xDuoo MT-603 Pre-Amplifier (tube buffer / audio switch) review

[olds1959special]

I have the xDuoo MT-603 tube buffer / switch box. It's not really a pre-amp since it doesn't have a volume control. It's got a nice sound with a Tung Sol 12AU7W, a noticeable upgrade over the stock tube. I use it to add tube warmth, punchiness and harmonics to my bookshelf speaker desktop setup based around class D amplification. It's a very quiet unit that adds a 12AU7 flavor to my music and I like it more than other tube buffers I've tried (Hagerman Baritone and TubeMagic D1+) because of how clean it sounds. Also it is totally quiet when powering on or off. This has become a permanent part of my system as a way to optionally add tube flavor. I just switch to the XLR input on the amp to listen without the tube.

 

[MaxwellsEq]

Looking at the manufacturer's website, they claim a flat frequency response (+-0.5db) , 0.01dB THD+N, SNR of 100dB. Given this, I'm surprised it has any audible impact!

 

[olds1959special]

Looking at the manufacturer's website, they claim a flat frequency response (+-0.5db) , 0.01dB THD+N, SNR of 100dB. Given this, I'm surprised it has any audible impact!

I can hear a definite tube sound character so I believe the tube is working. There is a light underneath to illuminate the tube but I can still see that it's on. When I first power up the sound is very low and it takes a few seconds for it come on gradually, indicating the audio is being passed through the tube.

Since I got this I generally don't use this system without the tube buffer, it adds a nice listenability, at the expense of some coherence with complex material, but overall details are retained well. It's a slightly rolled off and warmer sound, but the tube adds a little more dynamics (punchiness) and harmonic content (brightness/color.) All of this happens without any noticeable noise, hiss, or hum. Sorry for all the subjective descriptions.

 

[MaxwellsEq]

I can hear a definite tube sound character so I believe the tube is working. There is a light underneath to illuminate the tube but I can still see that it's on. When I first power up the sound is very low and it takes a few seconds for it come on gradually, indicating the audio is being passed through the tube.

Since I got this I generally don't use this system without the tube buffer, it adds a nice listenability, at the expense of some coherence with complex material, but overall details are retained well. It's a slightly rolled off and warmer sound, but the tube adds a little more dynamics (punchiness) and harmonic content (brightness/color.) All of this happens without any noticeable noise, hiss, or hum. Sorry for all the subjective descriptions.

I understand this is what you are hearing and are enjoying it. So that's great! What surprised me was, according to their published specifications, you should be hearing none of that!

 

[olds1959special]

I understand this is what you are hearing and are enjoying it. So that's great! What surprised me was, according to their published specifications, you should be hearing none of that!

Maybe they just made up the specs to look good?

 

[MAB]

Maybe they just made up the specs to look good. Who's going to do anything?

Maybe it just looks good to you.
I hope you appreciate there is an entire science behind the exact type of sighted listening you are doing here, and the pitfalls of trying to draw conclusions like what you are doing here. It's the point of this website, to provide actual actual reviews of gear, not beliefs and anecdotes that apply only to you at the moment you made them.

I see you doing this quite often. Are you here in good faith, or is this a long-term attempt to troll ASR? There are plenty of forums where people will put their heads in the sand and accept your beliefs at face value, leading to pointless purchases with no sonic merit.

I really have to ask directly, trolling? Or just trying to establish a fifth-column of woo woo here? And if so, is trolling really that rewarding?

 

[DVDdoug]

Sighted tests are ALWAYS suspect unless there is a really gross problem, like no sound out of the left speaker or something.

BUT the placebo effect can be strong, even with trained listeners, and "night and day" differences often go-away in a proper blind ABX test.

This a generalization, but tubes tend to make lousy buffers because you usually want low output impedance. Solid state electronics usually has lower output impedance.

When I first power up the sound is very low and it takes a few seconds for it come on gradually, indicating the audio is being passed through the tube.

That I believe. Tubes don't work properly until they warm-up.

it adds a nice listenability, at the expense of some coherence with complex material, but overall details are retained well. It's a slightly rolled off and warmer sound, but the tube adds a little more dynamics (punchiness) and harmonic content (brightness/color.)

That's hard to believe, given the specs.

Sorry for all the subjective descriptions.

You' are using a lot of undefined terminology (very common in the non-scientific audiophile community).

With electronics there is ONLY noise, frequency response, and distortion. (In the ASR reviews noise and distortion are combined as SINAD.) Frequency response is almost always flat. Distortion is usually below audibility unless an amplifier (or preamp, etc.) is over-driven into distortion. Sometimes there is audible noise (hum hiss, or whine, in the background). All analog electronics generates some noise and whether it's audible or not depends on the sensitivity or your speakers (or headphones), how close you are to the speakers, the ambient noise in the room, etc.

With speakers in a room, there are a couple of other factors that affect sound quality. Audiophoolery describes the REAL characterists of sound quality.

All of this happens without any noticeable noise, hiss, or hum.

That I believe too!!!

 

[BDWoody]

Maybe they just made up the specs to look good?

Maybe you didn't use any controls.

 

[olds1959special]

Maybe it just looks good to you.
I hope you appreciate there is an entire science behind the exact type of sighted listening you are doing here, and the pitfalls of trying to draw conclusions like what you are doing here. It's the point of this website, to provide actual actual reviews of gear, not beliefs and anecdotes that apply only to you at the moment you made them.

I see you doing this quite often. Are you here in good faith, or is this a long-term attempt to troll ASR? There are plenty of forums where people will put their heads in the sand and accept your beliefs at face value, leading to pointless purchases with no sonic merit.

I really have to ask directly, trolling? Or just trying to establish a fifth-column of woo woo here? And if so, is trolling really that rewarding?

My intention was to share the joy of what I'm experiencing. I posted to a few forums about this. I know ASR is not that tube friendly, and is more into measurements than subjective descriptions, but I didn't think it would hurt to post about this. Maybe there is someone out there like me who has a very clean or bright sounding system that can be hard to listen to and a tube buffer might help them. Or they just want to see what tube audio sounds like in their system.

I think using a real tube in the signal chain does something beyond what an EQ or software simulation can offer! I can imagine tube buffers being useful in recording studios too, as part of the mixing process, although in some cases the plug-ins are very good! I used a Fairchild 670 emulator that worked great.

 

[MAB]

My intention was to share the joy of what I'm experiencing. I posted to a few forums about this. I know ASR is not that tube friendly, and is more into measurements than subjective descriptions, but I didn't think it would hurt to post about this. Maybe there is someone out there like me who has a very clean or bright sounding system that can be hard to listen to and a tube buffer might help them. Or they just want to see what tube audio sounds like in their system.

That's all fine. I own tube gear that I like. Tubes are an incredibly ineffective and misguided way to EQ a bright system. While enjoyment of tubes is absolutely great, and completely supported, trying to convince people that they can EQ a bright system with tubes is really bad advice. That's what you need to consider. And perhaps do a measurement to convince yourself and everybody you are broadcasting to if there is really an effect worth spending money on.

Also, really avoid trying to make this into another 'ASR is anti-tube meme'. It's not true. It's the jumping to misleading conclusions that is frowned upon.

I think using a real tube in the signal chain does something beyond what an EQ or software simulation can offer! I can imagine tube buffers being useful in recording studios too, as part of the mixing process, although in some cases the plug-ins are very good! I used a Fairchild 670 emulator that worked great.

Studio effects are different than reproduction, you are mixing the two.

We all imagine many things. I do too. It's part of the way we interpret sound. Have you read much here about human perception of sound?

 

[olds1959special]

That's all fine. I own tube gear that I like. Tubes are an incredibly ineffective and misguided way to EQ a bright system. While enjoyment of tubes is absolutely great, and completely supported, trying to convince people that they can EQ a bright system with tubes is really bad advice. That's what you need to consider. And perhaps do a measurement to convince yourself and everybody you are broadcasting to if there is really an effect worth spending money on.

Also, really avoid trying to make this into another 'ASR is anti-tube meme'. It's not true. It's the jumping to misleading conclusions that is frowned upon.

Studio effects are different than reproduction, you are mixing the two.

We all imagine many things. I do too. It's part of the way we interpret sound. Have you read much here about human perception of sound?

I disagree. I like the results I'm getting! And I find your attitude a bit condescending.

This product is working for me in the way it was intended to, and I think that's a good thing.

 

[MAB]

Maybe there is someone out there like me who has a very clean or bright sounding system that can be hard to listen to and a tube buffer might help them.

Let's take this as an example. We hear people often say that a bright system can be fixed with tubes. Assuming we all agree on what bring sounds like, a speaker can be bring and a room can be bright. But can a tube buffer somehow impact that?

Do we think a tube EQ can tame the brightness? I have a bright speaker, and I have a vintage McIntosh preamp. Here is the frequency response of the speaker, with the frequency response of the preamp. Note the preamp scale is 20x magnified.

Here they are on the same scale.

The tube preamp doesn't solve the bright speaker's EQ problem. This isn't even the worst example of a bright speaker.

How about other tube gear? Here is a variety.

I hear people give advice to solve speaker or room EQ problems with tube gear all the time. The above McIntosh wont solve it. Neither will any of these other pieces. So the issue is, we are trying to have a somewhat data driven conversation. And you are recommending, as if reviewed, potentially expensive remedies that have no chance to fix the bright speaker.

I get that it is inconvenient to hear that purchasing gear for the visual effect rather than gear has no effect on the sound. But the point is to prioritize based on thigs that actually do improve sound, which is typically speakers and room

 

[MAB]

I disagree. I like the results I'm getting! And I find your attitude a bit condescending.

Perhaps. This is one of the few forums ever where people who want to discuss actual electronics topics as they relate to sound reproduction. Along the way lots of other topics on hearing and perception, as well. Other sites range from mildly to severely hostile to any discussion of actual electronics and acoustic principles. There are 100 members online, and nearly 3000 guests browsing our forum as I write this. You posted a 'review' here. What do you say to people who go out and buy something that to address your hypothetical bright speaker problem, but don't get one iota of benefit?

This product is working for me in the way it was intended to, and I think that's a good thing.

It took your money for no sonic benefit. That was the intent.

The bar for posting new threads on ASR needs to be raised a bit, especially for what is called a review.

 

[Somafunk]

I can hear a definite tube sound character so I believe the tube is working. There is a light underneath to illuminate the tube but I can still see that it's on. When I first power up the sound is very low and it takes a few seconds for it come on gradually, indicating the audio is being passed through the tube.

If you like the look of the tube as it glows and imparts a subtle influence on the tonality of your music music then you should buy yourself a cheap plug/play LED VU Spectrum meter such as the one below, watching the frequencies bouncing up n’ down is quite useful

https://www.amazon.co.uk/dp/B07C2NJLC3/?coliid=IUECR62CWE2GG&colid=2A4391BKTPDGK&psc=1&ref_=list_c_wl_lv_ov_lig_dp_it_im

The same item is available on aliexpress, rather cheaper at £28/$35, search for Nobsound AK2515 MIC Audio Spectrum Analyzer VFD and you’ll find it,

 

[olds1959special]

Perhaps. This is one of the few forums ever where people who want to discuss actual electronics topics as they relate to sound reproduction. Along the way lots of other topics on hearing and perception, as well. Other sites range from mildly to severely hostile to any discussion of actual electronics and acoustic principles. There are 100 members online, and nearly 3000 guests browsing our forum as I write this. You posted a 'review' here. What do you say to people who go out and buy something that to address your hypothetical bright speaker problem, but don't get one iota of benefit?

It took your money for no sonic benefit. That was the intent.

The bar for posting new threads on ASR needs to be raised a bit, especially for what is called a review.

I decided to test this out and so I played my music through Apple Music and then activated the Equalizer and experimented with different settings. Nothing I tried sounded as good as just using the tube buffer.

 

[dartinbout]

Is there a music hardware forum where they discuss, in detail, how much better their systems sound when they listen without wearing pants? The merits of the feel of plastic vs leather, on their bare thighs, and how it makes the music sound?

 

[MAB]

I decided to test this out and so I played my music through Apple Music and then activated the Equalizer and experimented with different settings. Nothing I tried sounded as good as just using the tube buffer.

Do you understand the need for blind testing?
Do you think that you would be able to identify the sound of this piece of gear if you compared in a proper blind test?
Do you read ASR topics on proper testing?

I ask because you have mentioned tinnitus and fatiguing sound in past posts. You seem to be searching in several threads for something to deal with harsh sound. While I can't tell what that is, I can tell you buying various tube buffers isn't going to fix harsh sound. The things that make harsh sound are speakers and rooms, not electronics (tube or otherwise). All of these DACs and amps and buffers are virtually transparent. There are certainly tube and solid state products that are so flawed that they have audible frequency response changes, or audible distortion, and fall into the category of broken.

So I have to ask, are you spending money on accessories because you have bad sounding speakers? It's a common issue, salespeople take extreme advantage of it, sell people thousands in accessories for no good reason because the customer got sold bad sounding speakers (often by the same salesperson). In fact, it's one of the main reasons ASR exists. I hope this doesn't sound condescending. I'm just giving you some direct advice, since this is ASR and you are spending money on stuff that has no chance of addressing the issues you seem to be struggling with.

 

[olds1959special]

Do you understand the need for blind testing?
Do you think that you would be able to identify the sound of this piece of gear if you compared in a proper blind test?
Do you read ASR topics on proper testing?

I ask because you have mentioned tinnitus and fatiguing sound in past posts. You seem to be searching in several threads for something to deal with harsh sound. While I can't tell what that is, I can tell you buying various tube buffers isn't going to fix harsh sound. The things that make harsh sound are speakers and rooms, not electronics (tube or otherwise). All of these DACs and amps and buffers are virtually transparent. There are certainly tube and solid state products that are so flawed that they have audible frequency response changes, or audible distortion, and fall into the category of broken.

So I have to ask, are you spending money on accessories because you have bad sounding speakers? It's a common issue, salespeople take extreme advantage of it, sell people thousands in accessories for no good reason because the customer got sold bad sounding speakers (often by the same salesperson). In fact, it's one of the main reasons ASR exists. I hope this doesn't sound condescending. I'm just giving you some direct advice, since this is ASR and you are spending money on stuff that has no chance of addressing the issues you seem to be struggling with.

I guess I could experiment with the higher end ELAC's which are reputed to have a warmer sound, but this would cost me a lot more than the $100 or so (+$25 for the tube) I spent on this - also I have always been a fan of the sound quality of tubes when they are engineered to sound good. Not all tube gear sounds good to me. I have also read these speakers are more accurate than the higher end models, which is important to me, especially when I want to analyze the sound content in which case I would not use the tube.

 

[MAB]

I guess I could experiment with the higher end ELAC's which are reputed to have a warmer sound, but this would cost me a lot more than the $100 or so (+$25 for the tube) I spent on this - also I have always been a fan of the sound quality of tubes when they are engineered to sound good. Not all tube gear sounds good to me. I have also read these speakers are more accurate than the higher end models, which is important to me, especially when I want to analyze the sound content in which case I would not use the tube.

I see, I didn't notice your signature and gear list. You are using this buffer with your Debut 2.0. Interesting, nice speakers. They have good directivity, meaning they actually can be EQ'ed with good results, unlike many speakers with poor off-axis behavior. I think this good behavior was discussed in the ASR review too.

I guess I leave you with the same feedback I see you got in other threads on this topic. Assuming the device isn't a complete mess, it is inaudibly passing the signal through.

 

[olds1959special]

I returned the tube buffer. I am thinking of trying this instead https://www.amazon.com/Nobsound-Pre...ext&ref_=fplfs&psc=1&smid=AUPFJPPJDLDRP&gQT=1

Or, just connecting the RCAs directly to the amp and done...