I must agree with all that has been said since my last reply and yes Helix there is a huge difference between good engineering practices and a well engineered product... primarily in that the well engineered product should best fit all the design criteria whereas a product that follows good engineering practices does not necessarily meet the design criteria.... indeed i could be asked to design an amp that costs $250 to manufacture and finish up with an amp that costs 5 times that to produce. It's not well engineered but it may well adopt good engineering practice in the design. Now personally i believe that it should be the job of the engineer to best produce a well engineered product while not sacrificing good engineering practice. I realise this is not the case because profits have become of all consuming importance but alot of things could be corrected for a matter of 5 or 10 dollars. It isnt going to send the big guys broke and the funds could easily be diverted from the almost useless features that PR make a song and dance about... but that would require PR to start advertising the truth and not a sack of whimsical garbage.. Anyway, that's just my 2 cents.
Please forgive me Mr. Pass
I must appologize to Mr. Pass for relegating him to "others". The Threshold 800a was one of Mr. Pass' first amps and one of the first amps to use the "dynamically biased" class A configuration back in the 70's. This is a method of getting more power from a class A amp with smaller (cheaper?) parts.
I must appologize to Mr. Pass for relegating him to "others". The Threshold 800a was one of Mr. Pass' first amps and one of the first amps to use the "dynamically biased" class A configuration back in the 70's. This is a method of getting more power from a class A amp with smaller (cheaper?) parts.
Attachments
Re: Please forgive me Mr. Pass
There are suitable methods of storing energy.
In caps or coils.
how effective they store energy
and the Quality of that energy
are matters
no fault in going your own way
that what you must do
anyway
he went his way
like a slaughtered lamb
We all must
"carry that weight" John Paul 1969 Abbey Road
what is an abbey - we do not sell tem in Land of Vikings
gro
roddyama said:
There are suitable methods of storing energy.
In caps or coils.
how effective they store energy
and the Quality of that energy
are matters
no fault in going your own way
that what you must do
anyway
he went his way
like a slaughtered lamb
We all must
"carry that weight" John Paul 1969 Abbey Road
what is an abbey - we do not sell tem in Land of Vikings
gro
"The NAD spec of having a 6 dB headroom is the marketing and sales department's way of saying that the amp has a lousy power transformer that sags badly, and low power rated output transistors."
Nothing could be further from the truth than the above statement. For people with an open mind I will try and explain some of the NAD design. But load the Nelson Pass patent first, I will refer to it later.
http://patft.uspto.gov/netacgi/nph-Parser?patentnumber=5343166
How does the NAD power envelope amplifier work? What trade-offs did they make?
The schematic for the 100W NAD power envelope amplifier looks almost like a Bryston 3B or an Accuphase P300, but with a tiered power supply. Cross coupled dual differential inputs, fully complimentary from input to output. But with a high voltage tier.
I have bench tested the 100W NAD with both channels driven at 8R with a 1Khz sine wave and got 360W/ch RMS. After a couple of seconds at this level the RayChem PolySwitch opens up and shuts down the high voltage tier. With the high voltage tier shut down the amp will do 100W/ch RMS.
As long as the peak to average ratio in the program material is better than about 6dB the high voltage tier will be available. Even highly compressed rock music meets this requirement.
Money is saved compared to a 400W amp in that the transformer and heatsink is sized for a 100W amp.
The downside is some noise where it switches to the high voltage tier.
There are ways to eliminate the switching. See the Pass patent. While the NAD used a hard switch for the high voltage tier, the Pass works like a normal amplifier up to the tier, and then cascodes itself for the rest of the swing! The higher voltage tier operates in a linear, rather than a switched mode.
Let's do some bench racing. You own some inefficient speakers like the B&W 801s that need 300W/4R to make them get up and go. Well class A is OK if you have $1,000 for heatsink. What about AB biased 10W into class A? OK, our supply voltage is +/- 57V to do 300W/4R, a brute force unregulated supply with lots of filter caps and a big low voltage transformer. Say 40-0-40 at 1KVA with 120,000µF filter capacitance (one 30,000µF per rail, per channel. To put this in perspective, an Adcom GFA555 puts out 325W/4R with a much higher +/- 75V and half the filter capacitance with only a 700VA transformer). 10W/8R is 1.58A peak, or 360W at idle for a stereo amp. This is a LOT of heat. A normal 300W stereo class AB amp would only have to get rid of about 240W of heat (60% efficency) at full power.
Now let's add a +/- 12V tier. With our same 1.58A bias we now only have 76W of heat for the stereo amp at idle! At full power the efficency would be about 70%, so we could either reduce the size of the heatsink, or choose to increase the class A power point a little higher.
I think one IRF 640/9640 pair in the TO247 package would do for the 12V tier (no matching dozens of transistors), and I would use two pair MJ21193/21194 for the cascode. The Apex jr 37-37-37-37 at 1KVA would be just right for the main rails, and for a stereo amp the low voltage tier need only be 3A or so.
Nothing could be further from the truth than the above statement. For people with an open mind I will try and explain some of the NAD design. But load the Nelson Pass patent first, I will refer to it later.
http://patft.uspto.gov/netacgi/nph-Parser?patentnumber=5343166
How does the NAD power envelope amplifier work? What trade-offs did they make?
The schematic for the 100W NAD power envelope amplifier looks almost like a Bryston 3B or an Accuphase P300, but with a tiered power supply. Cross coupled dual differential inputs, fully complimentary from input to output. But with a high voltage tier.
I have bench tested the 100W NAD with both channels driven at 8R with a 1Khz sine wave and got 360W/ch RMS. After a couple of seconds at this level the RayChem PolySwitch opens up and shuts down the high voltage tier. With the high voltage tier shut down the amp will do 100W/ch RMS.
As long as the peak to average ratio in the program material is better than about 6dB the high voltage tier will be available. Even highly compressed rock music meets this requirement.
Money is saved compared to a 400W amp in that the transformer and heatsink is sized for a 100W amp.
The downside is some noise where it switches to the high voltage tier.
There are ways to eliminate the switching. See the Pass patent. While the NAD used a hard switch for the high voltage tier, the Pass works like a normal amplifier up to the tier, and then cascodes itself for the rest of the swing! The higher voltage tier operates in a linear, rather than a switched mode.
Let's do some bench racing. You own some inefficient speakers like the B&W 801s that need 300W/4R to make them get up and go. Well class A is OK if you have $1,000 for heatsink. What about AB biased 10W into class A? OK, our supply voltage is +/- 57V to do 300W/4R, a brute force unregulated supply with lots of filter caps and a big low voltage transformer. Say 40-0-40 at 1KVA with 120,000µF filter capacitance (one 30,000µF per rail, per channel. To put this in perspective, an Adcom GFA555 puts out 325W/4R with a much higher +/- 75V and half the filter capacitance with only a 700VA transformer). 10W/8R is 1.58A peak, or 360W at idle for a stereo amp. This is a LOT of heat. A normal 300W stereo class AB amp would only have to get rid of about 240W of heat (60% efficency) at full power.
Now let's add a +/- 12V tier. With our same 1.58A bias we now only have 76W of heat for the stereo amp at idle! At full power the efficency would be about 70%, so we could either reduce the size of the heatsink, or choose to increase the class A power point a little higher.
I think one IRF 640/9640 pair in the TO247 package would do for the 12V tier (no matching dozens of transistors), and I would use two pair MJ21193/21194 for the cascode. The Apex jr 37-37-37-37 at 1KVA would be just right for the main rails, and for a stereo amp the low voltage tier need only be 3A or so.
Talking about power supplies in amplifiers...
I see audio amps as big power supplies controlled by small audio circuits to give power to loudspeakers. The better the power supply is, the better the thing works.
Headroom, as I understand it, means you have a bigger power supply then you will be using, so you have some extra power for the peaks.
That means, according to the above, that if you need 10 watts of power to listen to music, you will want some extra "space" over that. I think 10 times more is a good choice. 100 watts for the peaks. Thats + 10 dB of headroom.
I see audio amps as big power supplies controlled by small audio circuits to give power to loudspeakers. The better the power supply is, the better the thing works.
Headroom, as I understand it, means you have a bigger power supply then you will be using, so you have some extra power for the peaks.
That means, according to the above, that if you need 10 watts of power to listen to music, you will want some extra "space" over that. I think 10 times more is a good choice. 100 watts for the peaks. Thats + 10 dB of headroom.
promitheus said:
No because then the amp will be specced in the sales burlb at 100 watts and hence 0db of headroom
You are correct. I wasnt talking about what the specs would be. I was talking about what someone would want to choose.
The amplifier somebody would buy would of course be rated at 100 Watts. I meant if you needed 10 watts you should buy something with +10dB more.
The amplifier somebody would buy would of course be rated at 100 Watts. I meant if you needed 10 watts you should buy something with +10dB more.
Dynamic range is usually applied for sources I think or recordings, I am not sure anymore.
It means the difference of the smallest signal and the largest signal that can be reproducted or is recorded.
This wouldn´t apply to amplifiers. They play everything you give them if they are adjusted ok without clipping.
It means the difference of the smallest signal and the largest signal that can be reproducted or is recorded.
This wouldn´t apply to amplifiers. They play everything you give them if they are adjusted ok without clipping.
Hi All,
I suppose good or bad engineering can be viewed from different points.
For good market penetration, an economical retail price point is required and this can be achieved by scrimping on hardware - this is good from the marketing department point of view and can be expressed as " It's not a bug, it's a feature " justification in the glossy brochures.
An under specified power supply has merits of economy and power envelope limiting and this is quite acceptable for most domestic users.
For more serious applications, and high duty cycle music or soundtracks, this is not desirable, and can then be considered as bad engineering.
NAD amplifiers were very much a sales and marketing exercise.
Team them up with smallish speakers in a small english lounge room, and the result was quite acceptable in their day, and the English hi-fi press was happy to tag along with the joke.
The brocures will also tell you that they were european designed.
This is true, but they were infact Taiwan made and were built to be cheap - European semis, Taiwan pcb's, Taiwan passives, Taiwan metalwork, Taiwan solder, and in my opinion Taiwanese sound .
Against the cheap opposition of the time, they sounded ok, but against good gear of today, or any other day, they still sound cheap, and very coloured.
Rodd, I solved the SAF problem by setting up a nice system at her place, so she is happy when I am there, and happy when I am not there too - everybody is happy. 🙂
DJK, "The downside is some noise where it switches to the high voltage tier."
This is still bad engineering IMO when viewed from the sonics POV.
Hugh, I agree with your observations of power supply dependance, however this is largely telling me that this is due to inadequate PSRR, and electrical resonances all the way back to meter box.
Regards, Eric.
I suppose good or bad engineering can be viewed from different points.
For good market penetration, an economical retail price point is required and this can be achieved by scrimping on hardware - this is good from the marketing department point of view and can be expressed as " It's not a bug, it's a feature " justification in the glossy brochures.
An under specified power supply has merits of economy and power envelope limiting and this is quite acceptable for most domestic users.
For more serious applications, and high duty cycle music or soundtracks, this is not desirable, and can then be considered as bad engineering.
NAD amplifiers were very much a sales and marketing exercise.
Team them up with smallish speakers in a small english lounge room, and the result was quite acceptable in their day, and the English hi-fi press was happy to tag along with the joke.
The brocures will also tell you that they were european designed.
This is true, but they were infact Taiwan made and were built to be cheap - European semis, Taiwan pcb's, Taiwan passives, Taiwan metalwork, Taiwan solder, and in my opinion Taiwanese sound .
Against the cheap opposition of the time, they sounded ok, but against good gear of today, or any other day, they still sound cheap, and very coloured.
Rodd, I solved the SAF problem by setting up a nice system at her place, so she is happy when I am there, and happy when I am not there too - everybody is happy. 🙂
DJK, "The downside is some noise where it switches to the high voltage tier."
This is still bad engineering IMO when viewed from the sonics POV.
Hugh, I agree with your observations of power supply dependance, however this is largely telling me that this is due to inadequate PSRR, and electrical resonances all the way back to meter box.
Regards, Eric.
Absolutely, my View
Couldn't be anything else.
See also my 2-3 last STK4050V posts
MY Posting
Comments!!!!! 😛
promitheus said:
Couldn't be anything else.
See also my 2-3 last STK4050V posts
MY Posting
Comments!!!!! 😛
"gromanswe
DIYaudio Elder
Registered: Jul 2002
Location: Sweden
MJE 15030/31
Best TO220 bipolar power device
Inform Me
I use it a lot!
gro"
The MJE15030/31 make great driver transistors, remember to de-rate them for high voltage use. At 30V they only have 25W of safe area. If you need outputs for a small power amp the 2N6488/6491 are a much better choice, IC=15A with 75W of safe area at 30V.
"DJK, "The downside is some noise where it switches to the high voltage tier."
This is still bad engineering IMO when viewed from the sonics POV."
Most listeners cannot tell where it switches, and besides there is an alternative as I presented. Carver used both schemes in different versions of his amplifiers. Can you tell which is which without seeing the schematic?
DIYaudio Elder
Registered: Jul 2002
Location: Sweden
MJE 15030/31
Best TO220 bipolar power device
Inform Me
I use it a lot!
gro"
The MJE15030/31 make great driver transistors, remember to de-rate them for high voltage use. At 30V they only have 25W of safe area. If you need outputs for a small power amp the 2N6488/6491 are a much better choice, IC=15A with 75W of safe area at 30V.
"DJK, "The downside is some noise where it switches to the high voltage tier."
This is still bad engineering IMO when viewed from the sonics POV."
Most listeners cannot tell where it switches, and besides there is an alternative as I presented. Carver used both schemes in different versions of his amplifiers. Can you tell which is which without seeing the schematic?
Comparing Like With Like.
Hi DJK,
Never liked the Carvers either.
Anyway I agree that if additional HV rails can be bled in gracefully as required, or the supplies droop, and do this sonically nicely, then this is indeed quite good engineering.
I have to relent and say that modern mid to higher end shelf systems use the droopy psu method - That's how they get the 2000W total pmpo ratings, and at normal levels work rather well for the mr&mrs average home situation.
At higher and full levels (volume on 11), the supplies sag like crazy yet the amplifiers stay clean(ish), and the result is a quite fine compression characteristic, that can go quite loud and still easy(ish) on the ears, and the amplifiers and the loudspeakers remain reliable even when in the use of careless hands.
From the manufacturers warranty repairs claims department, this is perfect engineering.
A lesser rated psu gets the vote from the manufacturing, accounting and freighting departments.
The engineering department is somewhere in the middle.
Like I said it all depends on whose point of view, and by which criteria.
High energy efficiency + sonics ratio gets my vote.
Regards, Eric.
Hi DJK,
Never liked the Carvers either.
Anyway I agree that if additional HV rails can be bled in gracefully as required, or the supplies droop, and do this sonically nicely, then this is indeed quite good engineering.
I have to relent and say that modern mid to higher end shelf systems use the droopy psu method - That's how they get the 2000W total pmpo ratings, and at normal levels work rather well for the mr&mrs average home situation.
At higher and full levels (volume on 11), the supplies sag like crazy yet the amplifiers stay clean(ish), and the result is a quite fine compression characteristic, that can go quite loud and still easy(ish) on the ears, and the amplifiers and the loudspeakers remain reliable even when in the use of careless hands.
From the manufacturers warranty repairs claims department, this is perfect engineering.
A lesser rated psu gets the vote from the manufacturing, accounting and freighting departments.
The engineering department is somewhere in the middle.
Like I said it all depends on whose point of view, and by which criteria.
High energy efficiency + sonics ratio gets my vote.
Regards, Eric.
Dynamic headroom etc
Wow, these threads go fast. Get away for 2 days and they're 4 pages down....
Back to dynamic headroom, if I may. I just want to clarify my opinion on it.
Can we agree that in general we use our amps 99% of the time to put out just a couple of watts, and then once in a forthnight (OK, I exaggerate) there's this CD with the 1812 cannon shot that requires 50 Watts for a couple of 100mSecs.
We all run out and buy amps that can deliver 50Watts continues. What a waste! The NAD principle would be to build an amp that delivers say 10watts continuously, with the ability to deliver 50watts for a couple of 100msecs once in a while. I call that excellent engineering.
The cost of the amp are in the output stage (# of output devices & heatsinks) and the supply, notably the power xformer.
If the NAD would cost $ xx, the 50watts continously version would probably cost $ 2xx or even $ 3xx. What a waste!
There is a real benefit in high dynamic headroom, because it means that although you bought a reasonably priced amp, it still can hold its own against the powerfull "can do it continously" ones in actual reproduction, albeit not on the testbench.
And as far as the sales blurb is concerned, remember it's only in there because we suckers collectively fall for it...!
Cheers, Jan Didden
Wow, these threads go fast. Get away for 2 days and they're 4 pages down....
Back to dynamic headroom, if I may. I just want to clarify my opinion on it.
Can we agree that in general we use our amps 99% of the time to put out just a couple of watts, and then once in a forthnight (OK, I exaggerate) there's this CD with the 1812 cannon shot that requires 50 Watts for a couple of 100mSecs.
We all run out and buy amps that can deliver 50Watts continues. What a waste! The NAD principle would be to build an amp that delivers say 10watts continuously, with the ability to deliver 50watts for a couple of 100msecs once in a while. I call that excellent engineering.
The cost of the amp are in the output stage (# of output devices & heatsinks) and the supply, notably the power xformer.
If the NAD would cost $ xx, the 50watts continously version would probably cost $ 2xx or even $ 3xx. What a waste!
There is a real benefit in high dynamic headroom, because it means that although you bought a reasonably priced amp, it still can hold its own against the powerfull "can do it continously" ones in actual reproduction, albeit not on the testbench.
And as far as the sales blurb is concerned, remember it's only in there because we suckers collectively fall for it...!
Cheers, Jan Didden
You guys are meandering all around this thing so I'm going to try and reign you all in again. The issue I would like to resolve is if an amp delivering an excellent representation of the music signal at 0.5W to a speaker with an 80dB/8ohm sensitivity is good enough for us to hear a 21dB jump in dynamics at a 1 meter distance or are more watts in reserve necessary to accomplish this. For lack of a better term I used the NAD phrase "dynamic headroom" and it unfortunately sparked a debate on the merits of NAD engineering and its tangents. Lets focus and discern the truth. If my ambient noise level is 15dB and I want to fully hear a 21dB jump in sound dynamic in the music, the aforementioned speaker receiving 0.5W of power should be adequate to do the job with a sound floor of 4dB and a full level of 40dB (0.5Wx80dB). If my ambient noise is 55dB then I need twice as much power (1Wx80dB) to get the same sound levels reaching my ears at 1 meter. The difference is now that the total sound pressure reaching my ears is 80dB. Do we all concur on this or is there something missing from these examples?
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