Update...
well i'm a bit ashamed !!!
I had given up on this amp and was back on a valve amp i'm building
had a bad distorded noise with that amp. Could'nt find the problem.
Rings a bell ? Bad fuzzy sound ? can't find the fault ? DAMN ! what if it's my f*** test speaker ???
BINGO !
My speaker is fried ! With another speaker my valve amp was flawless.
How come i did not think about it earlier...
Well, back to that SS amp.
I don't know why my speaker fried but it must have happened as i was working on that SS amp. Might be a coincidence or not, but i get 400mV DC on the speaker output. Is it enough to fry a speaker ?
Well, i don't want DC so i installed 2 big 330uF before speaker out. Now i get 0mV DC accross my speaker and i was able to test the amp with another speaker. Good sound ! That amp is working.
Now i have to deal with some slight "hiss" so it's not over but damn, what a fool...
Thanks a lot for your help anyway ! still need to get rid of the hiss !
well i'm a bit ashamed !!!
I had given up on this amp and was back on a valve amp i'm building
had a bad distorded noise with that amp. Could'nt find the problem.
Rings a bell ? Bad fuzzy sound ? can't find the fault ? DAMN ! what if it's my f*** test speaker ???
BINGO !
My speaker is fried ! With another speaker my valve amp was flawless.
How come i did not think about it earlier...
Well, back to that SS amp.
I don't know why my speaker fried but it must have happened as i was working on that SS amp. Might be a coincidence or not, but i get 400mV DC on the speaker output. Is it enough to fry a speaker ?
Well, i don't want DC so i installed 2 big 330uF before speaker out. Now i get 0mV DC accross my speaker and i was able to test the amp with another speaker. Good sound ! That amp is working.
Now i have to deal with some slight "hiss" so it's not over but damn, what a fool...
Thanks a lot for your help anyway ! still need to get rid of the hiss !
Attachments
ok!
i have a bad inductor in the preampEQ
schematics says "10mH 78ohms"
where can i find a suitable replacement ? any smal inductor will do? or should it be special for audio ?
i have a bad inductor in the preampEQ
schematics says "10mH 78ohms"
where can i find a suitable replacement ? any smal inductor will do? or should it be special for audio ?
At my favorite distributor inductors are sold by inductance & current rating. A larger current rating than necessary would allow you to install series resistance to the right value. I've bought stock resistors of 1,1.2, 1,5,2.2,3.3,4.7,6.8,7.5,8.2 values over the years, your stock bin may not be so equipped.
About the hiss. This is so old it probably has carbon comp resistors, which hiss some at 100 k and above. I'd replace the 82k and the 100k with metal film resistors which were audibly quieter in my ST70 amp. Vishay, multicomp, welwyn have all been fine.
You may get away with 25 vac signal passing through a 315 WV electrolytic cap, but I put them back to back for speaker test. If the 330 uf capacitor has no + pin, it may be plastic film and hence perfect. Except for not passing much bass. 2200 uf speaker cap is more usual. My ST120 has 3300 uf at 60 W/channel. I've got 40 year old 6800 uf series a 10000 uf minus to minus I use for speaker checking amps under repair. It makes a little distortion at low volume on high frequency signals as top octave piano. Look at various speaker protection threads for better long term monitoring of your amp DC and disconnect. Dual nfets is compact, requires almost no heatsink.
About the hiss. This is so old it probably has carbon comp resistors, which hiss some at 100 k and above. I'd replace the 82k and the 100k with metal film resistors which were audibly quieter in my ST70 amp. Vishay, multicomp, welwyn have all been fine.
You may get away with 25 vac signal passing through a 315 WV electrolytic cap, but I put them back to back for speaker test. If the 330 uf capacitor has no + pin, it may be plastic film and hence perfect. Except for not passing much bass. 2200 uf speaker cap is more usual. My ST120 has 3300 uf at 60 W/channel. I've got 40 year old 6800 uf series a 10000 uf minus to minus I use for speaker checking amps under repair. It makes a little distortion at low volume on high frequency signals as top octave piano. Look at various speaker protection threads for better long term monitoring of your amp DC and disconnect. Dual nfets is compact, requires almost no heatsink.
BF315 is not on the amp schematic. Is that in the graphic equalizer? Have no euro transistor experience, Phillips&Telefunken were never big suppliers here. MPSA06/56 should replace any .5 W amp transistor with <60v rail, 2n5401/5551 replace anything 60 to 120 v rail, but they are ebc. If ecb .5 W I found some BC639/640 at farnell last year to replace 25 ecb counterfeit "transistors" in a swell engine repair pcb. If there are round heat sinks on them you'll have to look for TO5/TO39 parts which are quite rare in EBC.
If none of above post a thread under parts. Lots of europeans on this website.
If none of above post a thread under parts. Lots of europeans on this website.
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changed my wiring so the 330uF are back to back (minus to minus) and one + connected to speaker + and the other + to amp out +.
On my first wiring one cap was useless (from amp ground to speaker ground...)
i'm good with the power amp now. thanks !
i ordered some cheapos 2N3906 to swap with the BF315 to test.
On my first wiring one cap was useless (from amp ground to speaker ground...)
i'm good with the power amp now. thanks !
i ordered some cheapos 2N3906 to swap with the BF315 to test.