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Old 29th January 2013, 07:46 AM   #8301
dvv is offline dvv  Serbia
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Quote:
Originally Posted by fas42 View Post
dvv, I am surprised ... projects for electronic volume control are extremely thin on the ground; these were what I found on a first scan: MiniVol PGA2320 Volume Control - error404's Audio DIY Endeavours and a thread mentioning others, Looking for a PGA2320 PCB. All use processors to do the fiddly stuff, but the first one, MiniVol, seems to be well done - the processor is put to sleep when not needed - , people have had success with it.

Personally, I have no hangups about digital volume controls, they give me the sound that I'm after. In that live vs. playback clip, the "diluted" quality is exactly what I find mechanical, analogue, gives; hence I steer well away from it ...

Frank
Frank, most DIYers are put off the instant you utter the word "processor".

It appears we've been looking for solutions in similar places.

I dug up data from TI's site on chip power amps. I am currently mulling over TI's TAS 5630B, the well known LM 3886 and LM 4780. At first glance, they seem to be up to it all the way, my only quibble being their relatively low voltage slew rates. I honestly cannot say 20 V/uS is too low, but I would have liked to have seen something like 40 V/uS; on the other hand, this number corresponds well to their power levels, and IS above the bare minimum of 0.5 V/uS per every peak Volt of output with a reasonable margin.

I am particularly interested in a "double trouble" version, i.e. using them in both parallel and bridged verson. Bridging should theoretically produce four times the power, but in pratice this is more like three times the power, as there are always losses. Nevertheless, having well over 100 Wrms per channel is handy, even if you never actually need it all, but you do need to parallel them to restore good current delivery.

Another option would be Nat Semi's driver chips, LME 49811 bipolar and 48833 MOSFET. This approach has a very long tradition with Nat Semi, elders among us may remember their 381-xxx chip from the late 70ies, which did exactly the same, and did it well so long as you didn't ask for too much voltage gain and stuck to 26 dB maximum.

Much data to absorb.
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Old 29th January 2013, 10:20 AM   #8302
fas42 is offline fas42  Australia
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Originally Posted by dvv View Post
I dug up data from TI's site on chip power amps. I am currently mulling over TI's TAS 5630B, the well known LM 3886 and LM 4780. At first glance, they seem to be up to it all the way, my only quibble being their relatively low voltage slew rates. I honestly cannot say 20 V/uS is too low, but I would have liked to have seen something like 40 V/uS; on the other hand, this number corresponds well to their power levels, and IS above the bare minimum of 0.5 V/uS per every peak Volt of output with a reasonable margin.

I am particularly interested in a "double trouble" version, i.e. using them in both parallel and bridged verson. Bridging should theoretically produce four times the power, but in pratice this is more like three times the power, as there are always losses. Nevertheless, having well over 100 Wrms per channel is handy, even if you never actually need it all, but you do need to parallel them to restore good current delivery.
Using a single National chip amp worked well for me, with a really solid power supply to back it up. The biggest "flaw" was that when driven really hard, the chip's internal protection mechanism cut in - from a soprano's long held note, of all things! So, going the 4 way sounds good to me; just make sure you use plenty of good heatsinking and beef up the supply - at the prototype stage, when the heatsink wasn't doing its job 100% my unit's chip would overheat at the drop of a hat ...

Frank
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Old 29th January 2013, 12:36 PM   #8303
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I have just been doing a small job and have used a 4017 decade counter ( CMOS from 1968 ! ) . It is described in one makers notes as an electronic Mobius loop . It got me asking myself would not a feedback amplifier be a Mobius loop if so ? the 4017 is a cascade of flip-flops with a final NOT gate that inverts the output to start the counting again . Mobius is a 2D object in a 3 D word ( or even 1D in concept ) . I read recently that space-time might be simlar and might explain Quantum phsiscs rather well . Putting that to one side as it is of no immediate importance could there be something to criticize in feedback amps if so due to how the loop works if Mobius ?
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Old 29th January 2013, 12:39 PM   #8304
dvv is offline dvv  Serbia
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Don't you worry, Frank, I do have a solid stock of very efficient heat sinks (0.46) and I do plan on using them generously. I am in the habit of being an optimist with experience, i.e. a pessimist regarding cooling problems. You should see my PC, it's full of fans blowing each and every way, but it sure keeps the CPU cool enough. Check on it routinely every day.

I am not sure what you meant by "solid power supply". It's somewhat subjective, I find. To me, this means at least two 10,000 uF caps in parallel for every supply line used, usually with the same type, same make 4,700 uF cap thrown in to help out with the speed (a quirk Sony has been using forever, and while it may not help, it sure can't hurt). Backed up by a say 500 VA toroid per channel - haven't done any calculations, so this is an off hand figure. Point is, I like 'em big.

Off the cuff, enough is when the VA rating of the toroid matches what I would expect in Watts into 2 Ohms.

The true dilemma here is whether to use an all-in-one chip, or the one which does almost everything, but expects to drive output transistors. That way, one could scale the output stage to what one wants - even Wayne could. Given that I already have a sizeable stock of power devices, I do have to think about it. Discrete devices do have the advantage of using the heat sink much more efficiently that the all-in-one devuices do, even if I'd have to use four per channel, thus also spreading them around the heat sink(s).
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Old 29th January 2013, 10:42 PM   #8305
fas42 is offline fas42  Australia
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Originally Posted by nigel pearson View Post
Putting that to one side as it is of no immediate importance could there be something to criticize in feedback amps if so due to how the loop works if Mobius ?
Where feedback can go wrong is if it's treated as an afterthought, a by-the-way. Either don't use FB at all, or if you do use it go 100% in the effort. The way to think of it is that the FB is the most important thing to get right in an amp that does overtly use it. In high open loop gain opamps the behaviour in an ideal unit is completely set by the parts in the FB loop, the actual internal behaviours, idiosyncrasies of the opamp are completely swamped by the action of the FB mechanism.

Frank
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Old 29th January 2013, 10:56 PM   #8306
fas42 is offline fas42  Australia
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Originally Posted by dvv View Post
I am not sure what you meant by "solid power supply". It's somewhat subjective, I find. To me, this means at least two 10,000 uF caps in parallel for every supply line used, usually with the same type, same make 4,700 uF cap thrown in to help out with the speed (a quirk Sony has been using forever, and while it may not help, it sure can't hurt). Backed up by a say 500 VA toroid per channel - haven't done any calculations, so this is an off hand figure. Point is, I like 'em big.
I probably should have used the word "stiff", . To me, the power supply is everything to making the amp do dynamics well, so how I went about it was using a 300VA per side, extensive smoothing by caps going into regulation circuitry, so that heavy bass didn't cause the rails to sag, and then very extensive, extremely local high frequency decoupling on the chip amp itself. Completely OTT for a 60W amp, perhaps - but it worked. I have an old Perreaux 2150B monster, and the chip amp easily knocked that fellow off the perch.

A side benefit was tremendous energy reserves, I could pull the power cord out of the wall while playing at normal volume, and still get clean music for up to 5 minutes later ...

Frank

Last edited by fas42; 29th January 2013 at 10:59 PM.
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Old 29th January 2013, 11:54 PM   #8307
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I had a 2150B sometime ago , nice case , great boat anchor .......

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Old 30th January 2013, 12:31 AM   #8308
fas42 is offline fas42  Australia
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I had a 2150B sometime ago , nice case , great boat anchor .......

Is recoverable, like much gear back then the power supplies were not sorted out as well as would be done now. I went through the unit with a strong broom and it's now very decent. Put it this way -- it saw off most gear back then in raw form, and currently would keep back most of what I heard at the recent hifi show. I had a good listen to the Technical Brain monoblocks at the show, and it would be in the same ball park ...

Frank
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Old 30th January 2013, 04:09 AM   #8309
gootee is offline gootee  United States
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Originally Posted by dvv View Post
Frank, most DIYers are put off the instant you utter the word "processor".

It appears we've been looking for solutions in similar places.

I dug up data from TI's site on chip power amps. I am currently mulling over TI's TAS 5630B, the well known LM 3886 and LM 4780. At first glance, they seem to be up to it all the way, my only quibble being their relatively low voltage slew rates. I honestly cannot say 20 V/uS is too low, but I would have liked to have seen something like 40 V/uS; on the other hand, this number corresponds well to their power levels, and IS above the bare minimum of 0.5 V/uS per every peak Volt of output with a reasonable margin.

I am particularly interested in a "double trouble" version, i.e. using them in both parallel and bridged verson. Bridging should theoretically produce four times the power, but in pratice this is more like three times the power, as there are always losses. Nevertheless, having well over 100 Wrms per channel is handy, even if you never actually need it all, but you do need to parallel them to restore good current delivery.

Another option would be Nat Semi's driver chips, LME 49811 bipolar and 48833 MOSFET. This approach has a very long tradition with Nat Semi, elders among us may remember their 381-xxx chip from the late 70ies, which did exactly the same, and did it well so long as you didn't ask for too much voltage gain and stuck to 26 dB maximum.

Much data to absorb.
Just a thought, and I realize it would double some "bad" things, too, but if we "stacked" the outputs of two such 20V/us chipamps, or arithmetically summed them, then the combination would achieve 40 V/us.
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Old 30th January 2013, 04:40 AM   #8310
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Yep, it would. Needs fully floating PSUs though and then probably best to have a fully integrated DAC+AMP because input common mode range and rejection becomes an issue too. With digital in, the input isolation can be as near to perfect as you'd like to make it.
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