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REVIEW: Halo Audio SPM-40 Amplifier (Tube)

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Model: SPM-40
Category: Amplifier (Tube)
Suggested Retail Price: $995
Description: 40wpc EL34 (4 each) parallel single-ended monoblocks
Manufacturer URL: Halo Audio
Model Picture: View

Review by LineArrayNut ( A ) on June 04, 2003 at 15:37:14
IP Address: 208.63.172.234
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for the SPM-40


Background:
After sampling a few push-pull amps (Harman-Kardon Ballad A230 and Fisher 800B) and an OTL (AtmaSphere M-60MkII.2), I decided to try a SET design. But not knowing what I'd like or dislike about the SET's vaunted sound and presentation, and having a limited budget to "try-out" a different class of amplification, I looked for low cost alternatives to the big name manufacturers. Also knowing my habit of twisting the volume knob too much occasionally, I knew a 300B or some of it's like was not going to be enough watts with my various low to medium efficiency speakers.
Decision:
All my previous tube amps were used or vintage pieces; this time I wanted new. I looked all over the various sources' websites, cruised the online auction sites, searched the forums in a few different locations and finally let a review and a conversation with a previous owner influence me, along with the wallet. BTW, these amps are a house brand of www.audiooasis.com , a Toronto based retailer. They are basically warmed over versions of the venerable Antique Sound Labs MG-SPM 40.
Physical:
Upon receipt of the amps, my first impression was typical disgust with third-world build quality decisions. Stolid and unimaginative, the term utilitarian comes to mind. Not that there is any thing shoddy or flimsy about them, there's just not alot to note that is positive about the looks, fit or finish. The silver 1/2" brushed aluminum front piece is probably the nicest exterior element to comment on, incidently also available in gold and black. The tube compliment is 4 EL34 of chinese provenance and ASL branded chinese 6SN7, of which two were missing as shipped; thus the review as shipped were a EH6SN7 and a chinese per amp. These are arranged in one row at the front of the amp, EL's to the left and 6SN7 to the right, with ceramic sockets. An overly bright blue led and power switch of rocker design are on the left and a switch to select between triode strapped and pentode operation is on the right. Two large and one small cover hide the unpotted power, output, and choke transformers. A wobbly rotary switch for biasing is on the right with 4 holes that lead to ridiculously cheesy trimpots for biasing. The plastic trim pieces for the holes in the sheet metal accentuate the difficulty of getting a tool to seat in the off-center plastic trimpots. The rear of the amp has an IEC socket for power and nice heavy gold-plated output terminals for the 4,8, and 16 ohm taps for the speaker. A so-so thinly plated gold RCA jack is present as well. Opening the bottom cover reveals a reasonably tidy point to point wiring scheme, good parts and open to upgrading layout. SS rectification is used, with a small PC board with the offensive trimpots surface-mounted to it. The two chassis varied a bit from each other as to layout. The power cords provided are generic 18 ga.
Sound:
First impressions were heavily underwhelming. But the other amps in my stable are all stellar performers in their genre and well broken-in, so I was willing to reserve judgement for a while. After running them for a week with various types of music for about 8 hours a day in pentode and 4 hr/day in triode, I was ready to give them back for a refund. They were not bad, but not good either. I was persuaded to give them more opportunity to break-in and to try some more tube-rolling in them by the pleasant nature of the seller and his willingness to work with me for my satisfaction. So I got some Svetlana EL34, JJ E34L and EH6CA7 "fat bottle" to try and broke out my extensive collection of 6SN7's. Fitted them with big 10 ga. power cord with Marinco hospital grade plugs.A week later, I struck a good combination with the Svets and Raytheon VT-231 opposed plates and Raytheon parallel flat plate 6SN7. Admittedly, my speakers, DIY Peerless bass-reflex 6.5" MTM's are power hungry, a bit bright in the highs , and bass-shy. But I just couldn't get any bass out of them, and kept turning the treble control on my preamp down. Finally, I felt this combo was a winner, and the amps are very transparent to tube-rolling, so I'm sure that other combo's would work for different desires. Other amps on the speakers, notably Adcom 5802, Marantz PM84D and others work well in the bass area but are still bright in the treble. No, these amps are not, and never will be, bass monsters. But they do have a nice quality of detail, accuracy and listenability. After a while, I succumbed to the inevitable and pulled out an electronic crossover and a couple of subs with SS amplification and used them at a 24dB/octave 80hz highpass. Don't get me wrong, they will play down to 20 hz and have reasonable output. But my main 2 channel system has dual 18" Adire Audio Maelstrom's; my Jeep sports 4 Rockford Fosgate 15" DVC's. So I'm probably a basshead at heart and as usual, YMMV! As they continue to get age on them, they sound better and better. I may just keep them after all! Triode mode does sound better, with 40 watts in pentode mode lending itself nicely for more volume and "drive" for rock and pop, and the 20 watts or so available in triode working well for jazz or classical. A good value for the money, but lacking the last bit of refinement IMHO.


Product Weakness: Cheesy bias pots, typically miserable ASL owner's manual - no mention of bias adjustment procedure.
Product Strengths: Low intial cost for this type of amp.


Associated Equipment for this Review:
Amplifier: As above; Marantz PM-432A on subs
Preamplifier (or None if Integrated): Nikko Audio Beta III
Sources (CDP/Turntable): Philips SACD1000
Speakers: DIY Peerless MTM, Orion XTR 12
Cables/Interconnects: Phoenix Gold ARx.800
Music Used (Genre/Selections): SACD various all genre's except country/rap
Room Size (LxWxH): 30 x 20 x 10
Room Comments/Treatments: Rug wall hanging opposite speakers
Time Period/Length of Audition: one month
Other (Power Conditioner etc.): GE EMI/RF/surge suppressor
Type of Audition/Review: Product Owner




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Topic - REVIEW: Halo Audio SPM-40 Amplifier (Tube) - LineArrayNut 15:37:14 06/4/03 ( 0)