"WHAMMY" Pass DIY headphone amp guide

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bigskyaudio

bigskyaudio

Member
Joined 2009
DC Offset

Measure DC offset with no headphones connected and nothing connected to the input jacks. Volume attenuator should be at minimum.

The opamp should not be uncomfortably hot and may be oscillating. Try adding a .1uF XR7 (or better) multilayer ceramic cap from pin 4 (V-) to ground and one from pin 8 (V+) to ground. Keep the leads as short as possible.

Rick
 
John Ess

John Ess

Member
Joined 2018
Got the cosmetics and chassis finished on #2 WHAMMY...I like the look of the polycarbonate front panel. Now to start plans on the 3rd and slowly research and gather parts over the next few weeks.
 

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avdesignguru

avdesignguru

Member
Joined 2016
terenceng said:
Finally managed to get my opa1612aid working. Had my friend reflowed the solder joints for me. It seems the flux I used could possibly have some issues. Offset is now below 4mV both channels when headphones are not connected. But when headphones are connected the offset is weird.. When the volume knob is all the way down, offset for right channel is -110mV and left channel is -40mV. The offset approaches zero as the volume knob increases. Is this normal?

- Note this doesn't happens with my other opamps. Offset is close to 0 across the entire range of the volume knob

It runs really hot too! Almost too hot to touch after 2-3 seconds. Is that the case for you guys who's been playing with OPA1612aid? Pin 4 and 8 measures 16.2v and -16.2v (with 18v trannies).
Click to expand...

My Whammy with OPA1612AID after full warmup has -6mV left and -6.4mV right with the opamp not generating any heat at all. The offsets do not vary at all with VC position.

I am using bi-polar Nichicon UES caps in the C26 and C27 positions. C2 and C7 are not used, with the positions left open. I am using the specified input coupling caps.
 
YouAgain

YouAgain

Member
Joined 2008
6L6 said:
Of course!

Not entirely sure it would be any advantage to having the volume pot wide open, which is for all practical purposes the same as bypassed...

But remember if you adjust volume in digital you are throwing away bits and information in the digital realm, losing resolution and data. If you keep the digital level all the way up you can then attenuate the analog level (with the whammy’s pot) to a listening level that works for you.

There’s no right or wrong answer. In my experience and practice, I always have dac wide open and use the volume knob to adjust level, as this sounds best.
Click to expand...
Agree about controlling volume in the digital domain but there are many common products called digital pots which are analog domain devices with digital control. Basicaly FET switching of resistive ladders with a fancy display.
 
passive420

passive420

Member
Joined 2013
marcovtt8 said:
hi, is BOM at beginning of thread still valid ? or something changed through 257 pages ?
Click to expand...

Yes, all still valid.

dac2800 said:
Also, is there a preloaded Mouser order list? I tried entering the BOM there but a few things were OOS and others I could tell were missing from the BOM.
(FYI, DIYAudio is OOS on the parts bin)
Click to expand...

No Mouser file posted unless someone has compiled one. It's fun to order your own and you might not want everything for instance pay attention to the regulator options, if using the LED reference, you won't need R13/R19 & R10/R14.

I see that some Dale RN55D' values are not in stock at mouser (global shortage of 1K's?) but consider using Vishay MRS25, excellent low noise professional resistors.
Vishay MRS25 Series Metal Film Resistors - Through Hole | Mouser

You should find suitable options for every component value, Fairchild FQP's sound excellent, Nichicon UES 22uF are in stock. Lots of options for filter caps. Use 100uF for op-amp decoupling, install 100pF's to be safe.

Choose the right transformer secondary for your intended rail voltage.

Be creative ;)
 
passive420

passive420

Member
Joined 2013
dac2800 said:
With the DIYAudio parts bin OOS, does anyone have the full list of included items? The BOM in the thread is incomplete, as as a newbie (my first project) I’d prefer to order everything i need at once. TIA.
Click to expand...

The BOM on first page is entirely complete and correct for the PCB assembly, the finished Whammy is a personal thing.

A quick check and all the suggested caps seem in stock. You will have trouble with RN55 resistors so substitute to MRS25 as I linked to earlier. The only things not on the first page BOM that are included in the kit are basic power and audio connectors, nuts bolts and bits of wire - all easily sourced.

All the Mouser part numbers are there, work your way down as far as you can and come back with any questions. Your knowledge of the circuit will be greatly improved.

If this is your very first project then BOM building is basic training. Just do it man ;)
 
penmarker

penmarker

Member
Joined 2012
dac2800 said:
With the DIYAudio parts bin OOS, does anyone have the full list of included items? The BOM in the thread is incomplete, as as a newbie (my first project) I’d prefer to order everything i need at once. TIA.
Click to expand...

From my and a lot of my friends' experience, first builds will always show and remind you the things you will not forget for your next builds. Aspire to order everything you need once yes, but anticipate needing to replace or order correct/more parts later.
Usually its the little stuff like the opamp socket, RCA connectors, the plastic washers for the RCA connectors because some places sell non isolated ones, headphone jacks, enough wiring (because you'll inevitably measure just enough for the wire run but then after cutting and stripping you'll realize its too short and have to cut another length of slightly longer wire).

Can't remember how many times I've made the wiring length mistake. Cut them excessively longer, and trim the excess later. Makes very clean routing.

**added.
Here's a proposition for you. How about you tell us what sort of build you're looking at (vanilla build just as how its designed to be with no additional stuff like switches or mods LEDs etc, or something more fancy?) and then list out the BOM that you've compiled.
That way we can tell you what you have missed or might require, while at the same time you can go through the parts required yourself and dip your toes in the pond.
That sounds good?
 
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D

dac2800

Member
Joined 2020
penmarker said:
***
Here's a proposition for you. How about you tell us what sort of build you're looking at (vanilla build just as how its designed to be with no additional stuff like switches or mods LEDs etc, or something more fancy?) and then list out the BOM that you've compiled.
That way we can tell you what you have missed or might require, while at the same time you can go through the parts required yourself and dip your toes in the pond.
That sounds good?
Click to expand...


Much appreciated - I'll plan to do that. For now, I can say I am planning the standard build (since I don't know enough to know how to tweak it), with an opamp socket and likely adding a power light. That said, I'll be open to suggestions for tweaks/improvements based on my target sound. All while hoping I don't kill myself in the process. ;)
 
C

Co60

Member
Joined 2007
Just finished my WHAMMY and its sounds spectacular, thanks to Wayne and 6L6 for the work on this for us.

I'm looking to get some other opamps to roll and looking for suggestions particularly anyone running Focal headphones. I have the Elegia and Elexx (MassDrop Version).

I am currenly looking at:
OPA1612
OPA1642
OPA2134
AD823ANZ

Anything else to consider or take of the list?

Thanks!
 
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