"WHAMMY" Pass DIY headphone amp guide

WE

It is alive... no smoke so far.
Sounded awesome outside the case, but we will see what it now sound like later today.
This was so much fun to build, but I underestimated how much work with all the modifications

Have a pair of LM833 per 6L6's writeup in there for now and test others later.
I have s Preamp switch and a switch for balanced/unbalanced headphones.
Also, have adjustable gain installed to r12.
Do not have the 100ohm resistors on the preamp lines yet :(
Had to DIY the milling, learning as I went along, ;)
Cable tidy-up is also needed.

Will add MUSES volume with OLED display when parts become available and KHADAS DAC after.

Would have been lost without all the forum contributions, so thanks for all the help from as usual Wayne, 6L6, avdesignguru to name a few.
So it is all buttoned up now.

Final conclusion, I love it.
listening through Beyerdymanics DT770 Pro 80ohms.

I built it balanced for two reasons:
1. To fit into the Main Stereo which is fully balanced from the Modified OPPO CD >> BAT Preamp >> Whammy
2. For the sheer fun of it.

Otherwise built stock per 6L6's instructions.
The LM833 sounds wonderfully balanced.

Some of the issues I had:

1. Plugged straight into Modded Oppo BDP105 with Sen IV mod
Sounded distorted and noisy
Hum present rising with the volume and not really acceptable

2. Plugged into Tape Out of BAT vk50se
Sounded better than above, still slightly distorted and noisy, but not as bad as 1
Hum present but lower and changes with volume knob too

3. Pluged into PreamOut of BAT vk50se (Best Solution)
Max volume on Whammy and use the Volume knob on the BAT for adjustment.
No distortion and almost imperceptible hum at Whammy max volume.
Was able to achieve desired SPL in the headphones.
Sounds absolutely amazing and this is what made me understand what everyone is talking about.

4. In options 1 and 2 above, generally, the volume output of the Whammy is low. (Using a 10k pot)
I find I can max out the volume a lot of the time, and could use more.
Searching the thread to see if there are more suitable resistance values to correct this.

Any advice as to why is appreciated.

All in, it was worth it,
Proposed future mods, just cause it was so much fun
Upgrade opamps to the BursonV6 classics. (Based on reviews, this is probably, my preferred, but may do some comparisons)
Upgrade Input CAPS
Install the Khadas DAC, Muses Volume, and OLED display.

Thanks again for a fun project.
 

ahess

Member
2016-04-26 11:17 am
Hi all.
I'm jumping back into the Whammy after a few years of just...well, enjoying the music.
I'm waiting on a OPA2107AP to replace the LM833NG that is in there now. I'm assuming from what I've read that it's a plug and play replacement.
Question, based on my rereading of some of this thread:

The schematic says that C7 and C2 are optional, depending on the op amp used. I don't have them in. Should I keep it that way?

Any other changes recommended for this op amp? Or general tweaks you would recommend at this point -- My build is three years old, so I haven't kept up on tweaks!
 

sp33ls

Member
Paid Member
2018-04-06 7:09 pm
USA
I like the OPA2134, tho I've been rocking the overkill OPA828 for fun lately.

So, I have a couple of 3.3uF Mundorf Supreme's lying around from another build I decided to not pursue.

I think I can fit them in the open space between the chassis and PCB. I could place them inline with the input (before the pot) and then short the location on the PCB.

Technically, isn't 3.3uF (marginally) better than 1uF due to less distortion in the lowest frequencies and lower bass rolloff? Obviously, any difference would likely be indiscernible to my ears, but just from a technical perspective... :)

Just curious if there'd be any downside/trade-off to placing these in the WHAMMY instead of 1uF, and I'm guessing it'd be best to place before the pot, rather than increasing leads length from the PCB?
 

ahess

Member
2016-04-26 11:17 am
I just popped in the OPA2107AP to replace the LM833NG. I'm going to do some A/B listening later, but I noticed right away that the amp went from being dead quiet to having a slight static background with the 2107. It's the same whether the volume is all the way up or all the way down. What would account for that?

Correction: it actually seems to be worse when the pot is turned way down and get less as I turn it past 12 o'clock. (This is with the power on but no music playing, obviously)
 
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A Jedi

Member
Paid Member
2019-05-01 9:53 pm
I just popped in the OPA2107AP to replace the LM833NG. I'm going to do some A/B listening later, but I noticed right away that the amp went from being dead quiet to having a slight static background with the 2107. It's the same whether the volume is all the way up or all the way down. What would account for that?

Correction: it actually seems to be worse when the pot is turned way down and get less as I turn it past 12 o'clock. (This is with the power on but no music playing, obviously)

I have a higher noise floor with the 2107 as well. Don't know enough EE to know why though.
 

sp33ls

Member
Paid Member
2018-04-06 7:09 pm
USA
My Whammy has a 2107 and it's the preamp for a system that has 98db sensitive speakers. The volume control rarely gets past 9 or 10 o'clock and there is no audible hiss between songs. Even when close to the speakers.
Did you install bypass caps on your build? Per the datasheet, TI recommends:

"Power-supply connections should be bypassed with capacitors positioned close to the amplifier pins. In most cases, 0.1µF ceramic capacitors are adequate. Applications with larger load currents and fast transient signals may need up to 1µF tantalum bypass capacitors."

It'd be interesting if barryso had installed small bypass caps, and those who experience noise hadn't. Tho, I'd be somewhat surprised if doing so resolved the noise as the WHAMMY has a pretty clean supply based on what I've seen in other posts.

Still, could be worth a shot. And, could also be worth checking your grounding & chassis... not having your potentiometer not making a solid ground connection can cause some noise with certain opamps.
 
Did you install bypass caps on your build? Per the datasheet, TI recommends:

No bypass caps for the 2107. The build is the same as it was for the other opamps.

After my last post I paused the music and turned the volume control up to about 3 o'clock. Still no noise when right in front of the speakers. But even if there was some noise at that level it wouldn't make any difference as the system is too loud by about 10 or 11 o'clock so the volume control never gets turned any higher.

This Whammy is the standard kit from the store with the one exception of either 50 or 100 ohm resistors on the rca preamp outputs. This was talked about very early on in this thread.

I'm not a circuit wiz, just a follow the build guide and make good solder joints kind of guy, so my ability to answer questions is limited.
 

Eldergod

Member
2020-08-05 7:01 pm
Anxiously awaiting my kit to arrive hopefully tomorrow for the weekend. Went ahead and ordered some opamps to roll:

AD823 $11.69
LM833 $1.09
OPA2134 $6.15

For the cost, seemed like a few great places to start taking into consideration diminishing returns. Maybe at some point I'll try a $25 option or even one of the $40 ones, but seems like a tough call at those prices. Time and use will tell.

One question: I've read nearly this entire thread, and seen a few mentions of caps for C1 and C5. What are good places to start that won't break the bank and will they fit? I think I saw a Jantzen suggested?