IOM 500s Stereo Amplifier Review

[Velocipede_Acoustics]

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.

Yeah, turn the gain knob up and you'll still get excellent power at 2v input. I think you're just assuming it's performance is going to be bad if we turn up the knob. It's likely marginally worse but still excellent and I would put it against what any 90lb space heater you want to put it against anywhere near it's price point. Gone are the days of needing 50lbs of heatsinks, and 40% efficiency to get excellent performance.

 

[Rja4000]

I much rather see extra gain put in the source than in the amplifier.

To illustrate that, we could compare noise of, say, a 50 ohm resistor as source for
A. Low preamp gain and high power amp gain
B. High preamp gain and low power amp gain
for an identical output level

I guess the difference would be significant.

 

[JeremyFife]

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.

I guess that makes sense (of course it makes sense! but I now have to think differently)

Does this mean that "synergy" is a thing again - or, rather, that gain matching becomes important.
I'd just got used to thinking that 'standard' 2V/4V was all I needed to worry about.

My miniDSP can't provide these voltages, are step-up devices available?

I'm not making changes yet, just trying to understand

Thanks

 

[amirm]

Does this mean that "synergy" is a thing again - or, rather, that gain matching becomes important.

In this case yes. The audio industry in this regard is a mess with wild west attitude of every company making their own notion of sensitivity.

But please keep in mind that we are talking about the last bit of performance. If you don't care about that set the gain high and be done with it.

 

[ryanmh1]

Yeah, turn the gain knob up and you'll still get excellent power at 2v input. I think you're just assuming it's performance is going to be bad if we turn up the knob. It's likely marginally worse but still excellent and I would put it against what any 90lb space heater you want to put it against anywhere near it's price point. Gone are the days of needing 50lbs of heatsinks, and 40% efficiency to get excellent performance.

You misread what I was saying. IOM should be commended for having an option that allows for full output with under 2V. I'm also saying performance is fine at high gain. In fact, these low gain modes likely do nothing audible and in practice are likely to cause more harm than good.

So why make this design decision, and when did what Amir rightly calls this "wild west attitude" of gain/sensitivities start? Hypex. Benchmark cannot be blamed, although some might claim they were "first". But that amp was and is pro market gear. Hypex modules are not. Those modules in their default implementation, unlike almost every other consumer audio product for the last 40 years, often cannot be driven to full output with 2V. I think that decision was made, in large part, to inflate their measurements and specifications vis-a-vis the competition. Arguably, they corked their bats. The SNR levels here are not audible even at high gain, so I can't see any other reason for breaking the standard. It made their amps look (slightly) better than they were on a level 29dB playing field, which presumably sold more modules. But what it has resulted in, in some cases, are home theater amplifiers with Hypex modules sold by inexperienced companies that cannot be driven to full output with 2V--an amplifier very likely to be driven with receiver pre-outs limited at 2V. Fortunately, this amplifier is not one of those.

With the IOM, you can set it and forget at 33dB. It will be fine. You will likely never hear any difference at all between that and low gain. But you cannot "hook it up and expect it to be fine" in general with Hypex based amps. The fixed gain version of this very amp cannot be driven to full output with 2V. Unless you buy from an experienced company like NAD which sets the modules to the 29dB standard (and loses some shine on the ol' SINAD chart as a result), you the consumer must pay attention to gain structures. I think that's just too much to ask of the buyer of a 600wpc amplifier that sells for around $1000. For that power level, that is bargain basement for clean power. Commendably, IOM is one of the few where you could hook this to any receiver pre-out for the front channels, adjust to the highest gain, and be fine. But you still have to be aware of the issue to buy the "right" amp in the first place, and then set the switch properly.

 

[Velocipede_Acoustics]

Sure but the gain is not exactly a secret and a mild amount of attention to the input sensitivity is all that's needed. Also, setups like this are not exactly amateur. I think Buckeye amps using hypex need 2.5v and I think they say so on their product description. However, they do have XLR input and then you have the reverse issue of too much input voltage causing clipping when presented with 4v. Again, attention must be paid.

The ideal situation would be some sort of staged input where 2v or 4v would end up delivering max gain on either input. I don't think that exists anywhere. I'm happy to be wrong about that.

Even at 2v into the amp, compared to 2.5v, is approximately 1.9db in volume difference. Which may be entirely reasonable for just about every home theater set up around. If your powering some relatively inefficient tower speakers around 87db sensitivity, you'll still get 108 DB output when you use two volt input to the amp. That is well beyond what most speakers can do. That's well within THX loudness spec. My speakers are 91db, so 2v I would have to use my DSP to turn it down anyway. Those looking for loudness are probably using higher sensitivity speakers anyway.

I think this input sensitivity is a bit blown out of proportion. It's only a problem in some extreme cases.

 

[ryanmh1]

I think this input sensitivity is a bit blown out of proportion. It's only a problem in some extreme cases.

I disagree. That 1.9dB is over 200 watts of missing power that you paid for, and probably want.

Presumably, you bought the 300+ watts to power inefficient floorstanders, say 86dB. I have plenty of recordings with over 20dB of dynamic range mean/peak. Now run the math. 10W to 96dB, 100W to 106dB, and 200W to 109dB. Now back it down to get to the MLP. Each doubling cuts off 6dB (and since it's stereo, there's not necessarily an additive effect from 2 speakers). At 12 feet back, you're back down to 97dB. That's worst case, but I can guarantee you I exceed that on peaks, often. Can I stretch it to 112dB? With some compression on typical floorstanders, probably. Depends how many Hz the peaks are. Bass drum and 3 or 4 big 8" woofers? All good. 5.25" bookshelf speakers? What were you thinking buying this? Now, if I get 400W, I'm just barely clipping, and I'm back up to 100dB peaks, or "chainsaw/motorcycle/hairdryer" peaks. So let's put 20dB between the peak and the average SPL for a symphonic recording (some are more). Now to get my AVERAGE at 80dB and just barely drown out the vacuum cleaner, I need 400W of power to avoid clipping. And I'm still ~5dB lower than the reference level of the recording engineer, and still much quieter than the real deal at the first row (which you're unlikely ever to get since the recording engineer probably won't give you a 40dB dynamic range... but he might give you 30dB, which makes all this even worse). So, not really an extreme case. I would call it the case most audiophiles who drop big money are aiming for. So, now I've got my "preamp" cranked to provide at least 2.5V. Problem is, my "preamp" is an, oh, say, Yamaha AVR, since I'm doing all this on a streaming Atmos performance. And now the "preamp" is clipping. Bad. Real bad.

In the lead post, Amir mentioned that most audiophile systems were underpowered. He's right, and this is why. It's also why this gain structure can quickly turn into a problem.

I think the above is a likely case, and I personally think these cheapo (for the clean juice) Hypex amps ought to come with a disclaimer and the reviewers ought to be dragging them (and particularly Hypex) through the mud for this hogwash gain structure. The "improvement" in SINAD/SNR is totally inaudible in virtually every case. Problems are far more likely than any possible benefit. IOM gets a special award for at least giving you the option of making it work with an AVR. You just need to know enough to understand gain structures and turn the knob on the amp instead of the knob on the preamp. Get the fixed gain version of any of these Apollon/IOM/Buckeye things, and you're just screwed. That multichannel stream you're trying to feed these devices without having a pre/pro just went game over with clipping all over the place. That's why some of us were saying this gain structure on these Hypex amps is asinine.

 

[Velocipede_Acoustics]

I don't disagree that there will be situations where the gain from the RCA input won't be enough from a typical 2v output. However, there is an XLR input and it's not expensive to implement. A fraction of the cost of the amp.

As a side note, I don't like talking about wattage. I like speaking about gain. We know power is going to be frequency dependent. When I consider an amp, the first thing I'm curious about is it's gain, then it's other performance characteristics. Wattage would be one of the least important unless I'm specifically trying to power high current woofers.

If you so happen to be sitting 3 meters away, which I would call a large space, using inefficient speakers, which prompts questions about speaker choice, and you're running them full range, odd for a large space since subwoofers are going to be required, then you have an argument on all accounts. However, this seems extreme/niche to me.

I'm 2 meters away, towers are 91db, and crossed at 60z. In very bass heavy scenes and music, the towers are not consuming nearly the amount of power you quoted above. I have plenty of gain to hit the loudness and dynamic range. This is what I would call a more common situation.

Long story short, if you're trying to fill a large space with sound, with inefficient speakers, then just be sure to get XLR. Hinging all this on RCA 2v is a bit obtuse. It's not like the power is strictly unavailable. Dropping $1k on an amp but for some reason RCA is the only option seems a bit too much of a restriction on which to pin an argument. An enthusiast, which is the kind of person buying these amps, would likely to pay attention to such things. So I don't see much of an issue, especially when the product has clear descriptions of it's gain structure and outputs.

 

[ryanmh1]

Long story short, if you're trying to fill a large space with sound, with inefficient speakers, then just be sure to get XLR. Hinging all this on RCA 2v is a bit obtuse. It's not like the power is strictly unavailable. Dropping $1k on an amp but for some reason RCA is the only option seems a bit too much of a restriction on which to pin an argument. An enthusiast, which is the kind of person buying these amps, would likely to pay attention to such things. So I don't see much of an issue, especially when the product has clear descriptions of it's gain structure and outputs.

I would be my use case, so there's that. AV receiver (for easy room correction), output via RCA to run big towers with big woofers that I run full range since crossing them to a sub would defeat the point of buying them in the first place. Most Hypex amps need not apply. Got it. Interestingly, this has not come up with most other Hypex amp reviews which have similar issues, albeit not quite as bad. Glad it did. I, like most (I suspect), never would have thought to pay any attention since pre-Hypex it was not an issue.

 

[Velocipede_Acoustics]

To be clear, this particular hypex amp doesn't have this problem with it's high gain settings, which was a real shame they weren't tested since this is a stand out feature on this particular hypex.

I do have a powered RCA to XLR converter that would solve this problem. 1/10 the cost of the amp. What else would perform as well for $1000 + $100 or less?

 

[Mnyb]

Re gain you should consider your whole audio chain .

if you have a source for example a DAC that supplies a very high signal level and have volume control that low gain modes becomes useful to have a very low noise floor .
In fact state of the art performance is achievable this way if the signal becommes analog at the DAC at a 10v level you can cheat physics a bit . But you need to consider if its useful to you .

Benchmark provides such products combine their DAC and or preamps with their AHB2 for example ?

ON the other hand if you have use for a classic preamp situation with sources of varying pedigree cassete decks tuners phono ? the levels migth not be that high.
And the amp you consider must be able to perform as good as it can even in high gain modes and RCA connections .

The IOM products fails in this user situation .

Other manufactures manage to loose only a couple of dB's in high gain and RCA , buy amps from them instead .
You will inevitable loose some noise floor with gain and RCA , but again some brands manages this much better .

 

[Head_Unit]

Does anyone have concerns about thermal issues in that small space?

Oh yeah. Smooth cases look nice but not the best for shedding heat. Maybe I'll start a company making add-on water cooling kits. Then I will also sell add-on mineral kits using cheap swimming pool supplies but marked up to Audiofool, er, Audiophile prices for huge profit. I will claim that by changing the cooling characteristics the hysterics I mean hysteresis of the transistors will be modified for more emoluation and suavization.

 

[musicforcities]

Shoot. If I had known about that model, I would have asked for it!!!

They are not currently offering that model with the VU meter. You can get the same mono amp without the meter however. I inquired about it in early 2024 and they said there was an issue with supplies for fabrication. They said they could make a set on request however.

I am still tempted by that as I love elegant big VU meters, my favorite amp in terms of appearance being the Luxman M600/400/200. Those Luxman sound wonderful too if maintained. I doubt they compete with ncore or purifi based amps though. And decent vintage Luxman m4000 (dual mono, 170wpc +) cost about the same as two of the IOM VU mono blocks.


On this model’s performance: the large performance hit for single ended is very disappointing and would seem very avoidable judging by comparable amps. I understand that balanced should typically be better, but the difference here seems an issue with the implementation rather than inherent. Perhaps the buffer boards or I/O needs revision.

I agree as well that while the case is very elegant, there is a lot of circuitry in a small volume and I would be concerned about the effects of heat in regards to long term reliability. The ncore modules are pretty packed already from the factory and while I gather they are designed with proper heat dissipation (otherwise I suppose we would hear about it by now), usually one sees builds with more
Space between those modules and/or ventilation.


The electrolytic caps and ICs, even if rated for higher max temps, will perform to spec Much longer in a case with lower ambient temps. I have owned too many devices in which poor thermal management created issues down the road (and repair issues if caps leaked, or traces cooked, or resistors started cooking, etc)—I’m looking at you NAD.

It is very easy to add ventilation that could maintain the minimalist design (see recent Fosi units). Or indeed heat sinks on compact cases at reasonable costs (see Schiit Vidar). But the case still seems overly compact even. If it were vented, given that the case performs as a heat sink— the heat it dissipates will radiate to some degree both inwards and outwards from after all.

I could very well be wrong and there is no issue. A thermal map of the interior when this thing is running at reasonable power outputs after a couple hours would be great to see. Not that I’m asking Amir for such a thing or that such a map would be that easy to do. 6 -8 probes attached to key areas, or on in a grid of plastic temporarily mounted between the upper case and the boards, would do the trick.

But when IOM claims the case adequately dissipates the heat, I would appreciate seeing evidence of their own tests. I am NOT suggesting their claims are false and from my interactions they seem very forthcoming and quality. And I appreciate the attention to design in their products inside and out. And I presume they tested the heat management of this design in any case. Just be nice to see the results of their testing in this instance.