So that's quite different amount from you tought. In practice the advatange of C core will be as I said before. One can get high performance from M6 as well. The price to pay for best performance is just size in the end and something in the region above 50KHz! Nothing which I would lose sleep over.....
The main test for output transformer is not only frequency answer or square but the thd versus frequency at different output power. range from 10Hz to 30 kHz;
The test set must be of a high level stuff as Audio Precision One or Two.
Only with this test we can see the problem at low frequency ( low autoindictance, p.e.) and high frequency (parasitic).
After lot of test with different type of iron and coils, I found a C core with 0,1 mm lamination and now some good resuslts are coming
Walter
The test set must be of a high level stuff as Audio Precision One or Two.
Only with this test we can see the problem at low frequency ( low autoindictance, p.e.) and high frequency (parasitic).
After lot of test with different type of iron and coils, I found a C core with 0,1 mm lamination and now some good resuslts are coming
Walter
Actually i am a bit confused. I found out that they use a different testing methode.
If i compare toroid core with M6 vs 23zh085 materials then the differance between them is 60%.
So how can an EI have the saw values as toroidals?
If i compare toroid core with M6 vs 23zh085 materials then the differance between them is 60%.
So how can an EI have the saw values as toroidals?
So that's quite different amount from you tought. In practice the advatange of C core will be as I said before. One can get high performance from M6 as well. The price to pay for best performance is just size in the end and something in the region above 50KHz! Nothing which I would lose sleep over.....
Can this Audio Precision deliver 80- 100mA dc + 350Vrms ?
The main test for output transformer is not only frequency answer or square but the thd versus frequency at different output power. range from 10Hz to 30 kHz;
The test set must be of a high level stuff as Audio Precision One or Two.
Only with this test we can see the problem at low frequency ( low autoindictance, p.e.) and high frequency (parasitic).
After lot of test with different type of iron and coils, I found a C core with 0,1 mm lamination and now some good resuslts are coming
Walter
When I test the trafo I will test the output stage tubes included.
I can delivery the Vpp to drive the ouput trafo. For p-p and single end.
The AP one is the signal generator and the analyzer of the output signal on the load that can be resistive or complex (home made)
I think this test is the only way to understand the job of an output trafo.
This is a test fro thd vs freq of an Hammond p-p without feedback at 2 watts / 8 ohm out
http://www.multitask.it/thd vs freq/Hamm-4vout-noFB.jpg
Bye
Walter
I can delivery the Vpp to drive the ouput trafo. For p-p and single end.
The AP one is the signal generator and the analyzer of the output signal on the load that can be resistive or complex (home made)
I think this test is the only way to understand the job of an output trafo.
This is a test fro thd vs freq of an Hammond p-p without feedback at 2 watts / 8 ohm out
http://www.multitask.it/thd vs freq/Hamm-4vout-noFB.jpg
Bye
Walter
I don't know toroids and are not really interested in them. Check the frequency, the induction and all other conditions are the same and you cannot go wrong.
I know that measurements for EI are those and are standard procedure since a long time and they work. Thomas and Skinner are not novice for sure and they serve the army as well.
A PP amp with that distortion at 2W makes me think that the transformer cannot handle too much unbalance (typical of economy transformers) and the amp is badly made and DC unbalance saturates the core.
What is the point of achieving full or high output power at 10Hz? Especially for SE amplifier it is just a waste of resources. There is no music there. Below 30Hz there is barely something. Then add that most speakers cannot go so low and you get nothing.
Maybe you don't know how they test transformer materials?
Mostly they do on toroid cores
I not care if T&S deliver at army or not, it doesn't say anything.
I do know that all the top transformers use c-core, not EI and there is a reason for. You should change (in some case it is possible, EI for SG-range c-core) an EI for a c-core and you will see for your self that the performance will be better and the sound improves. It's just physics....
Mostly they do on toroid cores
I not care if T&S deliver at army or not, it doesn't say anything.
I do know that all the top transformers use c-core, not EI and there is a reason for. You should change (in some case it is possible, EI for SG-range c-core) an EI for a c-core and you will see for your self that the performance will be better and the sound improves. It's just physics....
If you test output transformer this way then you get mostly distortions produced by the output stage. Even if you connect spectrum analyzer straight to the primary (via voltage divider) and to secondary (to resistive load), transformer will be feed with distorted signal from the output stage. In other words, you must have very clean source (connected to primary) to properly measure THD level of the transformer, otherwise this method is totally flawed. Spectrum analyzer can't "clean" signal taken from primary which is enriched with high level harmonic / intermodulation distortions and which you try to use as reference.
If you are keen to test output transformer at high power level you have to build ultra-low distortion solid-state amplifier with high-voltage MOSFETs, capable of ~500V RMS on inductive load. Technically possible but very challenging.
BTW, THD numbers you posted are extremely high. I've got much less at power close to 30 - 40W with GNFB disconnected.
I am just working on an amp so.......
Actual numbers on a Hammond 1650N (60 watt 4300 ohm push pull EI core) driven by 2 x KT120 triode connected with no global feedback.
@ 5 watts output 4 ohm tap connected to 6.8 ohm resistor
1000Hz 0.54% THD
100Hz 0.72% THD
20Hz 2.9% THD
I don't know if the increasing distortion is my amplifier circuit or the output transformer really.
Actual numbers on a Hammond 1650N (60 watt 4300 ohm push pull EI core) driven by 2 x KT120 triode connected with no global feedback.
@ 5 watts output 4 ohm tap connected to 6.8 ohm resistor
1000Hz 0.54% THD
100Hz 0.72% THD
20Hz 2.9% THD
I don't know if the increasing distortion is my amplifier circuit or the output transformer really.
Did you checked the bias of each tube? You must have a good balance.
3% is high.
Maybe you can give a schematic too (there could be some weak points ther too)
3% is high.
Maybe you can give a schematic too (there could be some weak points ther too)
Did some measurements at an old Audionote transformer
It is a smaller transformer then my own, also lower Ra (2500 Ohm)
I could not find much details about this transformer, just 25W max 90mA.
It's a nice transformer with good reputation and good measurements.
Copper loss is a bit high 0,43dB, total weight 3,6kg
Oh, i forget the most important, It has an EI core ( i probably make friends now....)
Frequency response
Squarewave 1kHz
Squarewave 100Hz
Squarewave 10kHz
It is a smaller transformer then my own, also lower Ra (2500 Ohm)
I could not find much details about this transformer, just 25W max 90mA.
It's a nice transformer with good reputation and good measurements.
Copper loss is a bit high 0,43dB, total weight 3,6kg
Oh, i forget the most important, It has an EI core ( i probably make friends now....)
Frequency response
An externally hosted image should be here but it was not working when we last tested it.
Squarewave 1kHz
An externally hosted image should be here but it was not working when we last tested it.
Squarewave 100Hz
An externally hosted image should be here but it was not working when we last tested it.
Squarewave 10kHz
An externally hosted image should be here but it was not working when we last tested it.
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If you look on the diagram I sent you can see a low distortion at mid frequency, where we can consider the trafo as ideal ( is not correct but just to discuss), and the thd is reasonable. No FB is included (local or global)
Of course the tube ouput stage was checked and the distortion was reasonable, in this case I met 2% at the max Vout for this project of p-p 60 w on 8 ohm with KT120 this means that with a trafo of 1:27 ratio means 590 Vrms between the ends of the the primary. Pentode connection ( and I will use only this configuration for p-p trafo).
At low frequency, where we will meet, normaly, problems with autoinductance that in most cases is too low to have a reasonable reactance. In this case most of the problems came from a low quality iron then a not perfect windings.
It is an error if we haven't to consider the results at 20 Hz if we will get the best results; in the diagram you can see that the thd is increasing from 100 Hz.
Regarding the High frequency of course the problems came, normally, from parasitic (low quality windings) and we can see an increment from 20kHz that is not too bad.
I have check lot of prototype made with a little firm in Roma; we have test also some commercial trafo of different brand until the lasts with C core 0,1 mm and with a simple architecture I reach some good results.
We have done also a big job with Ciuffoli for his GM70 project where we test a Tango trafo and they made some proto until a good results was found. It was a C core, 0,3 mm but with a weight more than 6 kg.
for MelB
The diagram I sent came from Hammond 1650N; the thd you wrote confirm what I sent but if you use the UL tap you have a feddback only related to output stage that lower the thd.
More graph will come
Bye
Walter
Of course the tube ouput stage was checked and the distortion was reasonable, in this case I met 2% at the max Vout for this project of p-p 60 w on 8 ohm with KT120 this means that with a trafo of 1:27 ratio means 590 Vrms between the ends of the the primary. Pentode connection ( and I will use only this configuration for p-p trafo).
At low frequency, where we will meet, normaly, problems with autoinductance that in most cases is too low to have a reasonable reactance. In this case most of the problems came from a low quality iron then a not perfect windings.
It is an error if we haven't to consider the results at 20 Hz if we will get the best results; in the diagram you can see that the thd is increasing from 100 Hz.
Regarding the High frequency of course the problems came, normally, from parasitic (low quality windings) and we can see an increment from 20kHz that is not too bad.
I have check lot of prototype made with a little firm in Roma; we have test also some commercial trafo of different brand until the lasts with C core 0,1 mm and with a simple architecture I reach some good results.
We have done also a big job with Ciuffoli for his GM70 project where we test a Tango trafo and they made some proto until a good results was found. It was a C core, 0,3 mm but with a weight more than 6 kg.
for MelB
The diagram I sent came from Hammond 1650N; the thd you wrote confirm what I sent but if you use the UL tap you have a feddback only related to output stage that lower the thd.
More graph will come
Bye
Walter
It is not necessary to test at high power. You can do it properly for lower power amps with their properly sized transformer and then you can scale up for bigger amps. The design criteria don't change once you find them.
I guess that most of the distortion at 20Hz comes from the transformer. See below....
It is not an error to look at the results at 20Hz. I was referring to 10Hz before.
If the THD is already very high at 100Hz it is not a great amp design or the valves are too poor. At lower frequency it is a bit different...
When you look at the distortion at low frequency down to 20Hz you have to consider the different regime of a typical PP transformer in comparison to a SE transformer. They do not behave in the same way. As I have mentioned many times, having a huge inductance with minimum possible gap (the natural one) is NOT so good as it looks.
The "right" amount of gap will limit inductance but will also have a kind of linearizing effect. In a PP OT that only uses the natural gap the inductance is high only in ideal condition. Inductance variation is high both as function of signal and effective operative and dynamic conditions. Most of times this results in higher distortion at low frequency than a comparable SE OT!!!
It could well be that at 20Hz a PP amplifier with its OT has the same distortion of a SE amplifier with its OT, both a their max power for the same THD at 1KHz. For the PP most of the distortion will come from the transformer, for the SE most of the distortion will come from the valve.
Having the right gap for a PP amp as well will just make it better but it is a bit more complicated because the control of gap thickness becomes more difficult being rather small, typically. Another consequence of having a proper small gap rather than the natural one only is that the difference in size between a SE OT and a PP OT specified for the same power and total induction at the same low frequency is not so big as most people think.......
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The problems are quite the same for s.e. or pp trafos.
In every case the inductance and parasitic are always involved in both configurations.
I never seen trafos with a good value of inductance a low frequency that have a poor performance; some difference we found, as thd, are acceptable.
The commercial stuff have to reach a good performance/price ratio and we can get some reasonable results but if we look at some exception we can see a totally different construction as size and windings.
Regarding the gap we consider that pp doesn't have it; the best manifacturer also give the maximum unbalance current that can flow in a row because this is one of the problem we can get from this configuration and also in this case the size is very important. So we have to check carefully this aspect .
The distortion that we have comes also from tubes because the non perfect split of the phase at the primary means a poor thd at the output.
For s.e. the gap is very important mainly if we are using a trafo where the size is just enough for the job; in this case a little difference on gap means big trouble at low frequency. Every time I tested a big iron in s.e. with a acceptable winding the results told us that the differences was acceptable.
For a 300B the size I tested is exactly three times bigger than a commercial one and I use the same iron for a 60 w in p-p.
(note: For this use one of the best trafo was an Audio Note for Kit one; very good.)
In this case we can say that the thd comes mainly from the tube and it is 2nd harmonics.
for 45: are you a fan of MOSS?
Bye
Walter
In every case the inductance and parasitic are always involved in both configurations.
I never seen trafos with a good value of inductance a low frequency that have a poor performance; some difference we found, as thd, are acceptable.
The commercial stuff have to reach a good performance/price ratio and we can get some reasonable results but if we look at some exception we can see a totally different construction as size and windings.
Regarding the gap we consider that pp doesn't have it; the best manifacturer also give the maximum unbalance current that can flow in a row because this is one of the problem we can get from this configuration and also in this case the size is very important. So we have to check carefully this aspect .
The distortion that we have comes also from tubes because the non perfect split of the phase at the primary means a poor thd at the output.
For s.e. the gap is very important mainly if we are using a trafo where the size is just enough for the job; in this case a little difference on gap means big trouble at low frequency. Every time I tested a big iron in s.e. with a acceptable winding the results told us that the differences was acceptable.
For a 300B the size I tested is exactly three times bigger than a commercial one and I use the same iron for a 60 w in p-p.
(note: For this use one of the best trafo was an Audio Note for Kit one; very good.)
In this case we can say that the thd comes mainly from the tube and it is 2nd harmonics.
for 45: are you a fan of MOSS?
Bye
Walter
Not exactly Walter. If you consider the PP OT having a gap to cope with non idealities then I could agree and the rules are the same. It's just the ratio of the Bac and Bdc that changes for obvious reasons.....
There is very good commercial stuff. One just needs to pick the right one for his purposes.
There always is a natural gap, very small but there is. The only cores that don't have a gap are those that are one piece. The max DC unbalance specified by most manufactures doesn't mean that the transformer will still perform at its best. In fact for those that are a bit more transparent (mostly Japanese) you will find that the inductance value will drop quite a lot with the allowed unbalance. Power handling will be quite lower as well for the same total induction or you have to accept more distortion because closer, if not already at, saturation....for this reason often PP OT's add more distortion below 50Hz than properly sized SE's.
That's common thinking. It's a bit superficial. The right gap is important also for PP for best performance below 50 Hz. If you are "lucky" enough the natural gap for the PP could be enough but it's not a rule.
I would say so! That high amount of distortion at 100Hz with just 2W could not be otherwise. However the load is still provided by the OT and it gets worse and worse at lower frequency if doesn't work in best condition. As LinuksGuru told, with the kind of measurement you did, you are not in the condition to attribute the amounts to this and that.....
Not just a fan. We are friends.
Bye
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