Randy Slone's Optimos power amp demo Sydney Sunday Nov 9 2008

[HiFiNutNut]

I have built Randy Slone's Optimos power amplifiers. They are available as kits from www.ledeaudio.com.

I did AB comparisons to two high end amplifiers - the Ayre and Corad Johnson (Solid State). These are possibly in the price tags approaching AUD$8k-$10k each. Although they sound different, they are nevertheless in a similar performance level.

You can hear the Optimos this weekend when I demonstrate them along with John K's NaO speakers at the Sydney Audio Club meeting.

For details, please refer to the following thread. If you want to respond, please respond in that thread.


Invitation to audition John K's OB NaO Speakers in Sydney 9/11/2008


Regards,
Bill

[Greg Erskine]

Hi Bill,

Thanks for your efforts in setting up the demonstration. I loved the sound of your system, exceptional.

Those Randy Slone's Optimos power amplifiers must be the best kept secret in audio. How come you Optimos owners aren't telling us how good they are?

The only down side is I now have to decide if I want to build some "real" speakers and maybe upgrade my amps as well.

regards

[HiFiNutNut]

Those Randy Slone's Optimos power amplifiers must be the best kept secret in audio

I think you are probably right.

How come you Optimos owners aren't telling us how good they are?

That is a bit unfair! (I am only joking). I mentioned them quite a few times in this forum and sometimes I felt like acting like a salesman for Randy Slone and www.ledeaudio.com. Oh, of course, I would be very privileged to be a salesman for them, but unfortunately, even if I was given the privilege I have absolutely no interests in selling audio equipments. I am just a HiFiNut wanting to have "live-music" at my home and share the interests with others.

The fact is that Randy Slone and David from Lede Audio are scientists and engineers and they are not salesmen and don't care about marketing. People only know Randy Slone from his published power amplifier books.

The thing I like the Optimos is that, when using the right capacitors and having a good power supply, it has no sound of its own. This was evident when I compared it to other power amplifiers. Those nice sounding power amplifiers have a nice sound with them. The Optimos has no nice sound, just music. It is transparent.

So in that way, yes, the Optimos can sound bad if the rest in the audio chain sound bad. In that case, it is better to get a "nice sounding" amplifier to inject some nice distortions to make the music sound artificially better. However, if the rest in your audio chain are of very low distortion, the Optimos shines.

All of my subjective talks are pretty meaningless. The best is to look at the distortion figures. The Optimos boasts very good measurement results under strict conditions, not just a 1kHz tone. You can get the technical paper from the company that sells Randy Slone's Totem-Pole commercial amplifiers.

Best regards,
Bill

[HiFiNutNut]

For those who are interested, here is a site that contains some information:

http://www.zusaudio.com/technology/zusaudioengine.htm


Here are some of the specifications:

System Bandwidth: 10Hz to 100kHz or wider
0.01% THD+N or less across the entire audible Audio Bandwidth of 20Hz to 20kHz
0.1% THD+N or less at an Ultrasonic frequency of 50kHz
0.01% THD+N or less at a Subsonic frequency of 10Hz
0.01% THD+N or less across the entire Power Bandwidth (from lowest level output to 0dB full power) 20Hz - 20kHz
THD+N never rises above 0.01% levels at anytime or at any power level within the audible Audio Bandwidth of 20Hz to 20kHz
Ability to reproduce Subsonic and Ultrasonic frequencies with full power output (0dB) without ever exceeding 0.01% THD+N at 10Hz Subsonic and 0.1% THD+N at 50kHz Ultrasonic
Hum and Noise below -100dB
Symmetrical Soft Clipping. No hard clipping whatsoever when exceeding normal output levels

Here are some impressive claims:

Our first Ultrasonic test on one of our prototype amplifiers showed us clearly why our ZUS Audio Engine™ gave such a total audio experience to the listener. We first tested a very popular high-end amplifier at the standard 1kHz @ 1Watt RMS. This amplifier was rated at 300 Watts RMS into 8 ohms. We'll call it AMPx.

AMPx tested out extremely well with %THD+N readings around 0.005%. We auditioned AMPx and found it "sounded" quite decent - as we expected it to. We then hooked up our prototype ZUS OPTI-MOS amplifier rated at 400 Watts RMS and did an A-B comparison. The results were very revealing.

The ZUS amplifier reproduced sound that was much more detailed and was very natural. At bench tests done at 1kHz @ 1Watt RMS, the ZUS amplifier actually produced higher %THD+N readings than AMPx at around 0.008% THD+N. We thought it strange that although the ZUS amplifier tested "worse" on the bench, it definitely sounded superior than AMPx. We then decided to perform %THD+N tests at 20kHz and above. (Please note that this is an extremely brutal test for any audio power amplifier.)

We set the input signal to 20kHz, and powered AMPx to 1 Watt RMS output. Not surprisingly, AMPx showed huge amounts of %THD+N. We then slowly raised the power output and at only 6 Watts RMS, AMPx's heatsinks got dangerously hot. At that instant all the rails fuses blew. AMPx, although rated at 300 Watts RMS, was unable to output 6 Watts RMS at 20kHz.

We then set the ZUS amplifier on the bench and subjected it to the same brutal test. At 20kHz and 1 Watt RMS the %THD+N readings were less than 0.01%. We then started to raise the power output. We were able to achieve a power level of 400 Watts RMS (0dB) while still maintaining less than 0.01% THD+N at 20kHz. This was truly remarkable. In fact, we then raised the input signal to 40khz and were still able to output 400 Watts RMS and less than 0.01% THD+N.

Yet another:

Another revealing specification is the %THD+N versus the output power level of an audio power amplifier. Much emphasis has been placed on reducing %THD+N at the highest output levels (0dB) of the power amplifier. Indeed, this is a critical parameter as it is necessary to amplify the signal to realistic output level volumes without audible distortion. However, all music is dynamic. That is, it can get very loud one second and get very quiet the next. As well, the harmonics being reproduced are also of varying levels of amplitude (loudness).

It therefore becomes obvious that %THD+N levels are equally important at the lowest power output levels as they are at the highest power output levels.

Many power amplifiers actually have more distortion at power levels less than 1 Watt RMS compared to their full output (0dB) power levels.

With high distortion levels at very low power levels, there is a distinct loss of realism and tonal integrity of the music. A Stradivarius violin just doesn't sound quite right. A violin is heard, but the sonic signature of a Stradivarius violin is blurred and smeared. As the musical notes decay and the harmonics fade in intensity, there are distortion artifacts being introduced that were not there in the original source.

Ensuring the power amplifier produces inaudible distortion at high power levels as well as levels less than 1 Watt RMS, preserves the realism and tonal integrity of the music.

The ZUS Audio Engine™ allows for a very high-resolution and highly detailed audio soundstage by ensuring there is no audible distortion whatsoever in the entire output power range. From the very quietest note to the very loudest, the listener enjoys a near perfect reproduction of the original sonic source. Indeed, it is a most captivating and immersive experience.

[tjencks]

Hi Bill,

I am a newbie to Electronics and would like to embark on the Journey towards three Mono Block OptiMOS totem pole amplifiers. I will have a friend of mine who is an engineer but not an electrical engineer assisting me. So assisted by a variety of sources we hope to be able to finish this project.

However the first order of business is selecting the parts and when it comes to the Toroidal Transformer I am at a loss as to how these units get rated and what the Amplifier Rails require. I was reading a previous post on this site that stated the the OptiMOS amps can take up to 105 V a Rail. I guess I should also mention I'm looking at the kits which Lede Audio provides so I'd be looking at the Double Die version of the amp board hoping to achieve a 400watt mono block amp.

Can you guide me as to the Rail voltage of these amps and what ratings I should be looking for in a Transformer?

Best Regard,
TJ

[suzyj]

Damn, pity I missed it

[HiFiNutNut]

TJ,

Roughly, +/-56VDC rails give about 120W power. a +/-70VDC rails (maximum rail voltages for the Optimos published in Slone's book) give about 200W power. You can go over that up to 400W by using higher rail voltages and different MOSFET output divices. Details can be found in Slone's book and are given when you purchase the kits from www.ledeaudio.com

I have built 3 Optimos amps. One at 120W, one at 190W and one at 300W, all using 625VA toroidal transformers. The last two were mono-blocks so a pair of transformers were used for each pair of mono-blocks.

Regards,
Bill

[HiFiNutNut]

Suzyj,

It was suggested to me that the Audio club may demo my system again in a few months time, as people are curious about how it sounds in the bigger dampped room, because the smaller live room used in the last demo was too reverberant to reveal the true capability of the speakers.

The transformers in the demo amplifier were not good at all. After the previous show, I upgraded the transformers and the capacitors and they now sound even better.

Since I am curious too, I will probably accept the invite and do another demo in a few months time.

Regards,
Bill

[tjencks]

Bill,

Thanks for the info, I would love to get in touch with you directly or in another thread as I think my questions are a bit off topic for this one. I'm a new member so my account is under moderation and can't email you directly .

Regards,
Theo

[drowranger]

Originally Posted by HiFiNutNut

TJ,

Roughly, +/-56VDC rails give about 120W power. a +/-70VDC rails (maximum rail voltages for the Optimos published in Slone's book) give about 200W power. You can go over that up to 400W by using higher rail voltages and different MOSFET output divices. Details can be found in Slone's book and are given when you purchase the kits from www.ledeaudio.com

I have built 3 Optimos amps. One at 120W, one at 190W and one at 300W, all using 625VA toroidal transformers. The last two were mono-blocks so a pair of transformers were used for each pair of mono-blocks.

Regards,
Bill