Hi,
I'm thinking about having a 2A3 amplifier built and I have to choose from several output transformers. I was wondering if the biggest frequency response the better or does it come with downsides?
The transformers would be one of those (Lundahl is listed only for comparison):
Also read this interesting article which says that the range of human perception would be 20Hz to 20kHz.
And I also checked my speaker specs and they go from 30Hz to 30kHz.
Thanks for your help!
I'm thinking about having a 2A3 amplifier built and I have to choose from several output transformers. I was wondering if the biggest frequency response the better or does it come with downsides?
The transformers would be one of those (Lundahl is listed only for comparison):
Also read this interesting article which says that the range of human perception would be 20Hz to 20kHz.
And I also checked my speaker specs and they go from 30Hz to 30kHz.
Thanks for your help!
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There are quite a few other parameters I would use before looking at frequency response.
Your hearing is a theoretical 20kHz max. If you’re over 30, or if you’ve spent any amount of time with headphones and high volumes, it’s probably much lower. The easiest way to find out your limit is to get one of those “dog whistle” apps and set the frequency until you don’t hear it anymore.
For lower frequencies, I would concentrate on the power supply and the amplifier’s ability to swing large amounts of voltage to high energy transients (aka bass notes) keeping in mind that there are limits to the amount of capacitance you can reasonable add to a PS for a tube amp.
Manufacturers always over- promise on frequency response. What they don’t generally tell you is at what level the equipment can produce that sound. An 8” speaker can theoretically produce a 30hz sound that can be detected by a close mic but can it physically move enough air for you to get a satisfactory bass response sitting 4-5 metres away? Probably not. If you can get ahold of the frequency response charts for your speakers that would tell you a bit more.
The OTs can definitely affect the sound, but you’ll have a hard time picking “the best” just by looking at a spec sheet.
If I had to choose one of those at a moments notice with no other input, I would probably go with the ISO because it had a higher rated power handling, which means it might be slightly more capable of higher power loads. But then you should check the current of the circuit they’re tied to.
Your hearing is a theoretical 20kHz max. If you’re over 30, or if you’ve spent any amount of time with headphones and high volumes, it’s probably much lower. The easiest way to find out your limit is to get one of those “dog whistle” apps and set the frequency until you don’t hear it anymore.
For lower frequencies, I would concentrate on the power supply and the amplifier’s ability to swing large amounts of voltage to high energy transients (aka bass notes) keeping in mind that there are limits to the amount of capacitance you can reasonable add to a PS for a tube amp.
Manufacturers always over- promise on frequency response. What they don’t generally tell you is at what level the equipment can produce that sound. An 8” speaker can theoretically produce a 30hz sound that can be detected by a close mic but can it physically move enough air for you to get a satisfactory bass response sitting 4-5 metres away? Probably not. If you can get ahold of the frequency response charts for your speakers that would tell you a bit more.
The OTs can definitely affect the sound, but you’ll have a hard time picking “the best” just by looking at a spec sheet.
If I had to choose one of those at a moments notice with no other input, I would probably go with the ISO because it had a higher rated power handling, which means it might be slightly more capable of higher power loads. But then you should check the current of the circuit they’re tied to.
As mentioned above, there are a number of factors to consider when choosing an output transformer, but for a low-powered single-ended amplifier, it largely comes down to the quality of the build, because beauty of tone is going to be everything in this instance. Bear these factors in mind:
1) Bigger isn't always better. The larger a single-ended transformer is, the more more winding capacitance comes into play, and this can affect high frequency response. This applies to current-handling properties as well. More current capacity doesn't mean it's better.
2) On the other hand, too small a transformer will have inadequate primary inductance, leading to poor low frequency response.
3) Since you won't be employing large amounts of negative feedback, if any, the "naked" frequency response of the OPT will be all-important.
Generally speaking, for a single-ended amp you want a transformer that's "just right"--sized for the job but not compromised by attempts to be all things for all tubes. The frequency responce of a no-feedback single-ended amplifier is going to be somewhat limited for a number of reasons--damping factor, lack of feedback, power limits, etc.--so your expectations have to be tempered. A single-ended amp that makes full power from 30Hz to 30kHz would be a very exceptional one.
All the transformers on your list are known for quality. If I had to choose one, it would be the Tamura. I'm familiar with their quality and it's exceptional, and that model is built for the job and no more.
1) Bigger isn't always better. The larger a single-ended transformer is, the more more winding capacitance comes into play, and this can affect high frequency response. This applies to current-handling properties as well. More current capacity doesn't mean it's better.
2) On the other hand, too small a transformer will have inadequate primary inductance, leading to poor low frequency response.
3) Since you won't be employing large amounts of negative feedback, if any, the "naked" frequency response of the OPT will be all-important.
Generally speaking, for a single-ended amp you want a transformer that's "just right"--sized for the job but not compromised by attempts to be all things for all tubes. The frequency responce of a no-feedback single-ended amplifier is going to be somewhat limited for a number of reasons--damping factor, lack of feedback, power limits, etc.--so your expectations have to be tempered. A single-ended amp that makes full power from 30Hz to 30kHz would be a very exceptional one.
All the transformers on your list are known for quality. If I had to choose one, it would be the Tamura. I'm familiar with their quality and it's exceptional, and that model is built for the job and no more.
I want none of those transformers. (no, they are not bad, i prefer better)
Why? For a 2A3 or 300B all those transformers have to low impedance and Henry so low frequency will be to much limited by the tube who is not capable to deliver the current needed for those low frequencies. For me it starts at 3500 Ohm/ 30H/10W/20Hz at 60-80mA. It means a lot less distortion. Secondly i like also low copper losses, preferable below 0,25dB
@ahankinson & @grovergardner thanks for your reply!
@tubes4all thanks for your reply, which transformer would you choose for 2A3?
@tubes4all thanks for your reply, which transformer would you choose for 2A3?
tubes4all,
Thanks for your comments!
I calculated additional specifications of the transformer that you suggested for single ended 2A3 and 300B amplifiers, from your listed specifications:
3500 Ohm primary; and a total 0.25 dB insertion loss.
If the secondary is 8 Ohm,
Then with 0.25dB insertion loss:
If all of the insertion loss is from the primary and secondary DCRs,
Let - 0.125 dB loss be in the primary, and - 0.125 dB loss be in the secondary.
Then the approximate DCRs are:
Spec: DCR 51 Ohms of the 3500 Ohm primary.
Spec: DCR 0.116 Ohms (116 milli Ohms) of the 8 Ohm secondary.
That is a very good transformer.
I am thinking of one model that just might meet those specs.; it is very expensive.
Can I ask please, what is the manufacturer and model number of the transformer that you had in mind?
Thanks!
Thanks for your comments!
I calculated additional specifications of the transformer that you suggested for single ended 2A3 and 300B amplifiers, from your listed specifications:
3500 Ohm primary; and a total 0.25 dB insertion loss.
If the secondary is 8 Ohm,
Then with 0.25dB insertion loss:
If all of the insertion loss is from the primary and secondary DCRs,
Let - 0.125 dB loss be in the primary, and - 0.125 dB loss be in the secondary.
Then the approximate DCRs are:
Spec: DCR 51 Ohms of the 3500 Ohm primary.
Spec: DCR 0.116 Ohms (116 milli Ohms) of the 8 Ohm secondary.
That is a very good transformer.
I am thinking of one model that just might meet those specs.; it is very expensive.
Can I ask please, what is the manufacturer and model number of the transformer that you had in mind?
Thanks!
I would prefer the bigger Hasimoto:
http://www.tube-amps.net/images/Hashimoto_Specs/H-30-3.5S_1024.jpg
Or even better the (iso)Tango: http://www.acoustic-dimension.com/tango/datasheets/Tango-FC-30-3_5S-datasheet.pdf
Or the Dutch maker Menno van der Veen : https://mennovanderveen.nl/images/p...E_______/2018-10-23_VDV-3035-SE_datasheet.pdf
Unfortunately your calculations are not correct. For 3500Ω/8Ω 0,25dB that will be about 100Ω and 0,245Ω.
But on Hashimoto website they don't specify 2A3 as an application for H-30-3.5S. They recommend it for 300B, PX25, 6550A & 6L6GC. (http://www.hashimoto-trans.co.jp/frame/tubecateng17a.pdf)
Tango is not possible because they don't have 4Ω out.
Would the FC-12S be a good one?
https://isotransformers.tokyo/single-ended-output-trans/fc-12s英語/
edit: oh but the FC-30-3.5S is from ISO transformers, but it's the same as the hashimoto, they don't specify 2A3 as application for it.
https://isotransformers.tokyo/single-ended-output-trans/fc-30-2-5s英語/
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That “they” not recommend it doesn’t mean so much. It is still suitable. I prefer a higher load because there will be less distortion (but less power). Also more controle over your speaker (more demping)
ok understood.
But if you fall from let's say the 'standard' 3.5W to only 2W.... it might also be an issue depending on the speakers (speaking about 2A3).
I would even have preferred 45 tubes (~1.5-2W) but with my 92dB speakers I don't think it'll work well. (even if my room is small)
45 tubes and a 4800 Ohm plate load, gives a reasonable power out (for a 45 low power tube), low distortion, and reasonable damping factor.
A 3.5k or 2.5k plate load generally will not get results as good as the 4800 plate load.
Look at a 45 data sheet and you will find 3 different quiescent operating setups for the 45. Use one of them, just choose according to your needs and tradeoffs.
A 2A3 with 3.5k primary will have less power, but will give lower distortion, and better damping factor, than a 2.5k primary.
Tradeoffs.
A 3.5k or 2.5k plate load generally will not get results as good as the 4800 plate load.
Look at a 45 data sheet and you will find 3 different quiescent operating setups for the 45. Use one of them, just choose according to your needs and tradeoffs.
A 2A3 with 3.5k primary will have less power, but will give lower distortion, and better damping factor, than a 2.5k primary.
Tradeoffs.
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tubes4all,
A good output transformer at mid frequency (such as at 1 kHz), is generally a resistive load, not a reactive load.
(That is much easier to understand than it is at low frequencies where we also have to consider the primary inductance; and at high frequencies where we also have to consider both the distributed capacitance, and the leakage inductance).
Consider a 3400 Ohm primary (due to turns ratio of primary, secondary, and secondary load) in series with 100 Ohms of DCR resistance.
At 1kHz, that is 3500 Ohms total. We call that a 3500 Ohm primary.
That 3400 Ohms and 100 Ohms creates a voltage divider. The 3400 Ohm passes power to the secondary. But the 100 Ohm DCR creates a power loss.
Put the 100 Ohms at the top, and the 3400 Ohms at the bottom.
Now, apply 1 Volt to 3500 Ohms, but then sample the voltage across the 3400 Ohms.
At the junction of the 100 Ohms and the 3400 Ohms, we have 1 Volt x (3400 / (3400 + 100) Volts at the junction.
1 V x (3400 / 3500 ) = 1 V x 0.9714 = 0.9714 V.
20 x Log (0.9714) = -0.25 dB
So 100 Ohm DCR gives us -0.25 dB (loss) in that primary.
Now, we have to consider the additional Power loss due to the secondary DCR.
But with that addidtional loss, we will have more total loss than 0.25 dB.
I hope that you and all the other readers can understand that fact.
More than just an opinion.
A good output transformer at mid frequency (such as at 1 kHz), is generally a resistive load, not a reactive load.
(That is much easier to understand than it is at low frequencies where we also have to consider the primary inductance; and at high frequencies where we also have to consider both the distributed capacitance, and the leakage inductance).
Consider a 3400 Ohm primary (due to turns ratio of primary, secondary, and secondary load) in series with 100 Ohms of DCR resistance.
At 1kHz, that is 3500 Ohms total. We call that a 3500 Ohm primary.
That 3400 Ohms and 100 Ohms creates a voltage divider. The 3400 Ohm passes power to the secondary. But the 100 Ohm DCR creates a power loss.
Put the 100 Ohms at the top, and the 3400 Ohms at the bottom.
Now, apply 1 Volt to 3500 Ohms, but then sample the voltage across the 3400 Ohms.
At the junction of the 100 Ohms and the 3400 Ohms, we have 1 Volt x (3400 / (3400 + 100) Volts at the junction.
1 V x (3400 / 3500 ) = 1 V x 0.9714 = 0.9714 V.
20 x Log (0.9714) = -0.25 dB
So 100 Ohm DCR gives us -0.25 dB (loss) in that primary.
Now, we have to consider the additional Power loss due to the secondary DCR.
But with that addidtional loss, we will have more total loss than 0.25 dB.
I hope that you and all the other readers can understand that fact.
More than just an opinion.
You have not the same definition of copper losses as transformer manufactures have.
Have a look at a well documented transformer from Menno vd Veen. ( https://mennovanderveen.nl/images/p...E_______/2018-10-23_VDV-3035-SE_datasheet.pdf )
RdcP= 50Ω / RdcS=0,1Ω / Ra=3486Ω Rout=4Ω. This gives a copper loss of 0,168dB. With your calculation methode this loss would be a lot higher because you not use the same definition of copper loss.
Your transformer transforms ac signals but not dc…. (So the 3486/4 Ω is loss less😉 )
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tubes4all,
If you think DCR in the primary winding, and DCR in the secondary winding does not cause an AC insertion loss in the transformer,
Then put a 50 Ohm resistor in series with the primary, and put a 0.1 Ohm resistor in series with the secondary.
You will get an additional loss.
It does not make any difference whether you put the 50 Ohm inside (as DCR) or external to the winding.
It does not make any difference whether you put the 0.1 Ohm inside (as DCR), or external to the winding.
DCR, and external resistors have loss at DC, and have loss at AC.
From the Menno vd Veen specs for impedances and DCRs:
1. Voltage divider action, primary windings and primary DCR:
3486 / (3486 + 50) = 3486 / 3536 = 0.98586
. . . And from long ago, Delta Voltage to dB conversion: 20 Log x (delta voltage) = dB
20 Log x 0.98586 = -0.123 dB
Voltage divider action, secondary windings and secondary DCR:
4 / (4 + 0.1) = 4 / 4.1 = 0.9756
. . . And from long ago, Delta Voltage to dB conversion: 20 Log x (delta voltage) = dB
20 Log x 0.9756 = -0.215 dB
-0.123 dB primary DCR losses
-0.215 dB secondary DCR losses
That gives a total DCR loss of -0.338 dB.
When we calculate dB loss from a voltage divider, we use 20 Log (voltage ratio) Use this one for the voltage divider action.
When we calculate dB loss from a power loss, we use 10 Log (power ratio)
2. I am not a perfect mathemetician.
But neither are the marketing, engineering, data sheet producer, or sales people at Menno vd Veen perfect.
Notice, their -0.168 dB loss is very close to the primary DCR loss, and is very close to the secondary DCR loss.
Perhaps they very accurately measured the -0.168 dB loss, but did not accurately measure the primary DCR and/or the secondary DCR.
Or, perhaps they mistakenly used 10 Log (voltage divider ratio); please do not do that.
3. Please, Readers, will a good mathematician check my math in section 1. above?
Thank You!
If you think DCR in the primary winding, and DCR in the secondary winding does not cause an AC insertion loss in the transformer,
Then put a 50 Ohm resistor in series with the primary, and put a 0.1 Ohm resistor in series with the secondary.
You will get an additional loss.
It does not make any difference whether you put the 50 Ohm inside (as DCR) or external to the winding.
It does not make any difference whether you put the 0.1 Ohm inside (as DCR), or external to the winding.
DCR, and external resistors have loss at DC, and have loss at AC.
From the Menno vd Veen specs for impedances and DCRs:
1. Voltage divider action, primary windings and primary DCR:
3486 / (3486 + 50) = 3486 / 3536 = 0.98586
. . . And from long ago, Delta Voltage to dB conversion: 20 Log x (delta voltage) = dB
20 Log x 0.98586 = -0.123 dB
Voltage divider action, secondary windings and secondary DCR:
4 / (4 + 0.1) = 4 / 4.1 = 0.9756
. . . And from long ago, Delta Voltage to dB conversion: 20 Log x (delta voltage) = dB
20 Log x 0.9756 = -0.215 dB
-0.123 dB primary DCR losses
-0.215 dB secondary DCR losses
That gives a total DCR loss of -0.338 dB.
When we calculate dB loss from a voltage divider, we use 20 Log (voltage ratio) Use this one for the voltage divider action.
When we calculate dB loss from a power loss, we use 10 Log (power ratio)
2. I am not a perfect mathemetician.
But neither are the marketing, engineering, data sheet producer, or sales people at Menno vd Veen perfect.
Notice, their -0.168 dB loss is very close to the primary DCR loss, and is very close to the secondary DCR loss.
Perhaps they very accurately measured the -0.168 dB loss, but did not accurately measure the primary DCR and/or the secondary DCR.
Or, perhaps they mistakenly used 10 Log (voltage divider ratio); please do not do that.
3. Please, Readers, will a good mathematician check my math in section 1. above?
Thank You!
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The calculations of Menno van der Veen are correct as do mine and he did exactly what all other manufactures do, incl Tango, Tamura, Monolithmagnetic, Lundahl and so on.
You can calculate what you want but it helps to stay with the industry standard methods. We are talking about copperlosses, not other losses so you calculate the wrong things.
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I did some standards measurements using a Rhode & Schwarz $50,000 Vector Network Analyzer and $10,000 Precision Short, Open, and Load Calibration kit. I had various interstage and output transformers that I measured.
Measurements included primary impedance and phase angle versus frequency; secondary impedance and phase angle versus frequency; primary resonance; primary to secondary leakage reactance, primary to secondary phase versus frequency; primary distributed capacitance; insertion loss versus frequency; several types of measurements with loaded secondary, shorted secondary, and with open secondary.
I also measured square wave response.
And I made some very accurate DCR measurements on those transformers too.
Then the data was recorded and analyzed further.
I can not remember if I made more measurements beyond what I listed above.
When I talked about the copper losses on these threads, the total loss I listed was only the copper losses.
Thanks for telling me that my posts in this thread were not about copper losses.
(I am actually aware of some other losses: laminations, coupling factors, fields that were beyond the windings and laminations, etc).
Perhaps I need to find some of those other manufacturers test methods, test equipment manufacturers and model numbers, and the test methods and practices that they followed.
Then I will look at their research, and see where I made all those mistakes in making the measurements and calculations on the many transformers that I had and measured.
Measurements included primary impedance and phase angle versus frequency; secondary impedance and phase angle versus frequency; primary resonance; primary to secondary leakage reactance, primary to secondary phase versus frequency; primary distributed capacitance; insertion loss versus frequency; several types of measurements with loaded secondary, shorted secondary, and with open secondary.
I also measured square wave response.
And I made some very accurate DCR measurements on those transformers too.
Then the data was recorded and analyzed further.
I can not remember if I made more measurements beyond what I listed above.
When I talked about the copper losses on these threads, the total loss I listed was only the copper losses.
Thanks for telling me that my posts in this thread were not about copper losses.
(I am actually aware of some other losses: laminations, coupling factors, fields that were beyond the windings and laminations, etc).
Perhaps I need to find some of those other manufacturers test methods, test equipment manufacturers and model numbers, and the test methods and practices that they followed.
Then I will look at their research, and see where I made all those mistakes in making the measurements and calculations on the many transformers that I had and measured.
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