View Full Version : Arc Sp-3a-1


jaynemo
12-31-2007, 10:15 AM
I was lucky to find one locally at very decent price and have been contemplating the 3C factory upgrade. I see these stock bring in well over $1000. Other than the typical ARC value factor, what is so special regarding this preamp? I am going to mate it with my VTL Compact 80 monoblocks short term until I can find a matching ARC amp of the same era.

Blue Shadow
12-31-2007, 10:27 AM
They are special because of sound quality.

Careful thought needs to go into the decision about the upgrade.

jaynemo
12-31-2007, 11:20 AM
Yeah, I hear ya. One side says do it. Why would ARC offer the upgrade with claims of improved performance? Or better yet improved reliability? My other side says keep it stock and have it serviced for continued reliablity. I'm on the fence right now, I'm going to ponder this one for a little while, besides I need to financially dig out of X-Mmas.

Blue Shadow
12-31-2007, 02:13 PM
Well ARC did come out with the SP-4/SP-5 after the SP-3 as an improvement? and the SP-9 did not get good until the mk III version so what they say is not always the best.

The -C mod replaces with power supply with a much better one that eliminates the old NLA capacitors so there are credible reasons for doing it, but there are also ways to mod the unit without them doing the work. Since you recently acquired this unit, search the web will bring you a bunch of information on the mods out there. Many less money than the ARC upgrade.

I am not saying the mod is not good, I have not heard it. I am just spewing some of the stuff I have read.

crooner
12-31-2007, 06:57 PM
The SP-3 was the only US made tube preamp widely available during the dark ages of the early 1970s. The Conrad Johnson preamp came out later in 1977.

It was revolutionary in using top quality capacitors and other parts. The circuit borrows heavily from the Marantz 7. Ditto for the Conrad Johnson.

Given the circuit and quality parts, they are hard to beat in sound quality.

Great score!! :thmbsp:

crooner
12-31-2007, 07:03 PM
Well ARC did come out with the SP-4/SP-5 after the SP-3 as an improvement? .

The SP-4 and SP-5 were ARC's first attempts at solid-state sound. They used transistor circuits called "Analog Modules" which were enclosed in epoxy enclosures.

According to Bill Johnson, ARC's president, the market kept asking for solid-state units and they simply responded. Also, Audio Research was fearful that tubes, high voltage caps and other parts were going to disappear or become scarce.

Remember, this was the mid to late 70s and RCA had just shut down their huge tube manufacturing operation in Harrison, NJ.
Mallory and other high voltage filter capacitor companies were also scrapping their tooling. Dark days for tube related industries in the US.

These early solid-state ARC products were a disaster. Audio Research had to come out with the all vacuum tube SP-6 in 1978 to save its reputation. The rest, as they say, is history!

jaynemo
12-31-2007, 07:43 PM
Great comments and history. I'll follow up in due time I'm sure. :thmbsp:

goldear
12-31-2007, 08:39 PM
Great score! :thmbsp: Its going to need some rebuilding to be reliable, and the power supplys design is not the best. But regarding the circuit iself, I'd be much more careful about messing with this. As others have mentioned, a number of ARCs "upgrades" never actually sounded like upgrades to my ears...

crooner
12-31-2007, 08:44 PM
Yeah, the power supply uses way too many twist lock cans. I guess this was the sign of the times. Later, more compact Nichicon high voltage electrolytics appeared, rendering the FP type capacitor obsolete.

One nice feature of the SP-3 is the liberal use of CDE Mylar (yellow in color) film capacitors in critical areas. The CDE's are superb sounding caps and shouldn't need replacing. Being polyester, they shouldn't go bad in time.

My early 10B tuner has these capacitors from the factory and it sounds significantly better than my later 10B with Siemens coupling caps in the audio stages.

junkaudio
12-31-2007, 08:59 PM
i got new powersuply pcb i post pic later
the sp3 is the best preamp i experianced with tt so far (mc)
the sp3 is very sensual for the right tubes ,tube rolling is the key here

Brian
12-31-2007, 09:11 PM
My feeling is that the SP-3A1 is the best interation of the preamp and as mentioned is based on the Marantz 7C. I always said the SP3 would have been the Marantz 8C if Saul had stayed with tube designs. It reained all of the good things of the 7C and improved on the few things that where not quite there with the design. I'd suggest using the preamp as is for awhile to get a feeling for the sound and what you like and dislike. I think the consensus is that the latest available update for the unit from ARC takes away too much of the magic of the unit. It was developed from what I understand more to support the preamp's contunied maintenance as many of the parts of the original are no longer available in reliable numbers that ARC decided to make the mods rather than try to source acceptable replacements.

Not that it is bad as even Mc finally gave up supporting its pre-SS tube units for lack of obtaining parts.

crooner
12-31-2007, 09:36 PM
By the way, the direct successor to the SP-3 and SP-6 is the SP16. For a while, all ARC preamps were 6DJ8 based, including several hybrids.

The SP16 returned to the much loved 12AX7 tube, and added such niceties as relay source switching and electronically controlled volume, all by remote control.

I have recently learned the SP16 has been replaced with a new model: the SP17. Identical in cosmetics but totally different topology, using FETs in the input stages and the 6H30 Russian "Supertube" in subsequent gain stages.

Too bad they have again abandoned the 12AX7 in their preamp designs. Specially after they had demonstrated such units could be made musical and quiet at the same time!

jaynemo
01-01-2008, 11:50 AM
Perhaps its time to call my restoration expert who is a certified ARC service center and get a quote.

Bluelobster
01-01-2008, 06:29 PM
Perhaps its time to call my restoration expert who is a certified ARC service center and get a quote.
Be careful who you choose if you want to retain resale value. Usually only ARC or two or three outside shops are recognized and their work will enhance value.
The power supply can use a little help and will influence voicing for the better.
To find an amp of the same vintage you'll have to find a heavily modded ST70.
http://www.arcdb.ws/

Brian
01-01-2008, 08:29 PM
Let's not forget the Dual 50, D75 and D76 Arc series amps any of which will surpass a modded Dyna. I had a D75 decades ago and until a couple of year ago also had a pair of D76A. Provided the caps are in good condition and the bias is set they are not all that bad on tubes.

jaynemo
01-02-2008, 06:48 AM
I only use Sound-Smith for all my restorations. I'm close enough I drive all my equipment to him. So far he has worked on my:

Marantz 510M
Marantz 3600
Retipped my Grace F9E
Pioneer Spec-4
Pioneer Spec-1
Pioneer TX-9500 11
Pioneer RT-701

Like I mentioned he is an authorized ARC repair center and offers a one year warranty on all his repairs.

thanks for all the great comments:thmbsp:

junkaudio
01-02-2008, 08:26 AM
my sp3 with new powerboard (not jet finished )

GordonW
01-02-2008, 08:26 AM
Personally, I wouldn't touch ANY Audio Research preamps with a 'C' version "upgrade".

I knew the local ARC dealer here, back in the day... and MANY people who had MANY different ARC models upgraded to the 'C' revisions, were VERY unhappy. The preamps never had the same character that got them into the preamp in the first place- in many cases, they became hard, harsh, and bright sounding.

IME, most of the 'C" revisions were "reviewer driven"... ARC got a less-than-glowing review (usually from some dolt who had absolutely NO IDEA what to compare the unit to, to make a VALID judgement), and altered the amp to cater to the PERCEIVED problem. Usually it was NOT a change for the better!

IME, again... usually, the BEST versions of these were later numbered A (as in A1, A2, etc) or B versions... but by and large, the C versions were sonically crippled... at least IMHO.

Regards,
Gordon.

goldear
01-02-2008, 05:19 PM
By the way, the direct successor to the SP-3 and SP-6 is the SP16. For a while, all ARC preamps were 6DJ8 based, including several hybrids.

The SP16 returned to the much loved 12AX7 tube, and added such niceties as relay source switching and electronically controlled volume, all by remote control.

I have recently learned the SP16 has been replaced with a new model: the SP17. Identical in cosmetics but totally different topology, using FETs in the input stages and the 6H30 Russian "Supertube" in subsequent gain stages.

Too bad they have again abandoned the 12AX7 in their preamp designs. Specially after they had demonstrated such units could be made musical and quiet at the same time!
You forgot about the SP-8. That unit used 12AX7s in a classicly cascaded negative-feedback design based design. I've never seen a schematic for the SP-16, so I can't wonder if that might have been cascoded, and whether it used feedback like the older designs did. So I'm not certain if it is accurate to state that it is a direct successor or not. :scratch2:

crooner
01-02-2008, 06:14 PM
You forgot about the SP-8. That unit used 12AX7s in a classicly cascaded negative-feedback design based design. I've never seen a schematic for the SP-16, so I can't wonder if that might have been cascoded, and whether it used feedback like the older designs did. So I'm not certain if it is accurate to state that it is a direct successor or not. :scratch2:

True, the SP-8 was the last 12AX7 based ARC before the SP16 in the early 2000s.

I had thought the SP-8 was a SP-6 with tube regulation and other sonic improvements.

Celadon
01-02-2008, 06:19 PM
More pictures PLEASE !!!

And thank you Crooner for your input. Much appreciated. :)

crooner
01-02-2008, 06:28 PM
More pictures PLEASE !!!

And thank you Crooner for your input. Much appreciated. :)

You are most welcome!

Here are several pics from the predecessor of the SP-3, the super early Electronic Industries SP-1 circa 1969.

Audio Research was founded in 1970. Briefly before this, Bill Johnson introduced several super high-end tube units under the Electronics Industries/Peploe nameplate.

The SP-1 borrows heavily in chassis design from the McIntosh C20. I particularly like the top chassis configuration for easy tube rolling!

goldear
01-02-2008, 07:02 PM
You are most welcome!

Here are several pics from the predecessor of the SP-3, the super early Electronic Industries SP-1 circa 1969.

Audio Research was founded in 1970. Briefly before this, Bill Johnson introduced several super high-end tube units under the Electronics Industries/Peploe nameplate.

The SP-1 borrows heavily in chassis design from the McIntosh C20. I particularly like the top chassis configuration for easy tube rolling!
Wow, 14 tubes!!! The SP-3 didn't have nearly that many. What are all of those tubes doing inside there? Do you have a schematic for that unit?

crooner
01-02-2008, 09:56 PM
Wow, 14 tubes!!! The SP-3 didn't have nearly that many. What are all of those tubes doing inside there? Do you have a schematic for that unit?

It's a very impressive unit. It was not produced for very long and most probably not many were sold. It was also made under the more common Audio Research brand.

I don't have an schematic, unfortunately.

The pics were from a relatively recent eBay auction. I saved them for posterity. Now, I was checking the ARCDB website today, and they have been posted there also. Good thing since that SP-1 was a very rare example with a bronze like finish on the faceplate.

The orange drop caps are not original. I'm guessing it also came from the factory with the yellow CDE mylar caps.

According to the ARC database the tube complement is 13 12AX7s and a 1 6X4.

However, I recall seeing a SP-1 with a couple of "spare" positions for extra 12AX7s, but not connected to anything. I guess to keep some tubes in there for a rainy day!

Blue Shadow
01-03-2008, 12:04 AM
Now what is that gonna cost to retube with a nice set of matched NOS Telefunkens?