[activatorfly]

Thank you, It's not a major surprise to be honest, as I was looking to use this mainly balanced anyway. I know it's not true balanced but it's an intro of sorts, and you never know, the SE might synergise with something I own. It'll be fun trying. And the option to modify is also appealing.

I hope they address the poor SE issue with the release of V3 - which extends modification/sound signature tuning via three op-amps.
In my opinion, maybe V4 should include a balanced input & output - which would maintain a balanced synergy, rather than compromising the player with substandard SE output...
I guess we'll find out soon if the upgraded SE stage has improved?

 

[sfogar]

Hi, is the F1 suitable for IEM like KZ zs5 (i.e. multi dd+ba) ?
Currently I own a Zishan Z1 and the high output impedance is not suitable for the zs5.

 

[RyanM]

Hi, is the F1 suitable for IEM like KZ zs5 (i.e. multi dd+ba) ?
Currently I own a Zishan Z1 and the high output impedance is not suitable for the zs5.

The answer to this is no. In the same price range (check EBay) I’d look at the Topping NX1s - it’s a fantastic little budget amp with high/low gain and a bass boost. Awesome stuff.

 

[Yobster69]

Hi, has anybody measured the output impedance of both sockets of the F1?

 

[Ivan TT]

Changed gain-reducing resistors to smd (probably could get 0805 size instead):

Also upgraded opamp socket:

I recommend adding more solder around micro-USB socket's legs to secure it more firmly, as it easily gets loose/torn off over time, this happened on my F1, Z1 and Z2.

 

[Wiljen]

@Ivan TT any chance we could get of Build list of parts and a recommendation of where to order them? I think I am going to do at least the cap upgrades and the resistor mod and have been debating the muses or AD8610 swap.

 

[Wiljen]

Yes, I had a problem with background noise too, fixed it (and distortion on PO out, to a degree) by reducing opamp's gain, adding 12kOhm resistors between terminals 1-2 and 6-7.

I am reading those as Red, black, Orange, Gold which makes the resistor a 20K rather than 12 unless I am missing something. Also did you still have the 2 130k resistors in series with the input caps or is this instead of those? I noticed in post 20 you don't show the resistor mod on the input caps so am trying do determine if this is one or the other or both that are needed to reduce gain.

 

[Superluc]

Yup, I used a similar one that came with UE TF10, 100Om attenuator.

How much is the output impedance of the Walnut F1 ?

I have an impedance adapter of 75 ohm and a KZ ZS6 on the way, thinking about using the adapter for tune down the highs, as a graph from @hakuzen show that on the FR with this combo, on a near 1 ohm output source.

Anyway, my through was to buy a Zishan Z2, using directly it if it's higher impedance output work good on balancing the ZS6, or coupling it with my Topping NX2 on the LO, for my other IEMs, and eventually with the combo adapter-ZS6.

But it said that this F1 AMP is warm, almost tubey, and i may be interested on it, especially for "educate" brighter headphone.
Putting an adapter of 75 ohm between the Z2 LO and the F1, the F1's power may be that strong for work good with low impedance headphone ? The distortion you have talked about, on stock condition, it's more problematic to handle because of impedance output or too strong gain ?

 

[Ivan TT]

Quick recap of mods and parts needed:

1. Input capacitors: (next to opamp socket), I upgraded to 2x 10uF 16V Nichicon BP, arrow, mouser and digikey code UES1C100MDM

2. Output capacitors: 100uF 16V Nichicon BP, code UES1C101MPM

3. Opamp gain reduction (reduces noise and distortion at max level, tapers volume pot): 11kOhm resistors across opamp terminals 1-2 and 6-7, I suggest 0603 SMD, for example CRCW060311K0FKTA

4. Power supply capacitors: 4 x 470uF 16V, for example UHD1C471MPD should work and it is smaller than the one I used.

5. Single ended buffered output mod requires SHORT 3.5mm panel mounted socket (like this one: https://goo.gl/q25TL9 ) and a miniature 6 pin DPDT switch ( like this one: https://goo.gl/LdWSmZ ) They will require a bit of filing to make them fit.

Cables should be wired as per image below (central pins of the switch should be connected with a jumper cable and to the ground, connect 3.5mm socket's ground to them as well, 5 on the image below), when switch is engaged L and R negative outs (2 and 3) are grounded, as per SE buffer operation requirements:

Hope it helps.

PS: wire #1 at 2.5mm socket is tricky to solder in as it is way to easy to jump ground sleeve wrapping around the front of the socket from #3 with excessive solder. Insure that there is no solder (and no electrical contact) between solder joint #2 and the sleeve right above it.

F1 + Nichicon BP audio caps:

 

[Ivan TT]

I am reading those as Red, black, Orange, Gold which makes the resistor a 20K rather than 12 unless I am missing something.

I'm not that well versed in electronics, to be honest. I can confirm that 11k resistors work well though.

Also did you still have the 2 130k resistors in series with the input caps or is this instead of those? I noticed in post 20 you don't show the resistor mod on the input caps so am trying do determine if this is one or the other or both that are needed to reduce gain.

Not anymore, I only 11k resistors between opamp's terminals to reduce gain now.

 

[Merlin-PT]

I don't have the F1 and looking at posted photos (without mods), I have a basic question about how it works.

Considering these blocks of components (a, b and c):
a) 2x DRV134PA
b) 1x OPA2604
c) 4x what looks like some transistors

What is the audio path from 3,5" IN to 3,5" OUT ?
What is the audio path from 3,5" IN to 2,5" balanced OUT ?

TY

 

[Ivan TT]

What is the audio path from 3,5" IN to 3,5" OUT ?

Volume pot-input caps-opamp-output caps-3.5mm out (pretty much the same as other Walnut series headphone amps)

What is the audio path from 3,5" IN to 2,5" balanced OUT ?

The same as above, but with DRV134PA at the end of the signal flow chain.

There's another option, using 3.5mm OUT as INPUT , this bypasses caps, volume control and opamp, but engages DRV134PAs feeding into 2.5mm balanced out.

 

[DBaldock9]

Volume pot-input caps-opamp-output caps-3.5mm out (pretty much the same as other Walnut series headphone amps)

The same as above, but with DRV134PA at the end of the signal flow chain.

There's another option, using 3.5mm OUT as INPUT , this bypasses caps, volume control and opamp, but engages DRV134PAs feeding into 2.5mm balanced out.

Is that final option only valid if you install the switch on the front - to isolate the output of the Internal Op-Amp from the External Input that you're providing at the 3.5mm Output?

 

[Ivan TT]

Is that final option only valid if you install the switch on the front - to isolate the output of the Internal Op-Amp from the External Input that you're providing at the 3.5mm Output?

Not at all, it works quite fine in stock, but I feel it introduces some noise from the opamp's circuit, hence the solution to add gain reduction resistors in opamp's feedback loop.

 

[cqtek]

Hello.

I read all the thread and I know that this model without any modification is useful to use with high impedance earphones, I guess that makes reference for the two outputs, normal and balanced.
My first question is what impedance you consider high, above 64 Ohms, 100 Ohms?
The second question is possible to use this impedance adapters with good result connected to sensitive IEMS without any internal modification of F1?

https://es.aliexpress.com/item/DUNU...0-200-ohm-For-Headphone-HiFi/32832583027.html
https://es.aliexpress.com/store/pro...iFi-Player-Earphone/1994049_32810903635.html?

Also, are there some impedance adapaters for balanced connection?

Thank you.