I'm going to jump into this thread with an unsolicited, but maybe useful amp testing post. I've recently had to do some rearranging and ran across an old chip amp I acquired as part of a lot of test equipment. The amp in question is the Envision Audio Exact Series.
Courtesy of the Wayback Machine, here is some information:
Thanks for checking out the new 2 channel Exact amplifier!
Besides delivering excellent sound quality reproduction, the Exact is also the best value in stereo amplifiers on the market today! It is perfect for a slammin' multimedia setup or a micro-modular dorm or bedroom audio system. The best part about the Exact is its ability to hide...it literally disappears behind your speakers. What??
Exact mounts on the rear panel of your current speaker enclosure. If you're handy with the tools, simply cut a 5½ x 4½" hole in your right side speaker and you're set. Just mount it and plug it in. Then, connect the left speaker to the amplifier using standard 'banana' plugs. One amplifier, two speakers, more space. No problem. Now, you're thinking...what else does this little marvel do? Plenty!
Exact incorporates a 12dB/octave Butterworth high pass filter.It's also frequency-adjustable...you can use the SIP-X module (included) or create your own using four precision resistors. It's easy and all the details are included. What's under the hood?
Good question! At the heart of the Exact is a precision engineered IC called the LM4766T from National Semicondutor™. Its sibling amplifiers are the world renowned "GainClone" LM3875 and LM1875. The 4766T is simply a two channel version of these fantastic sounding "chips". It is rated to produce 40W per channel into 8 ohms, but the Exact has been designed to operate the IC comfortably within its operating parameters. By decreasing overall voltage potential and increasing current capacity, the IC runs cooler at 8 ohms and will easily drive 4 ohm loads without activating protection circuits. Achieving maximum performance requires careful component selection. So, the Exact amplfiier uses a space-age insulator of layered Kapton™ and Copper Film to transfer heat away from the IC to the high mass heatsink. In addition, we've exclusively used 105°C rated Electrolytic Capacitors in the voltage regulation/filtering stages. This translates into overall longer operating life.
The critical High Pass filter section uses a low noise LM837 Bipolar Input Quad Op-Amp (whew!). Genuine WIMA series capacitors are used to further maximize sound reproduction accuracy. Anything else?
You bet. An FR-4 double sided, plated through-hole PCB. That's techie speak for a super durable circuit board that won't crack, shatter or warp like lesser quality boards.
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I'll start with some measurements, then some more photos and observations.
Here is the dashboard.
SINAD of about 70 dB is nothing special, but distortion is quite low. The 2nd order peak is at about -87 dB and odd order is about 20 dB lower. The real limiting factor is power supply noise (60 Hz peak at about -72 dB and a couple of harmonics also above -80 dB. 8 ohm performance, below is a little cleaner but similar in character.
Frequency response is smooth and independent of load, which is good. As the ad copy mentions, this amp has a built in high pass filter and it appears this one is set at about 100 - 120 Hz. That could be a good thing for measurement purposes to protect sensitive tweeters (as long as you're not trying to do near field or ground plane bass measurements).
This amplifier makes about 20 watts per channel into 8 ohms, but is throttled back at 4 ohms and actually makes slightly less than that. I guess that is the design "feature" that allows running cool and driving 4 ohm loads without activating protection circuits... For a lot of applications, I guess this would be a reasonable approach.
Looking at the distortion vs. output power at different frequencies shows no real issues. I didn't test below 100 Hz due to the high pass filter.
Overall this testing shows good performance potential (linear response, low distortion) for the LM4766T chip. This particular implementation doesn't control power supply noise well and has a high pass filter that limits use cases to a 2.1 arrangement with a powered sub or a limited frequency measurement amp. Given the thread, I took a few more pictures.
It looks like Envision went pretty cheap and basic on the transformer. 3300uF filter capacitance for each channel.
Here is the LM4766T chip. It is a 2 channel chip, so only one needed.
This is the high pass filter section. According to the ad copy above, the 4 resistors can be used to set the frequency, but I haven't been able to locate any instructions for how to select values to change it and I don't have any information about the SIPS module either.
I recall trying this out to do some speaker measurements and the hum was considerable - so I quickly reverted back to my other options (Parasound Zamp while it was alive, then Sherbourn 2/100)
Keep an open mind, but don't let your brain fall out.
I first saw that at Dayton DIY 2004. Aaron Hammett was the guy behind Envision, and also made another product later. I still have 2 of those modules unused, or 4 channels. Had plans, haven't commenced. The main reason for having the highpass was to keep the smaller power supply happy and not need such a large heatsink. He tried to fill a niche for 2 channel plate amps, but it seemed only a few were sold.
The dim bulb lit up for a half second before going out. So it charged the power supply filter caps and that was it.
Hooked up the tube preamp and played some vinyl. It works! Had to keep it low as the wife was sleeping... Until even that woke her up and the party was over . Seems to have alot of gain baked in. I was just bumping the preamp knob to make volume adjustments.
Comments
I'm going to jump into this thread with an unsolicited, but maybe useful amp testing post. I've recently had to do some rearranging and ran across an old chip amp I acquired as part of a lot of test equipment. The amp in question is the Envision Audio Exact Series.
Courtesy of the Wayback Machine, here is some information:
>
I'll start with some measurements, then some more photos and observations.
Here is the dashboard.
SINAD of about 70 dB is nothing special, but distortion is quite low. The 2nd order peak is at about -87 dB and odd order is about 20 dB lower. The real limiting factor is power supply noise (60 Hz peak at about -72 dB and a couple of harmonics also above -80 dB. 8 ohm performance, below is a little cleaner but similar in character.
Frequency response is smooth and independent of load, which is good. As the ad copy mentions, this amp has a built in high pass filter and it appears this one is set at about 100 - 120 Hz. That could be a good thing for measurement purposes to protect sensitive tweeters (as long as you're not trying to do near field or ground plane bass measurements).
This amplifier makes about 20 watts per channel into 8 ohms, but is throttled back at 4 ohms and actually makes slightly less than that. I guess that is the design "feature" that allows running cool and driving 4 ohm loads without activating protection circuits... For a lot of applications, I guess this would be a reasonable approach.
Looking at the distortion vs. output power at different frequencies shows no real issues. I didn't test below 100 Hz due to the high pass filter.
Overall this testing shows good performance potential (linear response, low distortion) for the LM4766T chip. This particular implementation doesn't control power supply noise well and has a high pass filter that limits use cases to a 2.1 arrangement with a powered sub or a limited frequency measurement amp. Given the thread, I took a few more pictures.
It looks like Envision went pretty cheap and basic on the transformer. 3300uF filter capacitance for each channel.
Here is the LM4766T chip. It is a 2 channel chip, so only one needed.
This is the high pass filter section. According to the ad copy above, the 4 resistors can be used to set the frequency, but I haven't been able to locate any instructions for how to select values to change it and I don't have any information about the SIPS module either.
I recall trying this out to do some speaker measurements and the hum was considerable - so I quickly reverted back to my other options (Parasound Zamp while it was alive, then Sherbourn 2/100)
Sehlin Sound Solutions
I first saw that at Dayton DIY 2004. Aaron Hammett was the guy behind Envision, and also made another product later. I still have 2 of those modules unused, or 4 channels. Had plans, haven't commenced. The main reason for having the highpass was to keep the smaller power supply happy and not need such a large heatsink. He tried to fill a niche for 2 channel plate amps, but it seemed only a few were sold.
InDIYana Event Website
The dim bulb lit up for a half second before going out. So it charged the power supply filter caps and that was it.
Hooked up the tube preamp and played some vinyl. It works! Had to keep it low as the wife was sleeping... Until even that woke her up and the party was over
. Seems to have alot of gain baked in. I was just bumping the preamp knob to make volume adjustments.