Carlos from Burson asked if I would be interested in trying out the V5i in combination with the Walnut F1. The V5i was provided free and does not have to be returned.
Please note: this review should only be applied to the V5i as installed in the F1. I don't have any other amps available with swappable opamps to try the V5i in, and the F1 is...quirky.
I bought a Muses02 to have another point of comparison in addition to the stock opamp, which in my F1 is labeled OPA2134PA. You can't really A/B opamps in a single amplifier, so I compared each opamp to the other amps I have and tried to use that to triangulate the differences between the opamps themselves...
Amps: TEAC HA-250, Phatlab Phantasy, ALO CDM (Sonotone tubes)
Sources: Onkyo DP-S1, iPhone SE
Headphones: Modhouse Argon (ZMF protein pads), HD800 (Dekoni velour pads), B&O H6 (Rapha pads), iBasso IT01. (The IT01 was mainly just used to check hiss levels.)
tl;dr
Stock (labeled OPA2134PA): Generally unobjectionable, but feels a bit closed in compared to the other two. Hissy. A bit grainy?
Burson V5i: Slightly v-shaped. Bass hits a bit harder. Slightly more prone to sibilance. Even higher noise floor/hiss than the stock opamp. Soundstage/imaging slightly improved?
Muses02: Smooth. Some might find it too soft? Lowest noise floor of the three, more suitable for use with IEMs.
Note: I don't want to oversell the distinctions here, because the differences between amps are quite subtle. Also, my comparisons were made pretty casually, volume matched only by ear.
Installation
Changing out the opamp is a pretty easy affair, even for an entirely nontechnical user like me. Here's the process:
Unfortunately, the next step is not to reinstall the top of the F1's case, because it won't fit. The V5i is just a bit too tall, unfortunately. There are some possible solutions here. I believe Burson sells adapters/extenders ("Extension Lead"?) that would let you reposition the opamp and lay it on its side. I'm pretty sure this would let you get the top of the case on, but I don't have one to try. Otherwise, if you're DIY-inclined, you could source a new case. For testing purposes, I just gaffered-taped the case together to prevent inadvertently damaging the internals. That wouldn't be a very good long-term solution, however.
Impressions
Here are my notes. Please take with a mega grain of salt, b/c I'm not the most technical listener, and I don't normally review stuff.
Stock (labeled OPA2134PA): Generally unobjectionable, but feels a bit closed in compared to the other two. Hissy. A bit grainy?
Burson V5i: Slightly v-shaped. Bass hits a bit harder. Slightly more prone to sibilance. Even higher noise floor/hiss than the stock opamp. Soundstage/imaging slightly improved?
Muses02: Smooth. Some might find it too soft? Lowest noise floor of the three, more suitable for use with IEMs.
The Muses02 probably suits my personal preferences the most, but the V5i would make sense for anyone prioritizing bass over mids. Might be good in combination with a dark/warm heapdhone, also. The F1 is a great cheap option as a portable amp for Fostex RP driver headphones like the Argon, and for those who are running that or similar combinations and want a little more bass impact/detail, the V5i would make sense -- with the substantial caveat that you have to figure out a solution for the height problem.
In comparison to other amps I had available, I found that the stock F1 was very, very similar to my TEAC HA-250, which is a decent but outdated portable DAC/amp. (The TEAC uses an OPA1642 opamp, for whatever that's worth.) The only notable difference in sound is that the HA-250 has a lower noise floor. This isn't really useful information for this review, but it did make my comparison process a little easier. : )
Comparison to my tube amps is very unfair. They're bulky, expensive transportable units. That being said, the F1 stands up surprisingly well when it comes to hard-to-drive headphones. (If you're curious: the Phantasy (SET Class A) is very tube-y and mid-centric, with a surprisingly black background. The ALO CDM (hybrid)'s amp section is clean and clear, with particularly good separation, but a bit of a noise floor with sensitive IEMs.)
The F1 had no difficulties driving either the HD800 or the Argon with any of the opamps installed. The sound of the V5i is better suited to the Argon than the HD800. The B&O H6 doesn't really benefit from an amp, and in fact it picked up a fair bit of hiss, so I didn't spend too much time with it in testing. The IT01 does like amping (oddly) but it's quite hiss sensitive. The noise floor with the V5i in the F1 was too high for me to want to use the IT01 with it. (I would have tested the IT01 using an iFi IEMatch, but sadly my IEMatch disintegrated a few weeks ago.)
Please note: this review should only be applied to the V5i as installed in the F1. I don't have any other amps available with swappable opamps to try the V5i in, and the F1 is...quirky.
I bought a Muses02 to have another point of comparison in addition to the stock opamp, which in my F1 is labeled OPA2134PA. You can't really A/B opamps in a single amplifier, so I compared each opamp to the other amps I have and tried to use that to triangulate the differences between the opamps themselves...
Amps: TEAC HA-250, Phatlab Phantasy, ALO CDM (Sonotone tubes)
Sources: Onkyo DP-S1, iPhone SE
Headphones: Modhouse Argon (ZMF protein pads), HD800 (Dekoni velour pads), B&O H6 (Rapha pads), iBasso IT01. (The IT01 was mainly just used to check hiss levels.)
tl;dr
Stock (labeled OPA2134PA): Generally unobjectionable, but feels a bit closed in compared to the other two. Hissy. A bit grainy?
Burson V5i: Slightly v-shaped. Bass hits a bit harder. Slightly more prone to sibilance. Even higher noise floor/hiss than the stock opamp. Soundstage/imaging slightly improved?
Muses02: Smooth. Some might find it too soft? Lowest noise floor of the three, more suitable for use with IEMs.
Note: I don't want to oversell the distinctions here, because the differences between amps are quite subtle. Also, my comparisons were made pretty casually, volume matched only by ear.
Installation
Changing out the opamp is a pretty easy affair, even for an entirely nontechnical user like me. Here's the process:
- You only have to remove the top four screws (two front, two back) in order to remove the top of the F1's case
- But the screws are tiny and VERY easy to lose
- It's not particularly hard to remove the opamp from its socket, but a cheap "IC Extractor" tool can be handy. It's like tweezers with hooked tips that slide under the body of the chip and let you pull straight upward instead of having to lever it out from one side or the other.
- Once you have the top panel off, make a note of the direction of the dot or circle on the opamp. When you install the new opamp, the dot should face the same way
- Disconnect the battery. The IC extractor actually helps with this part, too.
- Remove the opamp, trying not to damage the legs.
- Install the new opamp. The V5i is sturdier than the stock opamp or the Muses02 and has nice strong legs, which makes it much easier to install and remove.
- Reconnect the battery
Unfortunately, the next step is not to reinstall the top of the F1's case, because it won't fit. The V5i is just a bit too tall, unfortunately. There are some possible solutions here. I believe Burson sells adapters/extenders ("Extension Lead"?) that would let you reposition the opamp and lay it on its side. I'm pretty sure this would let you get the top of the case on, but I don't have one to try. Otherwise, if you're DIY-inclined, you could source a new case. For testing purposes, I just gaffered-taped the case together to prevent inadvertently damaging the internals. That wouldn't be a very good long-term solution, however.
Impressions
Here are my notes. Please take with a mega grain of salt, b/c I'm not the most technical listener, and I don't normally review stuff.
Stock (labeled OPA2134PA): Generally unobjectionable, but feels a bit closed in compared to the other two. Hissy. A bit grainy?
Burson V5i: Slightly v-shaped. Bass hits a bit harder. Slightly more prone to sibilance. Even higher noise floor/hiss than the stock opamp. Soundstage/imaging slightly improved?
Muses02: Smooth. Some might find it too soft? Lowest noise floor of the three, more suitable for use with IEMs.
The Muses02 probably suits my personal preferences the most, but the V5i would make sense for anyone prioritizing bass over mids. Might be good in combination with a dark/warm heapdhone, also. The F1 is a great cheap option as a portable amp for Fostex RP driver headphones like the Argon, and for those who are running that or similar combinations and want a little more bass impact/detail, the V5i would make sense -- with the substantial caveat that you have to figure out a solution for the height problem.
In comparison to other amps I had available, I found that the stock F1 was very, very similar to my TEAC HA-250, which is a decent but outdated portable DAC/amp. (The TEAC uses an OPA1642 opamp, for whatever that's worth.) The only notable difference in sound is that the HA-250 has a lower noise floor. This isn't really useful information for this review, but it did make my comparison process a little easier. : )
Comparison to my tube amps is very unfair. They're bulky, expensive transportable units. That being said, the F1 stands up surprisingly well when it comes to hard-to-drive headphones. (If you're curious: the Phantasy (SET Class A) is very tube-y and mid-centric, with a surprisingly black background. The ALO CDM (hybrid)'s amp section is clean and clear, with particularly good separation, but a bit of a noise floor with sensitive IEMs.)
The F1 had no difficulties driving either the HD800 or the Argon with any of the opamps installed. The sound of the V5i is better suited to the Argon than the HD800. The B&O H6 doesn't really benefit from an amp, and in fact it picked up a fair bit of hiss, so I didn't spend too much time with it in testing. The IT01 does like amping (oddly) but it's quite hiss sensitive. The noise floor with the V5i in the F1 was too high for me to want to use the IT01 with it. (I would have tested the IT01 using an iFi IEMatch, but sadly my IEMatch disintegrated a few weeks ago.)
