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Hello everyone,
I have an Audio Research SP9 MK2 preamp, does anyone have any sudgestion to improve sonic sound similar to SP9 MK3? Like fast recovery rectified diodes, coupling capacitors?
Thank you in advance.
Thomas
Follow Ups:
I had extensive work done to my SP9 MKII by Parts Connexion. I am very pleased with the results. Parts include: DACT attenuator, Mundorf Supreme Poly Mcaps, Relcap Teflon Film caps, Jensen four pole PS cap, CREE schottky diodes, REIKEN and Tantalm resistors, gold plate ceramic tube sockets, some rewiring, Vampire RCAs and Sound Coat
Very interesting modification.
Is that expensive for this Mod?
TT
The parts were about $550 including the DACT which was near $200. I am sure that I could not get my money back if I sold the unit but since I love the way that it sounds I have no interest in selling.
The pics there indicate clearly different coupling caps among the versions, but there certainly are better ones around now compared with those available in the '90s.
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Tin-eared audiofool and parttime landscape fotografer.
http://community.webshots.com/user/jeffreybehr
I had a Mk3 years ago, it was pretty nice. I would not go poking around in there tring to upgrade things if I were you. They are all circuit boards so its not too easy, and will just depreciate the resale value.
The most I did to mine was install a IEC and roll tubes.
Your best bet is to send it to ARC and let them do the upgrade to MK3 status, or just sell it and get a nice MK3 off Audiogon.
Allan.
If you have some amp building experience, it's not very difficult to upgrade the coupling and output caps.
For the line stage section, Couplers are .47uF Wonder Caps (white)by-passed with .01 Wonder caps. The outputs are 5uF REL caps (yellow), also by-passed. Remove them along with all the by-passes (leave the 2 .01s on the bottom of the board) and replace with your fav flavor. Big improvement.
The 2 electrolytics are now old and Chris at ARC recommends replacing them now.
Don't fool with the diodes, with fancy diodes you will probably get too much voltage drop on the filaments. On that subject, on the bottom of the board are 2 paralleled WW resistors, prob'ly a 50 and a 75Ohm. Check your filament voltage. The resistors run hot (the board is prob'ly darkened there) and your voltage may well be too high as the Rs go out of spec. Replacing with the same values will cure but you may have to play with the values.
Biggest bang is to replace the horrid Alps pot with a TKD or PEC, but not a trivial excercise. I had to cut back the solder pins on a TKD to just below the perforations in the pins and run teeny-weeny, short wires from those holes to the board eyelets while I was suspended from the ceiling to leave my hands free
Remove the toroidal transformer from the side of the case and replace it after fixing EAR SD-40 damping layer to the case.
Thanks for your feedback, I do have a strong electronic backgound so hand on modification is not an issue. Just need a sudgestion from anyone own AR preamp with mod to bring more beautiful sound to my ears. I am thinking to replace yellow 5MF/250VDC output coupling cap to same value Paper oil cap, Wonder cap 0.47MF to Paper oil same value. All Bypass caps should keep it or removed permanently?
For the rectified diode , AR used 1N4006 on the High voltage supply but I think replace fast recovery diode NTE580 will do any better??? For the tube filamenton 6DJ8 AR used 1N4005.Should I replace all with fast recovery diode? Need more advise please.
Edits: 12/24/08 12/24/08 12/24/08
Definitely begin w/o the by-passess. ARC used them to improve the then SOTA Wonders and RELs that are dull sounding.
Whether you by-pass your upgrades is a matter of taste.
I'm a big fan of Obbligato caps and used a copper case .47 film and oil and film 5.0. No by-passes.
There is a parallel coil and resistor in series with the 100uF electrolytic; be very careful with it, the wire and plastic bobbin are quite fragile. Don't ask me how I know. Nothing that superglue couldn't fix, tho'.
Jim Hagerman always uses 1N5821 Schottkys on his filaments, the recovery and rise specs are very good and there is little voltage drop.They're in my Aikido. I recently tried Fairchild Stealth 4A, 600 volt from Michael Percy to replace them and lost more than 1/2 volt, 5.65 volts with a jumper. Silicone Carbide 600 or 1000 volt Cree or Infineon work well on HT and made an EL-34 amp noticeably quiter.
I've read that by-passing the delay circuit makes an audible improvement but haven't yet tried it. have fun.
Thanks,
The Obbligato does not sell 5.0MF cap, So I have to get 4.7MF in paralell with 0.33mf. I think that would be close to 5.0MF. The 6.8MF is a little over the original AR SP9 MK2 value.
TT
Most preamp manufacturers select output-cap values that are very large because they don't know what poweramp the preamp will be driving.
What's the value of the output cap's load resistor? (I asked about a schematic earlier but you've not responded.) That resistor and the poweramp's input-load resistor are in parallel. What's the resulting high-pass Filter Point with your poweramp? With tubed poweramps' high input impedances, the FP is often below 1Hz. One can end up with an output-cap value creating a FP of 1 - 2Hz with smaller-value caps if you know what poweramp the preamp is driving.
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Tin-eared audiofool and parttime landscape fotografer.
http://community.webshots.com/user/jeffreybehr
I am Sorry mis understood your question about the Schematic of Sp9 MK2 preamp. I did not have copy machine to scan that Schematic at home.
BTW, I used this preamp SP9 MK2 to drive Krell KSA 150 Amp.
My CD DA11 transport Counterpoint , Da-10 Digital converter, JBL wood horn, JBL 077 super tweeter, JBL 10" Mid range and JBL 15" woofer, all component are vintage , with customize cabinet ( cabinet plan came from Vintage JBL website).
Just want to improve the sound little more, not try to heavily modified preamp ( replace high quality coupling and output capacitors).
regards,
tt
"I am Sorry mis understood your question about the Schematic of Sp9 MK2 preamp. I did not have copy machine to scan that Schematic at home."
How 'bout a scanner and then post the pic? Or simply tell us the value of the output-cap load resistor.
"Just want to improve the sound little more, not try to heavily modified preamp (replace high quality coupling and output capacitors)."
I never suggested you heavily modify the preamp. If you're not interested in saving some money by buying correct-value instead of oversized output-coupling caps, that's OK with me.
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Tin-eared audiofool and parttime landscape fotografer.
http://community.webshots.com/user/jeffreybehr
'Depreciating the resale value' is NOT a consideration for me.
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Tin-eared audiofool and parttime landscape fotografer.
http://community.webshots.com/user/jeffreybehr
brands, or do you only upgrade by tweaking.
I'm merely responding to your advice NOT to improve some piece of equipment because you think the resale value will decrease.
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Tin-eared audiofool and parttime landscape fotografer.
http://community.webshots.com/user/jeffreybehr
Good morning,
Thank you for your responsed, I don't think modified to this SP9 MK2 will reduced the resale value unless I threw the original parts away, normaly I will keep them. If I decide to sale this preamp then I will put the parts back.
But at least the preamp after the Mod will make my ears happy, life to short, modified first before my ears go bad due to the Aging.
Happy Holiday
TT
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