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Audio Research SP10 mkII vs MkI Sound Signature question

M

marknoir

Active Member
Hello all. This is a question to audio research gurus.

What is the difference in sound between Audio Research SP10 mkI and mkII?

I used to have a MkI about 15 ys so, which I have restored from a total bucket case. It was fully rebuilt, and sounded great to my ears. It was very open, very clear, and one listener even found it s bit sterile/clinical. At some point m my situation changed and I had to sell it. About 6 months ago I picked up a mkII in need of repair. I’ve repaired it, replaced all electrolytics in PS, the dreaded tantalum in protection circuit, a few ICs and half of the regulators etc. Main chassis still has original yellow coupling Rel-Caps. It works like new, but sound signature it’s totally different - it’s very, VERY warm, fat and juicy, definitely on dark side. I’m not a fan of this kind of sound. I’m wondering why it sounds so different from that mkI.
Thx
 
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I don't have a direct answer to your question, but I will ask another which might help someone else

Do you know which revs specifically? Per ARCDB there are 7 revisions to the SP10, and it says rev 1-5 are called the MK1 and 6-7 are the MK2.

no modification instructions for this model so I have no clue what the technical differences could be. Also never heard either so no opinion there.
 
gadget73 said:
I don't have a direct answer to your question, but I will ask another which might help someone else

Do you know which revs specifically? Per ARCDB there are 7 revisions to the SP10, and it says rev 1-5 are called the MK1 and 6-7 are the MK2.

no schematics or modification instructions for this model so I have no clue what the technical differences could be. Also never heard either so no opinion there.
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I’m not sure which exactly rev mkII I have, but it’s easy to tell mkI from mkII: main visual clue: mkI has one additional solid state regulator for phono in the middle of the board in the main chassis, mkII was switched to fixed bias, there is a rather large empty space in that area, and has fat black wires with power resistors on board near the phono inputs. Both schematics exist. Early versions are all hand-drawn, and there is an updated version done on computer. I have both. I’m not sure which exact mods were done and at what date.
 
There were not many of these preamps in any version, 1-7 to be well compared out there. For this reason it seemed logical to use ai to scrape up all the discussions of them, process them and spit them out. I searched “ sonic differences in the 7 audio research SP-10 versions “ and got a good bit of info that might help.

I try not to post ai regurgitations on boards so leaving that to you. Even adjusting the search term to I vs II versions might improve the answer to your question.

Interesting you find the later version to have more tube bloom in the sound as ARC was moving away from that as the 80s progressed and have moved even further this century to the point that those that like the ‘tube bloom’ seek out earlier gear and those wanting the ARC clarity, detail and such prefer the more modern gear.

Hope we get some good answers in this discussion.
 
Blue Shadow said:
There were not many of these preamps in any version, 1-7 to be well compared out there. For this reason it seemed logical to use ai to scrape up all the discussions of them, process them and spit them out. I searched “ sonic differences in the 7 audio research SP-10 versions “ and got a good bit of info that might help.

I try not to post ai regurgitations on boards so leaving that to you. Even adjusting the search term to I vs II versions might improve the answer to your question.

Interesting you find the later version to have more tube bloom in the sound as ARC was moving away from that as the 80s progressed and have moved even further this century to the point that those that like the ‘tube bloom’ seek out earlier gear and those wanting the ARC clarity, detail and such prefer the more modern gear.

Hope we get some good answers in this discussion.
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I did use AI to find some answers. Got a lot of gibberish about old caps, old tubes etc, but omission of that separate regulator on mkII was mentioned as possible culprit. One thought has crossed my mind, that perhaps after mkI was seen by some as too “clinical”, ARC changed there sound to more “tubey” in mkII? I don’t know. Thx.
 
I've have had numerous ARC tube preamps, from the SP3 to the 40th anniversary and have to say, what your describe, and the one listener comments, pretty much nails their house sound during that time. I have listened to a SP10 at length but I cant remember which version it was. It did have the ARC house sound, and not sounding dark. It's a nice preamp.

"it’s very, VERY warm, fat and juicy, definitely on dark side"
is not something at all that sounds like what a ARC should sound like, especially during that period, as other have earlier said. Have you put this preamp on the scope and on distortion analyzer? Maybe something is going on inside from the rebuild, re-check the soldering? Maybe the certain caps and resistors you replaced is giving it a different sound? Was the power supply chassis worked on, and changed? Is it getting the correct voltages, and amperage into the pre chassis? You might also want to run music through the PRE for about 50-100 hrs (if you haven't yet) and see if there's any sonic changes?

Personally, I like a bit of the Conrad-Johnson preamp warm tube sound, but typically that is not the characteristic of ARC preamps of that era.
 
mr_macgee said:
I've have had numerous ARC tube preamps, from the SP3 to the 40th anniversary and have to say, what your describe, and the one listener comments, pretty much nails their house sound during that time. I have listened to a SP10 at length but I cant remember which version it was. It did have the ARC house sound, and not sounding dark. It's a nice preamp.

"it’s very, VERY warm, fat and juicy, definitely on dark side"
is not something at all that sounds like what a ARC should sound like, especially during that period, as other have earlier said. Have you put this preamp on the scope and on distortion analyzer? Maybe something is going on inside from the rebuild, re-check the soldering? Maybe the certain caps and resistors you replaced is giving it a different sound? Was the power supply chassis worked on, and changed? Is it getting the correct voltages, and amperage into the pre chassis? You might also want to run music through the PRE for about 50-100 hrs (if you haven't yet) and see if there's any sonic changes?

Personally, I like a bit of the Conrad-Johnson preamp warm tube sound, but typically that is not the characteristic of ARC preamps of that era.
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Agreed, it does sound right now more like a CJ.
Like I mentioned in the post, PS was rebuilt: all electrolytic caps were replaced, s well as there regulators, a couple of IC chips. New caps are as close to what ARC used as possible. Main chassis is pretty much all original. All vintages are close to spec. So far this is a mystery to me. I have a scope but not distortion analyzer.
 
Agreed that the SP10 should not sound "fat juicy"--- but it may sound that way versus modern preamps... I may have reviews of the pre from the time period from IAR or others if I can dig them out I will share. I have listened to an SP10 extensively back in the day and it was anything but fat , juicy and dark.. but who knows on your sample. No mention of the tubes in yours. they can make a profound difference. Amperex and Mullards are much warmer than Siemens and Telefunkens. If you are on new production then all bets are off. It is a tube eating machine. Very difficult to keep tubes in it ... hence the reason for the SP 11 that followed it.
 
Kcin, has a good point about trying different tubes, and their sound. It can be said Telefunken is more akin to the ARC house sound, and Mullard is more akin to a CJ sound.

I know it's no easy matter and costly re-tubing the SP10 with its 12 tubes, but perhaps borrowing or temporarily do some tube rolling on the valves that make the most difference in the sound. Maybe just roll the just the phono section, or line stage, whichever you use for critical listening and see if it returns back to some of the sound you remember. I know in my preamp it can make a big difference.

May I ask which amp is being fed from this preamp?
 
mr_macgee said:
Kcin, has a good point about trying different tubes, and their sound. It can be said Telefunken is more akin to the ARC house sound, and Mullard is more akin to a CJ sound.

I know it's no easy matter and costly re-tubing the SP10 with its 12 tubes, but perhaps borrowing or temporarily do some tube rolling on the valves that make the most difference in the sound. Maybe just roll the just the phono section, or line stage, whichever you use for critical listening and see if it returns back to some of the sound you remember. I know in my preamp it can make a big difference.

May I ask which amp is being fed from this preamp?
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I will roll tubes. I don’t have Teles, or Millards. I’ll see what I have, but they are probably lowly current production EH. I already played with different tubes in the phono section (which I find the darkest/fattest), and didn’t hear much difference. It feeds a pair of big Kavent monoblocks, solid state. Same amps that the mkI was going into. I used Parasound JC3+ as my phono stage before I got this SP-10, and still have it, and it sounds very open, sometimes even a bit to much so. Thx
 
I replaced all tubes in main chassis with matched pairs of new Electro Harmonix 6922. These are the tubes that - from what I know - ARC sells as standard, albeit screened for noise and microphonics. I have to give them a few hrs to burn in. So far I can tell it sounds a bit drier, not as smooth, but general balance is still the same. And these are the tubes that I had in it before, a mixture: 6N23P Voschod, Amperex Jan7308 goldpin, Amperex Bugle boys, and 2 Mullards. I tried different tubes in that mkI too, I remember, and its signature still remained generally the same.
 
I worked on an SP9 not long ago, and the original Rel-Caps were fine. I left them alone, and honestly I thought it sounded pretty good. Film caps tend to be reasonably neutral anyway.
 
gadget73 said:
I worked on an SP9 not long ago, and the original Rel-Caps were fine. I left them alone, and honestly I thought it sounded pretty good. Film caps tend to be reasonably neutral anyway.
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Thank you. I know that there was a factory mod on SP10, where they replaced all Rel-Caps with white InfiniCaps. I have them and some MIT MultiCaps. I find both more open/brighter sounding.
 
you know, I might be mixing up the SP9 MKII and the D70. The D70 definitely had RelCaps in it. The SP9 MKII had some white capacitors in there now that I think on it. Maybe those were the InfiniCaps. They were OEM, whatever they were.
 
gadget73 said:
you know, I might be mixing up the SP9 MKII and the D70. The D70 definitely had RelCaps in it. The SP9 MKII had some white capacitors in there now that I think on it. Maybe those were the InfiniCaps. They were OEM, whatever they were.
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You are correct. SP9 mkII came out later, so most likely had newer caps in it.
 
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