Can you design for me an output circuit using a transformer.
Power supply is +15V -15V
XLR line output, audio signal is up to 70Vpeak differential.
I am not familiar with audio transformers.
How to drive the transformer ?
Which part and sourcing ?
What sound quality can be expected, in terms of bandwidth and distortion ?
Power supply is +15V -15V
XLR line output, audio signal is up to 70Vpeak differential.
I am not familiar with audio transformers.
How to drive the transformer ?
Which part and sourcing ?
What sound quality can be expected, in terms of bandwidth and distortion ?
That is +36 dBu! What kind of equipment expects that? Most XLR line-in will die with such a high signal. Is it rather for 70V PA line? Those are typically used to connect actual speakers, not equipment. In any case, I would use the transformers made for those lines as they are common. Expect such a transformer with low distortion to be quite expensive.
If you just need an audio transformer for normal line level signals, the TY250-P is quite good, cheap and available. However, it can only be used for signal up to about +15 dBu, or +21 if two are used.
If you just need an audio transformer for normal line level signals, the TY250-P is quite good, cheap and available. However, it can only be used for signal up to about +15 dBu, or +21 if two are used.
Yes +36 dBu is beyond usual line levels.
This is experimental, +36dBu is an absolute max before clipping and care will be taken near that.
May be my question boils to: What is available in step up audio transformers at very high line levels ?
Based on such a transformer, how do I drive it ?
Is it simply an op amp output to the primary winding ?
This is experimental, +36dBu is an absolute max before clipping and care will be taken near that.
May be my question boils to: What is available in step up audio transformers at very high line levels ?
Based on such a transformer, how do I drive it ?
Is it simply an op amp output to the primary winding ?
I would look into low power 70V line transformer or tube amplifier output transformer used in reverse. A wide bandwidth will be expensive. A transformer (mostly) reflects the impedance on the secondary to primary multiplied by the transformer ratio. So the driver might be as simple as a power opamp like the NJM4556 if the transformer can step it up to the required level.
Good references are:
High Voltage Audio
Transformers for Audio
Good references are:
High Voltage Audio
Transformers for Audio
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I like ESP (did not think looking into it about line transformers).
I found this Lundahl LL7906 +37 dBu (54Vrms)
Here: Line input and line output audio transformers • Lundahl Transformers
LL7906 specs.
https://www.lundahltransformers.com/wp-content/uploads/datasheets/7906.pdf I am not familiar with audio transformers to figure from the specs wether it fits my need and how to design an output circuit with it.
I found this Lundahl LL7906 +37 dBu (54Vrms)
Here: Line input and line output audio transformers • Lundahl Transformers
LL7906 specs.
https://www.lundahltransformers.com/wp-content/uploads/datasheets/7906.pdf I am not familiar with audio transformers to figure from the specs wether it fits my need and how to design an output circuit with it.
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Still not sure about your needs but one option could be to make a 70Vpp output amplifier, I guess you want a line amplifier so some power involved but not speaker level, and drive a 1:1 line transformer.
The point being that it´s quite easier to wind a 1:1 transformer for various reasons (as seen by a transformer winder which I am):
* you have same number of turns on both windings
* being lowish impedance you use less turns of thicker wire (winding thousands of turns of very fine wire is a pest)
* you use same wire diameter on both coils so you set up the machine once
* in fact, you can even wind bifilar, unless you need high voltage insulation between primary and secondary (I guess not)
* bifilar disadvantage is relatively high capacitance between primary and secondary, but at the impedances involved (guess aound 600 ohm) , no big deal.
Absolute worst case, you wind separate coils; even side by side so as to minimize capacitance.
By the same token, primary-seconday coupling is improved, and leakage (parasitic series) inductance can be somewhat improved.
Being a simplish transformer (compared to other options) it´s more likely a winder accepts winding "just one" or you may find many commercial 1:1 transformers.
Most 600:600, you may find the odd 150:150 or 200:200
The point being that it´s quite easier to wind a 1:1 transformer for various reasons (as seen by a transformer winder which I am):
* you have same number of turns on both windings
* being lowish impedance you use less turns of thicker wire (winding thousands of turns of very fine wire is a pest)
* you use same wire diameter on both coils so you set up the machine once
* in fact, you can even wind bifilar, unless you need high voltage insulation between primary and secondary (I guess not)
* bifilar disadvantage is relatively high capacitance between primary and secondary, but at the impedances involved (guess aound 600 ohm) , no big deal.
Absolute worst case, you wind separate coils; even side by side so as to minimize capacitance.
By the same token, primary-seconday coupling is improved, and leakage (parasitic series) inductance can be somewhat improved.
Being a simplish transformer (compared to other options) it´s more likely a winder accepts winding "just one" or you may find many commercial 1:1 transformers.
Most 600:600, you may find the odd 150:150 or 200:200
Just to state the obvious: if you need "70V", why start with 30V?? This is not 1966 again. High-voltage parts are cheaper than ever.
Transformer is not "free gain". TranSistor gain is nearly free anyway. TransFormers have significant bandwidth limits; and low THD is not cheap. Step-up makes it worse.
You have not really specified your POWER level, except "not 600 ohms". 6r? 6Meg?
For "experimental" purpose, one hack is that half-dead Sansui hi-fi in your closet feeding a 12V:120V transformer. Separate-bobbin windings may not beat 1kHz but one-over-the-other power windings I have measured flat to over 15KHz.
Transformer is not "free gain". TranSistor gain is nearly free anyway. TransFormers have significant bandwidth limits; and low THD is not cheap. Step-up makes it worse.
You have not really specified your POWER level, except "not 600 ohms". 6r? 6Meg?
For "experimental" purpose, one hack is that half-dead Sansui hi-fi in your closet feeding a 12V:120V transformer. Separate-bobbin windings may not beat 1kHz but one-over-the-other power windings I have measured flat to over 15KHz.
Typical output load is 10K.
Most is analog running on +15v -15v
with max rating parts 2x18v.
Only the output is beyond this.
I could compromise to 40V peak differential mode output, using NE 5534 at max rating 2x22v.
Beyond that supply voltage there is just a few op amps.
I have some hope avoiding doubling the supply rails, with a step up transformer.
What is the best way to go ?
Most is analog running on +15v -15v
with max rating parts 2x18v.
Only the output is beyond this.
I could compromise to 40V peak differential mode output, using NE 5534 at max rating 2x22v.
Beyond that supply voltage there is just a few op amps.
I have some hope avoiding doubling the supply rails, with a step up transformer.
What is the best way to go ?
That LL7906 could do it. You could strap input to (1+1) // (1+1) and secondary parallel. Gives you 2:5.6 .
Output load is reflected to primary by square of turns ratio, so that 10k load becomes (2/5.6)^2 is about 0.13 x 10k = 1.3k if I got the numbers right. A good opamp can drive that I think.
But it'll cost you!
Jan
Output load is reflected to primary by square of turns ratio, so that 10k load becomes (2/5.6)^2 is about 0.13 x 10k = 1.3k if I got the numbers right. A good opamp can drive that I think.
But it'll cost you!
Jan
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I see no information in the specs that can relate to current or power.
It only gives dBu which is voltage and quotes a source impedance, it mentions load, but I cannot find where the value is.
Basically, what fries a transformer is power lost because of imperfect efficiency , a concern in main power transformer unknown here for audio.
At that price, I better ask the swedes.
It only gives dBu which is voltage and quotes a source impedance, it mentions load, but I cannot find where the value is.
Basically, what fries a transformer is power lost because of imperfect efficiency , a concern in main power transformer unknown here for audio.
At that price, I better ask the swedes.
If isolation is required, stick with transformer. Otherwise stack DCDC converters to bump voltage since current requirement is low and opamp/transistor solution is then much lower cost. There would be some HF (80KHz - 120KHz) PSU switching noise but this would probably cancel in a differential application, or could be filtered.
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