| st2_998 |
I'm very satistfied of my new old :D amp!
Due to its age, I was considering a power supply recapping, I'm pretty sure someone worked on it and can give me some valuable advice :)
And... where can I find the schematics? I took a glance to Model 1's one but the PS appears to be wired in a different way.
Thanks everybody for dropping opinions and help. |
|
|
| Nelson Pass |
| It's pretty much the same. Higher voltage, lower bias. |
|
|
| st2_998 |
I was thinking about swapping the two caps in series for each supply branch with one only (47.000 uF 100Vdc instead of 2x 24000 uF 65 Vdc, total Vdc present is 76 Vdc), leaving the secondaries' center taps unconnected (insulated). Possibily 10 uF poly bypass on each.
Is all that a bad idea?
Thanks. |
|
|
| Nelson Pass |
I think the amp uses those center taps to establish ground. You
would probably get some undesirable results if that's the case. |
|
|
| st2_998 |
| I believe this is surely true for the 1A, as far as I can understand from the schematics. Unfortunately I don't have the schematics for the 3A power supply, but in the amp it seems that ground (a star center) is tied to one each of the secondaries' outputs (one +, one -), center taps end inbetween the two series supply caps and nothing is connected to them except power LED. |
|
|
| jupiterjune |
| quote: | | was thinking about swapping the two caps in series for each supply branch with one only (47.000 uF 100Vdc instead of 2x 24000 uF 65 Vdc, total Vdc present is 76 Vdc), leaving the secondaries' center taps unconnected (insulated). Possibily 10 uF poly bypass on each. |
I recently opened up a Forte for a friend of mine. I believe it was a 3a. (did they make it up to 7a?)
If you can post a picture of the inside, I could provide some better comments (if its the same ps).
JJ |
|
|
| st2_998 |
Here's a schematic of the Forté Model 1A power supply
here is how it looks like (to me!) in the Model 3 I own
I'll post pics asap, thanks |
|
|
| P. Lambda |
Looks right. I saw some old usenet postings that led me to
turned my Forte 3 into a 1 -- I only had to reroute the wires.
Now completely class A -- sounds better. |
|
|
| st2_998 |
Here are the pics
Blue connected to ground (busbar)
Red connected to rectifier bridge and supply fuses to the channel boards
Orange should be center tap
It appears that using one cap instead of two could be possibile, center tap has to be disconnected but that shouldn't cause problems.
Is that right?
Thanks |
|
|
| jupiterjune |
Clearly that is different than the amp I worked on.
I wouldn't hazard to try to advise you on something I haven't done. If you don't mind the possibility of letting all the magic smoke out of your amp, then forge ahead with the PS re-do.
Otherwise, replacement in kind is always a safe way to go.
Good luck!
JJ |
|
|
| st2_998 |
Well, I don't really think of something possibily blowing up.
I don't have a variac but I can disconnect the channel fuses isolating the PS and checking voltages before reconnecting the audio circuitry.
Thanks. |
|
|
|
