Modding my Soundcraftsmen

splsaab · 18th November 2004, 07:14 AM

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/Soun...owerSupply.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

splsaab · 20th November 2004, 07:20 AM

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

SleeperSupra · 31st July 2006, 05:28 PM

I know I am bringing a really old thread back from the dead but I wanted to hear how the modifications went.

I am also thinking about doing some modifications to my Soundcraftsmen Class H amplifiers.

splsaab · 31st July 2006, 08:27 PM

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?

Netlist · 31st July 2006, 08:43 PM

If only we could find some schematics.
My old buddy (RA7501) is still collecting dust due to lack of data.

/Hugo

splsaab · 1st August 2006, 06:20 AM

The schematics are available. I bought mine online for around $25USD I believe. I don't remember where, but I can find out for you.

Netlist · 1st August 2006, 07:04 AM

That would be nice, thank you. I believe more members are on a quest for schematics over here.

/Hugo

SleeperSupra · 1st August 2006, 07:45 AM

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.

oPossum · 1st August 2006, 10:49 PM

Quote:

Originally posted by Netlist
If only we could find some schematics.
My old buddy (RA7501) is still collecting dust due to lack of data.

/Hugo

I have the old Class H schematics here:

http://soundcraftsmen.info/Class%20H/

SleeperSupra · 20th February 2007, 12:57 AM

splsaab,

Any updates?

Where did you get the larger Aerovox caps?

I plan to do the same modds with my MA5002A.

18th November 2004, 07:14 AM	#1
splsaab diyAudio Member Join Date: Oct 2004 Location: Fairfax County, VA	Modding my Soundcraftsmen 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/Soun...owerSupply.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

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20th November 2004, 07:20 AM	#2
splsaab diyAudio Member Join Date: Oct 2004 Location: Fairfax County, VA	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

31st July 2006, 05:28 PM	#3
SleeperSupra diyAudio Member Join Date: Aug 2005	I know I am bringing a really old thread back from the dead but I wanted to hear how the modifications went. I am also thinking about doing some modifications to my Soundcraftsmen Class H amplifiers.

31st July 2006, 08:27 PM	#4
splsaab diyAudio Member Join Date: Oct 2004 Location: Fairfax County, VA	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?

31st July 2006, 08:43 PM	#5
Netlist diyAudio Moderator Join Date: Jan 2003	If only we could find some schematics. My old buddy (RA7501) is still collecting dust due to lack of data. /Hugo

1st August 2006, 06:20 AM	#6
splsaab diyAudio Member Join Date: Oct 2004 Location: Fairfax County, VA	The schematics are available. I bought mine online for around $25USD I believe. I don't remember where, but I can find out for you.

1st August 2006, 07:04 AM	#7
Netlist diyAudio Moderator Join Date: Jan 2003	That would be nice, thank you. I believe more members are on a quest for schematics over here. /Hugo

1st August 2006, 07:45 AM	#8
SleeperSupra diyAudio Member Join Date: Aug 2005	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.

20th February 2007, 12:57 AM	#10
SleeperSupra diyAudio Member Join Date: Aug 2005	splsaab, Any updates? Where did you get the larger Aerovox caps? I plan to do the same modds with my MA5002A.

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