I found some nice transformer tests and i was wandering what my own transformer would do in a similar test.
First the site where you can read some tests:
SAC Thailand
http://diyhifisupply.com/files/silks325.pdf
I did my test with a real tube, EL34 in triode mode 80mA. (sorry the real 300B was not available and for this test there will be minor differences)
The transformer is a single ended double HiB c-core 3500 Ohm / 8 Ohm 60mA-120mA 30W at 18Hz. Copperloss 0,14dB.
I noticed that the best SE transformer have the most problems at low frequencies (core saturation or to low inductance)
Did anybody do similar tests?
frequency response
squarewaves
1kHz
10kHz
20kHz
100Hz
40Hz
First the site where you can read some tests:
SAC Thailand
http://diyhifisupply.com/files/silks325.pdf
I did my test with a real tube, EL34 in triode mode 80mA. (sorry the real 300B was not available and for this test there will be minor differences)
The transformer is a single ended double HiB c-core 3500 Ohm / 8 Ohm 60mA-120mA 30W at 18Hz. Copperloss 0,14dB.
I noticed that the best SE transformer have the most problems at low frequencies (core saturation or to low inductance)
Did anybody do similar tests?
frequency response
An externally hosted image should be here but it was not working when we last tested it.
squarewaves
1kHz
An externally hosted image should be here but it was not working when we last tested it.
10kHz
An externally hosted image should be here but it was not working when we last tested it.
20kHz
An externally hosted image should be here but it was not working when we last tested it.
100Hz
An externally hosted image should be here but it was not working when we last tested it.
40Hz
An externally hosted image should be here but it was not working when we last tested it.
Last edited:
Can you list your test equipment and testing procedure? I'd like to test a few transformers, but don't know where to start. Thanks.
I do.
I am not sure about your numbers. Even without considering that pretty small loss, what is the Bmax (AC + DC) you get for 30W at 18Hz with 120 mA DC current and 30H minimum (i.e. with 10 Gauss AC)? Although the C core has an advantage respect to E+I in terms of size for the same specs the difference is not like between night and day.
The biggest core I consider acceptable is the EI 150/70 (i.e. 50x70 core size) and this would not be enough! 50x75 would be the minimum to achieve 30W at 18Hz with 120 mA DC current at my usual Bmax = 7500 G. So I would need to accept higher B at that frequency for 30W (and thus more distortion because in less linear area). A 50x70 core alone weights about 8.5Kg!!! For a reasonably sized transformer those numbers are impossible. Specifying max power at 30Hz is more than enough for SE OT, provided that will work not so close to saturation (7500 Gauss total induction limit for E+I and a bit higher for C cores). Together with an inductance that gives a ratio between reactance at 30Hz (i.e. 2*pi*f*L) and equivalent resistance (i.e. the plate resistance in parallel to the nominal primary load) equal to 8 it will already guarantee low distortion at least down to 30Hz. Of course the higher the better but practicality cannot be ignored at some point..... what's the point of having a huge transformer to get those numbers down to 20Hz rather than 30?
I am not sure about your numbers. Even without considering that pretty small loss, what is the Bmax (AC + DC) you get for 30W at 18Hz with 120 mA DC current and 30H minimum (i.e. with 10 Gauss AC)? Although the C core has an advantage respect to E+I in terms of size for the same specs the difference is not like between night and day.
The biggest core I consider acceptable is the EI 150/70 (i.e. 50x70 core size) and this would not be enough! 50x75 would be the minimum to achieve 30W at 18Hz with 120 mA DC current at my usual Bmax = 7500 G. So I would need to accept higher B at that frequency for 30W (and thus more distortion because in less linear area). A 50x70 core alone weights about 8.5Kg!!! For a reasonably sized transformer those numbers are impossible. Specifying max power at 30Hz is more than enough for SE OT, provided that will work not so close to saturation (7500 Gauss total induction limit for E+I and a bit higher for C cores). Together with an inductance that gives a ratio between reactance at 30Hz (i.e. 2*pi*f*L) and equivalent resistance (i.e. the plate resistance in parallel to the nominal primary load) equal to 8 it will already guarantee low distortion at least down to 30Hz. Of course the higher the better but practicality cannot be ignored at some point..... what's the point of having a huge transformer to get those numbers down to 20Hz rather than 30?
Maybe i did better write at 120mA 18Hz 30W the transformer will just saturated (2,01T (ac + dc))
It was not specially made to "handle 30W", just for 300B and her sisters (so more up to 20W )
EI is far more less linear and can handle less power.
I did not wanted the standard 300B transformer what have saturation at 10W-13W 15-20Hz.
It was not specially made to "handle 30W", just for 300B and her sisters (so more up to 20W )
EI is far more less linear and can handle less power.
I did not wanted the standard 300B transformer what have saturation at 10W-13W 15-20Hz.
You can look at the link i already gave. This test set-up can be used, brand of test equipment is less important.
Here some datasheet from one of the best transformers i could find:
Tango FC-30-3.5S, this is the bigger brother of the Tango XE 20S
I don't know exactly what Tango mean by 30W (40Hz) is this core saturation? My guess is yes. So still a bit weak in the low frequency range.
Tango FC-30-3.5S, this is the bigger brother of the Tango XE 20S
I don't know exactly what Tango mean by 30W (40Hz) is this core saturation? My guess is yes. So still a bit weak in the low frequency range.
An externally hosted image should be here but it was not working when we last tested it.
Not so much, it is good in most cases. It means just below saturation. If you back it a bit it is still very good down to 30Hz for most 300B amps that don't do more than 10W. Often they only manage 8W.
esltransformer there is nothing you can teach Japanese about audio transformers....
Japanese brands usually do it the right way (i.e. 4-5V signal applied to the primary for inductance, for example) at 50Hz.
Of course not, but they have weaker bass, higher loss and very high prices. (but very nice finish) All thinks i not like so much.
I think they are able to make "a better" transformer if they wanted to but they do not.....
0.20-0.25 dB power loss is not high at all. It is low enough to be considered "transparent". Their big transformers can have 0.15 dB. As I said, at some point any little improvment will make things not practical. What is the point of making a 10W amplifier that weights 50Kg? Transformer design has to take into account also this. It's not just bench performance of the transformer alone.
I am not sure that distortion measurement is really representative of transformer performance. That amp really looks poor independently of the transformer they use!
If you look at distortion levels at 1KHz they are already high, about 4% at less than 6.5W output, and so their amp has already started clipping. At low frequency can only get a lot worse. Add that the 300B has a plate dissipation of 27.3W and it is also poor effeciency wise.....
If they had a proper 300B that makes 6.5W at less 1% at 1KHz the result could be better at least for some of those transformers.
But "their" (if you mean Tango) big transformers don't have 0,15dB.....0,2dB they have (or worse)
And why would it be 50 kg? A Fc-30-3.5S weight 4Kg and mine maybe 6 or 7 kg. It's just a little bit more weight for better low end. All(many) PP have better bass then SE. It is a weak point from SE .
Last edited:
I really don't think so. Their transformer can likely have a little different gap/turns/core combination and so they could play tricks to make it look better. That test amp is using the 300B at 350V/78 mA. Not to mention a 6V6 RC coupled to the 300B...
....The XE20 is recommended for 60 mA. If you run it at 78 mA you are only going to waste headroom at low frequency. At least one should get a better result above 50-60Hz and that is not really the case. With 350V/60 mA DC current you can still get about 6.5W (power loss already included) with half of their distortion down to 20Hz from a 300B. Less distortion and more efficiency!
I meant Japanese OT's in general. There are some models. Anyway, do you really think that 0.15 dB will make a difference in comparison to 0.20 by default? There are many other things to address before you can hope to hear a difference because of that and that's not even sure.
7 Kg per transformer makes 14 Kg for two of the stereo amp. Then add power supply transformer(s), chokes, chassis, all the other components and possibly interstage and signal transformers and see how much you get. If you want to keep the weight low you already have restrictions or you have to go for a mono block or separate supply. It just makes life more complicated not necessarily better.
No doubt about this but it doesn't mean that that test amp has benchmark performance....
Tango datasheets give for both transformers 80mA.
You can not say that from 60 to 80mA is a waste of headroom without knowing what the design criteria are. Al depends on how much premagnetization was used (optimum is 0.5 X maximum induction)
In general good SE transformers have 0,25dB-0,30dB copper loss. Some specials (Amplimo VDV3035SE for instance have better) but they are rare.
Lower is better.
I agree that a better distortion test is possible and maybe is more elegant.
For me, and maybe for others to, weight and size is less important. Important is sound and that is what good transformers can do better.
You can not say that from 60 to 80mA is a waste of headroom without knowing what the design criteria are. Al depends on how much premagnetization was used (optimum is 0.5 X maximum induction)
In general good SE transformers have 0,25dB-0,30dB copper loss. Some specials (Amplimo VDV3035SE for instance have better) but they are rare.
Lower is better.
I agree that a better distortion test is possible and maybe is more elegant.
For me, and maybe for others to, weight and size is less important. Important is sound and that is what good transformers can do better.
I really don't think so. Their transformer can likely have a little different gap/turns/core combination and so they could play tricks to make it look better. That test amp is using the 300B at 350V/78 mA. Not to mention a 6V6 RC coupled to the 300B...
The XE20 is recommended for 60 mA. If you run it at 78 mA you are only going to waste headroom at low frequency. At least one should get a better result above 50-60Hz and that is not really the case. With 350V/60 mA DC current you can still get about 6.5W (power loss already included) with half of their distortion down to 20Hz from a 300B. Less distortion and more efficiency!
I meant Japanese OT's in general. There are some models. Anyway, do you really think that 0.15 dB will make a difference in comparison to 0.20 by default? There are many other things to address before you can hope to hear a difference because of that and that's not even sure.
7 Kg per transformer makes 14 Kg for two of the stereo amp. Then add power supply transformer(s), chokes, chassis, all the other components and possibly interstage and signal transformers and see how much you get. If you want to keep the weight low you already have restrictions or you have to go for a mono block or separate supply. It just makes life more complicated not necessarily better.
No doubt about this but it doesn't mean that that test amp has benchmark performance....
I know the XE20.
80 mA is the max. usable, 60 mA is recommended. The XE20 is still a relatively small transformer. Going from 60 mA to 80 mA you will have 33% more DC induction and will have less for the signal. If the 300B amplifier has to have 7W nominal output then 80 mA DC at 27-28W dissipation with such high distortion levels is a waste from any point of view. Probably the actual 300B they used was really of poor quality.....
Well, from the point of view of a (good and smart) manufacturer the question is how many people would build a reasonably sized amplifier and how many a heavy weight amplifier.
If the amplifier does 7W instead of 10W it doesn't mean it will sound worse. It is not a relevant difference in real life in most cases. Actually if one goes for the 7W the rest of the amplifier will be easier and cheaper to make and possibly with better performance at the same time!
I could understand if you were comparing a 2W amp to a 10W amp.
I just tell you what is on the datasheet.....
Probably you are right but i don't know how many turns they used and not how big the gap is. Those 30% is a lot.
There are 300B on steroids (emmisionlabs 300b-xls ) and for those tubes these small transformers don't perform good enough and for people who like good bass also not good enough.
I am not going for quantity but quality so i really don't care if people buy such transformer as i have made. I am interested in transformer design and I like good performance.
So if people have nice measurements they are welcome
Probably you are right but i don't know how many turns they used and not how big the gap is. Those 30% is a lot.
There are 300B on steroids (emmisionlabs 300b-xls ) and for those tubes these small transformers don't perform good enough and for people who like good bass also not good enough.
I am not going for quantity but quality so i really don't care if people buy such transformer as i have made. I am interested in transformer design and I like good performance.
So if people have nice measurements they are welcome
33% is a relative increase going from 60 to 80 mA. The DC induction is proportional to the DC current regardless of the gap.
Yes but how many people buy the xls in comparison to normal 300B's? I have never seen a 300B XLS for real while I have had, used and seen countless normal 300B's.
I am not going for quantity but quality so i really don't care if people buy such transformer as i have made. I am interested in transformer design and I like good performance.
So if people have nice measurements they are welcome
It is only about using things properly! Your conclusion about the quality of Tango's is arbitrary and has no foundations. Sorry but that is.
Actually the more power you want the more you have to make compromises for the amplifier in general. Try to get 200-220V pp for driving a 300B-XLS at full power and see if this is easy as getting 140V for a 7-8W amp. Nothing comes for free.
I really wouldn't go for the xls if I wanted 20W or more....just my opinion though.
- Status
- Not open for further replies.