Hi, after playing with a dead Samson S700 amplifier with pretty good results after modification and upgrades, I've decided to also modify/upgrade my S500 tweeter amplifier.
The upgrade/modification was astonishing, the amplifier BIAS adjustment was very smooth and either pot adjust does not interfere with each other like previously did when adjusting, the previous hiss/noise was lowered significantly, however my tweeters now sound a lot clearer but also a bit analytical, I guess is due the possibly reduction in distortion/noise, however this is by hear and purely subjective opinion.
Parts used:
Profusion UTC 2SA1837 / 2SC4793 as drivers.
Toshiba 2SA1943N / 2SC5200N as VAS.
Between I've previously said that I will left the stock 2SA1492 / 2SC3856 Sanken transistors but opted to completely upgrade the whole unit regardless, also the modification is pretty much the same as I did on the Samson S700, note: I've also replaced the 47-ohm BASE resistors(R131/132/231/232) on the drivers for a 100-ohms fuse-resistors plus also replaced the BIAS pots with Bourns 3266W-1-103LF for smoother adjustments.
Here are the images of the modification and upgrade:
Jumpers closeup for reference.
Applying new thermal paste.
The amplifier module finished next to the removed lateral fets with the rest of its circuit parts, and the upgraded transistors/resistors/pots.
Module in place ready for testing and BIAS adjustment, I've used 150W the bulb for initially startup as usual.
Regards
The upgrade/modification was astonishing, the amplifier BIAS adjustment was very smooth and either pot adjust does not interfere with each other like previously did when adjusting, the previous hiss/noise was lowered significantly, however my tweeters now sound a lot clearer but also a bit analytical, I guess is due the possibly reduction in distortion/noise, however this is by hear and purely subjective opinion.
Parts used:
Profusion UTC 2SA1837 / 2SC4793 as drivers.
Toshiba 2SA1943N / 2SC5200N as VAS.
Between I've previously said that I will left the stock 2SA1492 / 2SC3856 Sanken transistors but opted to completely upgrade the whole unit regardless, also the modification is pretty much the same as I did on the Samson S700, note: I've also replaced the 47-ohm BASE resistors(R131/132/231/232) on the drivers for a 100-ohms fuse-resistors plus also replaced the BIAS pots with Bourns 3266W-1-103LF for smoother adjustments.
Here are the images of the modification and upgrade:
Jumpers closeup for reference. Applying new thermal paste. The amplifier module finished next to the removed lateral fets with the rest of its circuit parts, and the upgraded transistors/resistors/pots. Module in place ready for testing and BIAS adjustment, I've used 150W the bulb for initially startup as usual.Regards
Hi Craig, unlike the soft-gel(no filler inside) silicon rubber pads who molds to the contact surfaces(commonly found on laptops vga cards etc), this particular/generic thermal pads has a very uneven surface and somewhat hard for the transistor to mold-in plus they have filler fibers inside, hence they performance drastically improves with thermal paste, either ceramic based or the grey one without metal/carbon oxides who may corrode the pad.
My own experience with this fiber-filled thermal pads is that they need the compound regardless for high power applications while they are ok for low power ones.
Here is the closeup of this generic pads who sell around the net:
Here is what happens when a transistor overheat on this particular thermal pads:
Look closely how the surface changed its aspect, unfortunately I don't have the thermal pads who almost fully fusion to the transistor metal, I have to peel them and they where semi toast.Here the lower transistor has the normal/common look:
So concluded that running the transistors with the generic thermal pads plus thermal paste does make them work way cooler, and it was even easy to confirm by turning up the BIAS and just touching the front plastic body of the transistors, after added the thermal paste they where just cold and I had to even re-adjust the BIAS as it changed drastically.Regards