John Curl's Blowtorch preamplifier part II

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Tin which one bank charges while the other powers the component. Unfortunately, according to JA, the changeovers "are accompanied by a just-audible click".
Of course, i think some precautions must be taken. Limiting the peak currents during the switch with a slope slower than the following regulation stages, as a start. ;-)
But you confirm my idea is not new.
 
For a lower power circuit the choice is supercaps or lithium ion batteries. I have some nice 25F 2.7V caps and some 3.3V 2.3AH cells to try. The advantage moved to the batteries when I found a nice card to manage 4 of them for a few dollars.

The supercaps would power a small preamp for 40 minutes without boosting. C x dV/i =T

C is in farads, dV is the voltage sag which I estimate 2 Volts to be acceptable, i is the current draw which for my preamps is around 20 mA. Time is in seconds.

So supercaps would actually do for a recording where they can be boosted in between recording.

The batteries would go for around 100 hours, a bit long for a recording session.
 
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Well he did then correct and say the click was only audible if you were standing next to the unit with no music playing! But agree the measured performance of some parts raised a few eyebrows!

Edit: for those who want to read it Vinnie Rossi LIO modular integrated amplifier Measurements | Stereophile.com
I remembered the audible click but not the correction, thanks. Of course it must be an electromechanical relay and an acoustical click, not a audible pop in the audio.

Yes, modules with significant problems were the rule rather than the exception. But what do you want for a mere 8k$ or so? The subjective reviewer went wild with praise over nearly everything --- I dare not quote from the purple prose. About the only criticism for him was that the manufacturer's name was inscribed a bit too prominently and flamboyantly on the front panel! Oh, and that the MOSFET power amp modules (895 a crack for 25W/ch) did indeed sound bad when pushed into clipping. But hey that arc-welding power supply made all the difference.

This sort of thing (the notion of the joys and utility of modularity) reminds me of the many times that managers try to retire the engineering staff, save for a skeleton crew, by insisting that everything's been invented already, so why don't we make "new" products out of a handful of standardized modules, and put them together like Lego assemblages. No more invention "on the critical path", no more launch delays and launch disasters. Of course it emerges in the cost studies that the addition of all the connectors and mezzanines and so forth adds a burden --- a good thing, since unless they are very good connectors indeed, they will tend to be among the weakest links in the systems thus assembled.

For high-end test equipment the approach can still make sense. I think audio, less so.

Brad
 
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Looks to me your idea is a power version of Linear Tech's switched capacitor IC - http://www.linear.com/docs/3572 , useful for getting 120dB CMRR.
Yes, the flying capacitor approach is a venerable one --- it must go back quite a ways. I seem to recall that reed relays were popular. And let us not forget the technique where the capacitor electrodes don't actually touch anything, used in the vibrating reed electrometer.

It's instructive to look at the signal-to-noise limitations of the switched-capacitor approach. I had someone tell me that there was no 1/f noise in such systems, because he asserted that you have to have current flow for such to manifest. He was the company's CTO, and they were pitching chips for realizing analog signal processing functions for customers who were unable to design with op amps and resistors an capacitors. Fail!
 
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For high-end test equipment the approach can still make sense. I think audio, less so.

Brad

I always wanted to build a modular preamp in the style of the Cello units, but as soon as I discovered the cost of 19" rack parts gave up on that. I did score an open rack from a skip at work, but the panels needed to make it something that could be used stand alone were beyond my budget. Every few years I think about resurrecting the idea, and park it again.
 
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I always wanted to build a modular preamp in the style of the Cello units, but as soon as I discovered the cost of 19" rack parts gave up on that. I did score an open rack from a skip at work, but the panels needed to make it something that could be used stand alone were beyond my budget. Every few years I think about resurrecting the idea, and park it again.
Those Cello pieces were beautiful. The rotary controls were quite special too. And Burwen's notion of a gentle EQ capability was spot on, I think.
 
Your nudeness, what does nearly mean in this context ?

Tested , a dual bridge/dual capacitor bank PS will show a very small ripple
on the un-loaded supply. More like a faster fluctuation as both bridges load
the same secondary.

A true 2 trafo dual mono would just possibly show up as a line fluctuation ,
with a slow rail fluctuation at the unloaded supply.

If we use >100db PSSR amps , the dual mono would technically have less
cross-talk. Audibly , I can't hear it.

OS
 
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yes I noticed that too.

But JA does damn with faint praise here "
Spuriae at the wall AC frequency and its odd harmonics are primarily due to magnetic interference, so as the LIO does not have a hefty power transformer and has that hefty ultracap supply, I was puzzled by this. I did check the possibility that my test equipment had some ferrous content, like the switches in the load resistor bank, but this did not appear to affect the LIO's measurements.
The noise and distortion performance of some amplifiers is approaching the point where factors like this can be seen. But the LIO's power amplifier module doesn't get close to equaling those amplifiers."
 
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yes I noticed that too.

But JA does damn with faint praise here "
Spuriae at the wall AC frequency and its odd harmonics are primarily due to magnetic interference, so as the LIO does not have a hefty power transformer and has that hefty ultracap supply, I was puzzled by this. I did check the possibility that my test equipment had some ferrous content, like the switches in the load resistor bank, but this did not appear to affect the LIO's measurements.
The noise and distortion performance of some amplifiers is approaching the point where factors like this can be seen. But the LIO's power amplifier module doesn't get close to equaling those amplifiers."
Ferrous Bueller's Day Off?

I'd be really embarrassed to have been involved in this product. But read the subjective review. One would suppose the reviewer was testing the auto-suck module.
 
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