Technics SU-7700

[rhymeswthorange]

I just got a VERY nice, clean Technics SU-7700 on eBay. It sounds quite nice, but has one problem: the right channel is significantly louder than the left. On bass hits, the power meter for the right channel consistantly reaches higher maximums than the left. I have reversed the speakers and played every sort of music I have only to come to the same results.

I have pretty sensitive speakers (fostex fe207e's in a MLTL) and am only driving about 1 - 1.5 watts through them. Much louder is just too much in my little dorm room. Could slight differences in transistor bias, minute unmatchedness of transitors, positioning in my room, or the high sensitivity of my speakers be the culprit?


Thanks!!!
-'orange

 

[analog_sa]

Could slight differences in transistor bias, minute unmatchedness of transitors,

No. NFB takes care of this. Look at passive components, bad electrolytic coupling caps, unmatched volume pot etc

 

[anatech]

The cap that goes from the negative feedback to ground through a resistor is opening up. That will reduce the gain - to unity when the cap is completely open or anywhere in between for partial open.


-Chris

 

[rhymeswthorange]

How can I hunt this cap down?

 

[anatech]

C211 & C212 should be 47 uF. C201 & C202 are 1 uF, check those too.

-Chris

 

[rhymeswthorange]

do you have the schematic to my amp?

 

[rhymeswthorange]

C211 & C212 are 33uf
C201 & C202 are 1uf
C266 & C265 are 47uf

 

[rhymeswthorange]

By "check" you mean replace and see?

 

[kamskoma]

SU-3500

Hi,

It seems that this is the right place to find people with a Technics SU-3500 schematics I need it very badly.

Thanks

The Kamskoma

 

[anatech]

Hi rhymeswthorange,
Gottum service manual, but no scanner. I'll try to help best I can. For the cost, just replace the caps and see what comes out.

Hi kamskoma,
Don't know about yours, can't seem to find it. Sorry.
-Chris

 

[rhymeswthorange]

Have any suggestions as of brands to use? The caps in there actually look very similar to modern Xicon packaging... I wonder if they are original? 'Cause the power supply caps look nothing like them besides a common cylindrical shape. Can I use some plain old dirty Xicons, or should I opt for something a litte more refined like Elnas? Does it really matter in this application?

 

[K-amps]

If I had Fe207's.... I get a nice reliable amp and not muck with the Technics, one slip and you will blow those nice drivers..... Just my humble opinion.....

 

[rhymeswthorange]

so what kind of amp would you recommend? Remember that I am a humble college student and cannot spend a fortune.

 

[K-amps]

Whatever your budget allows..... whatever sounds good to your ears... just not a half broken amp.

 

[anatech]

Hi rhymeswthorange,
Use whatever new caps are in stock. They will be better than the original ones easy.

-Chris

 

[rhymeswthorange]

Nichon PW series OK? Low impedance... but says well suited for switched power supplies. I think I'm going to replace all the electrolytic caps in my amps using as many panasonic FC series as I can and filling the leftover values up with the Nichion PW's (FC's don't have very small capacitances with low voltages). Mayeb this question is a little absurd, but I really don't want anything damaged or sound worse... it sounds very nice now and putting aside the left channel being weak, this amp is awesome.

 

[anatech]

Hi rhymeswthorange,
They should be fine. Asking about brands of caps is like asking what wine is the best. Dangerous question at the best of times.

Newly manufactured caps are better than those made a while ago. Manufacturing processes are better. Except of course the terrible caps that went into many motherboards and some car decks.

-Chris

 

[rhymeswthorange]

Oh, one thing I just noticed - I can hear a radio broacast out of my right speaker (strong side) and it's silent on the left. Problem? Indication?

 

[anatech]

Change the caps first and report back. This may resolve other funny problems, or at lest make the clues more consistant.
-Chris