SX-1010 buzz

Continuation of this thread:
http://audiokarma.org/forums/showthread.php?t=297656

Here is a video of the buzz:


Buzz is from pre-amp section, as it is quiet with jumpers removed.
Amp boards rebuilt with new transistors and caps
Output transistors replaced
Amp brought up and buzz noticed
Protection board rebuilt
Power supply board rebuilt
Buzz remains regardless of power plug orientation
Buzz gets louder with volume pot

And volume pot replaced, correct?

meanwhile I must get audio out working on the(my) computer that can actually display video.... (my "usual" computer is an XP PRO 550mhz P3 - useless for video, only lately did I get something faster, and it's not fully integrated in yet)

With what we have done so far, and the time spent so far, it might be worth recapping and re transistoring the control amp.

Did I post that list of parts on this (excuse me, the old) thread? It's about 6 bucks worth of parts, 28 caps and 8 transistors, although it's the 725's and the input stage power filter I am suspicious of.

markthefixer said:

And volume pot replaced, correct?

meanwhile I must get audio out working on the(my) computer that can actually display video.... (my "usual" computer is an XP PRO 550mhz P3 - useless for video, only lately did I get something faster, and it's not fully integrated in yet)

With what we have done so far, and the time spent so far, it might be worth recapping and re transistoring the control amp.

Did I post that list of parts on this (excuse me, the old) thread? It's about 6 bucks worth of parts, 28 caps and 8 transistors, although it6's the 725's and the input stage power filter I am suspicious of.

Click to expand...

Volume pot was replaced and it did not change the buzz problem.

You posted the cap list for the control board, but not transistors.

Is it worth it to go back to ensure DC AND AC values on the bridge rectifiers? I am going to borrow a better DMM, and those rectifiers are available now.

Also let me know what you think if you can find a way to view the video

EDIT:
Found the transistors, here is the complete list:
control amp
awg-027 c1 0.33 25 cssa 0.33 50 667-ECQ-V1H334JL 0.15
awg-027 c2 0.33 25 cssa 0.33 50 667-ECQ-V1H334JL 0.15
awg-027 c7 100 10 cea 100 25 647-UPW1E101MED 0.26
awg-027 c8 100 10 cea 100 25 647-UPW1E101MED 0.26
awg-027 c13 2.2 25 cssa 2.2 50 647-UKL1H2R2KDDANA 0.21
awg-027 c14 2.2 25 cssa 2.2 50 647-UKL1H2R2KDDANA 0.21
awg-027 c15 4.7 35 cea 4.7 50 647-UPW1H4R7MDD 0.14
awg-027 c16 4.7 35 cea 4.7 50 647-UPW1H4R7MDD 0.14
awg-027 c23 4.7 25 ceanl 4.7 25 647-UKL1E4R7KDDANA 0.17
awg-027 c24 4.7 25 ceanl 4.7 25 647-UKL1E4R7KDDANA 0.17
awg-027 c25 10 16 cea 10 16 647-UKL1C100MDDANATD 0.08
awg-027 c26 10 16 cea 10 16 647-UKL1C100MDDANATD 0.08
awg-027 c29 100 10 cea 100 25 647-UPW1E101MED 0.26
awg-027 c30 100 10 cea 100 25 647-UPW1E101MED 0.26
awg-027 c31 4.7 35 cea 4.7 50 647-UPW1H4R7MDD 0.14
awg-027 c32 4.7 35 cea 4.7 50 647-UPW1H4R7MDD 0.14
awg-027 c39 4.7 25 ceanl 4.7 25 647-UKL1E4R7KDDANA 0.17
awg-027 c40 4.7 25 ceanl 4.7 25 647-UKL1E4R7KDDANA 0.17
awg-027 c41 10 16 cea 10 16 647-UKL1C100MDDANATD 0.08
awg-027 c42 10 16 cea 10 16 647-UKL1C100MDDANATD 0.08
awg-027 c45 100 10 cea 100 25 647-UPW1E101MED 0.26
awg-027 c46 100 10 cea 100 25 647-UPW1E101MED 0.26
awg-027 c47 2.2 25 cssa 2.2 50 647-UKL1H2R2KDDANA 0.21
awg-027 c48 2.2 25 cssa 2.2 50 647-UKL1H2R2KDDANA 0.21
awg-027 c49 47 16 cea 47 50 647-UPW1H470MED 0.25
awg-027 c50 47 16 cea 47 50 647-UPW1H470MED 0.25
awg-027 c51 47 16 cea 47 50 647-UPW1H470MED 0.25
awg-027 c52 47 16 cea 47 50 647-UPW1H470MED 0.25

Q1, q2 2sa725 35v 0.1a 0.2w 500hfe 100mhz
512-KSA992FBU (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea

Q3, Q4, Q5, Q6, Q7, Q8 2sc1312 35v 0.1a 0.2w 500hfe 150mhz
512-KSC1845UBU (ln)to-92 ecb 120v .05a .5w 100mhz 150-800hfe $0.05 ea

Beat me to it!!

Well, it would be a good idea to revisit the regulated power supply voltages, to check the AC component of the DC voltages, to see if the regulators are doing their jobs. BUT, I really don't expect to find anything there...

one thought is to make some zero ohm shorting RCA plugs, and short the different RCA jacks in the back to eliminate those line's possible internal/external noise pickup.

And what do you mean about:

and those rectifiers are available now.

Click to expand...

It made me think about D1 through D7 on the AWR054 power supply board, they are original? They could be replaced by 1n4004 (512-1n4004 $0.07 ea) in case one or more has a problem and is generating noise that is being picked up by the SECOND most sensitive part of the receiver... (the MOST sensitive is the phono input, how's THAT doing???)

markthefixer said:

Beat me to it!!

Click to expand...

You work hard enough!

ok, read my last in-progress post, and I have to get going on off-line things for now. BBL.

markthefixer said:

Beat me to it!!

Well, it would be a good idea to revisit the regulated power supply voltages, to check the AC component of the DC voltages, to see if the regulators are doing their jobs. BUT, I really don't expect to find anything there...

one thought is to make some zero ohm shorting RCA plugs, and short the different RCA jacks in the back to eliminate those line's possible internal/external noise pickup.

And what do you mean about:



It made me think about D1 through D7 on the AWR054 power supply board, they are original? They could be replaced by 1n4004 (512-1n4004 $0.07 ea) in case one or more has a problem and is generating noise that is being picked up by the SECOND most sensitive part of the receiver... (the MOST sensitive is the phono input, how's THAT doing???)

Click to expand...

The shorting plugs on the Aux in make a huge difference. Still some slight buzz, but really only at certain spots on the volume pot.

The Phono inputs hiss, and buzz only when the Aux input is not shorted. I think the hiss at high volume is normal though, right?

I found some used rectifiers from a 1010. I am sure others are looking at the parts too...

D1-D10 were replaced on the power supply board with no change to the buzz.

Looks like control amp shotgun is up next? Seems like it could be the culprit with both the volume pot and aux jack being connected directly to it.

Mine has the 100uF caps in place of the 47uF caps as I have seen elsewhere. I will probably go back and add MAYBE to those ones in my posts.

I will also be getting replacement caps for EQ board and muting. Anything else that should be added?

You mean the 1010 parts assemblage on eprey? I sure hope a lot of people don't fight me for them.

The big rectifiers aren't an issue iiac, that buzzing would show up in the power amps without the pre-outs/amp-ins connected. The regulators of the regulated supplies would keep the noise contained to just radiated junk that would be picked up elsewhere.

The aux shorting plugs clearing it mostly up is a huge clue. I will have to think on that, BUT if you're not using AUX, leaving them in won't hurt anything. I suspect a grounding issue in the rear.

I have a 1010 incoming now, that should shed light upon the grounding (and what may be missing on yours) for the inputs in back... (yup, that $30 dead one with cracked glass and water stained case from ebay...)

I scored a bottom panel and re-capped the rest of the unit. (Tone, eq, muting boards) With it all buttoned up, the buzz is practically gone. It is exagerated with treble set high. And more-so when nothing is connected to Aux in. Buzz is more pronounced in left channel. It can't be heard when more than 5 feet from the speakers though. Not sure if there is much more I can do. There is definitely more noise floor on this receiver than my original QX-949. Any more suggestions?

nbndtrain said:

I scored a bottom panel and re-capped the rest of the unit. (Tone, eq, muting boards) With it all buttoned up, the buzz is practically gone. It is exagerated with treble set high. And more-so when nothing is connected to Aux in. Buzz is more pronounced in left channel. It can't be heard when more than 5 feet from the speakers though. Not sure if there is much more I can do. There is definitely more noise floor on this receiver than my original QX-949. Any more suggestions?

Click to expand...

Not really, other than inspecting the aux wires looking for nicks or broken shield connections. One end of the shield is grounded, but the other end of the shield on the cable has no connection, so there are no inadvertent ground loops.

You could, if not using aux, ground them using shorting plugs, or plugs with say 50 ohms of resistance in them. This is what is done with unselected inputs in the higher end integrated amps, all function inputs except the selected one are connected to ground through a 47 ohm resistor.

If something else is plugged into the aux, even if not selected, it should take care of the pickup because of the circuitry's impedance at the other end of the cable.

I didn't realize your buzz level was low enough to be in this territory, when I get to that point working on a unit, I routinely button it back up completely so that the shielding effects of the covers are fully realized.

markthefixer said:

Not really, other than inspecting the aux wires looking for nicks or broken shield connections. One end of the shield is grounded, but the other end of the shield on the cable has no connection, so there are no inadvertent ground loops.

You could, if not using aux, ground them using shorting plugs, or plugs with say 50 ohms of resistance in them. This is what is done with unselected inputs in the higher end integrated amps, all function inputs except the selected one are connected to ground through a 47 ohm resistor.

If something else is plugged into the aux, even if not selected, it should take care of the pickup because of the circuitry's impedance at the other end of the cable.

I didn't realize your buzz level was low enough to be in this territory, when I get to that point working on a unit, I routinely button it back up completely so that the shielding effects of the covers are fully realized.

Click to expand...

The buzz was fairly extreme, check out the video when you are able to. There is definitely a problem somewhere, and I will look more closely at the aux inputs. As I mentioned, my QX-949 does not do this, even with the bottom cover off. It is down to a tolerable level though, and probably not worth a lot more time or effort. I assume this one will probably get sold at some point, just because it bugs me.

EDIT: Is it possible the bypass caps on the main caps are introducing the noise? I was considering reinstalling the main caps with resistors only, especially if I sell it.

nbndtrain said:

The buzz was fairly extreme, check out the video when you are able to. There is definitely a problem somewhere, and I will look more closely at the aux inputs. As I mentioned, my QX-949 does not do this, even with the bottom cover off. It is down to a tolerable level though, and probably not worth a lot more time or effort. I assume this one will probably get sold at some point, just because it bugs me.

EDIT: Is it possible the bypass caps on the main caps are introducing the noise? I was considering reinstalling the main caps with resistors only, especially if I sell it.

Click to expand...

Not likely. And the 1010 here will need extensive work before I even think of powering it up, besides everything else, the power supply board took a whack from the bottom and is cracked. And the far end of the aux signal line is buried deeply, and it will be hard to figure out which end of the cable has the shield connected.

You could try disconnecting the two aux wires AT the switch board's input pins and see if it goes away, then at least we'll know if it's something in the aux wiring or on the board. Normally I wouldn't advocate messing with the wire wrap connections.

The insulation on the shielded cable could have worn down at some spot, allowing the shield to become grounded at two points, setting up a ground current that is coupled into the center conductor.

Buzz was being introduced through the orange signal wire here:



I believe this is either the Dolby or Tape2 input. I moved it as far away from the power supply board as possible, and the buzz is gone.

The 1010 is playing beautifully through a set of HPM-100's. I am looking to find a nice Pioneer DD turntable to finish off the setup.