RIAA Inaccuracies

[tmazz]

Perhaps my editing screwed up the message. My point was that the rating of a resistor is within that % over the entire lifetime of the resistor. So theoretically if a resistor has an x% tolerance it can come off the assembly line at +x% of its rated value and shift to -x% overtime and still be with specs.  My experience with this has been with more run of the mill resistors. It seems from your later posts that you have not experienced this with the  ones you have used.  If the is the case I certainly yield to your expertise in that area and will modify my comment to say that unless you use carefully selected high quality parts, value shifts can cause inaccuracies over time. (And that does not have to mean super expensive tight tolerance resistors,  just high quality)

And on I certainly hope you did not take any of what I said as a negative comment on your posts. Quite the opposite I was trying to highlight  what I saw as at least one of the reasons why it is so difficult to get dead on right as opposed to just throwing something together that is just close enough to get out the door and on the market. Guys like you and Dave really sweat the details and are few and far between. One of my biggest career regrets is that although I started out as an EE, I quickly got tracked into the management and financial end of the business and although I used my engineering knowledge through the day I retired I actually got to spend very little time doing actual design work.  As a result I know
W enough to be dangerous. 

Even though I don’t have the level of detailed that you guys do, I know enough to have a deep appreciation for your expertise and what it took for you to get there. 

[steve]

Perhaps my editing screwed up the message. My point was that the rating of a resistor is within that % over the entire lifetime of the resistor. So theoretically if a resistor has an x% tolerance it can come off the assembly line at +x% of its rated value and shift to -x% overtime and still be with specs.  My experience with this has been with more run of the mill resistors. It seems from your later posts that you have not experienced this with the  ones you have used.  If the is the case I certainly yield to your expertise in that area and will modify my comment to say that unless you use carefully selected high quality parts, value shifts can cause inaccuracies over time. (And that does not have to mean super expensive tight tolerance resistors,  just high quality)

And on I certainly hope you did not take any of what I said as a negative comment on your posts. Quite the opposite I was trying to highlight  what I saw as at least one of the reasons why it is so difficult to get dead on right as opposed to just throwing something together that is just close enough to get out the door and on the market. Guys like you and Dave really sweat the details and are few and far between. One of my biggest career regrets is that although I started out as an EE, I quickly got tracked into the management and financial end of the business and although I used my engineering knowledge through the day I retired I actually got to spend very little time doing actual design work.  As a result I know
W enough to be dangerous. 

Even though I don’t have the level of detailed that you guys do, I know enough to have a deep appreciation for your expertise and what it took for you to get there. 

No sweat on this end Tom. All is good here. I appreciate the clarification and your findings and I have also noticed variations of a questionable brand or two; but been too long to remember. I have not had any problems with mills except a very rare noisy 5 watters. All seems to be well with copper leaded Resista, Holcos, Vishay, but I did have a little problem with the new PRPs with initial tolerance variations. Haven't had enough time with them for a longevity study either. I stay away from Caddock 132s, a metal oxide type, and a bland sound.

For general consumption, A + to - 1% variance will alter the RIAA in my circuit in the less than 0,1 dbs range. Three resistors are crucial in the RIAA network, plate, R1, and R2, as listed in my link based on Stanley's calculations. The good resistors seem to always measure within 0,25% or so using a Textronix meter. Resista, Holco, vishay resistors seem to measure less than 0,25% between dozens of resistors, pretty reliable. I see Michael Percy has Vishays for $12.00.

Thank you for the appreciation Tom. I cannot calculate all the R&D, sophisticated, proprietary listening test since 1980 or sooner. And for no pay; out of my own pocket. I have even tested if wires transmit in the audio realm and at what frequencies.

Cheers and all the best Tom.

steve

[tmazz]

Just so you know where I'm coming from, here is the story behind the resistor shifts. Back in the first generation of CD players there was a resistor in the transport across which a voltage was read that corresponded to the position of the laser. This resistor has to be an exact value to properly report the position but the first generation machines were selling in the $1000+ range so they could afford to put a high priced precision resistor in that spot. Fast forward a year or two and CD players had already dropped into the $150 price range. At that retail price the manufacturers could not afford to use those expensive resistors so instead they put in a cheap resistor and used a trim pot to dial the combination to the exact number of ohms they needed. At the time I had a frind who was a repair tech at one of the local brick and motor stereo shops. He told me that about a year after this new generation of CD player came out the started to get flooded with repairs of units that had begun to mistrack. The advice he got from the manufacturers on the problem was that the feedback resistor had shifted in value during break-in and all he needed top do was to adjust the trim pot to bring the combo back into spec. His advice to me when I bought a CD player during that time frame was to put in a disc when I first got it, set the machine for continuous repeat and let it play for a week or two strait the break in that resistor so if it shifted (and they didn't all shift out of spec) it did so before the player was out of warranty.

So I just wanted you to know that I didn't pull the resistor shift idea out of my left ear, it came from real world experience, not only of myself, but of a technician who probably spent 100s of hour making repairs on CD player that had the very problem I was talking about.

I am however glad to hear that you have not experience the same kind of thing. Maybe it is a thing of the past and there was some kind of factory flaw in resistors back then and also I think you would be much more picky about who you source things from than a mass market manufacturer like Sony or Sharp who would be planning production runs of literally millions of units.

[steve]

Just so you know where I'm coming from, here is the story behind the resistor shifts. Back in the first generation of CD players there was a resistor in the transport across which a voltage was read that corresponded to the position of the laser. This resistor has to be an exact value to properly report the position but the first generation machines were selling in the $1000+ range so they could afford to put a high priced precision resistor in that spot. Fast forward a year or two and CD players had already dropped into the $150 price range. At that retail price the manufacturers could not afford to use those expensive resistors so instead they put in a cheap resistor and used a trim pot to dial the combination to the exact number of ohms they needed. At the time I had a frind who was a repair tech at one of the local brick and motor stereo shops. He told me that about a year after this new generation of CD player came out the started to get flooded with repairs of units that had begun to mistrack. The advice he got from the manufacturers on the problem was that the feedback resistor had shifted in value during break-in and all he needed top do was to adjust the trim pot to bring the combo back into spec. His advice to me when I bought a CD player during that time frame was to put in a disc when I first got it, set the machine for continuous repeat and let it play for a week or two strait the break in that resistor so if it shifted (and they didn't all shift out of spec) it did so before the player was out of warranty.

So I just wanted you to know that I didn't pull the resistor shift idea out of my left ear, it came from real world experience, not only of myself, but of a technician who probably spent 100s of hour making repairs on CD player that had the very problem I was talking about.

I am however glad to hear that you have not experience the same kind of thing. Maybe it is a thing of the past and there was some kind of factory flaw in resistors back then and also I think you would be much more picky about who you source things from than a mass market manufacturer like Sony or Sharp who would be planning production runs of literally millions of units.

I don't doubt your experience with resistors. I have had two particular cd players, both the same model, that had the problem you described. The third one, same model, is still working, but I don't use it often. Will see if time causes the same drifting and subsequent problem.

Cheers and thanks Tom.

steve