Soundcraftsmen A5002 X2...

[Loud & Clear]

In my spare time, I am working on 2 Soundcraftsmen A5002 H class amplifiers. These will find a permanent home in my sound system. I have 1 pair of JBL 4350's. The 4350 has 2 - 15" woofers per cabinet. Therefore each 15" woofer, will get its own A5002 channel. That way I get the advantages that are found in running amplifiers into an 8 ohm load. I am working both these amplifiers at the same time.

These S.C. Amplifiers will be highly modified, to fit my particular system needs. This will be a work in progress, and I will Update this thread every chance I get. Which might not be that often, as I have other electronics that paying customers bring me. So this is a bit of a sideline, but my heart & "mind" will be deep into this project...

Note: The JBL 4350, is a biamped speaker system. So everything above 250 cycles will be finding it's way through a Soundcraftsmen A2502. I have tried, tested, and proven these amplifiers, and have found them to be "Extremely Good" amplifiers, and I have worked with "A Lot" of amplifier.

Anyway, I would encourage you to keep an eye on this thread at you leisure. You may find some interesting things you may want to incorporate in your Soundcraftsmen A5002 builds... Thanks... :thmbsp:

And so we begin:

 

[Loud & Clear]

A few parts. I buy em' when I can afford em'...

50K stepped attenuators, to replace the carbon film crap S.C. has installed. Not the very best stepped units, but I can't afford the $169.00ea. for the so called "state of the art" steppers. Also $300.00 worth 1/2W TAKMAN rey audio resistors. :thmbsp:

And I shall move forward... Thanks...

 

[Loud & Clear]

Little help here. Now where was that wire supposed to go again?

And we keep moving forward stay tuned... :thmbsp:

 

[Loud & Clear]

Soundcraftsmen does not keep a very clean house. Lots of wiring that is just "not" needed. Then as most techs. that have been involved with S.C. know, there right amplifiers are hooked to the left speaker terminals. This creates a mountain of criss crossed wiring, not to mention the surprise you receive when checking the DC offset voltage. I'm in the process of changing that scenario on my amplifiers. I have to build a grounding buss, then move on to the 2nd amplifier, to bring it to the 1st amplifiers status... :thmbsp:

Note: Normally I would change the speaker output terminals to the gold plated versions, but these are in good shape and should work just fine. :scratch2:

 

[Loud & Clear]

Capacitor & Rectifier removal... Capacitors will be replaced with my "home brew" capacitor banks... Much work will be involved in the capacitor banks. I like keeping the grey matter stirred up a little...:scratch2: I'll keep you posted... :thmbsp:

 

[hunter00]

http://www.audiokarma.org/forums/showthread.php?t=579967
goodluck with those Soundcraftsmen's ,they were one of my favorite SS amps with my old AR9 speakers

 

[Loud & Clear]

http://www.audiokarma.org/forums/showthread.php?t=579967
goodluck with those Soundcraftsmen's ,they were one of my favorite SS amps with my old AR9 speakers

Wow, those are a real nice pair of amplifiers hunter00... Thank you for the link, but looking at all those amplifiers gave me ideas, that I do not believe I have room within the chassis to try. I'm thinking along the lines of finding a couple "for parts or repair" A5002's, then remove the power transformers. Making a pair of dual mono's out of my A5002's??? Hmmmmm. :scratch2:

 

[hunter00]

Wow, those are a real nice pair of amplifiers hunter00... Thank you for the link, but looking at all those amplifiers gave me ideas, that I do not believe I have room within the chassis to try. I'm thinking along the lines of finding a couple "for parts or repair" A5002's, then remove the power transformers. Making a pair of dual mono's out of my A5002's??? Hmmmmm. :scratch2:

Thx ,Dual mono certainly has its merits.I started with a HK 930{1978,still have a 630}dual mono powered receiver and luved it so much with my ineffient speakers{ar's} that I moved up to the citation 16a's,had 2 of them as well.

The two Soundcraftsmens were great tho.Fueled many a party and always impressed with their seemingly endless power.There were riden hard and put away hot on many occasion!These 2 soundcraftmen ma5002's I bought from a former club owner that had put many miles on them as well,12 hrs a day,6 days a week.I recapped them and still got many yrs out of them,Industrial design,built like a brick shit house,with great SS sonics.

hunter

 

[Xtinc]

Hi Loud & Clear, I'm very interested in this thread and appreciate you taking the time to share. I have a Soundcraftsmen A5002 that is emitting a slight hissing sound in the left channel audible through the tweeter. I can't hear it with music playing, but can in idle with a quit room. I checked bias and left channel read 100mv. I'm hoping to put some effort into correcting the bias and determining/repairing cause of the hiss. I'll be following your rebuild. Thanks!

 

[Loud & Clear]

Hi Loud & Clear, I'm very interested in this thread and appreciate you taking the time to share. I have a Soundcraftsmen A5002 that is emitting a slight hissing sound in the left channel audible through the tweeter. I can't hear it with music playing, but can in idle with a quit room. I checked bias and left channel read 100mv. I'm hoping to put some effort into correcting the bias and determining/repairing cause of the hiss. I'll be following your rebuild. Thanks!

Thanks for tuning in xtinc. That bias seems to be set a little hot. Do the heat sinks warm up fairly rapidly? I've not come to any absolute values on bias voltage, but I am going to try 10mv, and see what I get when that time comes. From what I understand, you need a distortion analyzer and a service manual. However, I've yet to see anyone that can provide me with that documentation what so ever...

As for the hiss type noise in one channel, have you swapped input cables ch A to B and vice versa? What type work have you put into you A5002 i,e, electrolytic cap change out, etc... ?

 

[Xtinc]

Hey Loud & Clear,
I just recently acquired the A5002 and have not performed any maintenance on it. I did swap input cables and insured it was indeed the amp channel. I do have some electronic maintenance experience, but consider it limited. Still trying to decide if I should attempt an overhaul, find a local tech or pass on. I can say even with the high DC offset and low level hiss the amp sounded sweet...and what a beast!

 

[Loud & Clear]

Oh, you meant DC offset, not bias... On these 2 that I am working on, an offset of 100mv would be low lol. I have one channel that is 230mv lol. I'll get to that later when I finish the amp boards up. I'm only just getting started on these. I have to etch circuit boards for the capacitor banks, etc...

Yes, these are decent amplifiers, but generally take a lot of work. I'll even be firing up my powder coating system in the garage, as the top, bottom, and sides need to be glass blasted, then powder coated. Somehow, there is always rust under the factory paint. At least on the later models. I'm hoping they sound as good as the S.C. A2502 mosfet unit, or I'll end up ditching them, and going back to my original A2502 mosfet plan.

 

[Xtinc]

I'll admit I'm very green and just learning... 100mv DC was read on the left channel speaker terminals I believe is DC offset which I confused with bias. Should I try some deoxit on the pots and attenuators and adjust the pots to lower the DC offset?

 

[Loud & Clear]

I'll admit I'm very green and just learning... 100mv DC was read on the left channel speaker terminals I believe is DC offset which I confused with bias. Should I try some deoxit on the pots and attenuators and adjust the pots to lower the DC offset?

Very Nice Gear... Actually, in order to fix your DC offset situation, you have to change out the original differential input transistor pair on each channel, with a nice matched pair of new transistors. I can match a couple pair for you. But you have to be able to carefully solder them in place. The location of the amplifier boards, and there relative complexity, I would not recommend this project for the amateur.

 

[Smallies]

Attenuators are nice, how much? Google came up dry for me.

 

[Smallies]

But I did find a small list of resistors and whether they sounded better frontward or backwards on diy audio.

 

[Loud & Clear]

Attenuators are nice, how much? Google came up dry for me.

I was just planning on deleting the amplifier volume controls, then I decided "with the multiple amps" I will be running, I will need those controls to balance the amplifiers. However, I was "not" about to use the junk pots S.C. had provided for me.

Soundcraftsmen amplifier volume control pots are hooked right on the inputs at the RCA jacks. If you are planning to run just one amplifier, I would render those pots null & void by running directly from the RCA jacks, to the inputs on the amplifier boards, then use the balance control on the pre to take care of your left & right channel balance. Another plus on this type of mod. you can get rid of 10lbs of twisted copper wiring, possibly upping your SNR and making your wallet fatter, when you take all that excess copper to the recycler..

Just put "stepped attenuator" in the search box provided by ePay, and you will see several different varietys, some better than others. Any of those are better than a cheap ancient carbon film pot... :thmbsp:

EDIT: A lot of those attenuators come from china, and I have found them to be pretty darn decent. I realize there is "TONS" of garbage from China flooding the American continent. However, I know the chinese aren't unintelligent. I do believe you will find, behind every piece of chinese garbage lining American shelves, you will find an "American" CEO that is instructing those folks on how they want there items built... Kinda like shooting yourself in the foot... :yes:

 

[Loud & Clear]

Ok, here are the Capacitors & Rectifiers for one amplifier. I would have ordered twice this amount, but I had planned on using "one" capacitor bank. Instead, I've changed my mind - 12 capacitors and 2 rectifiers per channel. I'm going to be wiring to a single transformer. So I do not know if this will qualify for a "true" dual mono unit. I'm guessing not.

Advantages: Lower ESR - Higher Ripple Current - Etc... Then once the banks are in place, I can shorten the Power Supply to Amp Board wiring around 8 feet 8 x 12". So there will be a significant "Decrease" in the induction created by that much wire.

Now here is where it "Really" gets tough. I have to layout the cap & rectifier configuration, do the artwork, then actually etch & tin the boards... As far as I'm concerned, it is a must to tin these PC boards. #1 = Lower Inductance, #2 = copper trace oxidation, as I have never used circuit board masking...

Really stepping out on a limb here, but I think I have it under control. Just a Huge amount of work involved...

Note: These amplifiers will be operating, down to 20hz. I have configured the active crossover, for a 6db boost at 30hz. Hey, if it is on the recording, I want to hear it... :thmbsp:

EDIT: This configuration should "not" require any bypass capacitors... If it does, the bypass caps will be placed on the amplifier boards...

 

[Loud & Clear]

Thought it was time for an update. Here are some pictures of the circuit boards I am going to be etching. Also, I've finally finished the artwork for the pcb's, still need to Laser Jet 4 of the "artwork" images, 2 will be for the right channels, then I will have to do 2 mirror images for the left channels, then of course transfer the images onto the "heavy" copper clad board and then drill and tin the boards...

I decided to go with "vishay" 35 amp rectifiers instead of my previous choice. The .1 film caps that are pictured next to the rectifiers, will be placed across each diode in the rectifiers. This helps slow the diode switching down and help reduce any diode switching "harmonic oscillations"... I've seen this procedure accomplished in O scopes, and precision test gear. Nelson Pass uses this procedure in his amplifiers as well. Can't Hurt... :thmbsp:

 

[Jailtime]

Nice work. I rebuilt an MA5002 once, never again. Wonderful amp once it was finished though.

Your username seems quite fitting, considering you'll have a channel of 5002 for each JBL woofer. :thmbsp: