# IOM 500s Stereo Amplifier Review

## Rate this amplifier:

• ### 4. Great (golfing panther)

• Total voters
198
So Amir, tell me why this test makes any sense, other than presenting the best figures the "amplifier" is capable of by deliberately running at the lowest gain.

11dB with even your 5V source at full blast output knobbles the output to 39 Watts at 8 ohms.
13dB with your 5V source at full blast output knobbles the output to 62 Watts at 8 ohms.
What exactly are people buying a power amplifier for again? (that was a good pun- for a gain)

Based on your power output graph, it achieves 210W@8R at the knee. That's 41V RMS. So it would need 18dB+ for your 5V source, 20dB+ for a 4V source and 26dB+ for a 2V RCA source. And you tested at 11dB and 13dB...
Hi, can you or someone explain this for me - interested in having a future amp with enough headroom, and also in just understanding this ...

There's a chart in the review - "Power vs Distortion @ 8 Ohms, both channels driven". Power 'at the knee' is 210W tested at 16dB gain.
Does that say that the input voltage had to have been higher than 5V in order to reach that power output?

Is there somewhere that the input voltage for these tests is specified, or do I just have to learn some maths to be able to read them?
I'd assumed that the 'standard' 4V for balanced (2V for single-ended) would be used.

Thanks

Hi, can you or someone explain this for me - interested in having a future amp with enough headroom, and also in just understanding this ...

There's a chart in the review - "Power vs Distortion @ 8 Ohms, both channels driven". Power 'at the knee' is 210W tested at 16dB gain.
Does that say that the input voltage had to have been higher than 5V in order to reach that power output?

Is there somewhere that the input voltage for these tests is specified, or do I just have to learn some maths to be able to read them?
I'd assumed that the 'standard' 4V for balanced (2V for single-ended) would be used.

Thanks

It's hard to deduce because the math is complicated. You would need to know the gain of the amp and the input voltage. I'm guessing he cranked up the input voltage at the 11db gain setting for those tests. That's what the theme of this review is, which is kind of the point some of us are making. In the end, this is the choice Amir made and I respect that. However, unless I buy the expensive equipment, which I hoped to avoid with my Patreon sub, I wont know how this performs at a typical gain setting. And since I don't buy amps that haven't been tested, this test, for me, is next to useless. To be clear, Amir owes me nothing. I support his efforts even if I disagree with the testing methodology sometimes. It's better to have some data than none. I imagine there are like 2 people out there that will run 11 volts to this amp. I'm sure they loved this review!

edit; GPT basically say the input voltage was 11.5 volts assuming the gain is at 11db at 8ohms that made 210 watts. Roughly. Take that with a high input voltage grain of salt though.

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• fixed gain version: 26dB
• variable gain version, gain settings: 11/16/22/33 dB

JSmith

JSmith
Useful. So it's going to take more than 2V to drive the fixed gain version to full output. You would need to have maybe 2.5V on tap. That's not ideal for someone driving it with an AVR. The variable gain set to 33dB will ensure broadest compatibility, even with AVRs that can clip just past 1V or 1.5V. I really don't mean to pick on this thing so much, but it frustrates me to see products that are only compatible with "specialty" gear, when they selling for only \$1000. It's entirely possible and quite likely the supporting equipment may not be adequate in many instances. Outside of that, how these things performs really is pretty admirable.

Useful. So it's going to take more than 2V to drive the fixed gain version to full output. You would need to have maybe 2.5V on tap. That's not ideal for someone driving it with an AVR. The variable gain set to 33dB will ensure broadest compatibility, even with AVRs that can clip just past 1V or 1.5V. I really don't mean to pick on this thing so much, but it frustrates me to see products that are only compatible with "specialty" gear, when they selling for only \$1000. It's entirely possible and quite likely the supporting equipment may not be adequate in many instances. Outside of that, how these things performs really is pretty admirable.
The trouble is that we don't really know how it performans at the highest gain setting. We can speculate. But we don't REALLY know.

I'm still curious if anyone can actually hear the difference between this and an Aiyima A70 in a blind test.

So Amir, tell me why this test makes any sense, other than presenting the best figures the "amplifier" is capable of by deliberately running at the lowest gain.

11dB with even your 5V source at full blast output knobbles the output to 39 Watts at 8 ohms.
13dB with your 5V source at full blast output knobbles the output to 62 Watts at 8 ohms.
What exactly are people buying a power amplifier for again? (that was a good pun- for a gain)

Based on your power output graph, it achieves 210W@8R at the knee. That's 41V RMS. So it would need 18dB+ for your 5V source, 20dB+ for a 4V source and 26dB+ for a 2V RCA source. And you tested at 11dB and 13dB...
Thanks for putting that into perspective! It would have been much more useful to test with the lowest and highest gain settings. It’s more than a 20 dB difference, which is very significant vs the only 5 dB difference between the lower gain settings.

The trouble is that we don't really know how it performans at the highest gain setting. We can speculate. But we don't REALLY know.
Sort of do, assuming that it couldn't do better than the base module, it's at least a 7dB drop IIRC. Likely more to go to the high gain mode. Which is still fine performance, and likely of zero audible consequence. Not surprisingly, by goofing with the Hypex standard implementation, they've already reduced performance by 5dB, from .0002% to .0004%. So high gain might be -100 or .001%? Still largely irrelevant. Hypex did a nice job on these things, particularly if your goal is to have options that will let you win a THD+N at 1kHz drag race.

The real magic, again, is that the 20Hz to 20kHz specification at .03% and skimming along .00X% at 30dB gain at 1kHz via RCA is on par with an amp that 25 years ago always weighed about 50 pounds. A Monolith 2X still weighs that much, with its huge copper toroid, giant chassis, etc. Performance is basically the same in this amp that is about the size and weight of a ream of paper. Unappealing to me for the same money, but pretty cool. At this point, I still view Hypex amps as disposable appliances worth a fraction of a "real" amplifier, but time will tell. What I don't like is that they've cut out the shipping expense, the copper, and lots of other expensive stuff, and still charge just as much. They seem expensive. ¯\_(ツ)_/¯ The price of lightweighting, I guess. It's like a carbon fiber version of an amplifier.

At this point, I still view Hypex amps as disposable appliances worth a fraction of a "real" amplifier, but time will tell.
What do you determine to be a "real" amplifier?

Sort of do, assuming that it couldn't do better than the base module, it's at least a 7dB drop IIRC. Likely more to go to the high gain mode. Which is still fine performance, and likely of zero audible consequence. Not surprisingly, by goofing with the Hypex standard implementation, they've already reduced performance by 5dB, from .0002% to .0004%. So high gain might be -100 or .001%? Still largely irrelevant. Hypex did a nice job on these things, particularly if your goal is to have options that will let you win a THD+N at 1kHz drag race.

The real magic, again, is that the 20Hz to 20kHz specification at .03% and skimming along .00X% at 30dB gain at 1kHz via RCA is on par with an amp that 25 years ago always weighed about 50 pounds. A Monolith 2X still weighs that much, with its huge copper toroid, giant chassis, etc. Performance is basically the same in this amp that is about the size and weight of a ream of paper. Unappealing to me for the same money, but pretty cool. At this point, I still view Hypex amps as disposable appliances worth a fraction of a "real" amplifier, but time will tell. What I don't like is that they've cut out the shipping expense, the copper, and lots of other expensive stuff, and still charge just as much. They seem expensive. ¯\_(ツ)_/¯ The price of lightweighting, I guess. It's like a carbon fiber version of an amplifier.
If you want a "real amplifier" with class D modules like the Hypex Ncore or Purifi Eigentakt (both variations of the same basic design by Bruno Putzeys), you probally mean something in a more fancy case with more bells and wistles. That exist, look at many NAD amps as example. But that comes with an extra price. These amps like tested here are more functional amps in cheap but sturdy cases.

But i guess you can call this NAD M23 (with the Purifi Eigentakt) and it's precestor M22 (with Hypex modules) "real amps" in your definition and it's based on largely the same tech (but details different) with similar test results here and elswhere. And there are more brands doing this, Cambridge, Merill, Anthem and probally a few others that i don't know yet also use Ncore modules. Some like NAD build the modules themselves following plans (and having bought rights to do it), others just buy modules like we also see in the cheaper basic versions like tested here.

And 1K for an amp is in the "high end" cheap, a similar power Pass Labs amp cost more like 50-60K or even more. And objectivly that class D amp will be a better amp as the Pass Labs is build to colour to a signature sound and way noisier. I like both styles btw, but from engineering standpoint that Pass Labs is inferior to the class D hypex or Purifi amp, that is a scientific fact. You may not like the neutral sound (many don't), but you can't get arround that.

Btw, while i'm typing this, i listen to music from a vinyl record, going trough a full tube based setup to single driver fullrange speakers, and i'm loving it. It's coloured as hell and technically inferior to all mentioned above, but i'm loving it, and there is nothing wrong with that. And i have a setup with hypex based amps also in an other space...

I think the arbitrary classification of "real" is nothing more than a form of gatekeeping for price, materials, looks, etc. If it was performance, I would say this is plenty real. I would wager anyone who has these amps deployed in their systems don't have any problems with them. The deliver a transparent experience with plenty of headroom for dynamics. IDK how I would ever call that "fake".

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What do you determine to be a "real" amplifier?
Obviously, this is a real amplifier. By a "real" amplifier I was referring to what I described--a traditional amplifier which, to me, doesn't feel like a toy. I remember the first time I saw a Denon POA-S1 in person. You knew that 175 pound thing was serious, and so was the guy who had that monster in his house. Even a Monolith at 40 pound is serious. Big big old 100 pound Parasound is serious. These things are just toys to me. The emotion is ripped out of them, which is an entirely subjective judgment, so I'll go back and sulk in my corner now.

Maybe you can build a hypex amp and just attach it to a pretty steel case filled with audiophile sand to give it some 'serious' heft. You might feel better LOL.

GDK
Most preamps won't drive this to full output at that setting
True, but it isn‘t 1985 anymore, they’re not that rare. I would like a low gain amp to match with my RME and its 24dBu output level.
Not this amp in particular, it‘s one of the weaker implementations.

Maybe you can build a hypex amp and just attach it to a pretty steel case filled with audiophile sand to give it some 'serious' heft. You might feel better LOL.
It just needs a 2500VA toroid and giant capacitor bank, like 250,000+ microfarads? Now THAT would be serious!

It just needs a 2500VA toroid and giant capacitor bank, like 250,000+ microfarads? Now THAT would be serious!
Scrap the toroid,dual mono on 0.8 K/W heatshinks (like Aavid Thermalloy 0S489 - 100mm) on the sides of the case with the SMPSs flat on case,with couple of these to help down low:

(I'm actually not joking)

Edit: It would also need 16A IEC for mains,instead of the 10A normally used.

These things are just toys to me.
That impression vanishes the minute you connect them to an insensitive speaker and see them drive them to limits of their performance! Their efficiency means they are able to extract more juice from the outlet than traditional class AB can, no matter how many capacitors they have. Many audio systems are under-amped and these high power class D amps remedy that like nobody's business.

By a "real" amplifier I was referring to what I described--a traditional amplifier which, to me, doesn't feel like a toy.
You may prefer something along the lines of the ATI AT54XNC Series then... comes with a big linear toroidal, but using Hypex N-Core NC-500 Class D amplifier modules.

Using SMPS's cuts down on enclosure size and heat.

JSmith

You may prefer something along the lines of the ATI AT54XNC Series then... comes with a big linear toroidal, but using Hypex N-Core NC-500 Class D amplifier modules.

Using SMPS's cuts down on enclosure size and heat.

JSmith
Oh, I've got plenty of amplifiers. Probably well over a thousand pounds of them if I rounded them all up. I used to have a problem with buying Carver Amazing speakers and amplifiers to push them. Even this amp would be marginal.
That impression vanishes the minute you connect them to an insensitive speaker and see them drive them to limits of their performance! Their efficiency means they are able to extract more juice from the outlet than traditional class AB can, no matter how many capacitors they have. Many audio systems are under-amped and these high power class D amps remedy that like nobody's business.
I'm well aware how well they can perform. But it's more of the difference between an air cooled Porsche or a 426 Cuda and a new Golf R. Entirely unscientific. I do agree these are a good solution to underamplified speakers. Many are. Most people have never had the benefits of clip lights on symphonic material with good floor standers running at reference. They will be lighting up.

But, this is getting far afield. I'll sum up and move on with it... I think Hypex did a nice job here on their part of the package. I don't care for IOM's implementation at all, except the addition of a 33dB gain stage. For that, they do deserve credit because they did fix a problem with the Hypex default implementation. Even that cannot be driven to full output with 2V(!). Looked at that way, the IOM implementation is arguably one of the better ones, ignoring the apparent loss of SNR in their buffer stage when gain is run on par with Hypex. At high gain, 1.5V from and AVR is enough to get the power you paid for. But, when configured so that 2V or less does in fact drive them to full output on RCA (i.e. 29dB gain), SNR/SINAD is really not all that remarkable. They're pulling high numbers on low gain by allowing Audio Precision to do the job of gaining up the signal. Cheating? Some would say yes, some no. If you can drive it with something as clean as an APx555 and stuff it with 13V, you'll get the advertised performance. Otherwise, not so much. At high gain RCA, it will probably be on par with a well-designed 30 year old Class AB up, but lighter. End users must be very, very careful when selecting a gain setting to avoid clipping the preamp outputs. I think that's too much to ask of an end user on a \$1200 300wpc product. Topping and Benchmark get a pass (to a degree) since their products are part of an intended/available set.

Having noted the issue, I got curious: Were any bundlers selling multichannel "theater" high power Hypex amps that could not hit full power at 2V? Indeed there are. Hopefully no one tries to buy one of those things to hook it up to a receiver. Processors only, but how many users figured that one out? To IOM's credit, at least they aren't doing that. And it's also fair that this is not just their issue. Hypex is ultimately behind all of these "module in a box" kits that boast unrealistically good SNR by permitting all sorts of oddball gain structures outside of the 28+dB standard, including their default implementation.

Once again, this is not a budget amp. It aims to produce ton of power with excellent noise and distortion measurements. It is perfectly fine then to consider proper source to drive it in its low gain. Pro audio interfaces can do this as can high quality headphone amps such as:

Here you have 18 volts on tap with superb fidelity at that with a SINAD of 118 dB. It costs \$500. Not much to add to the total cost of the system.

I much rather see extra gain put in the source than in the amplifier. We can see the difficulty of getting very clean implementation inside of a switching, high current amplifier.

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