Modding my Soundcraftsmen

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Hi all, First time poster:)

I have a Soundcraftsmen RA7503 amplifier that I am planning to modify. I have the schematics and have done some lurking here plus some preliminary reseach. The amp is a Class H design with constant 62V rails and 93V variable rails controlled by a darlington pair. The output transistors are T03 type, and currently a mix of origonals plus some MJ15023 and MSJ 6343. This amp has obviously been repaired multiple times.

So the first two things I want to do is replace all the output transistors and beef up the power supply. Transistor options I am looking at are MJ15022/23, MJ15024/25, MJ21193/94. But I am looking for suggestions on the best transistors to use.

As for the power supply, I modified the schematic in photoshop. All the parts in red would be added.
http://umsis.miami.edu/~rcarter/SoundcraftsmenPowerSupply.JPG

It seems the filter caps are way too small, esp when the 93V rails are used. If I calculated it right, about 92,000uF would be ideal when the 93V rails are used. Oh, maybe I should state that the amp is rated at 750 WRMS @ 8ohms bridged. Unfortunately I have no clue what the rating of the transformer is, but for now I don't think I'll be replacing it.

So what would be reasonable for C2 an C3? I was thinking about just ditching the old caps, I seriously doubt the 24 year old caps in there now are as good as you can get today.

For the transformer caps C4 & C5 would 100nf be good?

For the series RC filters I'm not even sure the way I drew it on the schematic would work right, since the extra rails complicate things. So would this work ok and if so what values should I use?

Thanks so much any help you can give me.

Robert Carter
 
ok, so I know I'm a noob but all the more reason to help me right?
Please, if you can give any input at all, by all means do so. I know there are lots of smart people on this board! I only understand about 50% of what I read here! If you need more info, ask, and I'll try my best to deliver.

Thanks,
Robert
 
Hi SleeperSupra!

At long last someone is interested in my post!:)

well, I did swap out the big caps, and that is as far as I have gotten. I replaced the old 11,000uF caps with Aerovox M series 41,000uF caps, and the the 22,000uF caps were replaced with Aerovox M series 39,000uF caps. I also rewired the whole amp, rerouting wires to make runs shorter, neater, and increased the size of the wires between the AC input and the power supply transformer. The amp looks beautiful inside now, but more importantly, Just these mods alone made a huge difference in the performance. Like most people say, the bass was a lot more forceful, but it just all around sounds better. I do have a full set of transistors and the small bypass caps to go into the thing when I have time.
What Soundcraftsmen model(s) do you have?
 
My system consists of:

Audio/Video Gear
Hitachi Ultravision 60SBX72B 60" Rear Projection TV
Mitsubishi HSU780 S-VHS Stereo Hi-Fi VCR
Sony DVP-CX985V 400 DVD/SACD Player
Onkyo Integra TXDS939 AC3/THX Surround Receiver
Soundcraftsmen MA5002A Power Amplifier
2 (two) Soundcraftsmen PA5001 Amplifiers
Soundcraftsmen TG3044R Third Octave EQ
Monster Interconnects and Cables
Thiel CS2 Coherent Source Speakers (for two channel)
JBL HT1F THX Surround Speaker System (has two passive 12" subs, three MTTM speakers, and two dipole TM/MT surrounds)
Custom Center Channel Speaker (one 3 1/2" fiberglass mid tweeter with a phase plug, first order crossover, two 10" mid bass drivers and a 15" passive radiator)...

I also have an NAD 2400 PE Power Amplifier and a pair of Linn LS150 Helix's that I am using in my secondary system.
 
Robert are you still out there?If so hope things are going good these days!I'm posting here because my membership is still "under moderation" so can't e-mail directly.I wanted to find out how your mods have worked out and am wanting to do the same to my RA7501.Along with the cap changes/upgrade,I need to correct my DC offset which is reading up into the 213mv and 342mv range with a negative bias!This,I understand,is corrected by changing the output transistors.I'm the Noob this time!!I went to your schematic download but it was no longer avialable so was wondering if you've still got a copy of that to post or copy and sell me...John
 
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