john curl said:
Are you talking magnetically shielded E-I then, or do you consider plain E-I as superior to toroids too? Is capacitive coupling the main reason?
I think I have read the same recommendation elsewhere, that E-I are to be preferred, and yet toroids seem very common both in DIY and good commecial gear. Maybe toroids have simply become the standard so they are cheaper nowadays?
christer:
i've read the same. i've always suspected that toroids got popular primarily because of lower radiated fields (resulting in lower hum) for the large number of "general consumer" products that kept the transformer in the same chassis as the circuitry.
mlloyd1
i've read the same. i've always suspected that toroids got popular primarily because of lower radiated fields (resulting in lower hum) for the large number of "general consumer" products that kept the transformer in the same chassis as the circuitry.
mlloyd1
Christer said:
Still the problem of high capacitance exists with these shielded xformers, since the shield must be connected to somewhere (earth, that is). If one wants true low coupling (low leakage/"GND" currents) there is no other way than true low capacitance xformer design like R-Core, UI and specialist toroids with sectoral (non-concentric) windings (Avel-Lindberg has some small wattage models).
- Klaus
Zung said:
Too smooth for my taste. Less details and a treble I did not enjoy - all relative to a Elma stepped atten with Dale's light brown RN resistors.
Sigurd
Sigurd Ruschkow said:
Less treble? How come? Did you measure the frequency response of that pot?
Regards,
Edmond.
mlloyd1 said:
Yes, and I think toroids are also nowadays smaller and weigh less than correspond EI of same rating, so with machine winding they are probably chepaer too, which they were not a copule of decades ago.
It seem even difficult to find EI transformers nowadays, except for certain special voltages and purposes, and it is all toroids. OTOH, it is possible to buy EI cores, which seem more reasonable to wind by hand than a toroid.
mlloyd1 said:zinsula:
conceptually interesting ideas ...
does one need to be concerned about how the distortion spectral balance (is that the right phrase?) might change as the '"volume" is adjusted?
mlloyd1
Pavel (PMA) has posted some simulation results in this thread about higher harmonics appearing with higher degeneration resistor values. I should search for that.
Maybe someone else could comment?
Steve Eddy said:
Ah, sorry. "U" is typically used to denote an integrated circuit so my eyes immediately went to the opamp symbol in the schematic.
So now that I see what you're talking about, I have a question. Are you able to attenuate below unity gain with that arrangement?
se
Well yes, theoretically down to zero output swing, if the junction is "open". In that case, the current of the upper JFets flow completely into the lower one, and not to the other side.
Tino
1audio said:
Were the pot distortion measurements done with the wiper feeding an extremely hi-Z load, like a JFET input, or were they done with the wiper feeding a rather finite resistive load to ground. I would guess the former case, in which there is virtually no AC or DC current flowing in the wiper, would exhibit much less distortion. If any distortion is exhibited in that case, what is the distortion mechanism thought to be?
Thanks,
Bob
Bob Cordell said:
Do you mean contrary, i.e. oxide forming non linear junctions on very low currents?
zinsula said:
This is of particular interest to me and I have compared some
actual measurements to the simulations presented here, but
the results are ambiguous - specifically I was unable to confirm
the creation of higher orders with degeneration.
The subject does not seem to be popular, however.
You will find the discussion ranging approximately over posts
#2873 through about #3842.
Manufacturing bad spots are on many common, and even very high quality pots. First found in Levinson JC-2 in 1974. BIG PROBLEM Hi Z loading helps, but distortion can be modeled as lossy inverted side by side diodes. Have made the measurement comparisons, myself. Other pots can sometimes look mostly like 2'nd harmonic.
Nelson Pass said:
Hi Nelson,
Below is a simulation I did awhile back of distortion of a single common-emitter stage as a function of degeneration in dB. If you look at 5th and 7th, you can see that they start out quite low with no degeneration at -98 and -134, respectively, then increase as small amounts of NFB in the form of degeneration are added. By the time one reaches 20 dB of degeneration they are pretty much no longer rising (-80 and -110, respectively), and as degeneration is increased to 30 dB they get down to -85 and -110, respectively. It appears that they never quite make it back to their original very low values, although I can't say for sure because I did not degenerate them more than 30 dB. So, although the numbers are fairly low, and although the lower harmonics benefit more from the local degeneration, there is some truth to the observation that adding emitter degeneration increases upper harmonics, but it just needs to be interpreted carefully.
The conclusion I reached was that this effect of NFB is pretty much the same whether it is local degeneration or global NFB, and that what seems to count is the total amount of NFB.
Cheers,
Bob
Attachments
It is obvious that if to multiply a function by a function from itself the order goes up.
The problem "local vs global" almost leads to different results of frequency dependence and different behavior on transients.
The problem "local vs global" almost leads to different results of frequency dependence and different behavior on transients.
Wavebourn said:
Your first statement is correct, but one has to be very careful about drawing general conclusions from the observation. The analogous chart where the NFB is applied globally instead of by emitter degeneration looks pretty much the same. Every analysis depends on a careful balance of intuition and actually doing the numbers.
Cheers,
Bob
Bob Cordell said:
I recall this well, but decided that it was necessary to freeze the
voltage across the device in order to isolate the effect. As you
know, varying Vds or Vce introduces a subtle gain variation on its own.
So I cascoded a 2SK370 for constant Vds at 10V and measured
harmonics for a constant 1V output into 1 Kohm at an 8 mA bias
with varying degrees of degeneration.
What I saw was all harmonics declining with increasing
degeneration, although not initially in exact proportion.
When I find myself with more time, I intend to repeat the test
with enough precision to enable graphs with circles and arrows,
with a paragraph on the back of each one explaining what it's
about, and I'll also repeat the loop test with cascoding.
😎
Bob Cordell said:
In case of multiple local feedbacks you have by-products of modifications of each function by local feedback multiplied on each other, in case of a global feedback you have transfer functions of each stage multiplied then they are modified by a global signal. From mathematical point of view results will be very different. And they don't depend on who and how draw general conclusions from the observation.
Your "pretty much the same" probably don't include frequency dependence and transients... I can show you on fingers how and why, if you will be so kind to follow me...
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