Pass Labs New DIY "WHAMMY" Headphone Amp

Discussion in 'DIY' started by highflyin9, Apr 22, 2018.

  1. AllanMarcus

    AllanMarcus Friend

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    well, WHAMMY #2 for me is coming along. I replaced C3 and C4 with physically smaller caps, but still 220uf/25V just to get easier access to the opamp (for rolling). I also removed and jumped C1 and C5. DC offset when from 24mV to 1mV after remove the C1/C5 caps. Can I hear a difference? nope. maybe. probably not. But now that my DC offset is so low, I might try removing C26 & C27.

    Case is on order from Ali and will be here any week now :)

    I'm actually thinking of making a case like the Crack has. 4 walls of a box and an aluminum plate on top with the board mounted upside down on the plate. All the knobs, switches, jacks and inlets on the forward and rear part of the plate, and a knob it the middle to lift it up. Alternatively, if it's not too hot, I might put the Bifrost Multibit on top of it.

    So much fun.

    [​IMG]
     
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  2. Luckbad

    Luckbad Traded in a unicorn for a Corolla

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    Looks good! Do you have a Mouser BOM or anything put together? I put one together a while back (can't find it on the phone) but haven't ordered the parts still.
     
  3. AllanMarcus

    AllanMarcus Friend

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    I do, but it changed since I purchased everything, and I had to get the transformer and something else from Digi-Key. I did make a speadsheet that is linked on my web site (link in my sig) that might help.
     
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  4. msommers

    msommers High on Epipens

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    Surprised there aren't more impressions of this amp given the DIY feel around here...
     
  5. fraggler

    fraggler A Happy & Busy Life

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    Still using the WHAMMY daily as my speaker preamp and for background listening. Decided to start rolling some opamps to see if the sound changed. I started with the RC4580 which was a recommended one for the stock build. Sounded very good. Fairly balanced, nice bass, nothing stood out as amazing or bad. Lived with this for many months. Tried the OPA2134 next. Was a little more dynamic, maybe more detailed with more spaciousness, but introduced a glare in the upper mids, lower treble. Decided to give an Aliexpress opamp a try and went with this one: https://www.aliexpress.com/item/33027580243.html?spm=a2g0s.9042311.0.0.77b54c4dVNMegU Could be wishful thinking or placebo, but I hear more detail and more spacious sound. Glare is gone. I don't think I will roll any more opamps at this point, as this one gave me the more spacious sound I was looking for. If I could get a touch more warmth without any sacrifices in detail and spaciousness, I might consider it. At this point, I think the WHAMMY is just not a warm amp. I don't think it is necessarily bright, but for my tastes, could use a little more warmth. Still falls behind the ECP L2 in realism/3D, etc, but I enjoy it more than the Vali 2, MCTH, and SOHA II, even if giving up some of the warmth and smoothness of tubes. I think this sounds good enough now that I might get a new case for it. Really nice amp for $150-250.
    [​IMG]
    I don't think I did an internal shot of my build:
    [​IMG]
     
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  6. Azimuth

    Azimuth FKA rtaylor76, Friend

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    I think the stock called for an OPA2604, which is a warmish opamp if I remember correctly, but the 2134 was the replacement. From what I read, the 2604 was a bit warmer than the 2134, but both had complaints about grainy high mids and not the best at detail retrieval. Those are good buffers, but not the best driver opamps.

    I guess I never really studied the circuit until now...so I guess because of the 4N35 optocoupler that there is no need for any AC or DC coupling?

    There is also some rolloff in the bass. Only 0.5db at 20hz, but the rolloff starts at 100hz. I wonder if that would change under different loads.
     
  7. Jimmy24

    Jimmy24 Rando

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    @fraggler I like the LM833N. I'd say the soundstage is as big as the Vivid's but the main thing about it is that's it's very engaging. It definitely has a warm sound and it's my favorite. To me it beats the V6 both Classic and Vivid so I would give it a try.
     
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  8. fraggler

    fraggler A Happy & Busy Life

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    Thanks for the suggestion, I have 5 on the way from TI (min order). The Aliexpress opamps were sounding really good, but I started getting some pops and distortion. Haven't had time to really troubleshoot - just put the RC4580 back in and all is well, though lost the dynamics.
     
  9. Luckbad

    Luckbad Traded in a unicorn for a Corolla

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    Any updated recommendations on solid enclosures for this thing? It's likely my next project and I'm hung up on which case to get. I care more about the chassis being relatively easy to work in more than super compact.

    Also, @fraggler, is the preamp functionality something you added yourself? Any info on how to integrate that?
     
  10. Cspirou

    Cspirou They call me Sparky

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    Good news is that you have a lot of options. The heatsinks are on the PCB so you can use just about any type of enclosure and the fixed external components are only on the front side so you don't need a precision CNC'd rear panel.

    A basic Hammond, Hifi2000 or cheap chinese case will be just fine.
     
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  11. fraggler

    fraggler A Happy & Busy Life

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    I added the preamp functions via a shorting 1/4" jack. Just run some lines from the shorting jack to a set of RCA connectors at the back. The WHAMMY gurus recommended adding some in line resistors to protect sensitive amps. This is the simplest way. But if you were going to use an XLR out, or wanted to avoid the horrible screeching you inserted or removed the 1/4" plug while your amp is on, you could throw a toggle switch in as well.

    I definitely recommend something bigger than the Hammond that is in the build guide. While I made it work, I definitely wish I had more room for proper casework, especially around the power input. I forgot to bookmark it, but someone found one on Aliexpress that looked nice and was a reasonable price. I don't know how long you would have to wait still, but several months ago, the WHAMMY guys were going to come up with a kit case (probably a custom Hifi2000), but haven't heard an update in a while.

    Was looking at this one: https://www.aliexpress.com/item/32899427580.html Would only need to drill one hole for the headphone out. Has everything else you need if you wanted a switch for either the preamp or multiple inputs.
     
    Last edited: Oct 14, 2019
  12. Cspirou

    Cspirou They call me Sparky

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    Schiit preamp outputs are basically just the headphone outputs with 75ohm resistors. XLR is similar but don't know what resistors they use.
     
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  13. Jimmy24

    Jimmy24 Rando

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    @fraggler Hope you like it! The RC4850 was my least favorite. This was the first op-amp I used and I was really disappointed with how the Whammy sounded. Little did I know an op amp switch would make a big difference. Swapped out the RC4850 for the LM833 and music never sounded so good!

    On another note I have an OPA2210 and OPA2107 coming in which had very positive reviews so I will definitely post my impressions on those once i get them.
     
  14. Jimmy24

    Jimmy24 Rando

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    OPA2107 is out of this world. Biggest soundstage I've heard without compromising detail, punch, and clarity. Has the warmth of the LM833. Definitely definitely improved low end! Acoustic guitar sounds insanely good!
     
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    Last edited: Oct 14, 2019
  15. AllanMarcus

    AllanMarcus Friend

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    Her's a little preview of a Woody WHAMMY i've been working on for a while. I just finished all the finishing, and now I just need to assemble it. Hopefully I can get it done before the weekend.

    It's red oak, stained mahogany. 15 coats of poly wipe. I kept saying to my wife: I'm going into the garage to rub my wood until I'm satisfied. Now I'm satisfied :)

    [​IMG]
    [​IMG]
    [​IMG]
     
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  16. Luckbad

    Luckbad Traded in a unicorn for a Corolla

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    @AllanMarcus Looks outstanding! Did you build the case yourself or I can I steal your idea by buying the same one? Is it the Hammond HWCHAS1310BK?

    @Jimmy24 I've looked for the OPA2107 before for a guitar pedal at it was always a bit pricy. Where did you pick yours up?
     
    Last edited: Oct 15, 2019
  17. Jimmy24

    Jimmy24 Rando

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    @Luckbad Digikey has it for about $23. Mouser doesn't carry it with an 8DIP. Btw, is it worth it? It definitely is.

    @AllanMarcus Stunning work! I love that wood grain in front. Was thinking of doing something similar. Where did you get the metal chassis from?
     
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    Last edited: Oct 15, 2019
  18. nerone

    nerone Rando

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    Stunning work.
    Won't you need to add some ventilation holes on the top panel?
     
  19. AllanMarcus

    AllanMarcus Friend

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    it’s my own design. I prototyped one with cheap pine, made some mistakes, learned, then built with red oak.

    no metal chassis. It’s four walls are red oak. I router a slot about half an inch from the bottom, and slid in a 12x8 piece of aluminum. That is the piece I painted black and attached the board to. The top piece is also 12x8 and painted back, and sits on a rabbet I routed into the wood

    nope. I drilled some holes on the bottom, but the amp runs pretty cool. My other whammy is completely enclosed with no ventilation, and doesn’t even get warm to the touch.
     
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  20. AllanMarcus

    AllanMarcus Friend

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    Finally done with the Wood WHAMMY! Here are the pics:

    [​IMG]
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    [​IMG]


    I'll add some rubber feet tonight, and it's done. I love it. Now come opamp rolling.
     
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