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Review and Measurements of SMSL SP200 THX HP Amp

Cableaddict

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Hey guys.

I recently purchased an SMSL THX phones amp, and while I mostly love it, it does have a few serious faults.
I want to point them out, and see if maybe there's a way to mod the circuit to fix at least the worst problem.

Background:
I need a bunch of amps for both my recording studio (250 ohm - 600 ohm cans) and my band's live cue system (low impedance IEMs.) I already have two extremely high-end tube amps for the studio, but they don't play nice with low impedance, obviously. I also have a bunch of Massdrop O2 desktop editions. Being a lifelong pro recording engineer, I've spent my life doing audio comparisons, and I have well-trained ears. - So please no one tell me I need to do careful double-blind tests, etc. That will just waste time.

OK, so the O2's are great for the money, but I wanted something better for me, and something with hopefully more solid low end for the drummer. I decided to try a THX, and took a chance on the SMSL version.
Here are my thoughts, and questions: ( This will just concern the SMSL THX vs my Massdrop O2's:)
----------------------

First the good: (the great)

The SMSL seems even cleaner than the O2, with a more open (wider?) presentation. I’m tempted to say that the stereo perception is wider, but I’m not sure if that’s technically correct. The difference here, vs the O2, is not subtle. I love it.

There is also just a tad more bottom end fullness, which is what I had hoped for.
—————————————

A possible negative:

The upper mids seems a little recessed. Or possibly, the upper mids in all of my other amps are too forward, but I think it’s the former.

I don’t know what could cause this, since all amps test flat, but it’s absolutely the case. For instance, I find it slightly easier to sing through the O2 than through the SMSL, because my voice is more “in my face” so to speak. (Yes, I checked the levels.) - Even though the SMSL is nice to use just for listening to music. In this case, the difference IS subtle, and not enough to get hung up about, but it’s definitely there.
—————————————

A definite negative:

Even with proper gain structure, this amp drives 32 ohm IEMs with a slightly wimpy & somewhat distorted LF. I’m being picky here, but the problem exists.
I read somewhere that the true measured output impedance of the SMSL is 1.3 ohms. If so, well there you go.

# Is there any chance the output driver could be improved?
———————————————————


Finally, the BIG negative:
(One I’m hoping a circuit mod might fix)

With this amp, if I switch it to "low gain" and then compensate with the volume knob to get back to the original level, the sound COMPLETELY falls apart.
It sounds massively compressed, and maybe even distorted. Horrible. Hot garbage. You get the idea….

I’m pretty sure that what's happening is that the low gain setting must also be lowering the input headroom. I'm running a fairly hot signal to the amp. Not quite +4, but more than -10. Probably around 0 dBu. I tried lowering that level "significantly, and then doing the same test as before, except with the volume knob in its second half of travel. With 250 ohm cans, I no longer hear that compression & distortion, so it MUST have been the input overloading.

If I understand correctly, many headphone amps vary gain this way, including the Objective2, but it strikes me as a foolish design. Also, even though the Objective2 also does it this way, my O2's (which are Massdrop desktop versions with low & mid gain) do NOT run out of headroom the way the SMSL does. I have to hit them with a full +4dBu signal for that to happen, and even then it's subtle.

So, obvious final question:
Does anyone have a mod to increase the input stage’s headroom?
 
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snowsurfer

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I read somewhere that the true measured output impedance of the SMSL is 1.3 ohms. If so, well there you go.
What do you mean "there you go"? 1.3Ohms x 8 = 10.24Ohms, so there is a huge margin without damping to your 32Ohm IEMs?
 

Cableaddict

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What do you mean "there you go"? 1.3Ohms x 8 = 10.24Ohms, so there is a huge margin without damping to your 32Ohm IEMs?


8X is only a general rule, which you can find on some websites. (And a bad one, IMO.) And an Impedance mismatch has to do with much more than "damping." (Some even argue that damping is near meaningless with the low-mass drives in an IEM. Personally I don't know, but I suspect this is true. )

FWIW, what DOES influence damping, or motor control if you prefer, is the number of wire wraps around the driver. That's why higher impedance cans are usually better, within a given series. (This is also not arguable. Ask Beyer or Sennheiser techs, if you manage to talk to one.)

The big issue with Impedance mismatches is the resulting frequency shifts and distortion. - And headphones do not present the same impedance throughout the frequency range. Those same techs at Sennheiser & Beyer will tell you that 8X is too low. I know this, because I HAVE spoken with them, at various professional audio conventions over the years.

So there you go. :)
 

snowsurfer

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Finally received mine! After going through customs hell and splashing an extra 84€ on top of the 239€ I paid on 11/11.

So, just a quick comment after an hour of listening or so.

My system:

Source: PC - FLACs and Tidal Hi-Fi
DAC: SMSL SU8 v2
Main headphones: HD660s with original single ended cable

Cabling: Amazon USB cable with ferrite cores on both sides for PC to DAC connection

Two XLR Y splitter custom cables I ordered from my long time cable supplier:
Each cable is for one side: Neutrik XLR connector on one side, two fully balanced sides going to Neutrik Gold XLR connectors, all cabled with Mogami 2932 Multi cable (in order to be able to make a properly balanced connection).

On each side, there is a 50 and a 75 cm length. The 75 cm length goes to the SMSL SP200, the 50 cm length is connected to another Mogami/Neutrik cable made by the same guy which is connected to my JBL LSR 305s.

Yeah, long explanation on the cabling, but I feel that this is critical, having seen other messages in this thread.

I come from a Schiit Fulla 2 with a very scratchy pot, connected with a 2xRCA to minijack cable and powered by USB, which was also incredibly prone to ground loops (important disclaimer :D).

I've gone through some music on Tidal: Some usual suspects here, like Keith Don't Go by Nils Lofgren, Habanera from Carmen by Filippa Giordano, Get Lucky by Daft Punk, Bohemian Rhapsody, Sympathy for the Devil, etc. From my own music I went through some early Iron Maiden masters on FLAC, all stuff with no loudness bullshit, peaks on this stuff are at -20db, and also some Andrew Bird on HD FLAC (not that I care about HD).

There is no hiss on the HD660s for me. Completely black. Both on low and on high gain. Nothingness. After the Fulla 2 this is a revelation.

On the Fulla 2 complicated stuff like Maiden would basically start to disintegrate after about 3/4 volume, while I was missing still some oomph in the bass (I felt like I would like to increase the volume, but just couldn't). Here I am on low gain, volume at 6.5/10, volume on DAC at 100%, and it is just magic, stuff like Fear of the Dark sound as close to perfect as I've heard.

I am very, very happy to report that my experience is nothing like some other HD660s users reported in this thread.

I was thinking about trying some of my low impedance / high sensitivity IEMs and headphones, but right now I want to hear so much stuff on this that I'll be doing that some other time.

Peace!

EDIT: All listening done with Oratory's Harman preset for Peace/APO for the HD660s!
 
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snowsurfer

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8X is only a general rule, which you can find on some websites. (And a bad one, IMO.) And an Impedance mismatch has to do with much more than "damping." (Some even argue that damping is near meaningless with the low-mass drives in an IEM. Personally I don't know, but I suspect this is true. )

FWIW, what DOES influence damping, or motor control if you prefer, is the number of wire wraps around the driver. That's why higher impedance cans are usually better, within a given series. (This is also not arguable. Ask Beyer or Sennheiser techs, if you manage to talk to one.)

The big issue with Impedance mismatches is the resulting frequency shifts and distortion. - And headphones do not present the same impedance throughout the frequency range. Those same techs at Sennheiser & Beyer will tell you that 8X is too low. I know this, because I HAVE spoken with them, at various professional audio conventions over the years.

So there you go. :)

I'll take your word for it, I am no expert. I'm just a guy that likes music. That's what I read in a lengthy article by NwAvGuy, whom I took as somewhat of a respected persona in this field. I am probably mistaken then.
 
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Cableaddict

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I'll take your word for it, I am no expert. I'm just a guy that likes music. That's what I read in a lengthy article by NwAvGuy, whom I took as somewhat of a respected persona in this field. I am probably mistaken then.


I'm no expert, either, and I know this is a tricky. (And I appreciate your response.)
I'm going mostly by what very serious experts have told me over the years. (Again, as the owner of high end, pro recording studio, always loopking to maximize every aspect of things.) I'm also going, to a small extent, by my personal / limited tests that have born this out.

At the same time, again, it's an arcane subject, and may vary a lot with various specific setups. Amp loading is not exactly the same as low-power circuit loading, since you don't want to lose too much voltage.

So I'm open to new info, but only if it comes from very reliable sources.
===========================

Anyway, my main focus here is if there's a way to fix the SMSL's low-gain headroom issue, which I'm 99% sure exists.

I'd also love to tighten up the LF, if possible.
- I wish I had the funds to get the Monoprice & Drop versions of this amp, and compare, but money is very tight these days.
 

JohnYang1997

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I'm no expert, either, and I know this is a tricky. (And I appreciate your response.)
I'm going mostly by what very serious experts have told me over the years. (Again, as the owner of high end, pro recording studio, always loopking to maximize every aspect of things.) I'm also going, to a small extent, by my personal / limited tests that have born this out.

At the same time, again, it's an arcane subject, and may vary a lot with various specific setups. Amp loading is not exactly the same as low-power circuit loading, since you don't want to lose too much voltage.

So I'm open to new info, but only if it comes from very reliable sources.
===========================

Anyway, my main focus here is if there's a way to fix the SMSL's low-gain headroom issue, which I'm 99% sure exists.

I'd also love to tighten up the LF, if possible.
- I wish I had the funds to get the Monoprice & Drop versions of this amp, and compare, but money is very tight these days.
What the fuck is low gain headroom issue? There is no headroom loss using low gain, if you can input high enough voltage it's going to be as powerful in every way as high gain. And the high gain is stupidly high +18dB. There is absolutely no use for the high gain setting. And the low gain is +6db instead of 0db like many other amps.
 

headwhacker

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The big issue with Impedance mismatches is the resulting frequency shifts and distortion. - And headphones do not present the same impedance throughout the frequency range. Those same techs at Sennheiser & Beyer will tell you that 8X is too low. I know this, because I HAVE spoken with them, at various professional audio conventions over the years.

So there you go. :)
That is only true with Dynamic-driver type headphones from Beyer and Senn. Planar Magnetics like Audeze, DC Audio, etc are immune to source output impedance.
 

snowsurfer

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So, after going through the same songs on my Moondrop Kanas Pro IEMs no hiss at all at low and high gain, and, with the DAC on max volume, and the amp on low gain, I can go to about 40% volume for sustained use, 50% is bordering on pain. Yes I can notice channel imbalance at very low volumes but nowhere near where I want to be listening. With the Kanas Pro it's a non issue. I will probably use these with the DAC at about 80% volume, just so I have a less sensitive volume pot on the amp. The pot feels light, yes, but it is not noisy at all and is smooth enough. For me the sound of this combo is amazing, again. Oh and no EQ on these, I don't think they need it.
 

jaraheel

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So, after going through the same songs on my Moondrop Kanas Pro IEMs no hiss at all at low and high gain, and, with the DAC on max volume, and the amp on low gain, I can go to about 40% volume for sustained use, 50% is bordering on pain. Yes I can notice channel imbalance at very low volumes but nowhere near where I want to be listening. With the Kanas Pro it's a non issue. I will probably use these with the DAC at about 80% volume, just so I have a less sensitive volume pot on the amp. The pot feels light, yes, but it is not noisy at all and is smooth enough. For me the sound of this combo is amazing, again. Oh and no EQ on these, I don't think they need it.
That is interesting to know! Do you think the headphones (HD660S) are the culprits then?
 

Cableaddict

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What the fuck is low gain headroom issue? There is no headroom loss using low gain .

Yes, there is. As I explained in my first post.

Maybe their QC is lacking, and some units are worse than others?
Maybe I have to try and send mine back?
 

JohnYang1997

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Yes, there is. As I explained in my first post.

Maybe their QC is lacking, and some units are worse than others?
Maybe I have to try and send mine back?
Now I'm going to talk about something most people here don't know about.
Are you using the rca input? If so that's the issue. With smps, the low frequency mains noise from mains leakage is unavoidable. They grounded the output ground to the earth to reduce the issue. However, first, there are still residue which is quite high in my standard. Second, the earth can be noisy and can make your sound goes shit.
What you can try: use two terminal plug iec cable to bypass the earth and see what happens. Then if possible use xlr input and see does that fix the issue.
If NOT, then I'm positive that the things you are describing is from your head, you won't be hearing the difference in a controlled test. But there is high chance that it would be improved.

Also an if, if the issue appears the other way around, high gain having any issue then it's quite likely. But low gain shouldn't have issue.
 

Alerma

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Using my sp200 connected via RCA to M500 (while waiting XLR cables get shipped to me) - dead silent, no hiss at all. My headphones are SONY MDR-Z7 (70 Ohm 102dB/mW). BTW no apparent imbalance in working pot range.
 

AudioSonic

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It's really a pity that every THX amp does not come with a preamp section... if you need a pre, you still have to go on the Atom, which however is an incredible amp.
Anyone knows if it's a limitation of the THX circuitry not being able to have a pre out? Even the THX 887 lacks one, otherwise it would be the perfect endgame headphone amp.

Wait didn't the OP of this thread post that you can use the front panel, XLR connector as sort of a pass-through (pre-amp)? I hope that is true because this is one of the reason why I bought this after cancelling. Can you not use an adapter to use the XLR output in the front panel to hook up to an external power amp?

Also, if I misunderstood that, is there any other solution at all to connect the DAC to the SMSL SP200 and then to an external amp as well?

So far I have D30 connected to the K5 (which I am replacing with the SMSL SP200) which then has an output to a FOSI amp that drives my external speakers.

thanks!
 
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Cableaddict

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Now I'm going to talk about something most people here don't know about.
Are you using the rca input? If so that's the issue. With smps, the low frequency mains noise from mains leakage is unavoidable. They grounded the output ground to the earth to reduce the issue. However, first, there are still residue which is quite high in my standard. Second, the earth can be noisy and can make your sound goes shit.
What you can try: use two terminal plug iec cable to bypass the earth and see what happens. Then if possible use xlr input and see does that fix the issue.

Very interesting! (thx) - But I am using XLR inputs, balanced, and with a hospital-grade electrical / grounding scheme. (This is a professional recording studio.)

If NOT, then I'm positive that the things you are describing is from your head, you won't be hearing the difference in a controlled test. .

And you would be wrong.

This isn't my first rodeo. You don't know who I am, but just believe me I know what I'm doing. Over the years, I've conducted double-blind A-B tests, in NYC, for several major manufacturers of various gear, including ADC, outboard gear, speakers, tubes, etc. We used to invite all the "golden ears" in the pro audio community. I was literally the guy in charge. I also beta-test for several major software & hardware companies.

Really.
-------------------------------------------

- But I'm not an electronics expert (at all) which is why I post here, looking for help.

Well, aty this point I suspect that I must have a faulty unit.

Of course, I'd STILL like to lower the input gain if possible, but no one has addressed that issue. - though I guess I can just make some L pads, if headroom is not a problem on well-functioning units.
 
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