I was arranging some things today in preparation for an event this evening and happened to have a little Class-D amp in my office that I normally use in my wood shop. So I decided to try a little A/B testing.
Here is the little 8W / channel Class-D amp.
And here’s what it looks like inside.
This is a fairly simple amp that uses a Sure Audio AA-AB32231 2x8W Class D amplifier module with a Texas Instruments TPA3110 series chip. I installed this amplifier in my shop in April of 2019 to replace an old 1980s boom box that had seen better days.
Since I had this in my office I grabbed a set of identical speakers to the ones I have connected to the 6CY7 V2 Zebrawood and played the same songs through the little class D and the Zebrawood. To say that I was surprised is an understatement! I’ve always considered the Sure class D modules to be very good quality audio amplifiers. And I’ve always been very satisfied with their sound in standalone situations. But this is the first time I’ve ever directly compared them to something else.
I started my comparison with Diana Krall’s rendition of “Narrow Daylight” off of the Girl In The Other Room album. I lined up the tracks and started to switch between the amplifiers letting each play for 20 or 30 seconds then switching. The difference was astounding! I tried track after track, performer after performer, genre after genre. Every time the little 6CY7 Zebrawood was noticeably clearer, fuller, and richer sounding. It was only a subjective test, but what a test it was!
For anyone doubting the veracity of the claims of vacuum tube amplifier superiority, I challenge you to do the same test I did. You may be very surprised.
Hi Matt
First let me say thank you for a great site.
I just spend hours reading all your builds and now all your blogs.
I got here earlier this morning looking at data sheets and trying to find info on using different 12A*7 tubes in the first stage of a preamp. “4S Universal Preamplifier for 12A*7 Tubes” ,That’s what got me here . I have a few different single tube preamps that are for the front end of my guitar rig. I used to use (“vintage”) Well they weren’t vintage when I started using them 55 years ago! Fender and Ampeg tube amps but at 72, with a bad back, I can’t hall 45lb plus tube amps. I play very clean , Jazz and Blues and still gig a couple times a week.
This led me to using class D amps . Both Quilter amps and my own Sure builds.
I use 250 watt 4 ohm 12″ Neo speaker that weigh 5.5lbs! Under 20lbs with the cabinet! The Quilters sound good but still have a sterile sound unless pushed ( but adds too much distortion for me), the Sure even more so. So I have been using a single tube preamp in front of the Class D amps. This helps a lot but with a 12AX7 begins to get too noisy . So I was looking to put a variant with lower gain, noise and distortion in the preamp . 12AY7, 12AV7 but was concerned with higher plate dissipation, cathode biasing and heater current (12AV7 450ma vs 300ma)
All these pedal tube preamps run off 9V wall warts . ( I measured the plate voltage at 195V)
After reading your blog posting “Experts” I decided to just use my ears and roll some different tubes into the pedal preamp and see how it sounds 😉
My last thought is why not try your 4S Universal Preamplifier for 12A*7 Tubes in front of your Sure class D amp and see if it makes a difference ?
I have found after buying a lot of Sure class D amps that the bigger the wattage of the amp and the more current you supply the better . Especially if you don’t run it anywhere near its rated output.
Sure Audio AA-AB32231 2x8W Class D amplifier
Output power: 3W x 2 @ 8 ohms (<0.1% THD+N), 5W x 2 @ 8 ohms (<10% THD+N), 6W x 2 @ 4 ohms (<0.1% THD+N), 8W x 2 @ 4 ohms (<10.0% THD+N) Frequency response: 20 Hz to 20 kHz (±3 dB)
Pushing these amps to max output is not a good sound.
I use a Sure AA-AB31282 200 watt class D mono amp but run at 4 ohms I get about 80 watts at .1 % THD distortion , I never ever get close to 80 watts . Maybe 25-30 watts max. With a tube front end it sounds good, for guitar amp.
Thanks again
Port
Port; I’m glad you like the site. Just for reference, the 4S was designed specifically for color. With a 12AU7 and the volume set to 12:00, it is unity gain. Also thought you might be interested; Mark Houston down in Australia has a method he uses for preamp power supplies that can run off an AC wall wart. You can find the power supply circuit at this link.
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Class D amplifiers always sound “artificial” to me – probably due to how they work, switching vs. analog. The class D sound seems to lack “life”.
Gonna be a “heretic” here – my personal preference is for discrete transistor class AB capacitor coupled amplifiers – been building them for over 50 years. To my ears, they give tubes a real run for the money. But my personal tube experience has mostly been with push-pull class AB pentode or single ended class A pentodes (almost all have global NFB). I have heard it said that pentodes, especially push-pulI circuits and transistors sound almost alike.I have never heard a SET in the flesh, so I can’t comment here.