Would need to see the circuit really. If there were any resistive component on the output side of the 2.2uf (dc path to ground) then you can't really link it out.
Increasing the 0.47uf might cause a larger switch on thump. AC coupled amps like this have many time constants that all interact, coupling caps, feedback return cap, speaker coupling cap and so on.
Increasing the 0.47uf might cause a larger switch on thump. AC coupled amps like this have many time constants that all interact, coupling caps, feedback return cap, speaker coupling cap and so on.
It's alive! 
Thanks to everyone who's offered help in this thread over the past couple weeks, and thanks to you again Mooly - another amp resurrected due to your help & knowledge! Very much appreciated
After replacing TR1/1b and 2/2b I got it biased up with no problem this time. Twisting & insulating the transistor legs to fit the old pin-outs was a bit fiddly - drawing diagrams & triple checking the legs before soldering helped here. It's only been on for ten minutes but it's sounding just as good - if not better - than it did originally. I have no idea why this amp sounds as good as it does, as it was a budget item back in the 70s I believe, and second from the bottom in Akai's line-up of receivers. But after recapping one for my Brother in Law as he wanted a retro looking amp for Christmas, I had to buy one too. Perhaps I like the design conpromises or coloured sound or something, but I prefer it subjectively to my Quad 303 & 606 (both serviced).
At a later date I'll consider replacing the two front panel bulbs with an LED strip for more even lighting, and need to check the time constants/bass (see post above this one) are operating correctly since I've wired out the high/low filter pcb, but quite honestly I'm delighted with it right now.
Anyway, thanks again everyone! Very very happy chappy this evening!
Cheers,
John.
Thanks to everyone who's offered help in this thread over the past couple weeks, and thanks to you again Mooly - another amp resurrected due to your help & knowledge! Very much appreciated
After replacing TR1/1b and 2/2b I got it biased up with no problem this time. Twisting & insulating the transistor legs to fit the old pin-outs was a bit fiddly - drawing diagrams & triple checking the legs before soldering helped here. It's only been on for ten minutes but it's sounding just as good - if not better - than it did originally. I have no idea why this amp sounds as good as it does, as it was a budget item back in the 70s I believe, and second from the bottom in Akai's line-up of receivers. But after recapping one for my Brother in Law as he wanted a retro looking amp for Christmas, I had to buy one too. Perhaps I like the design conpromises or coloured sound or something, but I prefer it subjectively to my Quad 303 & 606 (both serviced).
At a later date I'll consider replacing the two front panel bulbs with an LED strip for more even lighting, and need to check the time constants/bass (see post above this one) are operating correctly since I've wired out the high/low filter pcb, but quite honestly I'm delighted with it right now.
Anyway, thanks again everyone! Very very happy chappy this evening!
Cheers,
John.
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That's great.
It sounds as good as it does because of the basic (single ended input) circuit topology. This is what many can't accept and 'don't get'. They criticise designs like this on technical grounds, and pursue ever lower distortion through increasingly complex circuits. Having done that, they never seem happy with the result but accept it 'must be correct'. We on the other hand, simply spin another disc and let the music flow
It sounds as good as it does because of the basic (single ended input) circuit topology. This is what many can't accept and 'don't get'. They criticise designs like this on technical grounds, and pursue ever lower distortion through increasingly complex circuits. Having done that, they never seem happy with the result but accept it 'must be correct'. We on the other hand, simply spin another disc and let the music flow
That's great.
It sounds as good as it does because of the basic (single ended input) circuit topology. This is what many can't accept and 'don't get'. They criticise designs like this on technical grounds, and pursue ever lower distortion through increasingly complex circuits. Having done that, they never seem happy with the result but accept it 'must be correct'. We on the other hand, simply spin another disc and let the music flow
Agreed to all of this. I think I may also like the sound quality of capacitor coupled outputs too. I find a similar level of sound quality (particularly in the bass) in the Quad 303, which is also capacitor coupled to the speakers. Whatever the reasons, it just makes me want to listen to music for as long as possible, so mission accomplished
I've attached a couple of diagrams below which should be readable via the direct link to Photobucket (assuming the frequently unreliable bucket hasn't kicked it!). Too large to post here legibly.
The following is the circuit as-is, with the signal paths highlighted in yellow and red:
http://s954.photobucket.com/user/John-M23/media/1020 Circuit Signal Path.jpg.html
This image shows the shortcut I've currently taken to wire out the high/low filter PCB:
http://s954.photobucket.com/user/John-M23/media/1020 signal path shortcut.jpg.html
As it stands in my amp at present, the signal goes out of the tone control board (pins 6 & 8 in the circuit diagram) via two 2.2uF caps. The signal wires are now directly wired to the input pins on the Main amp PC board, at pins 4 & 8. The input caps here are two 0.47uF electrolytics (though I'm using 1uF films as had them handy).
Was wondering whether I could/should perhaps wire out those two 2.2uF caps on the tone control PCB board, now I've wired past the filter board pcb, or the input coupling caps in the Main amp board instead?
Thanks,
- John
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Better to attach pictures directly to the forum really, or do a zoom in of the area of interest These external sites are often full of unwanted stuff.
If you have films at the power amp input then it looks like you can directly connect those to the preamp output. So you would link the 2.2uf caps and remove the 100k (was it ?) resistor that goes to ground at the junction of the two caps.
These external sites are often full of unwanted stuff.
If you have films at the power amp input then it looks like you can directly connect those to the preamp output. So you would link the 2.2uf caps and remove the 100k (was it ?) resistor that goes to ground at the junction of the two caps.
I usually endeavour to post photos 'in thread' Mooly, but the images were too big, and cutting the circuit into smaller chunks made it harder for others to read & piece together (I actually tried and the txt often wasn't legible). Photobucket is also a recognised/popular image hosting website so should be nasties free. Just click on the link, then click upon either the magnify icon, or the download icon. Should appear as its optimum resolution then.
So link out the 2.2uF (C13/13b) caps on the 'Tone Control PC Board', and remove the 100K resistors from input to ground (R1/R1b) on the 'Main Amp PC Board'? What would a typical/sensible value (after having done the mods just mentioned) be for the C1/C1b input cap on the Main Amp board Mooly? The circuit diagram shows 0.47uF. There was a 0.47uF electrolytic cap originally fitted, which I replaced with a 1uF film cap as I had it to hand at the time during the testing phases. The service manual in the parts lists confuses matters by then listing C1/1b as 3.3uF too!
Cheers,
- John
So link out the 2.2uF (C13/13b) caps on the 'Tone Control PC Board', and remove the 100K resistors from input to ground (R1/R1b) on the 'Main Amp PC Board'? What would a typical/sensible value (after having done the mods just mentioned) be for the C1/C1b input cap on the Main Amp board Mooly? The circuit diagram shows 0.47uF. There was a 0.47uF electrolytic cap originally fitted, which I replaced with a 1uF film cap as I had it to hand at the time during the testing phases. The service manual in the parts lists confuses matters by then listing C1/1b as 3.3uF too!
Cheers,
- John
That rapidly jumping and floating Window hoping to get someone to click on it is just malware in my book
So yes, link out the 2.2uf's and remove the 100k's. 1uf should be fine, in fact its not possible to give an exact answer because there are a lot of interacting time constants, the speaker coupling cap, the feedback return cap, in fact any cap in the signal path.
If you did revert to an electrolytic then you would (possibly) need to fit it the other way around compared to how it was originally because of the DC voltage on the collector of the preamp output transistor.
So yes, link out the 2.2uf's and remove the 100k's. 1uf should be fine, in fact its not possible to give an exact answer because there are a lot of interacting time constants, the speaker coupling cap, the feedback return cap, in fact any cap in the signal path.
If you did revert to an electrolytic then you would (possibly) need to fit it the other way around compared to how it was originally because of the DC voltage on the collector of the preamp output transistor.
That rapidly jumping and floating Window hoping to get someone to click on it is just malware in my book
So yes, link out the 2.2uf's and remove the 100k's. 1uf should be fine, in fact its not possible to give an exact answer because there are a lot of interacting time constants, the speaker coupling cap, the feedback return cap, in fact any cap in the signal path.
If you did revert to an electrolytic then you would (possibly) need to fit it the other way around compared to how it was originally because of the DC voltage on the collector of the preamp output transistor.
Well, unless something really does need updating & it's an honest alert window
I use either an iPad or my Mac computer and don't see any of that to be honest. But point taken for if I ever need to post a larger picture again.Great, thanks for confirming that. Out of interest, and trying to learn a little more, why do the 100K resistors need removing now? If that's too in-depth to get into here no problem
When you have two caps in series, the junction of them is not defined at a DC level. Tying that point to ground defines a zero DC voltage at that point.
If you don't remove the cap when you short out the 2.2uf then you are placing the 100k across the collector of the preamp transistor which would then slightly alter the DC conditions around the transistor.
If you don't remove the cap when you short out the 2.2uf then you are placing the 100k across the collector of the preamp transistor which would then slightly alter the DC conditions around the transistor.
Thanks for the explanation Mooly. I think I'll just remove the 2.2uFs altogether then & wire link the remaining pads. Remove those 100Ks (no wire link there I assume) on the power-amp input and job done
Ok have removed the two 2.2uF tone control pcb output caps, and replaced with wire links.
Have removed the two 100K signal-to-ground resistors at the input of the power-amp pcb.
Now I'm getting a sort of rustling sound from the left speaker as well as the music. Thought it was a dirty pot but they're all fine. Sound comes through the headphone output too.
Something else to track down now - I swear this damn amplifier is cursed! All the transistors on the power-amp pcb are new now, so I hope one of those isn't already going south after all that work.
Cue head exploding animation! :/
Have removed the two 100K signal-to-ground resistors at the input of the power-amp pcb.
Now I'm getting a sort of rustling sound from the left speaker as well as the music. Thought it was a dirty pot but they're all fine. Sound comes through the headphone output too.
Something else to track down now - I swear this damn amplifier is cursed! All the transistors on the power-amp pcb are new now, so I hope one of those isn't already going south after all that work.
Cue head exploding animation! :/
Guy, you said you were happy with the sound, and yet you went in there and fudged things around. Everybody seems to do this, and I just don't get it.
Return to stock and enjoy. Modding never does any good anyway.
As for your new issue. If it's not caused by your mods, you killed a transistor by discharging a capacitor through it. Begin with replacing all TO92s on that channel, it will probably fix it.
Return to stock and enjoy. Modding never does any good anyway.
As for your new issue. If it's not caused by your mods, you killed a transistor by discharging a capacitor through it. Begin with replacing all TO92s on that channel, it will probably fix it.
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Guy, you said you were happy with the sound, and yet you went in there and fudged things around. Everybody seems to do this, and I just don't get it.
Return to stock and enjoy. Modding never does any good anyway.
As for your new issue. If it's not caused by your mods, you killed a transistor by discharging a capacitor through it. Begin with replacing all TO92s on that channel, it will probably fix it.
I can not agree with your comment about modding not being any good. But that's a matter of personal opinion which I do not wish to get into.
I bypassed a mini pcb section (hi/low filter) that I do not (and will never) use, and wanted to make sure it was done correctly, which Mooly kindly clarified for me. No caps were discharged here, and I'm not about to dive in and replace all TO92s before I know what the problem is. That might cause more problems...
I'll start by restoring the 2.2uF output coupling caps in the tone control board & the 100K resistors on the main amp pcb and see if that cures it.
This may just be coincidental to doing the mods at any rate, as I had this very same issue when I first had the amp, prior to recapping it (which appeared to solve it at the time) and before any of the dramas mentioned in the first post here.
You are having fun aren't you
Just to be sure... the remaining input caps on the power amp are NON polarised ?
You are having fun aren't you
Just to be sure... the remaining input caps on the power amp are NON polarised ?
Hahah yuuuup! I swear it's the evil spirit of that Sony amp come back to cause chaos Mooly!
That's correct. 1uF Panasonic ECWF polypro caps. Nothing fancy. All fine before the 2.2uF link replacements, and 100K deletions. Wondering if the 2.2uFs when in place may have 'hidden' another inconsistant problem on the tone control pcb? That contains 4 more 2SC1222s. Perhaps the brief heat from desoldering the output caps was enough to damage the one nearest the output. And the problem is one channel only.
Too tired tonight but will get a scan uploaded of just the tone control schematic, and pcb layout up tomorrow. At least if it is a transistor I have plenty of the 2N5551 replacements now
It should be easy enough to isolate. Just keep lifting coupling caps to keep splitting the amp.
(When things happen that seem like coincidences then it can be a good thing to go back over what you did even to the point of reinstating the last mod. Unlikely that the new cap is faulty but I guess stranger things have happened)
(When things happen that seem like coincidences then it can be a good thing to go back over what you did even to the point of reinstating the last mod. Unlikely that the new cap is faulty but I guess stranger things have happened)
Well the 1uF input caps on the main amp pcb have been there since the initial recap (prior to the headphone socket shorting blunder that started this thread) and it was fine so I think that rules that one out. I have a hunch it's one of the old (and I believe you said a few pages back they can be unreliable) 2SC1222 transistors - there's one immediately next to the 2.2uF cap I took out and linked. Wouldn't surprise me if that was the cause.
I may try lightly tapping that suspect transistor with the tip of a long paint brush and see if the 'rustling' noise alters or momentarily disappears entirely.
I guess the next stage would be to roll back exactly what was altered this afternoon. And if that cures it fair enough (though a bit of a head scratcher why it was the left channel only in that instance).