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Comments on SE-1 Tube Amplifier Modifications - April, 1995

By Bill Yee

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Okay folks, the results are in on my tweaked Audio Electronic Supply SE-1 amplifier. For those of you who missed my first "preview" that was published on the newsgroup rec.audio.high-end, let me recap to bring you up to date...

You see, I had heard about, and was curious as to what this 300B triode tube, pure class A, single-ended, low power (7-watts per channel) fuss was all about. I sat on that curiosity for quite awhile, because I just plain could not afford, let alone justify spending close to $4000.00 to get a measly 7-watts per channel. A whole lotta explaining would have to be done to the big boss (read "wife!") as well as non-audiophile friends, family members and otherwise sane folks because they would not understand why the hell I would want to spend more money on additional hi-fi equipment. Well, then along came... (these words remind me about the song that goes "...along came Mary!...") the Audio Electronic Supply 300B triode tube, SE-1 amplifier available fully assembled for a hair over a grand.

That's $1050.00. Still not cheap I said, but close enough for me to scratch an itch, catch a piece of a dream, spoil myself rotten! Hey, at this price point, my attitude became, "Heck! Life is Short! I ain't gettin any younger, and I sure as heck ain't gonna wait till I am old and deaf to buy my rich boy toys!" Okay? So I bought one.

{Fade away to present time...}

As I was saying, in that "preview" review I mentioned that the SE-1 was real mellow and laid back sounding (maybe too laid back) but that it was not fully broken in yet. I said that an AES tech was sending me a resistor mod to tweak the amplifier up to increase its dynamic drive and make it sound less laid back and that I'd report the results in a follow-up review. Well, now comes the follow up review.

I received the DALE brand resistors (free I should mention) from AES to modify the SE-1, and I installed them as per the AES tech rep's description. Remove the current 4.7K resistor connecting pin 4 to pin 6 on the 6SL7 input tube. Replace it with the 2K resistor. Do this for each channel. That's the AES supplied modification. I should mention here that my stock amp came with another modification already applied by AES. They had removed the 10K grid stopper resistor from each channel. That is the resistor that goes to the grid of the 300B output tube in series with the 0.22uf coupling capacitor. This alone could conceivably explain why I think my AES SE-1 sounds "livelier" than what another magazine found their version of the AES SE-1 (without this mod) to sound like.

What did the SE-1 amplifier 2K resistor modification sound like? Well, it sounded brighter. Yes, it did liven up the sound and sharpen up the sound of transient attacks. It did so in such a way that it sounded almost as sharp and bright as my solid state Adcom amps. For a time there, I was enjoying it, I mean this SE-1 was sounding sharp and bright like my Adcoms but still with a more mellow touch to it. I think the upper midrange and lower treble frequencies were elevated by the 2K resistor modifications.

I let it play like that for a couple of days to live with it. Soon I began to notice that some radio stations sounded harsh to me again. I began getting that listening fatigue on some stations that are bright with solid state gear. Guess what? I removed the 2K resistor mod and the SE-1 sounded fine and dandy again. Liquid smooth, detailed but never fatiguing on all program material. I knew that this setting was it (for me anyway).

The SE-1 amp by now had been broken in almost to the 100 hours recommended by the AES tech rep I spoke to. It had become more dynamic and less laid back on its own! Transients that sounded rounded off before this amp broke in, now had attack to them. Yes, detail and transient attacks are all there now, without an elevated upper midrange or lower treble to etch and harshen things up. This is the most pleasant sound I have heard from my stereo set-up yet.

My wife just received some CD's she'd ordered from BMG Music Club. One of them was Walt Disney's "The Lion King". Boy! I just gotta tell you that that is one heck of a nice recording. Through the SE-1 and my home brew modified Aria-3 low efficiency speakers, the presentation was convincing enough such that it sounded like the cast of characters were right in front of me on the stage! Nice.

The sound is addicting. I really cannot stand switching back over to the etched, bright sound (to my ears) given when my Adcom solid state amps drive the same speakers. The Adcom amps sound great too, but the SE-1 just mellows it out in the right places and makes it a less fatiguing sound. In fact, the SE-1 is totally non- fatiguing. I can leave this amp on, playing music all day long without ever wanting to shut it off due to harshness or fatigue on the ears. I cannot say that about the other amps that I have heard in my house.

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My speakers consist of:

1) Home brew modified Aria-3's with 6th Order Bandpass, Push- Pull Subwoofers.

2) Old set of Acoustic Research AR-11's (with woofers replaced with Original AR-3a replacement parts because the foam rotted out).

3) Audio Concepts Sapphire II and Sub1 subwoofers.

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My front end electronics consist of:

1) SONY CDP-X707ES CD player.

2) Technics SL-1400 MKII turntable with Sumiko Blue Point Special cartridge.

3) Denon model TU-680NAB Broadcast Reference tuner.

4) Audible Illusions Modulus 3 all tube preamp.

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I mentioned that the SE-1 made my Adcom solid state GFA-5800 and GFA-585 (250 watts per channel) power houses sound real, real (as in too) bright by comparison. But I also must say that when driving the right speakers, the solid state Adcom GFA-5800 amp has its strengths too. Synergy in matching speakers to amps matters very much.

There are other reasons why I would still listen to the solid state power house stuff. Now just to snap some of you fanatical types out of a 300B SE trance, I never said this 300B stuff was perfect in every way, and I don't mean this to diminish my high praise and rave for the AES SE-1 amp. It does what it does nicely within certain constraints. If you are willing to accept or adjust yourself (mostly in the psychological arena) to these constraints, then you will be rewarded with the beauty of the SE-1.

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The main but minor constraints for me are that you should:

1) Have very high efficiency speakers to play at real loud levels, or else you must

2) listen at lower levels than house rockin' levels.

3) Get used to not having the tightest deep bass around. Unless of course you bi-amp, using a hefty solid state amp for the subwoofer.

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There really is something to this 300B tube, single ended, 7- watts per channel stuff. From what I was able to understand so far, the AES SE-1 is a modkateers delight. It is a simple amp that is easy to tweak and modify. You can change resistors, change capacitors, hell, change wires, change tubes and change the circuit if you are so inclined. Each and every change will result in some audible difference. That is the characteristic of this 300B SE-1 amp. Try different coupling capacitors and you'll get a different sound.

It must be obvious by now that I am happy with my version of the AES SE-1 as is, unmodified.

On leaving, I would like to remind you all who would tinker and modify the SE-1 or any tube equipment in general, BEWARE of the HIGH VOLTAGEs used in tube equipment! I used to work on tube equipment a long time ago, but then everything went solid state. I found that many like myself get kinda careless and develop habits working around low voltage solid state equipment that would NOT BE SAFE working around tube equipment. One quick jolt is all that it takes to remind a DIY of the danger involved with working around high voltage equipment (if you're lucky). Just don't let that one quick jolt kiss you goodbye! Tube voltages are less forgiving! Bye.

Bill Yee
Guest Writer
USA