I think you are missing the point of simulations. It is not to have something totally accurate, it’s to debug your ideas, find there limitations, weaknesses and requirements before prototyping.
Simulation and prototyping are complimentary tools for getting the job done.
I’m really grateful to people that enjoy simulation and are willing to share their work and face public constructive criticism. But being critical because you don’t like completely accurate simulation tools is not a fair critique.
Simulation and prototyping are complimentary tools for getting the job done.
I’m really grateful to people that enjoy simulation and are willing to share their work and face public constructive criticism. But being critical because you don’t like completely accurate simulation tools is not a fair critique.
On this subject, I built my amp first, and only after I started playing with LTspice. I have to say that the simulation was quite good, even instability when increasing gNF on the real amp was accurately shown. Is not perfect, by any means, but it is an excellent complementary tool.
Nothing beats prototyping with the real hardware though, at least for me.
Nothing beats prototyping with the real hardware though, at least for me.
HAMMOND 125A universal PUSH-PULL Output Transformer
For diyaudio fellow JoeAlders I made a hierarchical model of the Hammond 125A.
He was working on the Lingwendil flea amplifier project
https://www.diyaudio.com/community/threads/6sn7-push-pull-flea-amplifier-project.303846/
Based on the datasheet (and a 125A that Joe kindly sent me to take some measurements) I created this model. Measuring a transformer with simple equipment is not a trivial task, as we both experienced. The transformer K calculated from my L measurements was too high when looking at the frequency response. To correct this discrepancy, I cheated and adjusted K to match the LTspice results with my 3k-8 frequency response measurements. So there is certainly room for improvement.
The LTspice simulation of the ampfifier is made by Joe.
happy diy,
Ite
NOTE:
By adjusting a few parameters you can easily convert this 125A model to another type from the 125A..E series. Start with changing Lpp, R-brown/blue, and Rs-total, and go from there.
For diyaudio fellow JoeAlders I made a hierarchical model of the Hammond 125A.
He was working on the Lingwendil flea amplifier project
https://www.diyaudio.com/community/threads/6sn7-push-pull-flea-amplifier-project.303846/
Based on the datasheet (and a 125A that Joe kindly sent me to take some measurements) I created this model. Measuring a transformer with simple equipment is not a trivial task, as we both experienced. The transformer K calculated from my L measurements was too high when looking at the frequency response. To correct this discrepancy, I cheated and adjusted K to match the LTspice results with my 3k-8 frequency response measurements. So there is certainly room for improvement.
The LTspice simulation of the ampfifier is made by Joe.
happy diy,
Ite
NOTE:
By adjusting a few parameters you can easily convert this 125A model to another type from the 125A..E series. Start with changing Lpp, R-brown/blue, and Rs-total, and go from there.
The HF -3dB point is a good start, but lurking behind is the ugly resonance caused by the series cap (prim. to sec.).
This is what I found when modifying my Leak ST60: -3dB@55KHz, dip@70KHz, and peak@90KHz
@Ite: thanks for your model; it allows the parasitic caps to be specified. However, in order to approximate the actual response above, I need to use around 10nF between prim. and sec., but the actual measured value is about 2nF. Any thoughts?
This is what I found when modifying my Leak ST60: -3dB@55KHz, dip@70KHz, and peak@90KHz
@Ite: thanks for your model; it allows the parasitic caps to be specified. However, in order to approximate the actual response above, I need to use around 10nF between prim. and sec., but the actual measured value is about 2nF. Any thoughts?
LEAK-8615 transformer model
@Zung,
I am not a transformer expert, more an LTspice WYSIWYG transformer model promoter.
In your Leak-enstein thread I saw the Ray Whitcombe info on how the transformer is constructed internally.
I made a model that follows that recipe and got some promising results!
happy diy,
Ite
@Zung,
I am not a transformer expert, more an LTspice WYSIWYG transformer model promoter.
In your Leak-enstein thread I saw the Ray Whitcombe info on how the transformer is constructed internally.
I made a model that follows that recipe and got some promising results!
happy diy,
Ite
Hi Mo,
The asymmetry is caused by the distortion in the "out" signal. (use control-L to show it in the error log)
When you re-run the simulation with a lower input signal, the signal will have lower distortion and the symmetry will be better.
The distortion is not caused by the transformer model. It is only a simple lumped model, that doesn't incorporate core-saturation.
Press Right Mouse Button on the transformer, and click [Open Schematic] to view the model used.
The example circuit with the EL34 is only to show how to use the transformer model. It is by no means a perfect circuit.
happy diy,
Ite
The asymmetry is caused by the distortion in the "out" signal. (use control-L to show it in the error log)
When you re-run the simulation with a lower input signal, the signal will have lower distortion and the symmetry will be better.
The distortion is not caused by the transformer model. It is only a simple lumped model, that doesn't incorporate core-saturation.
Press Right Mouse Button on the transformer, and click [Open Schematic] to view the model used.
The example circuit with the EL34 is only to show how to use the transformer model. It is by no means a perfect circuit.
happy diy,
Ite
Hi, inhave been interested in this topic recently, and wondering what to measure on the output transformers to be able to judge their merit before trying to use them.
DC resistance of primaries and seconaries
primary inductance (at what frequency?)
secondary inductance
capacitance
overall weight
turns ratios
i have a de-5000 LCR meter that measures at 100, 120, 1000, 10000, and 100000hz, and it can within some limitations measure resitance, inductance, capacitance, both series and parallel. Also gives Q, and ø (not sure how to make a proper theta on this iPad). I have a bunch of other test equipment too if needed.
I’m Going to look closer at the models people have made and see if I can make sense of any of this…
DC resistance of primaries and seconaries
primary inductance (at what frequency?)
secondary inductance
capacitance
overall weight
turns ratios
i have a de-5000 LCR meter that measures at 100, 120, 1000, 10000, and 100000hz, and it can within some limitations measure resitance, inductance, capacitance, both series and parallel. Also gives Q, and ø (not sure how to make a proper theta on this iPad). I have a bunch of other test equipment too if needed.
I’m Going to look closer at the models people have made and see if I can make sense of any of this…