Finally measure the little composite amp
So the little guy is run on ±30 volts with this lame bad ground set up in the picture. Slew rate is 16V/µs. Test signals for wave forms is at 10 volts peak to peak. I hope the rest is clear by the pictures. Load conditions are under each image. Blank is just the resistor. The last row of three are capacitors only. Matrix is THD. Bottom values are with an 80kHz low pass filter on the distortion detection circuit. For the square wave a 50 ohm resistor was placed across the input. With the 50 ohm resistor and no signal output is 400µV rms wide band... 2-250kHz Av= 20 Higher gain would improve stability of course also.
Yes this amp will oscillate driving these bad loads as soon as it gets hot which happens really fast...I mean really fast with the 1µF at 50kHz. But that is to be expected. The amp design was just thrown together and there are at least 5 optimizations I know of to make it significantly better and more stable including a better input IC than the LF412.
The amp is just sort of there on the bench and not really proper ground with the power supply yonder. My hand for the camera is not to steady but should be good enough. Looks like a pretty good amp to me but others may disagree which is just fine. Said I would post the measured data so here it is. Believe it or not as you like but it is what it is.
Enjoy... I hope.
So the little guy is run on ±30 volts with this lame bad ground set up in the picture. Slew rate is 16V/µs. Test signals for wave forms is at 10 volts peak to peak. I hope the rest is clear by the pictures. Load conditions are under each image. Blank is just the resistor. The last row of three are capacitors only. Matrix is THD. Bottom values are with an 80kHz low pass filter on the distortion detection circuit. For the square wave a 50 ohm resistor was placed across the input. With the 50 ohm resistor and no signal output is 400µV rms wide band... 2-250kHz Av= 20 Higher gain would improve stability of course also.
Yes this amp will oscillate driving these bad loads as soon as it gets hot which happens really fast...I mean really fast with the 1µF at 50kHz. But that is to be expected. The amp design was just thrown together and there are at least 5 optimizations I know of to make it significantly better and more stable including a better input IC than the LF412.
The amp is just sort of there on the bench and not really proper ground with the power supply yonder. My hand for the camera is not to steady but should be good enough. Looks like a pretty good amp to me but others may disagree which is just fine. Said I would post the measured data so here it is. Believe it or not as you like but it is what it is.
Enjoy... I hope.
Attachments
Wildly low output impedance
Measured the output impedance at 10kHzand 12.5 Vrms... at least I tried hahaha. When I referenced to a different ground to the star and not the wire ground going to the load from the star and the feedback/ouput point I got no change in reading at all on a 5 3/4 digit meter. Yikes!
Certainly less than .008 ohms at the output wire and load ground wire so damping of 1000 into 8 ohms and 10kHz. These points include traces and one length of 18ga wire 3 inches long. Messed with this quite a while with the proper ground and decided a 5 count variation is about what the oscillator/meter does short term so 100µohms, non-sense 
I say! High gain with feedback should have low output impedance anyway.
If it was 10 ohms open loop (reasonable?) and 100db of feedback (feedback is correct) that is 100µohms. That is just plain crazy low. Damping of 80,000? I do not believe it! Have been simply switching the load (4 ohms) on and off and taking readings all the while. Anyone got a better idea? 
Never tried to measure this anyway because I knew it had to be extremely low so who cares?
Listening experience says this chip amp does have fantastic bass and sounds better than most amps I and other listeners ever heard contrary to some other post....not just my ears?
Measured the output impedance at 10kHzand 12.5 Vrms... at least I tried hahaha. When I referenced to a different ground to the star and not the wire ground going to the load from the star and the feedback/ouput point I got no change in reading at all on a 5 3/4 digit meter. Yikes!
Certainly less than .008 ohms at the output wire and load ground wire so damping of 1000 into 8 ohms and 10kHz. These points include traces and one length of 18ga wire 3 inches long. Messed with this quite a while with the proper ground and decided a 5 count variation is about what the oscillator/meter does short term so 100µohms, non-sense I say! High gain with feedback should have low output impedance anyway. If it was 10 ohms open loop (reasonable?) and 100db of feedback (feedback is correct) that is 100µohms. That is just plain crazy
low. Damping of 80,000? I do not believe it! Have been simply switching the load (4 ohms) on and off and taking readings all the while. Anyone got a better idea? Never tried to measure this anyway because I knew it had to be extremely low so who cares?Listening experience says this chip amp does have fantastic bass and sounds better than most amps I and other listeners ever heard contrary to some other post....not just my ears?
I went from all 1950s and 60s Fisher and Scott amps to a Bryston 4B to home built LM3886 amps.
The only thing I can say to people who claim discrete is better is, good luck matching your transistors even remotely as close as those in a chipamp. And to people who claim they can be matched close enough, I guess you can argue any point so use what makes you happy. My fisher and scott amps sounded great, the Bryston 4B sounded great and gave me bragging rights. The LM3886 amps give me great sound and simplicity. And since bragging rights are useless when it comes to getting the job done, I'm sticking to my lm3886's
Build and use what makes YOU happy. Thats what its about.
Theres more to a good amplifier than matching transitors.
You know- I tend to agree. Keen observation.
Glad my "chip (pronounced cheap
) amp" above does not sound as bad as the Bryston 4B! The others I have heard, yes.
It has only one problem - not good clip behavior. To fix that it is possible to use non-linear feedback, but it is quiet complicated do to with LM3886 (because of it's Spike protection). On the other hand if do not listen the amp in constant clip, this behavior has nothing to do with the sound.
Personally I do not see any problem to do it even greater than 100dB (using multi-pole compensation). However distortions could be not reduced as expected, cause there are other significant factors (such as input/output stage/power lines magnetic coupling).
I can say for ZD-50 - yes, it does. They are below the noise floor, as well as the noise floor (itself) is significantly reduced too. I could say it is almost perfect in all aspects except clipping. Clipping behavior is not good, but is not so bad
(I posted the worst cases in the thread, however with an output filter it is much better).PS. It looks like nobody got it here, but ZD-50 is not just a composite amplifier with a conventional feedback, it is rather an error correction. U2 works (almost) only with non-linear distortions, linear are compensated.
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Nickolay- Looked at the ZD-50 amp- pretty fancy stuff! Someone has gone to a lot of trouble to attempt solve problems. I used the "hit it with feedback" approach. I did not optimize this design and did not desire extremely low noise as parts in stock were used for values. I like the active LPF in front of the ZD-50 amp and when that is an option that is great! In post 60 of "MY ZD-50..." oscillation is visible in the clip recovery...hummm. Would like to see test data similar to my measurement just for comparison. Note I did not even trim DC offset but used a servo instead...easy but always increases distortion because of the differential pair imbalance. Many ways to improve my simple design.
I think the key point here is now there are clearly at least 2 designs which work very well and I know mine sounds very good according to over 30 listeners and hundreds of professional engineers who have used the system the amps are in.
Two great efforts!
I think the key point here is now there are clearly at least 2 designs which work very well and I know mine sounds very good according to over 30 listeners and hundreds of professional engineers who have used the system the amps are in.
Two great efforts!
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That is why I loved the Bryston amps, from the 4B till the 28B's so much, as well as the powerfull BPA chipamps (with nested feedback).
It is a matter of personal preference.
I like tight, clean and detailed. (don't confuse that with "harsh" or "aggressive") However even a single chip with good implemented nested feedback is tighter and more detailed in bass then any Bryston.
With kind regards,
Bas
sure, but unfortunately there are drawbacks, too.
E.g. "thermal feedback" from the power out stage to the previous ones is surely not welcome, as are shared power supply (and/or ground) lines which may (will) introduce other unwanted interactions between stages.
IMVHO, the best would be to have an integrated "front-end" driving an integrated power out stage... but with the two parts built on separate chips!
P.S.: sorry for "rewinding" the thread with a late answer to an old post...
I believe this is why the two "fancy" chip amps of the earlier post numbers in the 80s are both "composite" amps with separate front end ICs from the power stage IC. The early and highly copied BGW amp used IC front end with discrete output stage. ICs clearly have a lot of advantages BUT do not always have the best circuit design for a given application.
Walt Junge said much of the later audio IC work at Analog Devices was to assure thermal effects from the output stage of the ICs did not adversely affect the input and gain stages. He presented talks at AES meetings on this very subject with lots of graphs and explanations of newest designs- about year 2002.
Walt Junge said much of the later audio IC work at Analog Devices was to assure thermal effects from the output stage of the ICs did not adversely affect the input and gain stages. He presented talks at AES meetings on this very subject with lots of graphs and explanations of newest designs- about year 2002.
Is this a chip amp?
I'm not sure what is meant by chip amp.
This thread is interesting.
I have a link... 6moons.com - audio reviews: nOrh/IRD Le Amp
Is that a chip amp?
The referral to nOrh should be ignored as this unit is actually the IRD MB-100 and is available. the nOrh no longer is.
If it is a chip amp, it compared favorably to the Bel Canto, which was mentioned in this thread as a good amp.
The IRD is MUCH less expensive and I have no reason to doubt that the reviewer's audition of MB-100 is less than reliable.
If it is not a chip amp, what type is it please?
I'm not sure what is meant by chip amp.
This thread is interesting.
I have a link... 6moons.com - audio reviews: nOrh/IRD Le Amp
Is that a chip amp?
The referral to nOrh should be ignored as this unit is actually the IRD MB-100 and is available. the nOrh no longer is.
If it is a chip amp, it compared favorably to the Bel Canto, which was mentioned in this thread as a good amp.
The IRD is MUCH less expensive and I have no reason to doubt that the reviewer's audition of MB-100 is less than reliable.
If it is not a chip amp, what type is it please?
For sure, and one which is being hyped in its output power. The review says its a '100W monoblock' but the single TDA7294 its employing can't push out that much power. Even the datasheet for it (shown on the page) states '100W music power'.
Yes it is a chip amp.
IMHO the heat sink is scary small. It took 300 square inches of heat sink to keep two channels of mine cool running hard. I run two chips as balanced output as per earlier post which make 100 watts into 8 ohms and more into 4 ohms but I do not see my log book right this second so 4 ohm power is right this second a mystery. Sounds good in mono really!
Other than that the amp of the link looks just dandy.
=SUM
IMHO the heat sink is scary small. It took 300 square inches of heat sink to keep two channels of mine cool running hard. I run two chips as balanced output as per earlier post which make 100 watts into 8 ohms and more into 4 ohms but I do not see my log book right this second so 4 ohm power is right this second a mystery. Sounds good in mono really!
Other than that the amp of the link looks just dandy.
=SUM
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whatever the data sheet states, might it be possible within the design-as a whole- to be legitimate according to specs below.
I'll be auditioning this product very soon, so I'll see what is up with this unit, but I can not verify, technically, the stated specs below.
I've had several conversations with the designer who states that he has fully tested this unit and over a long period-at least 5 or 6 years in the market, almost zero failure rate.
His background in designing advanced medical equipment and their power supplies and other technical equipment allowed him excellent design skills.
However, I'm not qualified to test it technically.
I believe it should be possible to reach that design
IRD MB-100 MonoblockMB-100 Features
Input Interface
Single ended mono input RCA Input Impedance 22.1k Ohms Input Sensitivity 1.25Vrms Main Specifications
Gain AC Signal = 26 dB (x20) ; DC = 0 dB (x1) Frequency Response 7 Hz-50k Hz ±0.2 dB; 3 Hz-195kHz ±3 dB Slew Rate > 10 V/us MOSFET output stage Class AB Output Power (IEC 60268-3) 100 Watts (RMS) minimum @ 8 Ohm Load SNR 93dB @ 12.5W
102dB @ 80W THD+N 0.011 % @ 75W Continuous into 8 Ohms
0.014 % @105W Continuous into 4 Ohms Built-in protection circuits SOA + Overload protection
+ Thermal shutdown protection Output Interface
Mono speaker output Machined metal binding post (9mm spade ID + >10awg hole) Peak Output Current > 10 A DC Offset Typically < 2 mV Recommended loudspeakers 8 /6 / 4 Ohm with impedance minimum >3 ohms Power—Physical
Mains AC Supply 110-120Vac (or) 220-240Vac @ 50/60 Hz IEC type removable power cord 2m (6'); 16awg / 3 wire; USA style plug Size 165mm (6.5") W
178mm (7.0") H
325mm (12.8")D Weight 11 Kgs (24 lb)
I'll be auditioning this product very soon, so I'll see what is up with this unit, but I can not verify, technically, the stated specs below.
I've had several conversations with the designer who states that he has fully tested this unit and over a long period-at least 5 or 6 years in the market, almost zero failure rate.
His background in designing advanced medical equipment and their power supplies and other technical equipment allowed him excellent design skills.
However, I'm not qualified to test it technically.
I believe it should be possible to reach that design
IRD MB-100 MonoblockMB-100 Features
- True high-end audio at a reasonable price
- Heavy duty 400 watt oversized power supply
- Easily drives most 8/4 ohm loudspeakers (handles impedance dips to 3 ohms)
- Music program peaks of 125+ watts @8 and 250+ watts @4 ohm loads (observed on Oscilloscope)
- Low THD+N performance
- Powerful DMOS output stage - accurate bass, smooth midrange and extended highs - no irritating SS distortions
- Superior build quality at this price point, designed to last a lifetime
- Excellent thermal management, never gets hot even at full power for extended periods
- Built-in SOA overload, short circuit protection, and thermal shutdown protection
Input Interface
Single ended mono input RCA Input Impedance 22.1k Ohms Input Sensitivity 1.25Vrms Main Specifications
Gain AC Signal = 26 dB (x20) ; DC = 0 dB (x1) Frequency Response 7 Hz-50k Hz ±0.2 dB; 3 Hz-195kHz ±3 dB Slew Rate > 10 V/us MOSFET output stage Class AB Output Power (IEC 60268-3) 100 Watts (RMS) minimum @ 8 Ohm Load SNR 93dB @ 12.5W
102dB @ 80W THD+N 0.011 % @ 75W Continuous into 8 Ohms
0.014 % @105W Continuous into 4 Ohms Built-in protection circuits SOA + Overload protection
+ Thermal shutdown protection Output Interface
Mono speaker output Machined metal binding post (9mm spade ID + >10awg hole) Peak Output Current > 10 A DC Offset Typically < 2 mV Recommended loudspeakers 8 /6 / 4 Ohm with impedance minimum >3 ohms Power—Physical
Mains AC Supply 110-120Vac (or) 220-240Vac @ 50/60 Hz IEC type removable power cord 2m (6'); 16awg / 3 wire; USA style plug Size 165mm (6.5") W
178mm (7.0") H
325mm (12.8")D Weight 11 Kgs (24 lb)
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I'm not suggesting the design isn't legitimate, just that the specs are overly optimistic. But that's fairly common in the audio world.
It certainly suggests it should be a reliable piece of equipment. But what does he know about achieving high quality sound from the design of medical power supplies I wonder?
This is interesting. If my amps had low performance in THD+N I'd not be trumpeting the fact. Or is there something of the hair shirt mentality coming in here - low performance in THD means its optimised for something other than linearity?
Where full power is 100W into 8R? I can't help but see the irony here - the reason it never gets hot at full power is because it thermally limits and effectively shuts down.
More hype here - the min specified slew rate is 7V/uS for the chip, 10 is the typical figure. Are we to believe that he hand picks the chips for better than typical slew rate?
I don't have a copy of IEC 60268-3 so maybe it allows short term output power to be put on the spec sheet. Anyone else know about this?
Of the 8-or-so reviews, a consistent remark was: running this amp hard for long periods barely gets past lukewarm. Performed favorably against Bel Canto and was practically indistinguishable against AYRE- another highly rated amp manufacturer. 100+ watts/8, 200+ watts/4 reliably and sonically.
Many units sold and still running for at least 6 years that I know of with very little failure or complaints.
Don't say It can't be done unless you can prove it regarding that unit.
Many units sold and still running for at least 6 years that I know of with very little failure or complaints.
Don't say It can't be done unless you can prove it regarding that unit.
Running the amp hard with music would mean an average output power at least 14dB below clipping, even with the most compressed grunge imaginable. That's not really so difficult - I'm not taking issue with the performance when playing music just with its apparent claim of 100W RMS continuous. I do note though that the specs you showed do not give the distortion number at 100W, rather they show it at 75W. Interesting don't you think? I think a >100W continuous squarewave output is eminently do-able with that chip
I'm of the (perhaps biassed) view that if it was almost indistinguishable to the Ayre then those listeners need their ears syringing.
The Ayre is a seriously engineered piece of kit, but I must admit I've never auditioned one myself.- Status
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