Technics SU-7700

rhymeswthorange · 11th April 2005, 08:14 AM

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 · 11th April 2005, 08:19 AM

Quote:

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 · 12th April 2005, 01:24 AM

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 · 12th April 2005, 09:29 PM

How can I hunt this cap down?

anatech · 12th April 2005, 09:45 PM

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

-Chris

rhymeswthorange · 13th April 2005, 09:50 AM

do you have the schematic to my amp?

rhymeswthorange · 13th April 2005, 09:50 AM

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

rhymeswthorange · 13th April 2005, 09:50 AM

By "check" you mean replace and see?

kamskoma · 13th April 2005, 06:46 PM

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 · 14th April 2005, 12:43 AM

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

11th April 2005, 08:14 AM	#1
rhymeswthorange diyAudio Member Join Date: Apr 2005 Location: Grey Eagle, Minnesota	Technics SU-7700 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

13th April 2005, 06:46 PM	#9
kamskoma diyAudio Member Join Date: Feb 2003 Location: Nordkap	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 __________________ Generatore di Segnali Sinusoidali

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12th April 2005, 01:24 AM	#3
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	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

12th April 2005, 09:29 PM	#4
rhymeswthorange diyAudio Member Join Date: Apr 2005 Location: Grey Eagle, Minnesota	How can I hunt this cap down?

12th April 2005, 09:45 PM	#5
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	C211 & C212 should be 47 uF. C201 & C202 are 1 uF, check those too. -Chris

13th April 2005, 09:50 AM	#6
rhymeswthorange diyAudio Member Join Date: Apr 2005 Location: Grey Eagle, Minnesota	do you have the schematic to my amp?

14th April 2005, 12:43 AM	#10
anatech diyAudio Moderator Join Date: Jun 2004 Location: Georgetown, On	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

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