Hi there tube enthusiasts,
I have designed, built and analyzed over 150 Audio transformers projects, consisting of mostly output, line-in, interstage transformers, chokes and power transformers. And I'm happily creating a Discord chat channel that will be based on Q&A on Electrical aspects on Transformers for audio purposes, where I will be happy to answer you a variety of answers related to this topic.
You can visit the channel via this link: https://discord.gg/FT26dQzywB
Just keep in mind I will be randomly available throughout different times of the day, 8 to 10PM CET Time zone.
Best regards,
Alexander.
I have designed, built and analyzed over 150 Audio transformers projects, consisting of mostly output, line-in, interstage transformers, chokes and power transformers. And I'm happily creating a Discord chat channel that will be based on Q&A on Electrical aspects on Transformers for audio purposes, where I will be happy to answer you a variety of answers related to this topic.
You can visit the channel via this link: https://discord.gg/FT26dQzywB
Just keep in mind I will be randomly available throughout different times of the day, 8 to 10PM CET Time zone.
Best regards,
Alexander.
Interesting topic! Have been quickly there on the given address, but I am not really eager to apply to this yet another website and yet another login. Why not telling us about your experiences here? Would certainly be most appreciated.
Hi there,
Not sure yet the reason behind it? You do have registered a discord account?
It will be my pleasure, although I'm more open for quick Q&A for the moment due to scarce time. If you have a specific question to ask, go ahead!
Best regards,
Alexander.
I agree with others that it’s not practical to use another account for another website. At least it doesn’t work for me.
I get a message that the web address is invalid. I have no account and I don’t intend to create one (how?).
Regares, Gerrit
I get a message that the web address is invalid. I have no account and I don’t intend to create one (how?).
Regares, Gerrit
I have to agree; the maintenance costs of yet another account, on yet another forum is...too much. I deleted my Reddit account and dont participate in Facebook, Twitter, TikTok, Youtube.
Yet, I'm interested in transformers. I use them to generate a high Z source for driving loudspeakers with current. A place to talk about that - besides the "Black Hole" - would be great in this forum. I assume anything goes, as long as the transformer is transforming an audio signal -
Yet, I'm interested in transformers. I use them to generate a high Z source for driving loudspeakers with current. A place to talk about that - besides the "Black Hole" - would be great in this forum. I assume anything goes, as long as the transformer is transforming an audio signal -
I’m just getting started with understand audio output transformers, mainly from a guitar amplifier context, push-pull EL34 amps.
I know that the primary and secondary winding are interleaved, and the more sections the higher the bandwidth of the transformer
Can you explain a little bit what is going on here.
I’d also be interested to know about modern day supplies of all materials needed to make a push-pull output
transformer for an EL34 stage.
Particularly, where can I get,
I am sure I can think of more questions.
I know that the primary and secondary winding are interleaved, and the more sections the higher the bandwidth of the transformer
Can you explain a little bit what is going on here.
- What are the pros and cons of this approach?
- It must be reducing the capacitance?
- I’d like to understand why.
I’d also be interested to know about modern day supplies of all materials needed to make a push-pull output
transformer for an EL34 stage.
Particularly, where can I get,
- sheet metal which can be cut to make laminations or
- EI laminations already cut
- Bobbins
- What is a sensible selection of wire type and gauge to get for push-pull transformers
- What is a good potting material?
I am sure I can think of more questions.
Sure thing!
- What are the pros and cons of this approach?
You apply interleaving to reduce leakage inductance. The later reduces bandwidth due to leakage inductance representing an inductive reactance, or simply imagine an inductor in series with the transformer limiting your high frequencies.
- It must be reducing the capacitance?
Interleaving inevitably increases overall transformer capacitance.
- I’d like to understand why.
In a transformer, leakage inductance is dependent of the distance between primary and secondary layers. Capacitance increases with decreasing the distance and voltage gradient difference between layers. Now this is a quite basic answer, in practice you have more details to account for.
Although my blog in under reconstruction, you can check my basic article on transformer parasitic parameters here: https://musecoils.wordpress.com/2020/04/26/parasitic-parameters-of-audio-transformers/
- sheet metal which can be cut to make laminations or
Depends of your location. Try looking for local manufacturers, due to the weight of this stuff. You can also use C-cores for linear winding. - EI laminations already cut
Same - Bobbins
You can purchase online or make your own. - What is a sensible selection of wire type and gauge to get for push-pull transformers
You need to select your main transformer parameters, such us power output at the needed frequencies and primary to secondary impedance. For guitar OPTs, I'd wildly say primary wire diameters from 0.2 to 0.4mm - What is a good potting material?
Mostly often are used epoxy and polyurethane. These are already expensive, so it's recommended to use a filler. Many commercial potting materials already come with a filler. You could also use molten bitumen. Keep in mind the potting compound, if too watery and wetting properties, such as polyurethane or epoxy, can penetrate within windings and alter overall capacitance value.
Best regards!
Hi Alexander,
The equivalent circuit on your blog was the first time all of this stuff started to click. Really great post.
Do you have any experience with inter-stage transformers for valve pre-amps, this is the other things I was interested in looking into. I think this might be an easier thing to start with? What do you think?
If I start doing something for fun, I'll let you know! Thanks.
The equivalent circuit on your blog was the first time all of this stuff started to click. Really great post.
Do you have any experience with inter-stage transformers for valve pre-amps, this is the other things I was interested in looking into. I think this might be an easier thing to start with? What do you think?
If I start doing something for fun, I'll let you know! Thanks.
I would like to ask what coil winding machine would be good for a person to purchase if they were interested in winding their own chokes/output transformers for hifi tube amp purposes. I realize you could make your own machine with arduino controls / counters however from what I can gather it might be easier to purchase something with a wide variety of controls that is ready and purpose built.
I don't feel qualified enough to recommend machines as I haven't tried many brands, but I can confidently say, if you're going to do this in the long run, you need to pay extreme importance to comfort and smallest physical and psychological discrepancies, as for any professional job. You basically need to develop a "winding station". Think of this as a luxury plane cockpit. Otherwise your psyche will suffer. As a winder, you need the lesser distractions and discrepancies as possible. Winding adrenal fatigue is real and it's not the nicest thing on earth.
Your choice of winding will also dictate the kind of station you will develop.
The machine alone is not enough. You need a plan first. And you need to be capable of building your own tooling, meaning machining work. You also need good tensioners, all of them optimized for a range of wire thicknesses. They make a night and day difference, but are also expensive.
Lundahl for example make their machines in-house! Amazing job!
I'm currently winding on an already modified Meteor 301, but added some additional mods as well. You can't go wrong with old Meteors, but for some it's hard to find spare parts.
Your choice of winding will also dictate the kind of station you will develop.
The machine alone is not enough. You need a plan first. And you need to be capable of building your own tooling, meaning machining work. You also need good tensioners, all of them optimized for a range of wire thicknesses. They make a night and day difference, but are also expensive.
Lundahl for example make their machines in-house! Amazing job!
I'm currently winding on an already modified Meteor 301, but added some additional mods as well. You can't go wrong with old Meteors, but for some it's hard to find spare parts.
Hi there,
Yes, I've built interstage in ratios of Step-up, step-down and 1:1.
Only easy if you know what you're doing. Transformers are unforgiving for mistakes when you're not looking.
I'd say output transformers are somewhat harder to screw-up because of not-so much secondary leakage.
Here's an advanced tip - always keep in mind the Miller capacitance of the stage the secondary is driving, especially valid for Step-up transformer attempts.
Thanks!
Hello sir- I have been lurking DIY AUDIO for a while and as a novice in audio electronics, I have found myself completely over my head at times. There is a wealth of knowledge here and I feel quite fortunate to have access to all the wisdom and experience.
I am concentrating on the elementary tube amp designs (early Fender-style amps being the easiest for me to grasp), and there is one thing that I cannot get my head around....Why is unfiltered B+ DC voltage sent to the output transformer?
Thanks in advance.
I am concentrating on the elementary tube amp designs (early Fender-style amps being the easiest for me to grasp), and there is one thing that I cannot get my head around....Why is unfiltered B+ DC voltage sent to the output transformer?
Thanks in advance.
Can you post a schematic of what you are looking at?
For example, the Fender Deluxe connects the main reservoir cap to the center tap on the output transformer.
This provides DC to the plates, DC with a lots of ripple! However, the ripple is the same on both anodes. In push-pull only the difference is amplified. For example, one plate swinging up as the other swings down, will cause current to flow in the primary winding of the output transformer.
Also the inductance of the primary winding can be quite high, 50H or more. So this acts as an inductor in series with main filter cap which will filter ripple further.
For example, the Fender Deluxe connects the main reservoir cap to the center tap on the output transformer.
This provides DC to the plates, DC with a lots of ripple! However, the ripple is the same on both anodes. In push-pull only the difference is amplified. For example, one plate swinging up as the other swings down, will cause current to flow in the primary winding of the output transformer.
Also the inductance of the primary winding can be quite high, 50H or more. So this acts as an inductor in series with main filter cap which will filter ripple further.
I have other examples on the big computer, but here are two I can find right now. Every guitar amp schematic I have seen takes the highest unfiltered DC B+ voltage from the Power Transformer and puts it into one leg of the input of the Output Transformer. If its a push-pull amp, it goes to the center tap. Just trying to understand how one leg of HV DC combined with the HV audio signal can create a waveform through the transformer. I thought transformers and DC were a no-no. But since this is technically half AC, half DC, somehow it works? The audio signal somehow references its "neutral" against the DC as they pass through the windings? I'm sure this is as clear as day to the rest of the class...I just don't see how it can work.
Not sure if I understand completely your question.
The DC sent to the transformer is filtered. Or it would be more correctly to say, it powers the output stage, which is a tube(x2) and transformer tandem.
The DC is filtered but with a smallest filtration due to the reason it might be practically unnecessary to filter it more. The output stage not only is the least sensitive to ripple due to its nature of swinging high signal vs noise amplitudes, but also due to being a push-pull stage, which has higher PSRR than single-ended stages.
In a push pull transformer, DC is fed via the center tap and travels through both primary halves and both tubes until ground. But a push-pull has its windings reversed from POV of center tap, opposite DC flux densities are generated and cancel each other. Hence, PP output transformers work with DC through them without saturation. In a real world though, we should allow for small DC flux headroom in case of bias, current disbalance between tubes.
The DC sent to the transformer is filtered. Or it would be more correctly to say, it powers the output stage, which is a tube(x2) and transformer tandem.
The DC is filtered but with a smallest filtration due to the reason it might be practically unnecessary to filter it more. The output stage not only is the least sensitive to ripple due to its nature of swinging high signal vs noise amplitudes, but also due to being a push-pull stage, which has higher PSRR than single-ended stages.
In a push pull transformer, DC is fed via the center tap and travels through both primary halves and both tubes until ground. But a push-pull has its windings reversed from POV of center tap, opposite DC flux densities are generated and cancel each other. Hence, PP output transformers work with DC through them without saturation. In a real world though, we should allow for small DC flux headroom in case of bias, current disbalance between tubes.
dc is a transformer is undesirable but not exactly a no no. In a push pull transformer the dc travels through two windings of opposite phase. The magnetic field the dc causes in one is almost totally cancelled by the equal and opposite magnetic field created by the other.
In a single ended transformer design there is no cancellation and the transformer has to take the full dc. To prevent the dc causing core saturation a gap in the magnetic path is created (so you now have a magnetic path consisting of the transformer core and air in series). The unfortunate side effect of this is that is considerably reduces the inductance of the winding meaning you need many more turns and/or a bigger core to obtain sufficient inductance for good bass response.
Cheers
Ian
In a single ended transformer design there is no cancellation and the transformer has to take the full dc. To prevent the dc causing core saturation a gap in the magnetic path is created (so you now have a magnetic path consisting of the transformer core and air in series). The unfortunate side effect of this is that is considerably reduces the inductance of the winding meaning you need many more turns and/or a bigger core to obtain sufficient inductance for good bass response.
Cheers
Ian
Thanks everyone for the replies. My fear is this question is so elementary to most here that any answer will include aspects I had never considered, for example:
"....it powers the output stage, which is a tube(x2) and transformer tandem."
This is a new can of worms. I thought the tubes took power from the PS rail after DC filtering...? I'll dive into that next.
But to get the original question into the most simple terms, I don't understand why the output signal from the tubes does not simply enter the output XFMR as a high impedance, high voltage signal and exit the other side as a low voltage, low impedance version suitable to power a speaker. Why is the HV DC from the power supply needed?
Again, without any formal schooling, I have probably missed a very elementary chapter on design and function of XFMRs. So I am stumbling on this before I can really go much further. In all of my reading, I cannot find an answer as to why this leg of DC voltage is needed for the circuit to function.
It's embarrassing for me to ask something so simple, but I am thankful for the honest efforts to help me sort it out.
"....it powers the output stage, which is a tube(x2) and transformer tandem."
This is a new can of worms. I thought the tubes took power from the PS rail after DC filtering...? I'll dive into that next.
But to get the original question into the most simple terms, I don't understand why the output signal from the tubes does not simply enter the output XFMR as a high impedance, high voltage signal and exit the other side as a low voltage, low impedance version suitable to power a speaker. Why is the HV DC from the power supply needed?
Again, without any formal schooling, I have probably missed a very elementary chapter on design and function of XFMRs. So I am stumbling on this before I can really go much further. In all of my reading, I cannot find an answer as to why this leg of DC voltage is needed for the circuit to function.
It's embarrassing for me to ask something so simple, but I am thankful for the honest efforts to help me sort it out.