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Old 14th March 2012, 06:39 PM   #3431
SY is offline SY  United States
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Originally Posted by dvv View Post
The problem with LEDs is that they are rather different between them, depenind which you happen to have.

I've been buying Avago and Lumex. Very consistent.
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Old 14th March 2012, 06:44 PM   #3432
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I routinely use LEDs from Chicago Lamps for bias purposes. A bag of ~200 left.
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Old 14th March 2012, 09:02 PM   #3433
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Originally Posted by Wavebourn View Post
I routinely use LEDs from Chicago Lamps for bias purposes. A bag of ~200 left.
Bought a grab bag of 200 to build a "Red Light District" voltage bias tube amp. Man were they all over the place. I think I paid $1.50 for all, so it was worth sorting them to get strings of 11 Volts. Got sidetracked and did not complete it. What I have learned, I probably will go a different direction. It is a "Mengus" 6P1 amp I hacked up. Cheap as they come. I learned a lot about tubes. IIt is about time to just sell it and my HK.
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Old 14th March 2012, 09:03 PM   #3434
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"All over the place" in what way?

For my last few RLD builds, I just used Avago HLMP6000s right out of the bag. Worked perfectly.
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Old 14th March 2012, 09:07 PM   #3435
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Originally Posted by john curl View Post
Studer made great transports, but relatively lousy electronics, getting worst with each succeeding generation. Amazing, but true.
I 100% agree with you, Mr.Curl. They threw baby out with the bath water, when trying to fix phase response and also making the machines more "user friendly" with the help of numerous op-amps and logdacs. It still amazes me how people sing praise songs to these machines based on the looks only...
By the way, Fred Thal would love to see you on the Studer mailing list
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Old 14th March 2012, 09:16 PM   #3436
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So some of you lot have spent your entire lives designing and building audio amplifiers..? But never actually designed one that you could actually say was good enough? I'm just trying to imagine a different field of engineering where someone would spend decades re-hashing a basic design without ever getting it to work properly!

(slightly tongue-in-cheek, but not completely!)
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Old 14th March 2012, 09:34 PM   #3437
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Originally Posted by ThorstenL View Post
Hi,



All of this shows you how a devices parasitics change if voltage cross or current through the device change.

They allow you to derive the various parasitic resistance (early effect induced limited collector impedance, Beta changes, Changes of the internal emitter and base impedance as well as the parasitic capacitances), so they allow to tell you what goes wrong and where if you change voltages and/or currents (which you will as a transistor that works only static is not useful in an amplifier)...

Of course you can just blissfully ignore all the non-linear parasitics and throw a ton of looped feedback around the Amp instead...



That could be related to the fact that Motorola Semiconductors was spun off and is now called "On-Semi", just as Philips Semiconductors is now NXP and Hitatchi Semiconductors is now Renesas...

Ciao T
Sanyo bought Motorola? Guess it is better than Wang-Chung, but it seems the end result is the same. I new NXP as they say so. I did not know Renesas either. Hitachi completed selling their disk division to WD this week. Interesting.

Not ready to plug and pray yet, as I think I can understand a little more. My basic instinct is that loop feedback is how you fix what you can't in each stage. It is easier not to make a mess than to clean it up, but it will still need a bit of polishing. My level of understanding this could really only suggest my instinct means I need a shower.

I was playing in Spice with CCS's. Wow, not quite as constant as I had been lead to believe and way off a Spice model CCS. A thought occurred to me. Should not the CCS, and for that matter CM, be several times faster than the signal circuit? The other thing that surprised me was when doing AC analysis in the CCS, how it varied across the bandwidth a lot more than I expected. What I think this is telling me is how the gain of the transistor varies over frequency. I am going to play with different transistors in the model ( great how they don't blow up) and see what this teaches me about the topics I don't understand, all in the H parameters I guess. Baby steps. Waiting on Amazon. Books shipped. I need to fix my friends Kenwood. What a PITA to get into it. The phone stage is in a box behind the front panel.
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Old 14th March 2012, 10:31 PM   #3438
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Originally Posted by SY View Post
"All over the place" in what way?

For my last few RLD builds, I just used Avago HLMP6000s right out of the bag. Worked perfectly.
Voltage drop. I wanted to get each string within 50mV or so to prevent current hogging. I screened them at the current they would see and if I remember, as much as 30 mV difference. It was well over a year ago. I put the project aside when I remodeled by office. (Stickely style). Never pulled it back out.

You liked the result? Maybe I'll finish mine. I changed the inputs to 6ay7's, improved part quality and learned how to set the bias and balance with a spectrum analyzer. It is better, but was still by far the worst amp I owned for my wife's critical hearing test. Of course, now I understand the only thing worse that a BJT driven by a hi-z load is a tube. I should listen with a preamp and the input 50K pot all the way up, all screaming 6W of it. I bought different outputs, but I don't even remember what they are. I guess I got dissinterested in tubes. I have only heard one modern amp, a Cary. Highly distorted but in a very musical way. I can see why many would want to live with them.
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Old 14th March 2012, 10:36 PM   #3439
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Originally Posted by CopperTop View Post
So some of you lot have spent your entire lives designing and building audio amplifiers..? But never actually designed one that you could actually say was good enough? I'm just trying to imagine a different field of engineering where someone would spend decades re-hashing a basic design without ever getting it to work properly!

(slightly tongue-in-cheek, but not completely!)
I've designed several, but they did not go beyond prototypes. Now it is time to start some production.

"Time to throw stones ended, it is the time to collect stones".
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Last edited by Wavebourn; 14th March 2012 at 10:42 PM.
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Old 14th March 2012, 10:39 PM   #3440
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Set up properly (and built as shown), the distortion is negligible- not in the triple-ought class of the best solid state designs, but low enough (double-ought). The raison d'etre is overload recovery- it's much harder to hear clipping when it doesn't choke things for a few hundred milliseconds after each event.

30mV in a string is not a lot of difference (a couple percent) and doesn't change the array performance significantly. If it bothers you, put a 4R (or so) resistor in series with each string to balance things out. That adds less than an ohm of impedance at the cathode, which is as close to nil as you need to be.

Quality of the output iron is everything in a good tube amp.
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