Pop in Pioneer SX-950

[rcs16]

You said it was working just fine. I don't mean to be disrespectful, I'm just confused.

I said the 950 was working fine, to specifications and similar to my stock unit. You seem to be questioning the Pioneer design, and the substitute parts, that have been listed on this forum.
Thus, I am offering a possible design solution. I was not asked to re-design your unit, just investigate if it was working to specifications and to fix it if it was not.
I only recently discovered the mod that Pioneer had done to the same basic circuit used on the spec-4.

As for your diodes, D8, the original part was spec'd as a Hitachi 1S2473 or Toshiba 1S5555 which are small signal silicon diodes. I have the diode specification sheets if you want them. A 1N4004 is not a small signal silicon diode! The sub was to be a 1M4148 small signal silicon diode. Does it matter, I do not think so or very little.

If a designer spec's a certain part, it is best to use the one specified, if it was chosen correctly in the first place? In the case of 2sc945/2sa733, I would recommend the newer equivalents, ksc945c/ksa733c. Will it matter, if if you use something else, well you seem to think that it does, so then why use something that is different from original?
This has to be answered by the person(s) recommending the sub's in the first place.
All the 950's that have been modified, know one has discovered or reported the problems that you are questioning.
I spent most of my time and your money on soldering lose or poorly connected wires.
Karel, you can be as disrespectful as you seem fit. You seem to think that I burn't you out of some of your retirement money. So what are you implying? That you are confused, yes, I agree with you.

 

[karel.b]

I do not wish to discus money nor am I implying anything!!! I'm simply stating that I changed Q6 from KSC2383YTA to KSD1616AGBU and the pop at power off is gone. Do I know why? NO, I do not. Is it a solution for the problem, I do NOT know. Lucky shot? Maybe!!! Is it going to last? Again, I do not know. So, as you can see, I do not know much at all. It is a fact that I can not deny. That is why I seek help here!!! Obviously, if I knew, I would not do that.
I totally respect your knowledge about electronics and also hope you can read in between the lines!
So, please let us stick to what audiokarma is all about. Guys that know helping guys that do not. That should not be any problem, right?
As for me, I apologize, I did not expect that his would happen.
Thanks
PS
Read your own post #148!!!!

 

[Watthour]

It would seem highly coincidental that the component change solved the problem without some reason. Component specifications and characteristics may indeed have a role in operation of the circuit, and the "must forward" and "must reverse" bias points could have a substantial bearing on this circuit's operation. That could explain why my original, lightly used SX-950 didn't exhibit the same behavior as yours. That could also explain why a replacement component with generically acceptable operating ratings and characteristics didn't behave the same as the originally specified part, or even a different replacement device.

I also don't know, and without some serious breadboard mock-up of the circuit and bench testing, I can only make assumptions. However, your reasoning is at least plausible and arguable.

 

[karel.b]

I am as puzzled as you, Rick and others, who follow this thread. This happened once before, when I changed all the transistors in the board. And then it came back.
I will wait for Mark or some other expert for answer on those two components (D8 on AWM-062 and Q1, Q2 on AWG-038) and then I'll assemble the receiver regardless.
Thanks

 

[rcs16]

If we go back to the beginning, I believe my advise was,
1) Did you notice this before any comp changes?
Answer, not sure
2) Have you put the original comps back in?
Answer = no

I believe you, that changing the bjt (Q8) may cause a slight change in the behavior of the fine balanced DC type of ckt.
It must be the turn-off time.
Why? It is the characteristics of the transistors.

Lessons learnt, tread lightly when you are substituting parts. In some cases it does not make any difference, in cases like this, there are small changes in behavior. Some good and some not so good.
So are you now going to put in ksc945c and it complement ksa733c? Even the hfe grade of this part may make a difference, only testing will know for sure.

The tone control pop mod., requires you modify the flat amp, the same as they did for the 1050,1250,1280,1980 designs.

 

[karel.b]

I'll wait for craxx6969 and /or Watthour to test their sx-950 and I'll take it from there.

 

[craxx6969]

I'll wait for craxx6969 and /or Watthour to test their sx-950 and I'll take it from there.

Karel,

I have the 950 on my desk, when the tone switches are in the UP position and the volume is at minimum, there is NO pop when it is turned on. If I turn the volume up to half way, switches are still at the up position and AM is selected, then turn the unit off, there is a POP in the speakers.
Switches in the down position (turnover/tone/turnover) wait ten seconds, there IS a POP. No antenna was attached during any of the tests.

Next test, switch to FM with the switches in the up position, turn on and wait 10 seconds, no pop at 1/4 volume when I turned the unit off, next volume to the five mark (one from half), NO POP when I turned the unit off.

Next test, still on FM, switches in the up position, volume will be at 1/2 when I turn the unit off, waited 10 seconds, NO POP.

Now I have the Phono 1 button engaged (Star Trek?), volume will be at 1/4, NO POP when I turned it off.

Next will be at the 5 mark which is one before 1/2 way, wait 10 seconds, NO POP,

Next will be at 1/2 volume, switches still up, wait 10 seconds, NO POP.

Next switches (turnover/tone/turnover) in the down position, still on Phono 1, NO POP at 1/4 volume, No POP at one mark shy of 1/2, NO POP at 1/2 volume.

Next switches up, on PHONO 2, 1/4 volume, NO POP, one mark shy of 1/2 volume NO POP, NO POP at 1/2 volume.



Next AUX Switches NO POP

So it seems mine only has the pop on AM, no where else.

End of test.

 

[karel.b]

craxx6969,
Do these tests with all the function (push) switches OFF, with the exception of the speaker button. All lever switches on the flat amp and tone amp also should be in OFF position. Then test your receiver as I outlined it in my previous post.(#182)
THANK YOU for your participation!!!!!

 

[craxx6969]

Ok,

All switches in the up position, all buttons NOT engaged, out, except for spkr A.
Bass and Treble pots at full CCW (minimum volume), and the volume atw to minimum.

1. When I turn the unit on, immediately after the relay clicks I engage the bass turnover switch, from up to down, there is NO pop.

2. After letting the unit warm up, with the volume at 1 mark from top dead center or TDC, all the other switches and pots at the same level in scenario 1, I turn the unit off, there IS a POP.

3. I did the same scenario as #2 with the volume at 1/4, NO pop on turn off

4. Same scenario as #2 with the volume at 10 O'Clock, NO POP

Not until I reach 11:00, then there is a pop..

So it seems the issue could be inherent in the 950. Has anyone checked other xx50 units?

So ends the test.

Glad to be of help Karelb.

I always turn the volume to minimum before turning off the unit which is why we don't hear any pops or even think of this issue.

 

[karel.b]

THANK YOU!!!!!!
Just one more test. Turn the tone switch ON before powering the unit. Turn the power switch ON and immediately after the relay clicks in, turn the tone switch OFF, listen for a pop.

I think that is what I'm going to do from now on. Turn the volume down before power off.
Thanks again

 

[craxx6969]

THANK YOU!!!!!!
Just one more test. Turn the tone switch ON before powering the unit. Turn the power switch ON and immediately after the relay clicks in, turn the tone switch OFF, listen for a pop.

I think that is what I'm going to do from now on. Turn the volume down before power off.
Thanks again

Getting late here is IL. I'll do the last test tomorrow night, suspense is building..)..

 

[craxx6969]

After following the last request, there IS a pop when the tone switch is on and then after I turn the unit on, wait for relay to click, then the tone switch is moved to off.

Hopefully this will conclude the testing.

Has anyone tried this on any other similar receivers (Pioneer 50's series or others)

 

[karel.b]

I've rebuilt/recapped two SX-1280's and both work just fine, no popping at any time. But they are totally different beasts. And they sound fantastic. Power galore.
I have SX1250 that I've just purchased locally. It looks excellent from outside, but have not have time to hook it up yet. I can't spend any more time with the SX-950, I've had it on my bench for over two years. Thank god it's only a hobby after I've retired, else I would be in the poorhouse, if I would have to make living doing it!!!!!!!!(LOL)
Thanks again, you were very helpful.

 

[zebulon1]

Is this the end of the thread?

 

[karel.b]

Is this a "thank God it's over!!!!", or "oh no, what am I going to read now?" question?
Just kidding.
The verdict:
Actually, the sx-950 is just as good as the sx-1280, comparing sound, presence, clarity, bass, treble, midst. The sx-1280 does not get quite as warm as the 950 running my speakers.
The pop is still there, only referring to the tone switch. No pop at power off. (not yet, anyway)

Now, the sx1250!!!!!

 

[karel.b]

MTF,
Tried to send you a private message, but your space is full!!!
You should get it as soon as you clear some space.
karel.b

 

[karel.b]

Hi Mark,
Since your space for private messages is full, I'll try to reach you this way.
I'd like to buy your tone board, if possible. If not, I'll send it back to you, plus the shipping charge.
Please let me know ASAP.
THANKS,
karel

 

[karel.b]

I've ran this receiver for long time now and everything works well, it sounds very good.
But, I can't get the pop (tone switch) out of my mind, still !!!!!
I was thinking, could the 3-4 sec. relay delay be extended to say 10 sec's ? And would it be difficult to do it ?
This would be something that Mark and/or few others could answer. Not that I'm in any rush !!!!
Thanks for now

 

[Watthour]

Well, the lucky thing for you is that you're already ahead of the game. The 3-4 seconds is more like 5-6 second Canadian, so you're that much closer.

Actually, changing the values of C6 and R27 on the protection board should allow about any time delay you'd want.

 

[markthefixer]

Double the 100uf cap to 220uf. 647-UPW1V221MPD

Q6 has to be a 512-KSC2383YTA for the increased capacitance.

This is not ironclad, it is charged by a 68k resistor (R26), and capacitor leakage plus base draw of Q7 may affect it.