27 August, 2009

Home Visit: ARC SP6, SP9, CL30

Home Visit: ARC SP6, SP9, CL30
(From a thread that started here, on 15/03/2001)

"I have always regarded the ARC Classics 30 as a great bargain. Some years ago, a colleague lent me the amp, together with ARC SP9 MkI preamp and I was astonished by the transparency and drive of this so-called 30 wpc amp and preamp combination.

The CL30 is a hybrid design with a pair of 6CG7 as driver and just a pair of 6550 in triode PP each channel. There are matching concerns: A certain leaness can be ameliorated by cables...

The SP9 is also a hybrid design, with just ONE 6DJ8 tube in the line section and one in the phono section. Due to some "oscillation problems" in early MkI samples, it was quickly modified to MkII. It is a very dynamic preamp which also has some concerns: a leaness has to be matched with cables (like MIT) and tubes (Mullard is useful here; stock of MkII is Sovtek 6DJ8). It also needs a LONG warmup to sound good.

(The host's) system was a model of economy and the result he got is an example of value for money. A modified B&W CDM1 provided clarity that had nothing to do with the stock (which I had heard elsewhere). Gone are the somewhat fatty mid-bass and we get instead real transparency and bags of detail and air...DIY cables and a Toshiba DVD (!!!) hooked up to MF X-24k for source. We matched up the CL30 with the ARC SP6-B-II and the ARC SP9-II (the SP9 is a contemporary of ARC CL30).

Obviously the SP9 offered immediately noticeable dynamic performance, and hifi parameters excelled. The violins were a bit, hmmm, scratchy though. The SP6 offered more musical performance but hifi parameters were definitely behind the SP9. These were with very cheap tubes. As you may have read...a bit of (still within our budget) tube rolling produced dramatic results. But we will wait for him to finish his continuing little bit of tube rolling to discuss CHEAP but effective tube rolling (something that will be laughed off elsewhere).

The main point of this post is to suggest these as best buys:

-CL30. Condition of the output tube is critical. I would recommend getting a copy of ARC
manual (write to ARC; unfortunately no email) for a small fee, to make sure things are biasing up properly. Caleb, I'm not sure KT88 is a good choice for this amp. Write to ARC about this and biasing requirements. In any case, a matched quad or at least 2 matched pairs is essential.

-SP9 and SP6, along with SP8, and the even warmer (too warm for modern tastes) SP3, are all good buys. SP9 is definitely NOT for many people who like vintage and "wet" vocals. For SP6 and SP8 be extra careful of modifications. Some heavily modified units sell for cheap,
but should be avoided.

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