I would have thought you would get something at power up and down..? Maybe it depends on how you derive the half-supply voltage, and what the PSU rise and fall time is, as to whether it's audible. At the very least, though, wouldn't you want a 'bleeder' resistor at the output so that you could plug it into your power amp after powering on without damaging your speakers?
It's a good circuit for discussion - exactly what the OP was talking about.
Looking at it, my immediate thoughts are:
1. It's only a pre-amp but it needs a heatsink!
2. There may not be many, but the components are pretty big and expensive.
3. Transformer... it isolates which is good, but how is it at low frequencies?
4. What do I have to do in order to make it run from a mains-derived supply, possibly unregulated?
5. What's the THD?
It feels like a circuit that does an extremely simple function quite expensively, just asking for someone to make it out of brass, mahogany and paxolin.
I've tried this circuit- note the strong resemblance to the Heretical!
A small heatsink is not a big deal. Other than the transformer, the components are actually pretty cheap. The transformer has very low distortion at low frequencies at the voltage and impedance levels used. The THD is insanely low when used as a preamp, challenging my test equipment. At low load impedances (30R), well... ask Steve that one.
Yes, of course. That is why adding an extra zero after the decimal point may be silly. However, some distortions (especially IM) are audible so their generation by simpler circuits at higher volumes has to be tolerated by listeners; a little marketing/hypnosis can aid this toleration of something which would otherwise be objectionable.Pano said:
In audio we are in the rather ridiculous situation where people claim they can hear some distortion at -140dB yet cannot hear (or actually prefer) other distortion at -20dB.
Well, some people will consider "a lot of paralleled output transistors" already being too complex
Is for example Krell[Clone] KSA100MKII artificially complex amp?
I don't think so - it has what it should to do the job right.
There need to be a definition of "better" - is an amp transparent, or someone looking for a musical instrument that makes every crappy record sound "nicer"? Minimalistic designs, especially the tube ones are often the second.
Hi ! I have no doubt about it really ... for me a better amp is absolutely a transparent amp.
No noise, fast, no distortion ... clean and trasparent as a crystal glass
And actually I look a lot to measurements
If it is clynical ... I guess I will have to go to the hospital then
Thanks,
gino
Hi ! line transformers are not very easy to understand for me
I understand that they are indeed very popular expecially in high end mixer
So I assume that their effect on sound is very nice
Not very common in hifi audio anyway ... do not know why
Thanks,
gino
The preamp outputs are transformer coupled so the output has 80 ohms of DC resistance to ground.
No, it's a headphone amplifier that also has preamp outputs. If you wanted to use it solely as a preamp, you wouldn't need any heatsinking at all.
Never said it was cheap. And no one said anything about size or cost.
The transformers I'm using for this are rated (1% THD at 20Hz) at +10 dBu, which is about 2.5 VRMS.
Can't think of much music out there with full scale output at 20Hz. And as you go above 20Hz, distortion drops precipitously. By the time you're at 500Hz, you're in 0.001% territory.
Also, transformer harmonic distortion is quite benign. First, it's very low order. Second, for a given amount of THD, its IMD is considerably less than you would typically get with an active device.
Don't know. Haven't run it from an unregulated, mains-derived supply.
I think SY used an unregulated supply for his measurements and he might have a plot showing what levels the mains frequencies were at.
As SY said, if you're using it as a preamp into a relatively high impedance load, THD is vanishingly low.
Here's a spectrum plot into a 32 ohm headphone playing at levels you wouldn't want while wearing them on your head:
An externally hosted image should be here but it was not working when we last tested it.
It's completely monotonic with no components to speak of above the 4th. This distortion characteristic is well masked by our ears.
In this case, it will be ebonite and either maple, cherry or walnut. It does use some brass however, but only for stuff like the serial plate.
An externally hosted image should be here but it was not working when we last tested it.
There will be some linen-based paxolin used, but it will be for the ventilation plates, not the circuit boards which will be made using FR-4.
se
Transformers got a bit of a bad reputation because back in the day, poor quality transformers were fairly common. And good quality transformers cost more than a handful of transistors and resistors and are often avoided on economic grounds. But in high end audio, transformers are still sometimes used for stepping up the output of moving coil phono cartridges.
se
Round about 40 posts this thread had a certain minimalist elegance, but now that it's blossomed into a venue for playing numbers games or showing off your design chops or, for that matter, a font appreciation society, it has a certain overblown quality reminiscent of the worst type of overelaborated electronic equipment.
Thanks, Bas!
Still can't believe I had to end up doing it myself. Perhaps because it was primarily created using drafting templates and pantograph machines rather than as a regular typeface.
se
Perhaps. But I for one am an admirer of Steve Eddy's "quest" for simplicity, beauty, minimalism (not his words but mine). I've "known" about him for years now. And most every time he puts something on display I admire it for its simplicity and beauty. It is inspiring. Since I find that I tend to lose touch with that essence that singlemindedness.
I guess what I'm trying to say is that minimalism is more than just a simple design. It is a way of thinking...almost a way of life. And to demonstrate fonts and schematics can be a perfect metaphor...easily telling us more than a thousand words or posts can.
Thank you for the very interesting information.
As I said the sound through transformers seems to have a particular fascinating tone
Why not place it at the output instead ? very simple line stages have maybe the main drawback in an high output impedance
to adapt the impedance a trasformer would be just the nicest of the solution ?
I am thinking to a single ended line stage built using just one nice bjt/mosfet and the transformer at the output to lower the output impedance
Could it work ?
Thanks and regards,
gino
In order for a transformer to lower the output impedance, it has to be a step-down transformer. So in addition to providing the low output impedance, it's also attenuating the signal. So if you want a given amount of overall gain, your gain device needs to provide even more gain to overcome that which is lost by the output transformer.
And that's why I did things the way I did. Put the transformer up front to provide the signal amplification passively, and then use the active devices to ONLY provide the low output impedance without the penalty of giving up a bunch of the gain from the previous stage.
se
Er... yes, it is.
No, it hasn't to do with inefficiency.
Although realworld transformers have some losses, an ideal transformer reflects voltages as a function of its turns ratio and impedances as a function of the square of its turns ratio.
For example, in order to reflect an 8 ohm loudspeaker load back to the primary so that the output tube sees say, a 5k ohm load (and simultaneously reduce the tube's output impedance as seen by the loudspeaker), you need a transformer with a turns ratio of 25:1.
But that also means that the voltage seen by the transformer's primary is reduced (i.e. attenuated) by a factor of 25, or about 28dB at the transformer's secondary.
Has nothing to do with inefficiency but simply how transformers work, even the "ideal" lossless transformer.
se
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