Leak 2200 maintenance

[Kei-86]

Giving my dad a hand to perform some maintenance work on his Leak 2200 amplifier which he has owned from new. I've already been through it and replaced all of the electrolytic capacitors for panasonic FM/FC and rubycon ZLJ. The main filter caps were replaced with Kemet/BHC 10,000uF 63V. This yielded quite an improvement to the performance, which had been gradually getting worse.




There are still two residual issues that were not greatly improved or stopped.

1. There is a lot of residual mains hum that gets picked up by the preamp. It's worst when there is no input connected, but still present when there is.

2. The phono preamp section has very little HF, sounding quite muffled.

I am wondering if there is anything else that may well be worth replacing that may help improve things. I've got the circuit diagrams if it will help.

[13oots2]

Might well be worth looking at the diode rectification to see if that cures the mains hum. Unless you have re-biased the output section I would also do this if you have access to the recommended values.

[rhomanski]

You didn't mention if you have cleaned the pots and switches. Get some deoxit D5 if it's available in Wales. Also, sometimes with new caps it takes some time for them to burn in. The hum may lesson after some use. If the bias and offset are good and stable, run it for a while. I had a hum in the right channel of my preamp after a recap. About ten hours of use and it went away. Also I did have one bad cap in my new ones. I had to order it again to fix the hum in both channels. I found it with a multimeter, wouldn't charge or discharge, just stayed at a steady 6k ohms. After that I only had the hum in the right channel. That fixed itself when the caps reformed.

I should also say, if you are sure everything is installed correctly. None of the caps are in backward.

[Kei-86]

The hum is a bit bizarre as I plugged in my cd player directly via an RCA-din adaptor and the hum was extremely quiet, had to have the volume control near maximum to hear it. With it connected to my dads cd player via his own wiring (through an RCA switcher) it hums/buzzes at the same level as the disconnected inputs. His cd player via my amp was quiet, though i'm not certain if i plugged the RCA from the switcher into my amp or if i did it direct from the cd player. The noise is definitely picked up before the power amp section as it increases as the volume is turned up. All the pots and switches were cleaned at the time with electrolube contact treatment oil.

I did all the same sort of work on my luxman amp back at the start of the year (i really went to town on it replaced every capacitor and a fair number of resistors and so on, thread about that here) and it is near silent at maximum volume with only a faint audible hiss with my ear at the tweeter. The buzz that emanates from the speakers with the leak is audible at around 6-8 feet.

[Blue Angel]

The hum is a bit bizarre as I plugged in my cd player directly via an RCA-din adaptor and the hum was extremely quiet, had to have the volume control near maximum to hear it. With it connected to my dads cd player via his own wiring (through an RCA switcher) it hums/buzzes at the same level as the disconnected inputs. His cd player via my amp was quiet, though i'm not certain if i plugged the RCA from the switcher into my amp or if i did it direct from the cd player. The noise is definitely picked up before the power amp section as it increases as the volume is turned up. All the pots and switches were cleaned at the time with electrolube contact treatment oil.

I did all the same sort of work on my luxman amp back at the start of the year (i really went to town on it replaced every capacitor and a fair number of resistors and so on, thread about that here) and it is near silent at maximum volume with only a faint audible hiss with my ear at the tweeter. The buzz that emanates from the speakers with the leak is audible at around 6-8 feet.

Nice work on that spaghetti bolognaise

Have you thoroughly cleaned all rca jacks? Sometimes corroded or tarnished jacks can cause hum. I found that with my Dynaco SCA35 integrated valve amp.

ba

[Kei-86]

This amp is din throughout, though i have not cleaned the sockets.

[rhomanski]

Sounds like the wires to or from the switcher are picking up the hum. Try moving the cables away from everything else and see if the hum changes. If it only buzzes sometimes, then the hum is probably not internal to the amp. Sounds like you did a good job on the overhaul, you just need to sort out the wiring.

Regards,

Ron.

[Kei-86]

OK will double check the wiring, the residual noise when wired directly wasn't chronic. The phono stage still needs to be sorted out though. I've uploaded the schematic from the service manual. (shows the LH half) The issue is that there is little in the way of HF, giving an almost muffled sound. This is with the same tuntable combo i use with the luxman amp. (shure M75ED II with jico SAS) I know that it should be set to low sensitivity with this cart as it outputs somewhere around 5mV. (low on the amp is for 6mV and high is for 2.2mV)

[rhomanski]

If all you did was replace capacitors with new of the same value, I don't see what would cause a loss of high frequencies. You could check the coupling cap I suppose. The most usual reason for High Frequency loss is high capacitance in the turntable leads to the amp. I'm guessing disc input does not mean compact disc as I first thought. All the ones I've seen say phono. You guys in the UK are interesting. I found that out working with Rolls Royce Engines. I used to work on the RB-211 and later the Trent engine.

I would look the phono section over real good. For backwards caps and the like. I would also try a different cable for the phono as well. Since you didn't help or change the problems with the unit, the problems may not be in the unit. I just recently overhauled a different preamp for my brother and put in a thump when switching the source from phono to tuner. I just got in the transistors to fix it. I replaced one of the pair but didn't have the complementary. Had to order it. I'll get it finished eventually.

Regards,

Ron.

[Kei-86]

Forgot to state that the phonostage didn't work properly before the replacement of the capacitors, though their replacement fixed one of the problems. (one channel was silent) The turntable and its cable is fine as its the table i use with my luxman and it still works perfectly with that.

[rhomanski]

Both channels sound the same? If so, the problem would have to be something common to both. Before the function switch. Something like the connector on the back or the power supply. Your print shows the voltage at R48 as 15 volts and R49 as -13 volts. Check it on both channels and see if they agree. You can also check for fusible resistors. Sansui used them and they are notorious for climbing in resistance when they get old. I have no idea if Leak did or not.

[Kei-86]

I've decided to replace all of the film capacitors now. After having a closer look at what was fitted it's become apparent that the left and right channels have mismatched parts. I've got mostly polypropylene replacements coming along with some polystyrene and silver mica for the really small values. If that doesn't fix it, i'll look at doing the resistors last, as I found that replacing resistors can get very expensive with my luxman, especially if you buy exotic takman metal films and try to replace everything like i did.

[Kei-86]

I think i've now sorted the phono preamp issue. I replaced all of the ceramic and film capacitors. They were mismatched between the channels anyhow, left had 10nF and right had 1nF. (ceramic discs in C13 and C28) I also noticed that it picks up hum from me if i get within about 2" or so of the BC149's or the input wires. There are still some originals as i managed to screw up my order quantities and there are a pair of 270pF ceramics that i can't get at without some severe dismantling. Mains hum is still present even when wired up in another room with different sources and cables, though it was less obvious.

Power supply


Power amp


Phonostage


Preamp

[rhomanski]

If the hum gets louder as you approach it, that would make me think you might have a missing ground on one of the cards. Maybe the input plugs. Only you know what you have disturbed. Go over it carefully and look for something that could be put in backwards or something of that nature. Perhaps wires that could be swapped. A screw that should have had a wire under it but doesn't. Sometimes a wire can be holding on by one strand, or broken under the insulation.

Regards,

Ron.