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tomp
PostPosted: September 2nd, 2016, 1:40 pm 
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Joined: February 28th, 2013, 3:31 pm
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The construction session for the preamp and power supply is on for Saturday the 10th. If anyone in addition to Jeff wants to attend please let me know and I'll provide location and time details by private mail. I'll be discussing OP Amp basics, the differences in PS design for OP Amps vs other types of circuits, OP Amp limitations, servos, differences between active and passive RIAA equalization, and measurement techniques. I am in the process of re-doing my old pre for the new board. I'm enclosing a photo and you can see there is now a lot more room with the new PCB. Most of the case is now taken up with the PS. I just got the new Alps volume control pot to replace the old stepped attenuator that was intermittent.

Tom


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SoundMods
PostPosted: September 2nd, 2016, 3:47 pm 
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Joined: July 24th, 2015, 4:17 pm
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Location: Parkville, Maryland
Hi Tom!

As it turns out -- most I.C.s are rated to 85-degrees C. THAT'S HOT!! It says a lot about the "wiggle room" manufacturers use to cover their asses because in your case the I.C. still worked.

My claim to fame many decades ago was when I had a PS Audio pre-amp that I was "hot-rodding." I had the board out to enable working on it. It was DC-coupled so after some changes I stood the powered up board up so I could get to a point in the circuit to measure output off-set. As I raised the board I heard what turned out to be a piece of cut-wire play Pachinko among the components on the other side of the board. It landed across a transistor with a white flash. What added insult to injury was that the white flash generated a white/gray mushroom cloud like a sub-miniature nuclear explosion. YIKES!!!!

I was horrified!! :oops: But hey -- if you're not making mistakes you're not working -- RIGHT?

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tomp
PostPosted: September 3rd, 2016, 5:49 pm 
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You've got that right. I guess you can say that your experience can be measured in part by the number of dead devices you have fathered.

Tom
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Cogito
PostPosted: September 4th, 2016, 9:24 am 
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I am interested in learning. Count me in.
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SoundMods
PostPosted: September 4th, 2016, 11:43 am 
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Location: Parkville, Maryland
My worst audiophile experience was with a Futterman moving-coil head-amp. I hot-rodded it (of course -- that's what I do) -- when it worked it was sublime. Futterman based his design on Nuvistors -- a good choice -- YES? Hell no! After four sets of tubes going noisy I got so pissed off I went outside and dumped it in the garbage can and had no regrets. The ceramic seals on Nuvistor tubes have only to get a microscopic crack and when just a couple of molecules of air gets in even the getter is no match for a leak.

Makes one wonder what Conrad Johnson's experience with Nuvistors was. Noise is certainly the enemy of LP playback.

A Sony CD player was great until I either overheated the DAC chip or let a static charge slip to it (I couldn't feel anything -- but it was suspect). Sony used the Phillips Dynamic Element Matching DAC that had a brace of .1-ufd caps. A major POOGE mod to anything Phillips then was to replace the DAC caps (usually monolythic ceramics) with some nice polypropylene of polycarbonate caps. By that time in audio history outboard DACs became of age and the unit became a nice reliable transport. Waste not -- want not.

Over time experience teaches one to be careful and deliberate when working on this stuff. Like with carpentry -- measure twice -- cut once. Electronics -- evaluate three times -- then solder.

My best tool is a 5-power jewelers' head-set stereo magnifier. That way I get up close and personal to the job at hand. :character-oldtimer:

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randy warren
PostPosted: September 4th, 2016, 12:06 pm 
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Joined: March 12th, 2013, 1:49 pm
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Tom, if time allows me, I would like to come over and get educated, thanks!
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