SX-1010 tuner
- Thread starter Maddart
- Start date
Here's a technical update to close out the thread:
maddart (mark) did a great job with all the work on the amplifiers, he was concerned about powering up the amps after working in the bias sections, complicated by the presence of two PAIR of outputs per channel and the need to watch the balance on them as the bias is adjusted.
I checked over the work carefully, and (with even then just a bit of GENERAL aprehension, although everything checked good) powered it up. Worked fine, adjusted fine, balance pretty good.
Next problem was the tuner reportedly cutting in and out, and mark targeted the power supply for a recap to try to cure it, but i advised holding off on the recap until the amps were known solid. You don't want TWO things going wrong at the same time IF you can help it. So I did the recap after the amps were done, with caps supplied by mark.
Unfortunately afterwards the tuner continued to cut out. After the cutout I found that the only thing that would restore the tuner function was cycling the power, NOT cycling the power to the am and fm sections with the function switch. It was the 13.8v power and could have been either the transistor or a 3.3 ohm series resistor with paint-insulated leads that was hitting an electrically isolated heatsink, because the REST of the circuit was a base drive zener voltage and it was fine. So BOTH the transistor and resistor were replaced with more robust new versions.
Tuner ran for over 10 hours without a burp.
In the course of checking the 1010 out, it was found that the phono amp right channel was popping violently every few seconds. Since I have had good results with using low noise ksa992 and ksc1845 transistors (and they WERE appropriate for the circuit) I replaced the 8 in the phono amp, and two tantalum input caps (they could have been in the process of failing). maddart will do the rest of the phono caps at his convienence. The phono amp gain (41 vs 35.5 dB) , distortion ( 0.02% or less vs. 0.05%) and s/n ratio (70 db or better, setup induced low level hum) were at or better than new specs.
maddart (mark) did a great job with all the work on the amplifiers, he was concerned about powering up the amps after working in the bias sections, complicated by the presence of two PAIR of outputs per channel and the need to watch the balance on them as the bias is adjusted.
I checked over the work carefully, and (with even then just a bit of GENERAL aprehension, although everything checked good) powered it up. Worked fine, adjusted fine, balance pretty good.
Next problem was the tuner reportedly cutting in and out, and mark targeted the power supply for a recap to try to cure it, but i advised holding off on the recap until the amps were known solid. You don't want TWO things going wrong at the same time IF you can help it. So I did the recap after the amps were done, with caps supplied by mark.
Unfortunately afterwards the tuner continued to cut out. After the cutout I found that the only thing that would restore the tuner function was cycling the power, NOT cycling the power to the am and fm sections with the function switch. It was the 13.8v power and could have been either the transistor or a 3.3 ohm series resistor with paint-insulated leads that was hitting an electrically isolated heatsink, because the REST of the circuit was a base drive zener voltage and it was fine. So BOTH the transistor and resistor were replaced with more robust new versions.
Tuner ran for over 10 hours without a burp.
In the course of checking the 1010 out, it was found that the phono amp right channel was popping violently every few seconds. Since I have had good results with using low noise ksa992 and ksc1845 transistors (and they WERE appropriate for the circuit) I replaced the 8 in the phono amp, and two tantalum input caps (they could have been in the process of failing). maddart will do the rest of the phono caps at his convienence. The phono amp gain (41 vs 35.5 dB) , distortion ( 0.02% or less vs. 0.05%) and s/n ratio (70 db or better, setup induced low level hum) were at or better than new specs.
Last edited:
marantzfan
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You are an absolute asset to this comminity Mark. Thanks for doing what you do for us!:thmbsp:
Phono hint: The 2N4401 and 2N4403 are cheap as dirt, and quiet as a churchmouse (but the KSA992 and the KSC1845 are peachy as well, and probably give better input impedance). I too have had lots of problems with those 2SA725's Pioneer used.
Edit: I had no idea the KSA992 and KSC1845 were so cheap from Mouser. I just ordered a good sized pile of them. :thmbsp:
Edit: I had no idea the KSA992 and KSC1845 were so cheap from Mouser. I just ordered a good sized pile of them. :thmbsp:
They've got a lot higher Vceo, and when I get the chance I'll A/B (Left/Right really) a set of 2n4401/2n4403 versus ksa992/ksc1845 .
I've got a nice shielded box with battery power I use to run raw phono amp boards inside. That plus the AA501's milli/microvolts range might fill the bill for some repeatable results. (yes, I now have an sg505, aa501 combination, no gpib but what the hay)