the headphones. Guitar also sounds good when plugged in.
Unfortunately, there's an awful whine through the circuit (sounds similar to Eb, top E string 11th fret) even when there's nothing plugged into either input. It is emphasised by the vol and gain knobs (to the point of howl) , and pans left/right with the balance knob.
Any ideas?

Thanks mate!

[MAO]

That sounds like the dreaded charge pump high frequency whine.

There were a lot of bad ICL7660SCPA selling on ebay. The bad ones were most likely the noisy ICL7660CPA but labeled as the quiet ICL7660SCPA.

If you have two 9v batteries, you can find out fairly easily.

Test: Disconnect your dc adapter and remove the charge pump.
Attach the + terminal from Battery 1 to the top rail, at the top right corner of the board is fine. (Pin 8 of the charge pump socket)
Attach the (-) terminal from Battery 2 to rail 4, again at the right side of the charge pump socket (pin 5 charge pump socket)
So both are attached to the right most column.(or pin 8 and pin 5 on the charge pump socket)
Then connect the (-) of Battery 1 and  (+) of Battery 2 to ground.
This will supply the circuit with Clean +/- 9v.

If the whining goes away, the charge pump is the issue.

[MAO]

I should have asked, it the noise always there?

[bones79]

Thanks, Mao. It's labelled "7660S CPAZ V17184P", and is indeed from ebay. Tomorrow I'll get some 9v batteries and try your suggestion. There is an electronics shop close by, so I may also pop in and see if they have a 7660S.
Is ebay a bit risky for such items in general? I try to order most things from bitsbox, where possible.
Yes, whine is constant, and affected by pot levels.

Thanks again, and apologies for the late reply.

[MAO]

You can also use a TC1044SCPA or MAX1044CPA or LT1054. You would need to lift pin 1 if using LT1054.

Most people on the forums recommend against random Ebay sellers, only those listed as 'confirmed' legit. There may be a thread about this in the forums.

And even if you get lucky with a random vendor, there is no gaurentee the next order will be legit...ask me how I know :0)

For good or for worse, I have had good experience with ICs from Polida on Ebay so far, usually only ordering when it says genuine, oem, or legitimate in the description. But warning, others have not had a good experience with Polida and refuse to order anything else from them.

Tayda is definately a good cheap alternative.

BTW, I used my headphone amp quite a bit this past week, along with my Android phone as the audio source. Mostly plugged straight in, a little dark straight in, but gets the job done.

I may add a treble boost, or some kind of tone control in the next version for stand alone use. When I built this one, it was mainly for testing pedals.

[bones79]

Hi Mao,
You nailed it, no whine when using the batteries
I'm pretty chuffed it wasn't due to my crappy soldering
I'll replace the IC and get to enjoying the amp, can't wait!
Regarding your comment about it sounding a bit dark... Do you think an EQ pedal with sliders (like the mxr 6/10 band pedal) is a realistic vero build? If not, is there an alternative you could recommend?
Thanks again for all the help and insight, I'd be lost without it.

[MAO]

Well, unfortunately, I did learn about the charge pump whine the hard way.

Fakes


But glad you got it sorted out fairly quickly.

As for the EQ, yes IMO vero is a great option as it easier to tweak the EQ bands with vero rather than a pcb.

Cutting nice looking slots into an enclosure is a different story, although John K has posted some really nice ones.  

1776 has a 6 band EQ using 20kW pots, rather than sliders, won't look as cool but much easier to deal with.  The build doc has a couple links showing how to tweak the EQ bands to your liking.

Not sure if someone has already drawn up a layout for it. If not, and you're interested, I'll give the layout a shot. Doesn't look like it would be too hard to draw up.



 

[bones79]

Hi Mao,

So I got a new 7660S from the local shop, and the headphone amp works great now :)
That EQ looks interesting. Will do some research. I'm also considering building some amp emulation pedals to try out with the headphone amp... Have you tried any of the fender/marshall/dumble emulator veros on here?

Thanks!

[MAO]

Excellent!

Any of the emulators from Wampler or Catalinbread are great. Also Runoffgroove.

My favorite though is the Ethos TWE, as is, or modded for a little less gain. I also converted one from a 1 knob tone control to a 3 knob tone stack.

I have also built the baja 59 plexi, which is lower gain than most, but comes alive when pushed with an overdrive, fuzz or boost pedal. Based on that one build, my guess is all the Baja are probably decent. These are probably a good choice for use with the headphone amp.

BTW, the Wamplers are a bit tricky as you really need jfets that bias properly at the original drain resistor values.

[jimtom]

Hi MAO,

I built the headphone amp you made as it was exactly what I was looking for. However I need some help as I have issues with it.

When it works, the sound is great but most of the time there is no sound coming from the guitar. I have to turn the volume and gain to the maximum to hear the guitar at very low volume. Sometimes, the sound comes back and goes without changing anything. the audio-in works.
also, when it works, if the gain is high and the volume above 25%, I get a loud buzz without the sound from the guitar.

[MAO]

Hey jimtom,
Sorry yours is acting up. Unfortunately with what you described, it could be a whole host of things.

My suggestion would be to reflow all the solder joints and make sure your grounds are solid, particularly the input and output jacks. After reflowing the solder, you may want to run a knife blade up and down all the tracks.

If you have an audio probe (very easy to make) you could probe a couple places while the pedal is working  to get a baseline. Then when it acts up, try to find exactly where the audio is dropping out by probing along the circuit path. I'll be glad to help you through that if you like.

Once you use an audio probe, you'll wonder how you got along without one.

[jimtom]

hi Mao,
thanks for the tips. there was indeed a bit of solder betwwen two tracks. the amp works now. I still have the issue with the buzz but I can live with it.