I had been thinking /researched on this, found some mentioning that the LF OPT could be rather made of 2 separate coils (only primary and secondary each) put on two sides of C-core. This way the HF in such decline naturally.
Then for HF the air-core toroid design was proposed.
Quite doable IMO, but will take a lot of experimenting.
Completely unnecessary. HF transformer can be made small, with high permeability low distortion core. Even at highest audio frequencies, magnetic coupling will be through the core, with none or negligible capacitive coupling.
Having high DCR on an interstage transformer's windings is one thing.
Take a 1:1 interstage. Let a plate of a triode drive the interstage, and the secondary signal drive a grid with a signal that is not large enough to draw grid current, thats OK.
Driving the grid into grid current will cause clipping, and will be more severe due to
the insertion loss of the interstage (DCR insertion loss) when secondary current is drawn.
Put the DCR in the primary of the 1:1, put it in the secondary, put 1/2 in both places, you get the same effect when there is grid current.
High DCR in an output transformer will always have large power losses.
If DCR = 0.1 of the winding impedance, that is a 1 dB loss (20% power loss).
Let DCR = 0.2 of the winding impedance, that is a 2 dB loss (37% power loss).
Your 10 Watt amp is now a 6.3 Watt amp.
Take a 1:1 interstage. Let a plate of a triode drive the interstage, and the secondary signal drive a grid with a signal that is not large enough to draw grid current, thats OK.
Driving the grid into grid current will cause clipping, and will be more severe due to
the insertion loss of the interstage (DCR insertion loss) when secondary current is drawn.
Put the DCR in the primary of the 1:1, put it in the secondary, put 1/2 in both places, you get the same effect when there is grid current.
High DCR in an output transformer will always have large power losses.
If DCR = 0.1 of the winding impedance, that is a 1 dB loss (20% power loss).
Let DCR = 0.2 of the winding impedance, that is a 2 dB loss (37% power loss).
Your 10 Watt amp is now a 6.3 Watt amp.
Khe-m. The point of two these is that each NATURALLY discards the unneeded frequencies. The air-core kicks-in at exactly where C-core is getting out. You (ideally) can have zero filtering in the speaker.
How primaries of two transformers are connected to the source to achieve low frequency and high frequency separation?
First see the Broskie's article for the options.
What I came to are 2 (best, IMO) options for e.g. SE: two separate amps for LF and HF with where the HF range adjusted more precisely with an input cap (the different kinds of tubes, though the LF can be a PP);
or, for pure SE the CL (here L means the HF OPT) serial circuit for HF, and the LF OPT is in parallel to C.
What I came to are 2 (best, IMO) options for e.g. SE: two separate amps for LF and HF with where the HF range adjusted more precisely with an input cap (the different kinds of tubes, though the LF can be a PP);
or, for pure SE the CL (here L means the HF OPT) serial circuit for HF, and the LF OPT is in parallel to C.
Amen, but only for Class B, where winding DCR causes insertion loss. Moreover, secondary's loading with low impedance of Class B input provides effective damping of transformer's self-resonance, so winding's DCR is not necessary for damping.
But for Class A IT, which I referred to, there no real power transfer involved. If the secondary is unloaded, high winding DCR remains the only way of damping transformer's self resonance.
So, this way or that way, it cannot be done without a capacitor. Small core HF transformer with high pass capacitor achieves the same goal. With transformer primaries in parallel, LF transformer's leakage inductance serves as low pass filter. No need for air core transformer.
Only way? IME high plate resistance of the driver tube also damps self resonance.
You mean low plate resistance?
Low source resistance would work indeed, but practically it means high DC current in the transformer with all its associated troubles. This remedy makes more problems than it solves, whereas secondary with high DCR is like a free lunch.
No I mean high plate resistance.
But speaking of interstage transformers: in case of 1:1 ratio and tight coupling between primary and secondary (does not have to be bifilar) there is no HF peaking.
Lower grade IT's with a limited number of primary and secondary sections however show peaking, and with higher source impedance it can be "tamed" but at risk of overall loss of HF.
But speaking of interstage transformers: in case of 1:1 ratio and tight coupling between primary and secondary (does not have to be bifilar) there is no HF peaking.
Lower grade IT's with a limited number of primary and secondary sections however show peaking, and with higher source impedance it can be "tamed" but at risk of overall loss of HF.
How could it be like this? High plate resistance increases Q of self resonance.
Post # 8
One way to use 2 transformers on one output stage is to use a crossover on the 2 primaries. C to the low frequency transformer, and L to the high frequency transformer.
Of course now we have created new problems: DC on the high frequency transformer, and resonance of the crossover reacting with the transformers.
So we use a current source on the plate, and C and L in series with the high frequency transformer, that takes care of the DC on the primary of the HF transformer. But now we have lots of resonators, the crossover, the transformers, and the loudspeakers.
I will not try and make this work successfully.
Post # 10
Huh?
Put a resistor in series with the primary. Test the insertion loss.
Or put a resistor in series with the secondary. Test the insertion loss.
Since when does DCR not cause an insertion loss, whenever the transformer is loaded?
Aren't output transformers meant to be loaded (i.e, by a loudspeaker or headphones)?
A vacuum tube grid is a load, even if it is only the input capacitance, including the miller C.
And if there is grid current, there is a very non linear resistive load too (that works that way for Interstage transformers).
Yes, I realize we have moved from output transformers to interstage transformers, and back and forth.
but my statement copied to post #10 was about output transformers.
One way to use 2 transformers on one output stage is to use a crossover on the 2 primaries. C to the low frequency transformer, and L to the high frequency transformer.
Of course now we have created new problems: DC on the high frequency transformer, and resonance of the crossover reacting with the transformers.
So we use a current source on the plate, and C and L in series with the high frequency transformer, that takes care of the DC on the primary of the HF transformer. But now we have lots of resonators, the crossover, the transformers, and the loudspeakers.
I will not try and make this work successfully.
Post # 10
Huh?
Put a resistor in series with the primary. Test the insertion loss.
Or put a resistor in series with the secondary. Test the insertion loss.
Since when does DCR not cause an insertion loss, whenever the transformer is loaded?
Aren't output transformers meant to be loaded (i.e, by a loudspeaker or headphones)?
A vacuum tube grid is a load, even if it is only the input capacitance, including the miller C.
And if there is grid current, there is a very non linear resistive load too (that works that way for Interstage transformers).
Yes, I realize we have moved from output transformers to interstage transformers, and back and forth.
but my statement copied to post #10 was about output transformers.
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Most transformers are very complex, especially if they are not a bifilar pair of windings.
Resonance and Q was mentioned. There can be more than one resonance.
Midband: You have primary L and distributed capacitance of the primary.
Very High Frequency: You have the secondary L and distributed capacitance of the secondary.
You also have the resonance of the Leakage reactance and various capacitances.
If the leakage reactance is rated by the manufacturer, it may be rated either of
these ways: leakage L of the primary referred to the secondary, or leakage L referred from the secondary to the primary. Those ratings will be of the same ratio to each other, as the transformer primary to secondary ratio.
Driving some transformers with lower rp can sometimes cause some of these resonances to have higher Q. Many transformers have an optimum driving impedance. You will not get the best performance by driving with too large of rp, or too small of rp.
Square waves with fast rise and fall times can often show up high frequency problems when driving with the wrong impedance, and can show the low frequency response tradeoff versus rp value too.
Resonance and Q was mentioned. There can be more than one resonance.
Midband: You have primary L and distributed capacitance of the primary.
Very High Frequency: You have the secondary L and distributed capacitance of the secondary.
You also have the resonance of the Leakage reactance and various capacitances.
If the leakage reactance is rated by the manufacturer, it may be rated either of
these ways: leakage L of the primary referred to the secondary, or leakage L referred from the secondary to the primary. Those ratings will be of the same ratio to each other, as the transformer primary to secondary ratio.
Driving some transformers with lower rp can sometimes cause some of these resonances to have higher Q. Many transformers have an optimum driving impedance. You will not get the best performance by driving with too large of rp, or too small of rp.
Square waves with fast rise and fall times can often show up high frequency problems when driving with the wrong impedance, and can show the low frequency response tradeoff versus rp value too.
In my previous post I meant to say to drive non air gapped HF and LF transformers with one output stage:
Use a current source on the plate to B+
Connect a capacitor from the plate to the HF transformer.
Connect an inductor and capacitor from the plate to the LF transformer.
Now the HF transformer secondary drives the tweeter, and the LF transformer secondary drives the woofer.
However, I would not prefer this kind of configuration, too may parts, to many resonances, too complex.
I would rather use a true bi-amping setup, or just use a good quality output transformer and speaker with its own crossover.
Use a current source on the plate to B+
Connect a capacitor from the plate to the HF transformer.
Connect an inductor and capacitor from the plate to the LF transformer.
Now the HF transformer secondary drives the tweeter, and the LF transformer secondary drives the woofer.
However, I would not prefer this kind of configuration, too may parts, to many resonances, too complex.
I would rather use a true bi-amping setup, or just use a good quality output transformer and speaker with its own crossover.
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