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Schiit Magni Heresy

solderdude

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Such a circuit usually triggers (after a short delay as to not trigger on rumble for instance) on a DC voltage of around 0.6V (a simple transistor BE voltage) but could be smaller in IC's.

This could still blow up your sensitive IEM but one should connect those via a passive attenuator instead of directlt to a device that can pump 3W into a low impedance anyway.
 

JohnYang1997

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There are a few different implementation / very different methods.
Most common way is to detect extremely low frequency say 1hz 2hz. Let the output signal go through a full bridge rectifier a low pass filter a peak detector a comparator then you can detect essentially dc and disable the output accordingly.

Another way is to compare input signal with normalized output signal. The residue then feed into peak detect and then the comparator. You can do more than just dc protection.
 

Cahudson42

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@solderdude

It seems relevant and not too far off-topic (hopefully) - Do the competitors in this price bracket ($100 -$150) all have DC protection?

My Liquid Spark?
Geshelli?
Atom?

I'm also thinking that it's not just a $3000 HP issue. I would think it might be quite an exciting event to have this happen while they were on your ears..Plus given my wallet, even my $170 HE400i getting blown up would be at least a bit of an annoyance..
 
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solderdude

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There doesn't seem to be on the LS and Atom.
Doesn't look like Archel 2 has it either.

It will be hard to blow up the 400i.

personally I would not worry about it.
The chances are very very slim when these devices are used properly (so not as speaker amps for instance) but not 0 and why I asked.
It is more likely headphones are destroyed by careless usage than by failure of amps like these (simple op-amp amplifiers directly driving headphones)
 

threni

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There doesn't seem to be on the LS and Atom.
Doesn't look like Archel 2 has it either.
Ssshh!! We're busy hating on Schiit! In an entirely rational justified-by-the-facts kind of way!
 

makmeksam

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There doesn't seem to be on the LS and Atom.
Doesn't look like Archel 2 has it either.
So this is good opportunity for a manufacturer to lead the competition. Add DC protection and tell people how important that is. Also tell only they have it in the price range. (Or later market that they were the first to do it).
 

Cahudson42

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Hmmm...With a supposedly 94db sensitivity, I wonder how well the Heresy would work as the amp in a low/modest volume (but very low noise/distortion?) desktop system with these?

Klipsch R-15M Bookshelf Speaker (Pair) https://www.amazon.com/dp/B00LMF41IY/
 
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LTig

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There is a snag when doing this.
The output is 0V (so no big thumbs or anything on switching on/off it will be completely silent) but in order to get a good LF extension you would need to put 2 electrolytic caps of say 2200uF/25V in antiseries or use a single bipolar (non polar) electrolytic.
These capacitors will have to be electrolytics and to work properly they would like to have a DC voltage on them otherwise they would induce measurable distortion that defeats the purpose of the low distortion amps.
I learned about the latter from the designer of Avantgarde Acoustic. He told me that he uses a nonrechargable battery to create a DC voltage for the caps in the crossover. However this seems to an audiophile myth. According to Cyril Batemans measurements (see part 6) a DC voltage actually (very slightly) increases THD of elcaps.

Douglas Self published measurements of elcaps done with an AP 2702 in his book Small Signal Audio Design (pages 59 + 60). THD rises with voltage drop so to prevent THD you have to use an elcap which has such a high capacity that a signal with maximum desired amplitude and lowest desired frequency passes it with a voltage drop below 80 mVrms, resulting in THD below 0.0002%. I'm too lazy to calculate a cap suited for this headphone amp when driving the lowest specified impedance but I think it'll be rather very big.
 
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LTig

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There are a few different implementation / very different methods.
Most common way is to detect extremely low frequency say 1hz 2hz. Let the output signal go through a full bridge rectifier a low pass filter a peak detector a comparator then you can detect essentially dc and disable the output accordingly.

Another way is to compare input signal with normalized output signal. The residue then feed into peak detect and then the comparator. You can do more than just dc protection.
The latter is the way how my O300D protects its drivers from clipping amps.
 

trl

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Aren't upc1237ha or nte7100 dedicated for DC protection?

Also, for few volts only, even a simple opamp-based DC-servo should do.
 

solderdude

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Hmmm...With a supposedly 94db sensitivity, I wonder how well the Heresy would work as the amp in a low/modest volume (but very low noise/distortion?) desktop system with these?

Klipsch R-15M Bookshelf Speaker (Pair) https://www.amazon.com/dp/B00LMF41IY/

1.25W and the Heresy output op-amps would get quite hot. Not recommended.
 

solderdude

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But, if the amplifier measures so well, why wouldn't someone pair it with a $3k headphones?

I would ... if I had one, but then again would also have the funds to buy something with protection. That's what restorer-John was saying I reckon.
 

makmeksam

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I would ... if I had one, but then again would also have the funds to buy something with protection. That's what restorer-John was saying I reckon.
Do you know any other amps with this good measured performance and DC protection?
 

solderdude

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Aren't upc1237ha or nte7100 dedicated for DC protection?

Also, for few volts only, even a simple opamp-based DC-servo should do.

Yes, If one is really anal about this you can always put this between the amp and headphone

It would cost about $ 2.- in extra parts to add it to an amp (as the relay is already in there)
 

JohnYang1997

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Honestly, amps like atom already has output relays for turn on delay. It would be really easy to just add a protection circuitry. And not only dc protection, add a distortion protection circuitry, over current shut down etc. Often times opamps fail oscillating not shorting to rail. It would be better just to cover anything that would be wrong.
 

Cahudson42

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op-amps would get quite hot.
If the heat problem could be solved:
Easycargo 100pcs Heatsink Kit Small Cooler Heat Sink Set for Cooling Development Board Laptop CPU GPU VGA RAM VRAM VRM IC Chips LED MOSFET Transistor SCR Southbridge Northbridge Voltage Regulator https://www.amazon.com/dp/B078KB7V5J/

any guesses as to performance, say against other $100 choices:

Yamaha R-S202BL Stereo Receiver https://www.amazon.com/dp/B01EMQI2CU/

My thinking is as follows: I have basically switched from room speakers to HP system with LG V20, Liquid Spark, and HE400i. No more 'Turn down that noise!' from wife.

But in my home office I could likely get away with a relatively modest volume desktop setup. It would be nice to use, say, my V20 with an amp that gives great HP performance, but could also be switched over to very efficient small desktop speakers when I'm moving around and the HPs wires would be a nuisance..

Just thinking.. Any comments suggestions appreciated.. But wallet is pretty thin, and the Heresy/Klipsch setup would fly - anything much more $ than that - probably not...

Thanks!
 
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