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Old 30th December 2012, 06:09 PM   #71
bcmbob is offline bcmbob  United States
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Thanks Daniel. The bell wire is 1 mm on my calipers. I didn't see those Mouser caps this morning but that's not surprising I'll place an order later today. Using your crystal ball, can you foresee anything, other than the diodes, I should add preemptively? I have the LEDs and resistors for the PS indicator/safety mod.
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Old 30th December 2012, 06:29 PM   #72
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Quote:
Originally Posted by Jay View Post
What you can get with the complex FB setup is a high input impedance with minimal feedback and feedback resistance, without losing the drive. Contrary to it, your setup is strange, where you use 10K lowish input impedance and 60K highish feedback resistance.

Your 60K/2K7 FB resistances is probably not too low nor too high. It is problematic actually, to find a win-win setup. With the complex FB OTOH you can get better drive even with lower feedback.
When I tried to calc the average between the two examples, I came out with 330u with 1k2 vs 33k. There's a little bit more of that warm sound, but if you want the pretty treble and the warm sound together, that's a lot more like 100u with 3k3 vs 100k (or just barely slightly less than the 100k feedback resistor, like 180k||180K for 90K). So, one option is warm with regular treble and the second option is warm with airy treble. I'd suggest to test drive the second option (100u+3k3 vs 100k), which is not boring. However, I'm quite curious about your advanced feedback and will have to try it.
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Last edited by danielwritesbac; 30th December 2012 at 06:44 PM.
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Old 30th December 2012, 06:37 PM   #73
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Quote:
Originally Posted by bcmbob View Post
Thanks Daniel. The bell wire is 1 mm on my calipers. I didn't see those Mouser caps this morning but that's not surprising I'll place an order later today. Using your crystal ball, can you foresee anything, other than the diodes, I should add preemptively? I have the LEDs and resistors for the PS indicator/safety mod.
Possibly some favorable varieties (Panasonic FC, Nichicon FW, Nichicon KZ, etc. . .) that you can try for NFB caps and amplifier board power caps, especially since caps in that range are inexpensive and shipping is not.

And a pair of 0.22R 5w in case you want to adapt your power board to a CRC. Ordinary wirewound of 0.22R and less is not significantly inductive, so the inexpensive Xicon will do fine.

Also, a Nichicon ES 1u cap for a good "standard" hi-fi input cap performance, to have around for comparison purposes. If a fancy audiophile cap can't beat that Nichicon, well that's informative.

Fun and easy bypass caps (for improving NFB cap performance) include 22n and 10n polyester (easily found at the radio shack), and a selection of 0.47u and smaller Nichicon from Mouser.
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Last edited by danielwritesbac; 30th December 2012 at 06:40 PM.
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Old 30th December 2012, 06:45 PM   #74
bcmbob is offline bcmbob  United States
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O.K. I'll check what I have and fill as needed.
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Old 31st December 2012, 08:07 PM   #75
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Before parts swapping tinkering/tuning with the amplifier, I'd like to see an LED's, amber or red, per each rail on that power board and a drainer resistor per each rail. Parts: 2 led's and 4 of 5.6k resistors. Each LED needs its own resistor. Each rail also has a 5.6k drainer resistor. Of course you could do 2 led's per rail if you wanted to--they'll drain it down 1.9v per rail, shortly after power off. The combination creates a dual-duty drainer and a safety indicator, useful for. . . waiting for the LED's to go dark before tinkering with the amp. The drain is very mild (doesn't interfere with audio performance) and will take a little time for the LED's to go dark. The LED's are inexpensive and they might save your life.
Daniel, Just a double check. Is this correct?
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Old 31st December 2012, 08:27 PM   #76
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Daniel, Just a double check. Is this correct?
Well, that's really close to right, except that one of the LED's is reverse and won't light.
Remember 0v is 35v higher than negative rail.

Click the image to open in full size.
That's a pretty good drawing except that some types of LED's are marked backwards, such as white high brightness is sometimes opposite of amber and red. They can break if installed backwards, and so, you might want to buy several LED's rather than just two.

see also
Quote:
Originally Posted by danielwritesbac
Click the image to open in full size.
The spots for 3k3 are at least 1/2w resistors, the 10R is at least a 3w resistor, for longevity.

I do have a question: Do you have a center tap or a dual secondaries transformer?
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Last edited by danielwritesbac; 31st December 2012 at 08:34 PM.
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Old 31st December 2012, 09:33 PM   #77
bcmbob is offline bcmbob  United States
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This is for the kit build PS I already have. The new P2P stuff is on order. From your post it looks like the drain resistors belong before the caps - correct?

I just flipped the icon in the drawing program but am aware of the LEDs polarity thing. I have about two dozen LED on hand from other projects - red, green and amber - but I'm one resistor short that I'll get at RS tomorrow.
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Old 1st January 2013, 04:09 AM   #78
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Ah well, the drain resistors don't go on the AC side, since we don't need to drain the power company. On that board, drainer resistors go underneath, at C1 and C2.
notes:
When using 1/4W resistors, 3k3 drainer resistors can be made up of 3 of 10k (3/4W 3k3) at C1, AND 3 of 10k (3/4W 3k3) at C2.
Both rails have identical drain.
That's an extremely light/slow drain--good for audio quality, bad for fingers, and therefore requires adding LED warning indicators for better safety.
Click the image to open in full size.
Radio shack's thick variety pack of resistors are Xicon, with quite good quality and nice thick leads. To make the experience faster, I have a colored containers like the red container has resistors in the range of 1K to 9K, the orange container has resistors in the range of 10K to 99K, and then the search is not too long.

I have some of those yellow painted LED's and will go measure one of them to estimate an appropriate resistor value--painted LED's may have a voltage drop anywhere between 1.6v to 3.2v, so I'll go check. The schematic has the resistor value for a clear body red (1.7v) or amber (1.9v), However a white LED (~3v), regardless of the paint job would take a different resistor.

At the radio shack, don't forget the white canister of gel flux, because, using a toothpick, you can dob any non-shiny connection and re-heat to secure the connection (as shiny as a chrome Buick bumper). I'd never be able to do tight p2p perfectly without it. Their gel flux is also perfect to combat those nonstick gold plated vias/holes. It is also fairly vital for high quality re-work like component swapping.

Bob, here (attached below) is a layout method, for perfboard.
This easy construction method has three thick solid copper conductors. That photo below is not specifically your power supply, but really the point of these simple power supplies is a good head start with decent performance. And, then you accessorize to suit for a given transformer--all transformers have unique needs. The cap tank is universally useful but there are many rectifier and filter options, so I will attempt to re-draw it modular and this will take a little while.
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Last edited by danielwritesbac; 1st January 2013 at 04:16 AM.
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Old 1st January 2013, 06:23 AM   #79
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I didn't find the Radio Shack painted LED's but I did find several different models of colored body LED. They're all internally yellow LED's 1.86v to 2v range. You can check yours by just lighting one up (low current low voltage wall pack and don't forget the LED's series resistor) and measuring the forward voltage drop across the LED, with DC voltmeter.

Just enough current to light it is the diode knee voltage. Its slightly lower than the average figures, but knee voltage (switch-on voltage) is what we need for the calculator and for a bit of safety derating.

Next: LED Resistor Calculator
We put in 37 for voltage, and we put in LED diode drop of 1.86 (put your real figures here).
Current highpoint is led constant current datasheet figure multiplied by 0.43, which is max (and definitely try less, until the output just starts to decrease, which is the actual max). However, a 1/4w resistor is the real limiting factor here. Decrease current until the calculator's "safe pick" resistor is 0.250mw or less.
Result:
With 1.86 diode knee voltage, I get 4.27ma, or in other words. . .
8.2K resistors.
Of course, you could use 10k resistors--just slightly dimmer light.
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Last edited by danielwritesbac; 1st January 2013 at 06:27 AM.
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Old 1st January 2013, 06:16 PM   #80
bcmbob is offline bcmbob  United States
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The faster I am, the behinder I go!

I see one must be more precise when placing arrows I was just too lazy to unscrew the board at the time to take a photo. When I did the 0V - CT element is not so obvious as in the diagrams/examples. Before I build a bomb, where to connect the drain resistors at C1 & C2? It doesn't appear to be a two layer board from what I can see - though that may be deceptive. I don't see any links to the pads on either end.

Also. when using the LED resistor calculator it appears a pot/rheostat is needed to get "actual values". Is that correct.

We are a stretch away from the TDA chip fixes, but I (and hopefully others) appreciate the mini PS tutorials.
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