MOSFETs IRFP150
Supply 34.00
Vbias 3.88
Q1 bias 0.217
Q2 bias 0.233
Load 8.02
Frequency 1.00 kHz
Watts AC-RMS DIST%
40.4 18.00 0.340
36.1 17.03 0.268
32.3 16.11 0.250
28.5 15.11 0.305
24.6 14.06 0.374
21.2 13.04 0.411
18.0 12.01 0.449
15.4 11.13 0.485
12.5 10.00 0.526
10.1 9.00 0.570
7.98 8.00 0.616
6.18 7.04 0.654
4.56 6.05 0.679
3.20 5.07 0.684
2.00 4.01 0.612
1.18 3.08 0.437
0.78 2.50 0.275
0.50 2.00 0.156
0.38 1.75 0.115
0.28 1.50 0.076
0.19 1.25 0.048
0.12 1.00 0.034
0.10 0.90 0.030
0.080 0.80 0.026
0.061 0.70 0.027
0.045 0.60 0.016
0.031 0.50 0.028
0.020 0.40 0.041
0.011 0.30 0.028
0.008 0.25 0.030
0.005 0.20 0.030
0.003 0.15 0.055
0.001 0.10 0.115
Notes:
This test uses the original ST brand IRFP150 mosfets as fitted to the amp in the picture.
The mid power bump is at a little higher power than that with the IR IRFP140, but slightly lower in distortion.
The amplifier starts becoming power supply limited at 17 volts RMS.
100 Hz distortion figures are similar or slightly lower.
Tested with 500 kHz measurment bandwidth.
========
Low frequency power curve - Hz versum maximum AC-RMS at that frequency.
Load 8.02
Hz AC-RMS Watts
10.0 8.03 8.036
11.0 8.69 9.411
12.0 9.20 10.548
13.0 9.90 12.215
14.0 10.51 13.766
15.0 11.03 15.162
16.0 11.76 17.235
17.0 12.29 18.824
18.0 13.10 21.387
19.0 13.60 23.051
20.0 14.10 24.777
21.0 14.64 26.711
22.0 14.93 27.780
23.0 15.40 29.556
24.0 16.14 32.465
25.0 16.39 33.479
26.0 17.05 36.229
27.0 17.55 38.385
The above is limited by the line driver's ability to drive the input transformer.
=====
4 ohm load distortion figures are higher (this transformer does not have split secondaries - so it is not properly matched to this lower impedance).
Load 4.00
Frequency 1.00 kHz
Watt AC-RMS DIST%
25.0 10.00 1.853
20.3 9.00 1.302
16.0 8.00 0.768
12.3 7.00 0.846
9.0 6.00 0.933
6.3 5.00 1.031
4.0 4.00 1.135
2.3 3.00 1.232
1.6 2.50 1.230
1.0 2.00 1.094
0.77 1.75 0.942
0.56 1.50 0.727
0.39 1.25 0.408
0.25 1.00 0.282
0.20 0.90 0.194
0.16 0.80 0.152
0.12 0.70 0.122
0.09 0.60 0.089
0.06 0.50 0.072
0.040 0.40 0.060
0.023 0.30 0.044
0.016 0.25 0.027
0.010 0.20 0.011
0.006 0.15 0.010
0.003 0.10 0.058
=====
Best wishes,
Susan.
Supply 34.00
Vbias 3.88
Q1 bias 0.217
Q2 bias 0.233
Load 8.02
Frequency 1.00 kHz
Watts AC-RMS DIST%
40.4 18.00 0.340
36.1 17.03 0.268
32.3 16.11 0.250
28.5 15.11 0.305
24.6 14.06 0.374
21.2 13.04 0.411
18.0 12.01 0.449
15.4 11.13 0.485
12.5 10.00 0.526
10.1 9.00 0.570
7.98 8.00 0.616
6.18 7.04 0.654
4.56 6.05 0.679
3.20 5.07 0.684
2.00 4.01 0.612
1.18 3.08 0.437
0.78 2.50 0.275
0.50 2.00 0.156
0.38 1.75 0.115
0.28 1.50 0.076
0.19 1.25 0.048
0.12 1.00 0.034
0.10 0.90 0.030
0.080 0.80 0.026
0.061 0.70 0.027
0.045 0.60 0.016
0.031 0.50 0.028
0.020 0.40 0.041
0.011 0.30 0.028
0.008 0.25 0.030
0.005 0.20 0.030
0.003 0.15 0.055
0.001 0.10 0.115
Notes:
This test uses the original ST brand IRFP150 mosfets as fitted to the amp in the picture.
The mid power bump is at a little higher power than that with the IR IRFP140, but slightly lower in distortion.
The amplifier starts becoming power supply limited at 17 volts RMS.
100 Hz distortion figures are similar or slightly lower.
Tested with 500 kHz measurment bandwidth.
========
Low frequency power curve - Hz versum maximum AC-RMS at that frequency.
Load 8.02
Hz AC-RMS Watts
10.0 8.03 8.036
11.0 8.69 9.411
12.0 9.20 10.548
13.0 9.90 12.215
14.0 10.51 13.766
15.0 11.03 15.162
16.0 11.76 17.235
17.0 12.29 18.824
18.0 13.10 21.387
19.0 13.60 23.051
20.0 14.10 24.777
21.0 14.64 26.711
22.0 14.93 27.780
23.0 15.40 29.556
24.0 16.14 32.465
25.0 16.39 33.479
26.0 17.05 36.229
27.0 17.55 38.385
The above is limited by the line driver's ability to drive the input transformer.
=====
4 ohm load distortion figures are higher (this transformer does not have split secondaries - so it is not properly matched to this lower impedance).
Load 4.00
Frequency 1.00 kHz
Watt AC-RMS DIST%
25.0 10.00 1.853
20.3 9.00 1.302
16.0 8.00 0.768
12.3 7.00 0.846
9.0 6.00 0.933
6.3 5.00 1.031
4.0 4.00 1.135
2.3 3.00 1.232
1.6 2.50 1.230
1.0 2.00 1.094
0.77 1.75 0.942
0.56 1.50 0.727
0.39 1.25 0.408
0.25 1.00 0.282
0.20 0.90 0.194
0.16 0.80 0.152
0.12 0.70 0.122
0.09 0.60 0.089
0.06 0.50 0.072
0.040 0.40 0.060
0.023 0.30 0.044
0.016 0.25 0.027
0.010 0.20 0.011
0.006 0.15 0.010
0.003 0.10 0.058
=====
Best wishes,
Susan.
Hi,
Good
The figures do not change when I use the 80 kHz or 30 kHz low pass filters.
Once one has the input transformer any HF is filtered out.
... but it is important to know how the circuit sections behave.
I was involved in EMC/RFI conducted and radiated emissions testing of a battery/mains powered smoke alarm recently. All very low power stuff and a low few hundred hertz tick for its internal function.
Perfectly safe one would assume, and no emissions to worry about.
However it nearly failed the radiated emissions tests. Whilst in quiescent mode there wasn't a problem, but when the smoke unit was alarmed i.e. sounding it's pizzo horn, it was radiating up into several megahertz at a figure than was 80% of the test level failure point!
So much for low power and innocuous!
Best wishes,
Susan.
mikeks said:
With no filter, performance is excellent for such a simple design....even at 1KHz.....
Assuming of course, that there are no nasty surprises at HF with non-standard loads....
Good
The figures do not change when I use the 80 kHz or 30 kHz low pass filters.
Once one has the input transformer any HF is filtered out.
... but it is important to know how the circuit sections behave.
I was involved in EMC/RFI conducted and radiated emissions testing of a battery/mains powered smoke alarm recently. All very low power stuff and a low few hundred hertz tick for its internal function.
Perfectly safe one would assume, and no emissions to worry about.
However it nearly failed the radiated emissions tests. Whilst in quiescent mode there wasn't a problem, but when the smoke unit was alarmed i.e. sounding it's pizzo horn, it was radiating up into several megahertz at a figure than was 80% of the test level failure point!
So much for low power and innocuous!
Best wishes,
Susan.
Susan,
I've followed this thread with some interest...
Of course, you've fed bits and pieces out to the hungry little birdies!
It would be nice if ur webpages had an index so that someone could look at the parts of the design? If there is one, I don't know where to find it... certainly not from your home page?
With regard to the transformer specs, imho it's a bit like cheating to lightly load the transformer and test it. There's a certain "toroidal" output transformer company that shows rather remarkably good specs, but if you read the fine print they're testing it at a fraction of the practical operational levels for core saturation.
In general, for everyone else reading along, the multi-filar wound output transformer in the *low impedance* & *low turns ratio* variety tend to have substantially better resulting specs than do the usual output transformers. Typically bandwidths out to 250kHz. are possible whereas doing the same thing with even relatively low plate Z output transformers (like for a 300B) is not quite so easy, if acheivable at all.
No doubt this design has all the hallmarks of the most popular "DIY" style amps - like the original ZEN. What are those? Almost no parts, nothing to align or test, and ultimate simplicity. Hey, that's good!
The rub comes in the details - while almost anyone can build such amps, and they do make sound (sometimes good sound), there are usually several points of detail that do require some careful control and measurement to make the final practical project operate as well as the expectation of the "test bench" results indicate. This one is no different in that regard.
Among the points that need to be addressed still are:
- the effect of DC offset (device to device)
- the effect of bias offset to correct the DC offset wrt linearity
- what the optimal bias point is on the curve
- effect on power and frequency response of non-flat impedance loads
- and some other stuff that escapes me at the moment
Wrt the square wave response - I would not be satisfied with that result in any amp that came across my bench. It holds potential, but that ringing (imho) is a defict that is audible. Damping it might screw the overall response, or it might not depending on how or what the cause is/was... is it inherent to the output xfmr or? Important detail.
The use of unity coupled output transformers is nothing new, in case anyone thinks otherwise.
What's still not clear to me from a casual following of the thread is the design bias points, and how this design's power output varies with load (with and without the restrapped secondary) -
or is it truly a "current amplifier" at all?
But there is food for thought here...
Put up an index page, please?
Regards,
_-_-bear
http://www.bearlabs.com
PS. I have a precision coil winding machine here (USA)
I've followed this thread with some interest...
Of course, you've fed bits and pieces out to the hungry little birdies!
It would be nice if ur webpages had an index so that someone could look at the parts of the design? If there is one, I don't know where to find it... certainly not from your home page?
With regard to the transformer specs, imho it's a bit like cheating to lightly load the transformer and test it. There's a certain "toroidal" output transformer company that shows rather remarkably good specs, but if you read the fine print they're testing it at a fraction of the practical operational levels for core saturation.
In general, for everyone else reading along, the multi-filar wound output transformer in the *low impedance* & *low turns ratio* variety tend to have substantially better resulting specs than do the usual output transformers. Typically bandwidths out to 250kHz. are possible whereas doing the same thing with even relatively low plate Z output transformers (like for a 300B) is not quite so easy, if acheivable at all.
No doubt this design has all the hallmarks of the most popular "DIY" style amps - like the original ZEN. What are those? Almost no parts, nothing to align or test, and ultimate simplicity. Hey, that's good!
The rub comes in the details - while almost anyone can build such amps, and they do make sound (sometimes good sound), there are usually several points of detail that do require some careful control and measurement to make the final practical project operate as well as the expectation of the "test bench" results indicate. This one is no different in that regard.
Among the points that need to be addressed still are:
- the effect of DC offset (device to device)
- the effect of bias offset to correct the DC offset wrt linearity
- what the optimal bias point is on the curve
- effect on power and frequency response of non-flat impedance loads
- and some other stuff that escapes me at the moment
Wrt the square wave response - I would not be satisfied with that result in any amp that came across my bench. It holds potential, but that ringing (imho) is a defict that is audible. Damping it might screw the overall response, or it might not depending on how or what the cause is/was... is it inherent to the output xfmr or? Important detail.
The use of unity coupled output transformers is nothing new, in case anyone thinks otherwise.
What's still not clear to me from a casual following of the thread is the design bias points, and how this design's power output varies with load (with and without the restrapped secondary) -
or is it truly a "current amplifier" at all?
But there is food for thought here...
Put up an index page, please?
Regards,
_-_-bear
http://www.bearlabs.com
PS. I have a precision coil winding machine here (USA)
Hi,
Yes, it is interesting how the bump happens and then falls back to lower levels until the power rail starts to become a limiting factor.
From valve triode data I would expect it to just keep on rising - so I guess there are two data sheet graphs interacting here.
There is a small but noticeable difference between the IRFP140 and IRFP150 device characteristics. This indicates that it should be possible to optimize device type, load and power to maximize the performance of the amplifier to a given speaker.
Perhaps not so practical in a commercial product but less of a problem if one is building for oneself.
Thanks.
Best wishes,
Susan.
P.S. I would note that the IRFP150s are less well matched than the IRFP140s.
Graham Maynard said:
Yes, it is interesting how the bump happens and then falls back to lower levels until the power rail starts to become a limiting factor.
From valve triode data I would expect it to just keep on rising - so I guess there are two data sheet graphs interacting here.
There is a small but noticeable difference between the IRFP140 and IRFP150 device characteristics. This indicates that it should be possible to optimize device type, load and power to maximize the performance of the amplifier to a given speaker.
Perhaps not so practical in a commercial product but less of a problem if one is building for oneself.
Thanks.
Best wishes,
Susan.
P.S. I would note that the IRFP150s are less well matched than the IRFP140s.
Hi Bear,
Thank you for your interest and post.
I too have sought "clarity".
I would mention that I have not been deliberatly feeding out bits n' peices. I worked on the audio bits up to a decade ago and whilst many people have good memory for things I don't. I have also moved several times, ditiching at least 90% of my reference material, and it is a wonder to me that I have anything at all remaining from that time.
People have asked questions and I have been going away and actually doing measuments, to the best of my ability and with what I have to hand, in order to give an answer.
I have added the other pages to give background and scope to why I got started on my amplifier design in the first place.
There is a links section in the zeus page near the bottom to the other pages.
I haven't linked this stuff from my homepage as the amplifier discussion was in this forum, and I have been creating the additional web pages on the fly during the course of this last week.
Now that I have done this, when I have time, I may well put up a past projects page along with some other things I have done.
It is not cheating to do some tests if the conditions of the tests are specified - there was not any small print. Also I would query the case of the load which is 50 ohms and at these higher frequencies it is not unlikely that the speakers could also be in that ballpark.
It may be less relevant to audio but it is relevant to compliance testing where one has to demonstrate from 100kHz (or lower) to 2 GHz (or higher) the conducted and radiated conditions for the amplifier.
In Europe there are stringent rules for the assembly and use of electronics commercially and although most people are building for personal hobby use it is prudent to make sure that one isn't transmitting somewhere in the VHF or UHF bands where speaker cables and the like are more than adequate as antenna.
Yes, but there is little reference to this in the literature (that I knew of). I have clearly explained the importance of the multi-filar windings to the sucess of building this amplifier.
Thank you - however I hear a BUT in there somewhare...
I am using standard off the shelf components with the exception of the input transformer, which I would and have admitted is a little more difficult to make, most is readily to hand. The output transformer bits are perhaps not quite so easy to get but I am sure this is not a problem to the valve purists to advise us on.
My test bench results are vanilla and anyone building my design with the components and levels described should get equal or better results.
My line driver to the input transformer is now obviously the limiting factor, and this needs to be addressed.
However the amplifier works quite happily from the headphone output of a CD player or walkman/iPod. So it is easy to get a basic rig running and then be able to spend time working on the preamp side of things in the knowledge that the overall system will be working at the end of the day.
Whilst on paper the quite high distortion levels might seem off-putting they need to be equated with tride valve amplifiers, not semiconductor ones.
Yes, and this is all part and parcel of somehting called "DIY Audio".
But to give you some answers:
1. One needs to match the device as well as one can. I would suggest to aim for better than 10 mV matching at a bias of 225 mV at each primary of the transformer with respect to ground.
2. See 1 above. Seperating out the bias levels and adjusting them seperatly doesn't seem to make improvments.
3. Optimum bias point depends on a number of things including the device type - the bais levels I am using are at anywhere from 3.5 to 5.1 volts depending on the mosfet. Higher levels van be used with bigger heatsinks, a matter of experimantation. Big heatsinks are very expensive to buy, so a lower bias and therefor lower heat disapation is an advantage.
4. Non flat impedance loads will have effects on any amplifier. Some speakers will work better than others, just the same as with any system. I would look at types favioured by the low power single ended triode brigade as a starting point.
BTW The amplifier is designed for normal listning in personal environments, not for Carnige Hall, so I am not trying to address higher power levels.
I agree, I am not happy either. However at least half the problem is in the line driver to the input transformer and as such until I can sort out something better for that there is no point in fiddling with the output side of things.
I have never claimed this.
The bias point is where I found that it works, without overly heating up.
I don't have the equipment to do the proper measurments to be able to answer the power output bit.
It may not be a "current amplifier" but this is how I understand transformers to operate. Maybe I am wrong in this detail, but it is better than describing the amplifier as a "flux convertor".
I come from a digital and instrumentation/control electronics background - so my understanding of these definitions may be different.
Ah, is that an offer to supply transformer bits - or kits for that matter?
As a matter of curiosity what are the performance figures for your single ended mosfet amp?
Many thanks.
Best wishes,
Susan.
bear said:Susan,
I've followed this thread with some interest...
Of course, you've fed bits and pieces out to the hungry little birdies!
Thank you for your interest and post.
I too have sought "clarity".
I would mention that I have not been deliberatly feeding out bits n' peices. I worked on the audio bits up to a decade ago and whilst many people have good memory for things I don't. I have also moved several times, ditiching at least 90% of my reference material, and it is a wonder to me that I have anything at all remaining from that time.
People have asked questions and I have been going away and actually doing measuments, to the best of my ability and with what I have to hand, in order to give an answer.
I have added the other pages to give background and scope to why I got started on my amplifier design in the first place.
There is a links section in the zeus page near the bottom to the other pages.
I haven't linked this stuff from my homepage as the amplifier discussion was in this forum, and I have been creating the additional web pages on the fly during the course of this last week.
Now that I have done this, when I have time, I may well put up a past projects page along with some other things I have done.
It is not cheating to do some tests if the conditions of the tests are specified - there was not any small print. Also I would query the case of the load which is 50 ohms and at these higher frequencies it is not unlikely that the speakers could also be in that ballpark.
It may be less relevant to audio but it is relevant to compliance testing where one has to demonstrate from 100kHz (or lower) to 2 GHz (or higher) the conducted and radiated conditions for the amplifier.
In Europe there are stringent rules for the assembly and use of electronics commercially and although most people are building for personal hobby use it is prudent to make sure that one isn't transmitting somewhere in the VHF or UHF bands where speaker cables and the like are more than adequate as antenna.
Yes, but there is little reference to this in the literature (that I knew of). I have clearly explained the importance of the multi-filar windings to the sucess of building this amplifier.
Thank you - however I hear a BUT in there somewhare...
I am using standard off the shelf components with the exception of the input transformer, which I would and have admitted is a little more difficult to make, most is readily to hand. The output transformer bits are perhaps not quite so easy to get but I am sure this is not a problem to the valve purists to advise us on.
My test bench results are vanilla and anyone building my design with the components and levels described should get equal or better results.
My line driver to the input transformer is now obviously the limiting factor, and this needs to be addressed.
However the amplifier works quite happily from the headphone output of a CD player or walkman/iPod. So it is easy to get a basic rig running and then be able to spend time working on the preamp side of things in the knowledge that the overall system will be working at the end of the day.
Whilst on paper the quite high distortion levels might seem off-putting they need to be equated with tride valve amplifiers, not semiconductor ones.
Yes, and this is all part and parcel of somehting called "DIY Audio".
But to give you some answers:
1. One needs to match the device as well as one can. I would suggest to aim for better than 10 mV matching at a bias of 225 mV at each primary of the transformer with respect to ground.
2. See 1 above. Seperating out the bias levels and adjusting them seperatly doesn't seem to make improvments.
3. Optimum bias point depends on a number of things including the device type - the bais levels I am using are at anywhere from 3.5 to 5.1 volts depending on the mosfet. Higher levels van be used with bigger heatsinks, a matter of experimantation. Big heatsinks are very expensive to buy, so a lower bias and therefor lower heat disapation is an advantage.
4. Non flat impedance loads will have effects on any amplifier. Some speakers will work better than others, just the same as with any system. I would look at types favioured by the low power single ended triode brigade as a starting point.
BTW The amplifier is designed for normal listning in personal environments, not for Carnige Hall, so I am not trying to address higher power levels.
I agree, I am not happy either. However at least half the problem is in the line driver to the input transformer and as such until I can sort out something better for that there is no point in fiddling with the output side of things.
I have never claimed this.
The bias point is where I found that it works, without overly heating up.
I don't have the equipment to do the proper measurments to be able to answer the power output bit.
It may not be a "current amplifier" but this is how I understand transformers to operate. Maybe I am wrong in this detail, but it is better than describing the amplifier as a "flux convertor".
I come from a digital and instrumentation/control electronics background - so my understanding of these definitions may be different.
But there is food for thought here...
Put up an index page, please?
Regards,
_-_-bear
http://www.bearlabs.com
PS. I have a precision coil winding machine here (USA)
Ah, is that an offer to supply transformer bits - or kits for that matter?
As a matter of curiosity what are the performance figures for your single ended mosfet amp?
Many thanks.
Best wishes,
Susan.
RF mosfets - MRF148s
Hi,
I have run a test using MRF148 mosfets (which are spec'ed for use up to 175 MHz) the results are below.
I stopped the measurements at 15 watts as the mosfets were becoming supply limited - however the power up to 8 watts looks promising as the band between 2 and 8 watts is half the distortion levels of the IRFP150s
MOSFETs = MRF148
Supply = 34.00
Vbias = 2.57 volts
Q1 bias = 47.1 mV
Q2 bias = 50.7 mV
Load = 8.02 ohms
Frequency = 1.00 Khz
Watts AC-RMS DIST%
-----------------------------
15.1 11.00 1.246
12.6 10.04 0.982
10.2 9.05 0.657
--------------------------
8.02 8.02 0.321
6.18 7.04 0.357
4.49 6.00 0.355
3.19 5.06 0.343
2.04 4.05 0.307
1.17 3.07 0.251
0.78 2.50 0.203
0.50 2.00 0.168
0.38 1.75 0.163
0.28 1.50 0.200
0.19 1.25 0.240
0.12 1.00 0.288
0.10 0.90 0.290
0.080 0.80 0.279
0.061 0.70 0.275
0.045 0.60 0.234
0.031 0.50 0.205
0.020 0.40 0.140
0.011 0.30 0.130
0.008 0.25 0.160
0.005 0.20 0.110
0.003 0.15 0.110
0.001 0.10 0.150
A nice improvement.
The point of the exercise, to show that different mosfet types can have an effect, and that experimentation can produce worthwhile results!
Best wishes,
Susan.
Hi,
I have run a test using MRF148 mosfets (which are spec'ed for use up to 175 MHz) the results are below.
I stopped the measurements at 15 watts as the mosfets were becoming supply limited - however the power up to 8 watts looks promising as the band between 2 and 8 watts is half the distortion levels of the IRFP150s
MOSFETs = MRF148
Supply = 34.00
Vbias = 2.57 volts
Q1 bias = 47.1 mV
Q2 bias = 50.7 mV
Load = 8.02 ohms
Frequency = 1.00 Khz
Watts AC-RMS DIST%
-----------------------------
15.1 11.00 1.246
12.6 10.04 0.982
10.2 9.05 0.657
--------------------------
8.02 8.02 0.321
6.18 7.04 0.357
4.49 6.00 0.355
3.19 5.06 0.343
2.04 4.05 0.307
1.17 3.07 0.251
0.78 2.50 0.203
0.50 2.00 0.168
0.38 1.75 0.163
0.28 1.50 0.200
0.19 1.25 0.240
0.12 1.00 0.288
0.10 0.90 0.290
0.080 0.80 0.279
0.061 0.70 0.275
0.045 0.60 0.234
0.031 0.50 0.205
0.020 0.40 0.140
0.011 0.30 0.130
0.008 0.25 0.160
0.005 0.20 0.110
0.003 0.15 0.110
0.001 0.10 0.150
A nice improvement.
The point of the exercise, to show that different mosfet types can have an effect, and that experimentation can produce worthwhile results!
Best wishes,
Susan.
Well, doing this post is/was a royal PIA… editing in Word and cut and pasting parts,
one at a time… arrgh!
Imho transformers should be tested at real world power levels and with real world loads… 8 ohms is a nominal impedance that is standard. Iirc, there was some mention of using this amp with 0.5 ohm line sources?
All for testing at supersonic freqs, but gotta make sure the audible range is covered…
there’s quite a bit out there, mostly in the older literature… virtually every possible variation of output transformer has been tried at this point. It’s out there!
The question that I have concerns the power* required to drive the mosfet’s gates… I presume ur using the headphone jack of these units to drive the amp??
It is understood that ur distortion figures are to be compared to valve amps… the main thing isn’t the distortion levels so much as it what the relationships and relative levels are for which harmonics.
From this I take it you are biasing ur mosfets at a quiescent current of 225ma?? Current is the question here – if you’ve got 225mv somewhere, then we need to know what the current drawn is??
The actual bias voltage required is not an issue at all.
For class A operation, significant amounts of power will be dissipated by the mosfet. So, it would be useful to know where you’ve biased the mosfet in terms of current for a given rail voltage so that the class of operation is clearer?
As far as “Carnegie Hall” is concerned, my horns do 109dB/1w/1m (16 ohms), so the SPL listening level is relative to how you apply any amplifier. Most SE 300B and smaller tube amps are in the <20watt class anyhow.
This was the first part… let’s see how this posting works…
_-_-bear
one at a time… arrgh!
Imho transformers should be tested at real world power levels and with real world loads… 8 ohms is a nominal impedance that is standard. Iirc, there was some mention of using this amp with 0.5 ohm line sources?
All for testing at supersonic freqs, but gotta make sure the audible range is covered…
there’s quite a bit out there, mostly in the older literature… virtually every possible variation of output transformer has been tried at this point. It’s out there!
The question that I have concerns the power* required to drive the mosfet’s gates… I presume ur using the headphone jack of these units to drive the amp??
It is understood that ur distortion figures are to be compared to valve amps… the main thing isn’t the distortion levels so much as it what the relationships and relative levels are for which harmonics.
From this I take it you are biasing ur mosfets at a quiescent current of 225ma?? Current is the question here – if you’ve got 225mv somewhere, then we need to know what the current drawn is??
The actual bias voltage required is not an issue at all.
For class A operation, significant amounts of power will be dissipated by the mosfet. So, it would be useful to know where you’ve biased the mosfet in terms of current for a given rail voltage so that the class of operation is clearer?
As far as “Carnegie Hall” is concerned, my horns do 109dB/1w/1m (16 ohms), so the SPL listening level is relative to how you apply any amplifier. Most SE 300B and smaller tube amps are in the <20watt class anyhow.
This was the first part… let’s see how this posting works…
_-_-bear
Dear Bear,
I am sorry that this has been such a problem for you.
I bow to your superior Alpha Male position but would tentatively wish to query your statement in this matter.
Real world is 50 to 100 ohms at frequencies up to 2 GHz. Both for injected signals and for emissions. For inputs, power and outputs, at levels up to circa 50 volts peak to peak (carrier with 80% am modulation).
... plus all the insulation tests, ESD and pulsed stuff.
You obviously do not export your products to Europe otherwise you would have had the pleasure of CE compliance testing, or self certification.
Remember in Europe selling equipment that fails to meet the requirements (and that has been "falsely" marked with a CE logo) can result in a prison sentence and/or a large fine.
Please quote references:
I did this design work 8 to 10 years ago and Internet access was in it's infancy so much of the obscure literature which may now be "common knowledge" was not available unless you were "in the know".
I obtained all the reference material that I could.
None of this had any mention of multi-filar wound wide band audio output transformers.
So any references you may have would be greatly appreciated.
Yes, using the headphone drive is more than adequate to drive the amplifier for initial testing.
Understood, but I don't have the equipment to hand at the moment to make any further tests. I do have some PC software, but since a computer hard drive restore last summer I find that the security stuff won't allow me to run it anymore.
Again I am puzzled at this. The bias set point to the mosfet gate is surely something that is required.
The 225 mV is the voltage across the transformer primary winding from the mosfet source to ground.
FYI the quiescent current is under an amp.
bear said:
I am sorry that this has been such a problem for you.
I bow to your superior Alpha Male position but would tentatively wish to query your statement in this matter.
Real world is 50 to 100 ohms at frequencies up to 2 GHz. Both for injected signals and for emissions. For inputs, power and outputs, at levels up to circa 50 volts peak to peak (carrier with 80% am modulation).
... plus all the insulation tests, ESD and pulsed stuff.
You obviously do not export your products to Europe otherwise you would have had the pleasure of CE compliance testing, or self certification.
Remember in Europe selling equipment that fails to meet the requirements (and that has been "falsely" marked with a CE logo) can result in a prison sentence and/or a large fine.
there’s quite a bit out there, mostly in the older literature… virtually every possible variation of output transformer has been tried at this point. It’s out there!
Please quote references:
I did this design work 8 to 10 years ago and Internet access was in it's infancy so much of the obscure literature which may now be "common knowledge" was not available unless you were "in the know".
I obtained all the reference material that I could.
None of this had any mention of multi-filar wound wide band audio output transformers.
So any references you may have would be greatly appreciated.
Yes, using the headphone drive is more than adequate to drive the amplifier for initial testing.
Understood, but I don't have the equipment to hand at the moment to make any further tests. I do have some PC software, but since a computer hard drive restore last summer I find that the security stuff won't allow me to run it anymore.
Again I am puzzled at this. The bias set point to the mosfet gate is surely something that is required.
The 225 mV is the voltage across the transformer primary winding from the mosfet source to ground.
FYI the quiescent current is under an amp.
As far as “Carnegie Hall” is concerned, my horns do 109dB/1w/1m (16 ohms), so the SPL listening level is relative to how you apply any amplifier. Most SE 300B and smaller tube amps are in the <20watt class anyhow.Excellent, then the 8 watt version using the MRF148s will work very nicely for you
However I am impoverished as I have a very small living room of only 16 by 14 feet (which is not unusual here in the UK, of course in the US this would be a closet) so a nice pair of horn speakers are not possible. I can't even have my beloved Quad electrostatics
Horns are of course the best form of speakers.
Susan-Parker said:I agree, I would love to use Macs, but the electronics design software that I use (Mentor DxDesigner and PowerPCB) don't give me the choice
In a case like that, i'd just have 2 puters... and the PC not connected to the internet for its own good.
For the few PC programs i use i get away with VirtualPC -- and i've got a PC somewhere too.
dave
quote from some website:
The "Alpha" male has evolved for millions of generations and the genetic adaptations are quite profound. The Human Alpha Male evolved from these early animal and "Hominid" ancesters. He is gifted with many adaptations that predispose Him to leaderhip. He is usually, large, strong, intelligent, attractive, and possesses a charismatic ability to generate trust, foster calm, and promote cooperation within His group. Quite often He has a similar but less profound effect on others outside His immediate sphere of influence.
Doesn't sound so bad.
I reckon I'm a delta-male.
The "Alpha" male has evolved for millions of generations and the genetic adaptations are quite profound. The Human Alpha Male evolved from these early animal and "Hominid" ancesters. He is gifted with many adaptations that predispose Him to leaderhip. He is usually, large, strong, intelligent, attractive, and possesses a charismatic ability to generate trust, foster calm, and promote cooperation within His group. Quite often He has a similar but less profound effect on others outside His immediate sphere of influence.
Doesn't sound so bad.
I reckon I'm a delta-male.
Ok,
From memory...
The quiescent current through the mosfets vs voltage determines the operation point. If you look at the characteristic curves (available online) you'll see the point.
It's how much *power* the device is sitting at with no signal that determines the linearity and the class of operation.
If it is "under an amp" with a 35 v rail, this is a class AB operating point. How much under determines how much AB it is.
Measure the current, determine the operating point, tell us the class of operation...
The voltage required to produce said current flow is incidental to this part of the discussion
Ok, as far as output transformers start with your library and back issues of Wireless World. That should be easy enough.
Then the venerable Radiotron Designer's Handbook covers a number of them with citations to the original source.
--> The next thing I'd like to see is a power vs. load impedance chart for fixed input signal... that would tell us more about how this amplifier is actually operating. <--
Didn't you say something about using it for running low Z loads, like 0.5 ohms??
My other thought is that with a current amp, like a "current opamp" the voltage produced at the output for a given input signal level is proportional to the value of load impedance. Whereas with a standard "voltage amplifier" (the variety we usually use in audio) the voltage tracks the input signal and the current varies with the load, increasing current & power with decreasing load. The amplifier tries to keep the voltage constant.
Toobe amps produce maximum power and current at one single optimal impedance, at all other impedances the power is *less*.
So the power vs. load chart will tell us how this amp is actually working... to measure: input signal, load resistors, scope (DVM worst case), keep the secondary taps the same as you vary only
the load, chart the power out.
Also, the testing at 50 ohms is for RF, not audio. This is audio, test the transformers with a real world load and power level.
A certain "well known" toroidal output transformer company has apparently great specs, but the fine print shows that they are testing the tranny at milliwatt levels...
As far as Euro requirements... they apply only if you are building a commercially distributed product... DIYers not, afaik. So, that's a moot point as far as the "meat" of the design... test audio output transformers with real world audio loads and power levels.
Anyhow, rooms are larger in the US, but you could probably fit horns... surely the little tiny Quad 63s will fit?? Heck, hang 'em from the ceiling!!
Oh, as far as a "kit" - I might be willing to try to do quadfilar windings if enough people wanted that... it's tough to do bifilar.
A full kit would likely cost more than most DIYers are willing to fork over... dunno.
Eitherway, to make it practical at all there needs to be considerable interest... and then mostly if not all needs to be in the US... at a certain point it pays to just order what you want from a place like Sowter, Luhndahl etc...
_-_-bear
From memory...
The quiescent current through the mosfets vs voltage determines the operation point. If you look at the characteristic curves (available online) you'll see the point.
It's how much *power* the device is sitting at with no signal that determines the linearity and the class of operation.
If it is "under an amp" with a 35 v rail, this is a class AB operating point. How much under determines how much AB it is.
Measure the current, determine the operating point, tell us the class of operation...
The voltage required to produce said current flow is incidental to this part of the discussion
Ok, as far as output transformers start with your library and back issues of Wireless World. That should be easy enough.
Then the venerable Radiotron Designer's Handbook covers a number of them with citations to the original source.
--> The next thing I'd like to see is a power vs. load impedance chart for fixed input signal... that would tell us more about how this amplifier is actually operating. <--
Didn't you say something about using it for running low Z loads, like 0.5 ohms??
My other thought is that with a current amp, like a "current opamp" the voltage produced at the output for a given input signal level is proportional to the value of load impedance. Whereas with a standard "voltage amplifier" (the variety we usually use in audio) the voltage tracks the input signal and the current varies with the load, increasing current & power with decreasing load. The amplifier tries to keep the voltage constant.
Toobe amps produce maximum power and current at one single optimal impedance, at all other impedances the power is *less*.
So the power vs. load chart will tell us how this amp is actually working... to measure: input signal, load resistors, scope (DVM worst case), keep the secondary taps the same as you vary only
the load, chart the power out.
Also, the testing at 50 ohms is for RF, not audio. This is audio, test the transformers with a real world load and power level.
A certain "well known" toroidal output transformer company has apparently great specs, but the fine print shows that they are testing the tranny at milliwatt levels...
As far as Euro requirements... they apply only if you are building a commercially distributed product... DIYers not, afaik. So, that's a moot point as far as the "meat" of the design... test audio output transformers with real world audio loads and power levels.
Anyhow, rooms are larger in the US, but you could probably fit horns... surely the little tiny Quad 63s will fit?? Heck, hang 'em from the ceiling!!
Oh, as far as a "kit" - I might be willing to try to do quadfilar windings if enough people wanted that... it's tough to do bifilar.
A full kit would likely cost more than most DIYers are willing to fork over... dunno.
Eitherway, to make it practical at all there needs to be considerable interest... and then mostly if not all needs to be in the US... at a certain point it pays to just order what you want from a place like Sowter, Luhndahl etc...
_-_-bear