[DBaldock9]

Figured I’d post my thoughts on this Loxjie P20 amp since I’ve been using it for about half a year now. IMO, this little amp is only worth it if most of your headphones can use a balanced connector (because the single-ended output is quite noisy) and if your DAC has balanced outputs it can connect to this amp’s balanced inputs. Using the RCA inputs with the balanced headphone output on this amp is still good, but balanced in + balanced out is the way to go with this amp.

As is, I think it just sounds ok; it needs some upgrades to sound great. The first upgrade is the power supply, I bought the Jameco Reliapro KPL-060F power supply along with a Tripp Lite P007-006 Power Cord, 14AWG. Next, I had some Dim It Light Dimming Sheets (basically static cling tint film) lying around so I cut a part of that to cover up the ridiculously bright blue LED screen - much better with the dimming sheet applied. Third, I got some 9-pin tube socket savers, which accomplished several things at once: 1) it raised up the tubes so they could more efficiently dissipate heat and the amp wouldn’t get so hot, 2) it covered up most of the blue LEDs coming from inside the amp, and 3) it allowed me to use shorter tubes if I wanted.

I tried the 6N3P-E tubes, which instantly sounded better than the stock tubes. I also tried the JAN-5670W GE tubes, but I liked the 6N3P-E tubes better. I lastly tried the GE 5670 5 Star tubes and liked them the best. I have not tried the 6N3P-DR tubes, maybe at some point in the future, I will try them.

I’ll note three of the headphones I’ve used this amp with (@dimoniet79 this might answer your question): The Sennheiser HD600, the AKG K712 Pro, and the Beyerdynamic DT880 600 ohm. I’ve modified all three of those headphones to run balanced and this little amp has no problem powering any of those three headphones. The DT880 600 ohm takes the most power, but it is only powered enough by the balanced output, not on the single-ended output. The HD600 and AKG K712 Pro can be powered just fine by this amp’s single-ended output, but as I said earlier, the balanced output is really what you want to be using on this amp because its noise floor is way lower than that of the single-ended output.

With all these upgrades (including at least the JAN-5670W GE tubes), if I’m using the balanced in + balanced out configuration on this amp, I enjoy listening to this Loxjie P20 more than my THX AAA 789 (my DAC being the Topping DX7s). If I ever must use the RCA inputs on the amp (my DAC being the Sennheiser GSX 1000), then it’s a very close call between the Loxjie P20 and the THX AAA 789, but I must give the edge to the THX in this case. If I must use the single-ended output on the amp, then the THX AAA 789 for sure sounds better than this Loxjie P20. Hope this helps future readers trying to decide what amp to buy.

Since I had cut my P20's case in half - https://www.head-fi.org/threads/lox...nformation-on-this-thing.903733/post-15188418
- it's fairly easy to take the top off, for better cooling. But, in order to leave the case together, adding some tube socket savers sounded like a good idea.
I searched around some, and found these Cary Gold 9-Pin Bakelite Tube Sockets - https://www.amazon.com/gp/product/B00KOTBMMM/
They're tall enough that their top is flush with the top of the case.
After using my P20 for several hours last night, with the tubes sitting up above the case, it was much cooler than previously, when the tubes were down inside it.
.
I've done other mods, which are shown in various posts here - installed sockets for the op-amps, added additional bypass capacitors for the op-amp sockets' V+ & V- pins, replaced the power supply with a 12V @ 3A linear, removed the series resistors for the LEDs under the tube sockets, added longer ribbon cables to the front panel.
.
The one mod that has thwarted me, is reducing the op-amp supply voltage from ±18VDC to ±15VDC, or lower (to allow for more varied op-amp rolling). That's because they're apparently producing the ±18VDC with the custom wound transformer that's back near the DC input. There aren't any voltage regulator chips being used on the board to output the ±18VDC, where the voltage can be easily adjusted with external resistor value changes.

 

[JazzArtist123]

The one mod that has thwarted me, is reducing the op-amp supply voltage from ±18VDC to ±15VDC, or lower (to allow for more varied op-amp rolling).

I'm not sure exactly where the circuit components are on the board and how much room there is but would adding something like these Linear Voltage Regulator IC chips enable you to obtain ±12 VDC?

+18 VDC to +12 VDC: https://www.digikey.com/en/products/detail/texas-instruments/LM340T-12-NOPB/6233

-18 VDC to -12 VDC: https://www.digikey.com/en/products/detail/texas-instruments/LM7912CT-NOPB/6355

The only thing I don't know is how much current you need them rated for. Those ones are rated for 1.5 A.

Also, @DBaldock9, are you able to say how much better the Pyramid 5 Amp Linear Regulated Power Supply would sound over the Jameco 5 Amp Switching power supply? Do you think the linear power supply would help reduce the overall noise on the single-ended output?

 

[DBaldock9]

I'm not sure exactly where the circuit components are on the board and how much room there is but would adding something like these Linear Voltage Regulator IC chips enable you to obtain ±12 VDC?

+18 VDC to +12 VDC: https://www.digikey.com/en/products/detail/texas-instruments/LM340T-12-NOPB/6233

-18 VDC to -12 VDC: https://www.digikey.com/en/products/detail/texas-instruments/LM7912CT-NOPB/6355

The only thing I don't know is how much current you need them rated for. Those ones are rated for 1.5 A.

Also, @DBaldock9, are you able to say how much better the Pyramid 5 Amp Linear Regulated Power Supply would sound over the Jameco 5 Amp Switching power supply? Do you think the linear power supply would help reduce the overall noise on the single-ended output?

I had thought about adding additional regulators, when I saw that there aren't any for the ±18VDC rails - but that would mean isolating the V+ & V- pins on each of the four op-amp sockets, and changing how I've got all of the additional bypass capacitors installed (they're currently soldered to the V+ & V- pins on the back of the circuit board).
.
Since the +12VDC input goes directly into a switching power supply in the P20 (to create all of the needed voltage rails), it's doubtful that there's any audio performance difference between using a good linear or switcher supply. I suppose it's possible that if a switcher supply with exactly the same frequency as the internal switcher is used, they might interact with each other.

 

[arielext]

I recently pulled out this amp again, now fed by a RME ADI-2 DAC (balanced) and feeding either a Sash Tres V2 or DCA ether c flow 1.1 (both balanced) and it still holds up. This amp does magic for neutral to light sounding headphones.
I'm using the standard power supply and 6Н3П-ЕВ tubes. Smoothed out highs and a small increase in bass.

In my book this amp is one of the hidden gems.

 

[Jimmyblues1959]

I recently pulled out this amp again, now fed by a RME ADI-2 DAC (balanced) and feeding either a Sash Tres V2 or DCA ether c flow 1.1 (both balanced) and it still holds up. This amp does magic for neutral to light sounding headphones.
I'm using the standard power supply and 6Н3П-ЕВ tubes. Smoothed out highs and a small increase in bass.

In my book this amp is one of the hidden gems.

I agree. I have owned the P20 for a few years now and I really enjoy it fully balanced with my Hifiman HE4XX and Fostex T50RP MK3.
It is my favorite headphone amplifier in the $100 price range.

 

[Basick]

Ok so I've just received my DROP Grace SDAC balanced, and have been trying to run my entire setup through balanced connections with my loxjie amp but I just can't get it to work properly! I have the DAC plugged into my motherboard via the USB that was in the packaging, and balanced XLRs into the balanced outputs on the DAC, then running those into the balanced inputs on the loxjie amp. The only way I get sound coming out of this setup is on "Output 1, and Input 1"

If I run the setup with my balanced output on the amp and a SE input from the computer to the amp straight up its "Output 1, and Input 2"
But even though I am getting sound my Soundblaster X-fi MB3 isn't picking up the DAC as a sound input (see picture below)
I get sound with Output1, and input1 running a fully balanced setup, but the sound isn't what I was expecting, possibly a downgrade from SE straight from the computer to the amp.
I also noticed that I have to raise the volume significantly higher for equal levels of listening when im using this fully balanced setup

Please help!

 

[Basick]

Am I supposed to have drivers installed?

I'm thinking the sound just doesn't sound as good because my soundblaster x-fi MB3 isn't being used since it has the "crystallizer, bass boost, equalizer" all on it.
Now running it straight through my DAC I suppose it doesn't use the software stuff that comes from my motherboard audio such as the Soundblaster X-Fi MB3 or Realtek HD Audio Manager where I could fine-tune my audio to my liking.

 

[Mellowship]

Am I supposed to have drivers installed?



I'm thinking the sound just doesn't sound as good because my soundblaster x-fi MB3 isn't being used since it has the "crystallizer, bass boost, equalizer" all on it.
Now running it straight through my DAC I suppose it doesn't use the software stuff that comes from my motherboard audio such as the Soundblaster X-Fi MB3 or Realtek HD Audio Manager where I could fine-tune my audio to my liking.

It seems to be a software problem, indeed. But first try to input your DAC with other thing just to check if the sound is satisfactory. When in full balanced mode and properly fed with a good balanced signal from the DAC, the p20 will sound much louder and much better than in single ended.
After ruling out hardware problems with the DAC and P20, try using the Asio drivers and Foobar2000.

 

[Basick]

Am I right in saying that when using an external dac, you are bypassing the onboard audio? Therefore will not be able to use the Realtek HD Audio Manager or the Soundblaster X-Fi MB3?

I keep getting this message pop up everytime:

 

[DBaldock9]

Ok so I've just received my DROP Grace SDAC balanced, and have been trying to run my entire setup through balanced connections with my loxjie amp but I just can't get it to work properly! I have the DAC plugged into my motherboard via the USB that was in the packaging, and balanced XLRs into the balanced outputs on the DAC, then running those into the balanced inputs on the loxjie amp. The only way I get sound coming out of this setup is on "Output 1, and Input 1"

If I run the setup with my balanced output on the amp and a SE input from the computer to the amp straight up its "Output 1, and Input 2"
But even though I am getting sound my Soundblaster X-fi MB3 isn't picking up the DAC as a sound input (see picture below)
I get sound with Output1, and input1 running a fully balanced setup, but the sound isn't what I was expecting, possibly a downgrade from SE straight from the computer to the amp.
I also noticed that I have to raise the volume significantly higher for equal levels of listening when im using this fully balanced setup

Please help!

Are you saying that your P20 is working with the settings = Input-2 & Output-1?
According to the P20 Manual that's on the Loxjie website, that should be Balanced Input & Balanced Output.
.

 

[Basick]

Are you saying that your P20 is working with the settings = Input-2 & Output-1?
According to the P20 Manual that's on the Loxjie website, that should be Balanced Input & Balanced Output.
.

No it works with In1 and Out1 for balanced, I know that the manual says something different. Even looking at the back of the unit, the labelling for the balanced outs are "IN 1 R and IN 1 L" suggesting Input1 for balanced rather than Input2. In comparison, the single ended RCA inputs on the back of the loxjie are labelled "In 2"

I only have the balanced inputs in the loxjie at the moment, and the Out1 and In1 only work to get sound

 

[Basick]

Got it !!!
Thanks turbomustang84 and Shane D

The Loxjie P20's way of selecting input/output connections is a bit unphasing.
In the manual it says "Input menu ... in2 Balanced input", but on the chassis the XLR ports are marked IN1, and let there be light!!! Or not, cause the Chinese tubes are plain horrible!! Could barely id Haydn's Opus 76 from my DAP

Thanks again guys,

It looks like the manual is just wrong, he also had the same issue. So the balanced setup should be In1 and Out1

 

[joseG86]

I really love this amp with 5670W JAN fully balanced, Focal Clear shine with it Bass becomes something else

 

[JazzArtist123]

@Basick,

You are probably close to getting your new SDAC working correctly. For example, your DROP Grace SDAC is only going to show up as an output sound device as it does not have any microphone inputs to go back to your computer, so that part is correct.

When you are comparing Balance vs SE inputs to your Loxjie P20, are they both coming from your DROP Grace SDAC, or is the SE input coming from your computer (not through the SDAC)? If the SE input is coming from your computer (not through the SDAC), then you might check inside your computer's sound level for the DROP Grace SDAC and make sure it is at 100%. See the below picture for an example of my DX7s:

It sounds like your DROP Grace SDAC probably has its Speaker Level set to around 50 instead of 100 (I can't tell you how many times this has happened to me!). Are you able to check this?

Also,

Am I right in saying that when using an external DAC, you are bypassing the onboard audio?

That should be correct, however, it looks like your Soundblaster X-fi MB3 has an optical output. Remember the DROP Grace SDAC has a digital coax input, so if you really want to use certain sound effects from your Soundblaster, you might be able to buy a small optical-to-coaxial converter, such as https://www.amazon.com/Optical-Converter-Bi-Directional-Repeater-ROOFULL/dp/B01N32C5GT, and then you could use both the SDAC and your Soundblaster X-fi MB3 software.

Best of luck!

 

[Basick]

@Basick,

You are probably close to getting your new SDAC working correctly. For example, your DROP Grace SDAC is only going to show up as an output sound device as it does not have any microphone inputs to go back to your computer, so that part is correct.

When you are comparing Balance vs SE inputs to your Loxjie P20, are they both coming from your DROP Grace SDAC, or is the SE input coming from your computer (not through the SDAC)? If the SE input is coming from your computer (not through the SDAC), then you might check inside your computer's sound level for the DROP Grace SDAC and make sure it is at 100%. See the below picture for an example of my DX7s:



It sounds like your DROP Grace SDAC probably has its Speaker Level set to around 50 instead of 100 (I can't tell you how many times this has happened to me!). Are you able to check this?

Also,

That should be correct, however, it looks like your Soundblaster X-fi MB3 has an optical output. Remember the DROP Grace SDAC has a digital coax input, so if you really want to use certain sound effects from your Soundblaster, you might be able to buy a small optical-to-coaxial converter, such as https://www.amazon.com/Optical-Converter-Bi-Directional-Repeater-ROOFULL/dp/B01N32C5GT, and then you could use both the SDAC and your Soundblaster X-fi MB3 software.

Best of luck!

Wow thank you for such a detailed response!
Yes, I've tried running the setup single ended both ways, either connected to the DAC or straight into the computer. Only way I get to utilize the soundblaster x-fi is through the connection from the loxjie straight into the computer's 3.5mm rear port.

Also I have the SDAC at 100% in those settings as well, I'm assuming why it has lower volume levels compared to when I plug the amp straight into the computer is that because when im plugged straight into the computer it gets to utilize the soundblaster X-Fi which has an equalizer on it that naturally boosts the volume already because of all the gains I have on it on the sliders.

Now question is, it seems though that the use of these software audio enhancers are not very popular among the audiophile community but even when I run single ended straight into my computer it just sounds so much better to me (because of all the enhancers I have on the software: crystallizer, manual bass adjust, EQ, 7.1 surround), am I just doing an injustice to the sound quality that was meant to be for my headphones by not doing any enhancements on it?

I have downloaded APO EQ and have preset it to oratory's recommendations for my HE-4xx's, its definitely better sounding compared to no EQ but not to the satisfaction that I get when I'm able to utilize my settings from the Soundblaster X-Fi MB3. When I switch back and forth between SE input (utilizing the soundblaster software) and the fully balanced setup (utilizing oratory's APO Eq with Peace) the sound is more muffled (trebles) and just overall doesn't sound higher quality compared to when I'm running SE with the utilization of all my settings in the Soundblaster. I've looked around and I've seen posts about "APO Driver" and all those Dolby Atmos softwares... Are there any unanimously good audio enhancer software that I should look into?

This is what I have on my Soundblaster that makes me prefer going single ended straight into the computer without a DAC:

Edit: After fiddling with Oratory's EQ settings, I think I found the sound I like