Back to the board! 
The work is "finished" (not yet!), and I want to show you some pictures on what how it was and some progress...
This is how all the solder points were across the boards and solder joints as well!!
Then a good work on replace/re-shining all the solder points...
All the electrolytics were replaced for fresh new ones. I don't use "audio-grade" caps because they are expensive, my ears can't hear the difference, and after all manufacturers in late 70s (Kenwood, Sansui, Pioneer, Yamaha, etc) used pretty normal caps as you can see the left one.
The new Opamp installed. Later I'll tell you why I didn't like it. Very boring sound (to me!)
The installation of the 10uF and a 3.9 ohm resistor across pins 4- and 8+
The amplifier and its old components.
Almost finished...
I want to try original 4558 opamp again to see if I like the sound more than with the OPA2604. I hear a very small "buzzz" with the volume completely attenuated...
Thanks, folks! I'll report it back later!
The work is "finished" (not yet!), and I want to show you some pictures on what how it was and some progress...
This is how all the solder points were across the boards and solder joints as well!!
An externally hosted image should be here but it was not working when we last tested it.
Then a good work on replace/re-shining all the solder points...
An externally hosted image should be here but it was not working when we last tested it.
All the electrolytics were replaced for fresh new ones. I don't use "audio-grade" caps because they are expensive, my ears can't hear the difference, and after all manufacturers in late 70s (Kenwood, Sansui, Pioneer, Yamaha, etc) used pretty normal caps as you can see the left one.
An externally hosted image should be here but it was not working when we last tested it.
The new Opamp installed. Later I'll tell you why I didn't like it. Very boring sound (to me!)
An externally hosted image should be here but it was not working when we last tested it.
The installation of the 10uF and a 3.9 ohm resistor across pins 4- and 8+
An externally hosted image should be here but it was not working when we last tested it.
The amplifier and its old components.
An externally hosted image should be here but it was not working when we last tested it.
Almost finished...
An externally hosted image should be here but it was not working when we last tested it.
I want to try original 4558 opamp again to see if I like the sound more than with the OPA2604. I hear a very small "buzzz" with the volume completely attenuated...
Thanks, folks! I'll report it back later!
Hi Sakis! I think the output relay is ok. Before, I opened it because at the beginning the right channel was missing and I knew the gold contacts inside it could be consumed. However it was still god, I cleaned inside and closed/sealed it again. Right now it's not missing any channel, playing really smooth.
An externally hosted image should be here but it was not working when we last tested it.
But one thing you are right: both the DC Offset and Bias Adjustment. I have its Service Manual, but I could not find about them. Only the VU meter adjustments.....
It is written on the main schematic 20ma !!! BUT there is no adjustment there is just a couple of resistors and you need to cut one of them if bias is not proper .
Most of the times in amplifiers like that i replace the resistor block with a multi turn trimmer which also gives the ability to play a bit with the bias in case a little bit sounds better .
I sense that something is wrong around the resistor and the capacitor you placed between pins 4-8 on the op amp i am not sure that these are the instructions you are given
One should try a 0.1 ufd across pins 4-8 or 0.1 from rails to ground or both ...
PS
I see that you squeezed the most of the forum ,got your self plenty of useful advice ,and been tele -repairing one amplifier from scratch with very good results ...Though i see no reaction on my ""payment "" issue the nasi thing
Most of the times in amplifiers like that i replace the resistor block with a multi turn trimmer which also gives the ability to play a bit with the bias in case a little bit sounds better .
I sense that something is wrong around the resistor and the capacitor you placed between pins 4-8 on the op amp i am not sure that these are the instructions you are given
One should try a 0.1 ufd across pins 4-8 or 0.1 from rails to ground or both ...
PS
I see that you squeezed the most of the forum ,got your self plenty of useful advice ,and been tele -repairing one amplifier from scratch with very good results ...Though i see no reaction on my ""payment "" issue the nasi thing
Great pictures Solder joints like those are all to typical on stuff of that era and it pays to do as you have and go over them all.
Hmmm... so you don't like the 2604 Yes, certainly try a 4558 as a "reference" again. When you've done a lot of work I find that sometimes your expectations are sky high and you listen expecting great things and it doesn't happen Live with it for a few days and see.
Other you could try... well I guess the NE5532 that Sakis mentioned or the LM4562 which is the 5532's successor.
Solder joints like those are all to typical on stuff of that era and it pays to do as you have and go over them all.Hmmm... so you don't like the 2604
Yes, certainly try a 4558 as a "reference" again. When you've done a lot of work I find that sometimes your expectations are sky high and you listen expecting great things and it doesn't happen Live with it for a few days and see.Other you could try... well I guess the NE5532 that Sakis mentioned or the LM4562 which is the 5532's successor.
I have to find this resistor block and figure it out to put a Bournes VR of similar value in order to have everything working properly.It is written on the main schematic 20ma !!! BUT there is no adjustment there is just a couple of resistors and you need to cut one of them if bias is not proper .
Most of the times in amplifiers like that i replace the resistor block with a multi turn trimmer which also gives the ability to play a bit with the bias in case a little bit sounds better .
PS
I see that you squeezed the most of the forum ,got your self plenty of useful advice ,and been tele -repairing one amplifier from scratch with very good results ...Though i see no reaction on my ""payment "" issue the nasi thing
And for the nasi bami I'd be happy to send it to you, but the easiest way is coming to A'dam and then I can offer you that dish.
Molly, I think you are right. We tend to expect sky-rocket performance after these works, but I start to like the sound as it is now. Maybe my ears are already getting used to it. I'll leave like this for a couple of days...Great pictures
Hmmm... so you don't like the 2604
Other you could try... well I guess the NE5532 that Sakis mentioned or the LM4562 which is the 5532's successor.
But I'll still try the "reference" 4558 to see if there is really any improvement or if is just my expectations playing weird.
One VERY POSITIVE THING is that the whole amp is playing well!
I mean, no intermitent breaks as before, nor "cracks" and "pops" from any pot nor switch! More pictures!
An externally hosted image should be here but it was not working when we last tested it.
The shop didn't have the 50V version of the 220uF, so I had to take the 100V version and make a little extension.
An externally hosted image should be here but it was not working when we last tested it.
I have always a few fresh 3300uF 100V in my boxes. I rather buy them than a single big power cap like 8.200uF, 10.000uF or 12.000uF 50V/63V because it cost MUCH LE$$ to me and I can make arrangements with few of them in parallel, performing better than a big single boutique expensive power cap.
Here, the original value for the power cap was 7500uF 50V. So, I put 3x 3300uF 100V, giving something like 9900uF 100V with a higher ripple current. Plenty of capacitance without exaggeranting...
An externally hosted image should be here but it was not working when we last tested it.
Here below, we have the seried 0.1uF 250V with a 1 Ohm 2W resistor across the red wires from trafo's secondary.
An externally hosted image should be here but it was not working when we last tested it.
One thing: having put these two components at the beginning of power supply, was it neccessary with the 10uF cap and 3.9 Ohm resistor acroos Opamp's 4 and 8 pins? Or don't they hurt being both?
Another picture of her without the cover
An externally hosted image should be here but it was not working when we last tested it.
Looking good.
The decoupling directly at the opamp is needed no matter what decoupling of filtering is further back in the PSU. It has to be "local" to the IC. Even a few cm of print has enough inductance to render the PSU decoupling ineffective at high frequencies.
If you start altering the bias (and there is no reason to suspect it to be in error with fixed resistors) then you have to be extremely careful and understand what you are doing as it is easy to fry the output stage in seconds.
The decoupling directly at the opamp is needed no matter what decoupling of filtering is further back in the PSU. It has to be "local" to the IC. Even a few cm of print has enough inductance to render the PSU decoupling ineffective at high frequencies.
If you start altering the bias (and there is no reason to suspect it to be in error with fixed resistors) then you have to be extremely careful and understand what you are doing as it is easy to fry the output stage in seconds.
Yes, I was suspicious about it. Better not touch.
The "buzzz" can be heard only when the Tone On switch is activated. If I leave it in Power Amp Direct it stops that buzzz background noise.
Overall it's pretty ok. It's the highs not that silky, crisp. I have to put the Treble at a higher level to listen the open and fast cymbals, for example. Can an Opamp being behind this??
Anyway, I'll try later after a few days and report it back.
Thanks, folks! You've been absolutelly great!
Hums and buzzes can be difficult to pin down and without knowing the amp I wouldn't like to say.
Did it do this before you started modifying things ? It can be caused by stray pickup perhaps by signal leads being routed incorrectly etc etc.
The opamp itself shouldn't cause any change in the amplitude of the signals whatsoever. Or to expand on that, the OPA2604 can only increase or improve the high frequency performance compared to the 4558.
Definitive test with anything like this is as always a scope
As long as you haven't changed any components in the signal path (R's and C's) and got a value wrong somewhere then it can be guaranteed the opamp won't alter the response at all compared to the original.
The 2604 is smooth sounding opamp and I find it very "musical". Some say it can be a bit "dark" sounding... and I know all these are all really subjective terms, which make it difficult. In comparison I would describe the 4558 as a little "hard" sounding but perhaps you like that, sound is subjective.
If you really don't like the 2604 then I would say try the 5532 as that's pretty neutral and was the gold standard for a couple of decades, even in studio gear.
Did it do this before you started modifying things ? It can be caused by stray pickup perhaps by signal leads being routed incorrectly etc etc.
The opamp itself shouldn't cause any change in the amplitude of the signals whatsoever. Or to expand on that, the OPA2604 can only increase or improve the high frequency performance compared to the 4558.
Definitive test with anything like this is as always a scope
As long as you haven't changed any components in the signal path (R's and C's) and got a value wrong somewhere then it can be guaranteed the opamp won't alter the response at all compared to the original.
The 2604 is smooth sounding opamp and I find it very "musical". Some say it can be a bit "dark" sounding... and I know all these are all really subjective terms, which make it difficult. In comparison I would describe the 4558 as a little "hard" sounding but perhaps you like that, sound is subjective.
If you really don't like the 2604 then I would say try the 5532 as that's pretty neutral and was the gold standard for a couple of decades, even in studio gear.
That bit doesn't read very well.
For example, at whatever point the high frequency response of the 4558 starts to fall away (beyond the audio band) then the 2604 will exceed that point by a huge margin and as a bonus give much lower distortion within the audio band too.
I think we are coming at THE point: subjectiveness.Hums and buzzes can be difficult to pin down and without knowing the amp I wouldn't like to say.
Did it do this before you started modifying things ? It can be caused by stray pickup perhaps by signal leads being routed incorrectly etc etc.
The opamp itself shouldn't cause any change in the amplitude of the signals whatsoever. Or to expand on that, the OPA2604 can only increase or improve the high frequency performance compared to the 4558.
Definitive test with anything like this is as always a scope
As long as you haven't changed any components in the signal path (R's and C's) and got a value wrong somewhere then it can be guaranteed the opamp won't alter the response at all compared to the original.
The 2604 is smooth sounding opamp and I find it very "musical". Some say it can be a bit "dark" sounding... and I know all these are all really subjective terms, which make it difficult. In comparison I would describe the 4558 as a little "hard" sounding but perhaps you like that, sound is subjective.
If you really don't like the 2604 then I would say try the 5532 as that's pretty neutral and was the gold standard for a couple of decades, even in studio gear.
Actually, the above mentioned word is behind all the things, brands, models, eras, etc...
I do really like a little more brittle sound sometimes. I'll get the 5532. Could be a good compromise.
As for hums and buzzes, it can also be my mains at wall are not properly grounded. Now I remember this.
The only components changed were two MKT 220nF 63V 1% caps (C5, C6) in place of the two old 0.22uF 50V electrolytics in the Tone Control board, as seem below:
An externally hosted image should be here but it was not working when we last tested it.
They are under the Treble control...
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Hello Greg!
After your remark I went to look well, and the electrolytics (C5, C6) were .22uF indeed. They were the only 2 yellow caps in the tone control boards. The other 4 electrolytics were 10uF 25V, and I replaced those with 10uF 50V.
An externally hosted image should be here but it was not working when we last tested it.
I think the amp is actually ok. The sound is getting better and better. Not sure if all the new components need "to settle" a bit before they go into "synergy"...
Cheers!
I think the amp is actually ok. The sound is getting better and better. Not sure if all the new components need "to settle" a bit before they go into "synergy"...
Cheers!
Believe it or not, they do!
It's your ears that are settling, not the components. This is just normal human behaviour.
To quote Rod Elliot: "Our audio memory is notoriously short, and it is simply impossible to hear a change that takes weeks to occur. What really happens is that we become 'acclimatised' to the sound - there is rarely any significant change at all."
Yes, our ears get used very fast to a new situation, indeed.It's your ears that are settling, not the components. This is just normal human behaviour.
But knowing it, this morning I started a very hard test listening more times to a single selected track I know and have listened to for many years: Steve Winwood's Night Train. This songs has an incredible bass extension and also nice and constant cymbal hits.
Started listening to the track with the 2604 already fit in the amp for about 5 times. Then, with same volume and tone parameters, without changing anything, I swapped 2604 with the 4558. Unbeliavable. The poor 4558 had/has a better perfomance through the full audio spectrum. How come???
Then, I remembered I had another opamp somewhere in my component boxes and I find this NJM 4565 thing. I swapped it again and... boom! Slightly better than the 4558, specially with the highs! So, the one or the other (4558 and 4565) have "good sound" to my ears. Or maybe this KA-405 was designed to perform optimal with such kind of old and slower opamps. I don't know.
The 4558 is 3MHz 1.7V/us, whereas the 4565 is 10MHz 4V/us. Not that far from each other.
But I still have the amplifier open and I might try the 5532. I'll try one more IC and call it a day!
Definitely I will!There is certainly an audible difference in a 4558 and 2604 and if you prefer the 4558 then that's great
The 4558 was put aside. Right now the 4565 is into the amp.
This thread (and nice discussions) has been really good to my knowledge specially with a number of issues involving restoring/refurbishing old gear, etc. I have worked on different brands and models and everytime you have a new challenge in front of you!
Obrigado, amigo! Valeu!
Your welcome
As it happens I'm just listening to a 7 (seven duals) op-amp tone evaluating LM4562's vs TLE2072 vs NE5532.
Describing sonic differences is not easy. My own personal description of the 4558 vs later audio oriented devices would be like comparing a £$€800 CD player vs a £$€100 one. Its that kind of difference in sonics, one that's pretty noticeable but hard to describe. But... there's nothing wrong knowing the sort of sound you like.
Another mad thought I had was whether your 2604 was a genuine device or something else although it "looks" OK from the picture.
As it happens I'm just listening to a 7 (seven duals) op-amp tone evaluating LM4562's vs TLE2072 vs NE5532.
Describing sonic differences is not easy. My own personal description of the 4558 vs later audio oriented devices would be like comparing a £$€800 CD player vs a £$€100 one. Its that kind of difference in sonics, one that's pretty noticeable but hard to describe. But... there's nothing wrong knowing the sort of sound you like.
Another mad thought I had was whether your 2604 was a genuine device or something else although it "looks" OK from the picture.
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