allanmatters
Active Member
Recently picked up a pair of Pioneer HPM-700 speakers which i hoped to use with my vintage Pioneer A-7 amplifier. Unfortunately on the day i bought the two babies home my amp was giving distortion on the left channel. After thorough checking by my dad said he found the transistor legs(one of them connected to the left heat sink) was loose from its body inside!! Every time we used to press the mother board it use to come clear(no dry or loose solder- checked with meter for reading everywhere). But I wanted to do a good job so i bought 4 pairs of Sanken transistors which where equivalents, before changing all 4 i tried just one channel with the new transistors . so it was right channel old transistors (Toshiba 12 amperes) & the left channel new transistors (15 amperes), this was wrong i guess cause when i started it . the protection circuit dint even kick in! It went straight to the main fuse and BOOM. then i changed all 4 transistors to the Sanken(15amperes) ones and the left side was perfect, no distortion like before. Right side was giving distortion now. the fault was the transistor on the pre amp board A985. It was short, got a new one and changed it but still no difference. the new transistors are good even checked them by taking them out. But still stuck with distortion.
my dad has studied the diagram from the book too. But hes so slow & this is taking ages like weeks . i was thinking of buying all the small mini transistors for the right side which is on the preamp mother board to fix the problem cause the main board where i fixed all 4 transistors are perfectly getting the desired voltage except 1 single transistor on the right channel. SO frustrating
Pioneer a-7
this amp is amazing it really matches the HPM-700 i bought with a rich bass i have missed hearing for a long time, the midrange is simply beautifull , the sound of the vocals is so calming on a low volume especially . Never heard such a sound, reminded me of a couple of Bose speakers which i used to listen too . But the a-7 dangerous if you dont know how to use it you could burn the two speakers.
my dad burnt his jamo proffessionals with this same amp. they were rated at 200 wpc and maximum 280 wpc. this pioneer a-7 is 70 wpc with 75 or 78 being max
he was telling me the jamo woofer coils were burnt inside
here below is a pic of the old transistors which were bleeding. I couldent find them anywhere so i had to buy equilants
the new Sanken transistors which did the job well , almost . If only i had changed all 4 of them i wouldent have blown anything else
my dad has studied the diagram from the book too. But hes so slow & this is taking ages like weeks . i was thinking of buying all the small mini transistors for the right side which is on the preamp mother board to fix the problem cause the main board where i fixed all 4 transistors are perfectly getting the desired voltage except 1 single transistor on the right channel. SO frustrating
Pioneer a-7
this amp is amazing it really matches the HPM-700 i bought with a rich bass i have missed hearing for a long time, the midrange is simply beautifull , the sound of the vocals is so calming on a low volume especially . Never heard such a sound, reminded me of a couple of Bose speakers which i used to listen too . But the a-7 dangerous if you dont know how to use it you could burn the two speakers.
my dad burnt his jamo proffessionals with this same amp. they were rated at 200 wpc and maximum 280 wpc. this pioneer a-7 is 70 wpc with 75 or 78 being max
he was telling me the jamo woofer coils were burnt inside
here is the two new babies i cant enjoy completely only because of the distortion
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