Walnut F1

Discussion in 'Portable Headphone Amps' started by Ivan TT, Aug 21, 2017.
  1. Ivan TT
    Balanced Version= With 2.5mm Balanced out Interface and still have 3.5mm interface
    Standard Version= Only have 3.5mm interface

    WARNING! F1 is designed to drive high-impedance earphones, essentially set to what is high-gain mode on other amps. This leads to distortion (when using 3.5mm se out) or extremely high output level (when using 2.5mm balanced output). Solution is in post #9.

    If you have 2.5mm earphones, you can plug the output of your DAP or phone into "Power out" socket. This will utilise balanced output buffers only, bypassing opamp and volume control altogether. See post #17 for details.

    1. Interface: 3.5MM or 2.5 interface
    2. Output power:300mW
    3. Operational Amplifier Chips Model: OPA2134
    4. SNR: 90DB
    6. Lithium battery capacity: 1500MAH
    7. Charging Interface: Standard MICRO USB.

    1 X Headphone Amplifier(earphone not include)
    1 X Charging Cable
    1 X AUX Cable
    2 X Silicone straps


    Walnut F1 amp size is small, 80 * 50 * 20mm than a bank card is slightly smaller, but the small head also has great wisdom, this section of the sound of the amp should be said that the bile is more foot, simply is the sound more sweet The Plus after the amp; Can feel out the sound field is significantly large, opener is the original BB of the OPA2134. Sound characteristics in general are warm and delicate type, strong driving force, "bile". Low-frequency quality and quantity. At the same time 2.5mm version with a balanced output, balanced output has been applied to professional recording field, balanced output is characterized by high degree of separation, the thrust is about twice the power output.


    operational amatement OPA2134, OPA2134 is designed for audio and designed for the op amp, sound mellow, rounded, neutral warm, bile is very strong, is known as the most electronic tube audio amplifier. Feeling like the upgraded version of 5532, all aspects have greatly improved, good resolution, music taste better, there is bile, the sound is relatively thick and a bit rigid, comprehensive quality is very good. Especially for music performance.
    The amp can be replaced by the op amp. Direct plug design. Is now the mainstream design, different op amp to bring a different tone.





    Almost completely using the machine's power supply circuit, up to 24V (+12 V gnd -12V) of the pressure, easy to control the various types of op amp on the market, the strength of the launch of the loud field. While supporting the side of the charge while listening to music.


    Power supply part of the selection is 24v 1A power supply, ripple very small (using the commonly used three-terminal regulator 78M12 79M12, under normal circumstances no noise at the end), the filter capacitor is Ina vr series and gold fw series of high-quality capacitors The Imported high current full-shielded inductors.

    (16 ohm-400 ohm), and due to the high supply voltage, long-term use of the shell will be a slight signs of fever (not more than 30% of the use of a class of current amplification and op amp voltage amplification, degree).

    The use of 3.7V high-capacity lithium battery-powered, boost to 24v maximum current 1A, battery capacity 1500mah, life 4 to 5 hours or so. When charging the use of Andrews can be a common charging line. Do not use when charging. Charging time about 2 and a half hours. (When charging red light, stop charging green light)


    Output coupling DC blocking capacitor using Ina SILMICII 220uF ELNA silk fiber purple palm brown audio electrolytic capacitors, the strength of the extraordinary enough to be among the ranks of the world's advanced audio capacitors. Using the OFC oxygen-free copper feet, very low distortion (third harmonic distortion-120dB), very small tangential loss, natural silk fiber media, high-quality sound, play silk soft and natural, enhanced resistance to acoustic oscillation design, Increase the sense of low-frequency thick, reduce the high-pass part of the peak value of the Peak and the middle part of the rough sound quality.
    Last edited: Aug 22, 2017
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  2. Ivan TT
    More eye-candy:
    Last edited: Aug 21, 2017
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  3. Ivan TT
    After a bit of research and experiments I think it's been made to drive high-impedance earphones, hence distortion from the 3.5mm SE output and extremely loud 2.5mm balanced output when using low-impedance IEMs.
    I found a pair of 600Ohm AKG 240 (not even mkII verision!) and indeed, no distrtion from 3.5mm SE output.
    So, essentially F1 is permanently set to High gain to drive high-impedance earphones, so when using LO from Z1's output and low-impedance earphones you either get distortion and low headroom on 3.5mm SE output, or extremely high output on 2.5mm balanced one.
    Possible solutions are: use attenuator (either on the input, or on the output, but I'm not aware of 2.5mm balanced attenuators even existing), or try to feed F1 from PO output:

    My solution (warning! this is now obsolete and better solution is in post #9) was to reduce the gain by employing two 5kOhm resistors in parallel with the stock one in opamps feedback loop, over contacts 1-2 and 6-7 of opamp's socket:


    I'm still experimenting with the resistors values and other ways to solve this issue (i.e. adding resistor before input cap), but distortion is all but gone and 2.5mm se output volume control range is about 80% before it becomes too loud, eventually I plan to solder resistors in when I find a value that works 100% for me.
    Last edited: Aug 21, 2017
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  4. Ivan TT
    After reducing op-amps gain as described above, I finally could evaluate F1's sound and I like it very, very much, even after returning to stock BB opamp and using se 3.5mm output, in my view definitely an upgrade to using Z2's PO out. I will post more impressions later on as I'm still going trough my reference tracks, but so far I like what I hear a lot.
    dmz555 likes this.
  5. benedium
    Is this headphone amplifier good for full size headphone like Superlux HD681 (32ohm impedance)? Or still have to do modìfications? Also wondering if i should buy this or the Fiio a1.
    Last edited: Aug 21, 2017
  6. Ivan TT
    I have some 32-55-64ohm headphones at work, will check in couple of hours, standby.
  7. Ynot1
    Any chance there is a high impedance balanced earphone cable, using resistors that are sonically pleasing?
    I think the VE Zen balance might be a good match for this amp. Actually VE has a new flagship coming up. And maybe some headphones with high impedance, but I can't think of any except hd600 and beyers. And those may have aftermarket balance cables.
    Last edited: Aug 21, 2017
  8. dmz555
    Thanks alot Ivan TT.
    Im really interested in walnut f1's 2.5mm balanced PO and pair it with zishan z2's LO.
    The big question is.
    Out of the box without performing any modifications, can f1 sweetly drive a 32 ohm 2.5 balanced earbuds?
  9. Ivan TT
    Distortion solution #1 did not work as nicely as I expected, so here comes solution #2:
    260k resistors (actually 130kx2) in series with input capacitors.


    This brought output level on 3.5mm se out to exactly same level as Z2, obviously balanced will be 6dB louder.

    I tried a range of values for input resistors, from 100kOhm to 330kOhm, 260kOhm gave a touch of distortion at the very end of the volume potentiometer's travel, unlike lower values where distortion would kick in earlier on).

    Replacement capacitors are 110uF (not 220uF as in stock and I don't think 220uF Muse BPs would fit) as CH9T is too good at ultra LF reproduction, which was bothering me a bit.

    I also had to move battery back as Nichicons are wider.

    Input caps are Elna Silmic II 10uF 35v
    Last edited: Aug 22, 2017
  10. Ivan TT
    Yes, but only about first 10-15% of volume pot travel would be usable, as anything above that is obscenely loud (albeit distortion-free unlike on 3.5mm out).

    Also I believe it's a safety hazard as it's way to easy to accidentally turn the volume dial too far with about 90% of it's travel are in painfully loud territory.
    Fox2twenty and dmz555 like this.
  11. Ivan TT
    Now, how do I take the output from buffers and send it to 3.5mm, preferably with automatic switching between the two?


    Has anyone seen 8 pole 4 pin 2.5mm sockets anywhere?
  12. dmz555
    Thank you so much Ivan for that quick reply! This f1 really gets your tech side in action. I will be looking forward on your project to make this f1 work flawlessly.
    Ivan TT likes this.
  13. MuZo2
  14. Ivan TT
    I'm not a designer, not even related.
    My understanding is that it's been designed to be used with high-impedance transducers, but not advertised as such. Why designers did not include gain switch is beyond me.

    By the way, after putting in LME49720NA I'm in the Audiophile heaven, I have Muses02 in Z2 and muses absolutely pales in comparison, not even close.
  15. MuZo2
    Is this with your mod?

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