Help needed to Fix Inward connections Pre

[Tempestb]

here is

 

[ruffrecords]

Looks like a pretty straightforward power supply to me. You need to put a scope on each rail, set it to ac coupled and see if there is any hum/noise there.

Cheers

Ian

 

[Tempestb]

So - to sum up
i'm ordered oscilloscope
and few fresh  Nippon capacitors for PSU and few voltage regulators
...yesterday swapped the big 2200uf  with general quality caps- just to see if it help - and nothing changed

 

[pucho812]

which one or all 2200uF?

I would not go about shotgunning caps just because although it doesn't harm anything.  I also am wondering  why the new regulators? were the old ones a problem and not working properly?

 

[Tempestb]

on the PSU schematics first two 2200uf capacitors after diode bridge (50 Hz filtering i think )
..on of the regulators on the picture (the right one ) not original - it also have some burned color of base ...it does the job but who knows ...since i don't have the osciloscope - i cant tell nothing
i think in a couple of weeks - i'll receive the parts  ...
..this weekend i planing to check the back side of plate for bad solder points

 

[Tempestb]

wow - just got some tough 
the caps i swapped (2200uf) they only electrolytics in the main Power supply  - since the 1000uf - not included in the chain - there is place for them on the plate but looks like them never been soldered there
....so power supply recap - did nothing

 

[Tempestb]

i'm somehow figured out following thing
if i increase value of only one of input capacitors from 2200uf  to 4400db by adding one more capacitor on the top of it - the hum falls  for a number of db and working with preamp became much more comfortable - i'm tried different combinations - but only this work

 

[ruffrecords]

In a simple power supply using standard regulator chips, the raw power supply hum is set by the big capacitor value. The job of the regulator chip is to reduce this to a tiny amount. The fact that doubling its size make a noticeable reduction in hum implies to me that the regulator chip is not doing its job properly.

Cheers

Ian

 

[Tempestb]

got it - thanks you very much

 

[Tempestb]

finally got some scope

 

[Tempestb]

1 ripple wave very unstable - jumps very often

 

[Tempestb]

here

 

[Tempestb]

second one

 

[Tempestb]

looks very straight ...as i get around 110 hz ripple

 

[QUEEF BAG]

hmm looks like ripple

if the 15 volt rails are as unfiltered as they look, i hope they are unused, and the
DOA is + & -  24 volts... which would make sense for an inward connections unit...

are those the SPA 690  op amps?

 

[Tempestb]

its 24v -  :-[
amps are 690

 

[Tempestb]

i'll receive the regulator next week maybe - i hope it will fix this

 

[keefaz]

Could you put the scope probes at regulators outputs (voltage between pins of small ceramic caps in front left of 7924 & 7824 from your psu pic) or at opamp psu V+/gnd and psu V-/gnd

Ripple at caps after diode bridge is normal

 

[Tempestb]

7824 (1)

 

[Tempestb]

scope looks fine