Anybody have any idea what the caps below marked "F2 22 50V" are? I gather that they're 22uF SMD aluminum electrolytic (or hybrid?) caps rated for 50V. But I hear that matching other characteristics (such as ESR) is important when doing a recap project. Thanks in advance!
I think those are just production codes. Nichicon show them as lot numbers. Those look like standard 22uF 50V 'chip' type electrolytics. Unless you have good reason to suspect they are a problem then I would leave them.
Mooly, thanks for the reply! You think I should also leave alone the large Elna LP5 caps and the smaller Rubycon through-hole caps? The amp is 20+ years old so I'm just wondering if all the electrolytics are degrading to the point where it's now audible.
My other idea here is that just visually inspecting this Linn LK85 and the more powerful LK140, it seems the only difference between the two is two extra TDA7293 ICs (to add to the two at the bottom right above the heatsink), two of these "F2" caps (one of which is marked C208 in the bottom left), and two extra Elna caps by the transformer.
Any idea if it's a bad idea to try to add in these extra parts (or their equivalents) to get more power out of the amp?
My other idea here is that just visually inspecting this Linn LK85 and the more powerful LK140, it seems the only difference between the two is two extra TDA7293 ICs (to add to the two at the bottom right above the heatsink), two of these "F2" caps (one of which is marked C208 in the bottom left), and two extra Elna caps by the transformer.
Any idea if it's a bad idea to try to add in these extra parts (or their equivalents) to get more power out of the amp?
I wouldn't like to say on adding the extra chips simply because you would need to be 100% sure all the required connectivity and so on was in place.
The TDA7293 is often used in parallel mode to get more current capability... the voltage rails set the maximum output, the load impedance determines the current output and so provided the current can be met by one TDA then you won't gain anything. It won't be louder in normal use or anything like that.
This is a typical arrangement from the data sheets.
I think you will find all the caps are perfect but I can understand wanting to experiment 🙂 If you have never replaced the surface mounted chip type electrolytics before then be aware they may not unsolder as easily as you think and it is super easy to rip and damage print. They are flush to the board, there is no 'wiggle' room to heat one end hoping to lift it a little while heating the other end... the print will rip if you try that.
The big Elna's are very lightly stressed in a Class AB amp and should be perfect.
The TDA7293 is often used in parallel mode to get more current capability... the voltage rails set the maximum output, the load impedance determines the current output and so provided the current can be met by one TDA then you won't gain anything. It won't be louder in normal use or anything like that.
This is a typical arrangement from the data sheets.
I think you will find all the caps are perfect but I can understand wanting to experiment 🙂 If you have never replaced the surface mounted chip type electrolytics before then be aware they may not unsolder as easily as you think and it is super easy to rip and damage print. They are flush to the board, there is no 'wiggle' room to heat one end hoping to lift it a little while heating the other end... the print will rip if you try that.
The big Elna's are very lightly stressed in a Class AB amp and should be perfect.
You're right, it doesn't make sense that adding an extra TDA per channel would change the sound if the extra current is not required. But the strange thing is that the general consensus is that the LK140 is a better sounding amp than the LK85.
There is, btw, connectivity on my board between TDA pin 11 and the empty pad where 11 would be on a second TDA. I understand that there may well be other differences besides this and a few extra capacitors, though. Just so tempting to try since the board is the exact same and there are so few obvious differences.
There is, btw, connectivity on my board between TDA pin 11 and the empty pad where 11 would be on a second TDA. I understand that there may well be other differences besides this and a few extra capacitors, though. Just so tempting to try since the board is the exact same and there are so few obvious differences.
If would measure voltage out at maximum before replacing rail caps. P=(V^2)/z where z is speaker impedance (~4/3 resistance). power equals rating, no problem with the rail caps.
If too little bass, electrolytic coupler cap could be dried up. If too much treble, dried up parallel e-cap filter could be at fault. If my amp doesn't sound funny or polite (no power peaks on classical music) then I don't repair it. I use classical recordings for standard because the instruments have a known sound, whereas guitar signals can be heavily modified by pedals, amp, or recording process. Steinway grand piano is the toughest sound to get right. Recordings post condensor mike era required; RCA used inaccurate ribbon mikes until ~1963.
If too little bass, electrolytic coupler cap could be dried up. If too much treble, dried up parallel e-cap filter could be at fault. If my amp doesn't sound funny or polite (no power peaks on classical music) then I don't repair it. I use classical recordings for standard because the instruments have a known sound, whereas guitar signals can be heavily modified by pedals, amp, or recording process. Steinway grand piano is the toughest sound to get right. Recordings post condensor mike era required; RCA used inaccurate ribbon mikes until ~1963.
You would have to look at each pin in turn on the vacant location and see and confirm by measurement where they go. I would think it follows the data sheet example very closely though.
Well... 🙂 Yes.
(Sometimes those kind of parts can also be glued down, probably done during assembly to initially secure them)
Thanks, Jo, I'll have to try to measure the output power.
Mooly, so I guess that hot air reflow isn't the silver bullet I thought it was. 🙂 I verified the other connections between the TDAs. Looks like they all check out except Pin 9 only has continuity through to a missing resistor pad and the two Pin 10s don't seem to be connected AFAICT (though Pin 10 on the missing TDA does connect to Pin 1, I suppose b/c they're both connected to ground).
I think both of you have talked me out of trying to recap. Maybe I can focus on seeing whether I can add the missing components just to see if that makes any audible difference. Thanks for all the information!
Mooly, so I guess that hot air reflow isn't the silver bullet I thought it was. 🙂 I verified the other connections between the TDAs. Looks like they all check out except Pin 9 only has continuity through to a missing resistor pad and the two Pin 10s don't seem to be connected AFAICT (though Pin 10 on the missing TDA does connect to Pin 1, I suppose b/c they're both connected to ground).
I think both of you have talked me out of trying to recap. Maybe I can focus on seeing whether I can add the missing components just to see if that makes any audible difference. Thanks for all the information!
Those pins may not be used functionally in this amp. For example if it uses a speaker relay as a delay then it doesn't need to use the chips option for mute and so on and so they may just be tied to the appropriate 'logic' levels.
Pin 9 I would say has to do the same for both chips. You can't have one chip doing one thing and the other something different. The same for pin 10. Whatever one does the other must follow.
Pin 9 I would say has to do the same for both chips. You can't have one chip doing one thing and the other something different. The same for pin 10. Whatever one does the other must follow.