BL Rhumba questions

tonyb

I though after this next review we get Bob to answer some questions. Lets post them all in one thread ahead of time and give Bob some time to mull them over.

I'll start with one question that everyone is somewhat curious about....that darn power supply.

How did you come about this particular design and what in your opinion is the pro's and cons over others who are using standard regulated power supplies and off the shelf caps ?

What discovery pointed you in this direction....and when did that "ah-ha" moment happen for you ?
Personally I would like to see a HT pass thru option, is there a reason why or you just wanted to maintain a strict 2 channel pre ?

Maybe a little background on yourself so we get an idea where your coming from tech wise, gear wise.

I didn't pop the top on the pre...being it's a demo unit and felt like that would be a bit of stretch to take that upon myself. Not seeing the inside, so my questions are more general.

Andy has been a great ambassador for BL, worked hard making sure this demo was a success and addressed all our concerns while keeping everyone on task. Your lucky to have him in your organization. I personally want to thank you for allowing this to happen, and I sincerely wish you well and much success as I'm also sure we at the very least created a few BL fanboys.

tonyb

It appears Tony had a senior moment. When mentioning the HT pass thru I had the rear end of another pre in the back of my mind. Oh well, excuse me while I go hunt up my marriage license to catch my wife's name.

BackertLabs

tonyb wrote: »

I'll start with one question that everyone is somewhat curious about....that darn power supply. How did you come about this particular design?

First of all, it's a pleasure to address the Polk group. Your comments have been very gratifying and have allowed us to improve our new preamp. We thank you for that.

The answer is, after years of working on amplifier repair when I was younger, I gradually realized that the power supply is very important, even more than some people think. I realized that the power supply signal is actually the signal that emerges from the gain stage. Meaning that the music signal coming from the output jacks of a preamp is in fact the power supply signal. It's just been imprinted with the source/music signal.

I started focusing on what produced the power supply signal. The answer was, an electrolytic capacitor with a large amount of capacitance; hundreds, and more often, thousands of microfarads (uF) of capacitance. Such a large amount of capacitance puts a fingerprint on the sound, one that is not desirable. And regardless of how many uF, the electrolytic type of capacitor also leaves a sonic fingerprint because of its design.

So, I decided that I wanted to eliminate as much as possible (1) capacitance and (2) the electrolytic type of capacitor. I couldn't just replace electrolytic caps with film caps (film caps are the most desirable type sonically) because I would still have a lot of capacitance in the way. Also the size would be impossible – an electrolytic cap is the size of a C battery, but a film cap with the same uF would be the size of a brick or larger, and extremely heavy. So I thought about the problem quite a lot. I wanted to start fresh and not copy anything else out there. I tried to think "outside the box." I wasn't getting anywhere, so because my faith has always been very important to me, I began to pray to the Lord about it. A few days after I began asking Him for help, an idea came to me and I began to draw a circuit on a napkin at breakfast. That turned out to be our power supply, which we call GreenForce. Instead of hundreds or thousands of uF to power a preamp, GreenForce only requires 1 or 2 uF. This satisfied both my goals, minimal capacitance and getting away from electrolytic capacitors. Although our patent attorney and others have said it was a good idea, it came so directly from my prayers that I have never felt I deserve the credit for it.

tonyb wrote: »

what in your opinion is the pro's and cons over others who are using standard regulated power supplies and off the shelf caps ?

The benefit of using less capacitance and higher quality capacitors is that the power supply can more accurately follow the demands of the music signal. So it can be more accurate in terms of timing ("when" more or less power is delivered) and dynamics ("how much" power at each given instant). From the listener's perspective this provides advantages including more accurate rhythm, dynamics and tone. So in my experience music is more lively, toe tapping, and compelling with GreenForce. More like real, live music.

Other benefits are that the film capacitors used in GreenForce virtually never die. Electrolytics begin to dry out and lose performance quality after some number of years. Also electrolytics sometimes "explode" or swell. These failures do not happen with film caps. Finally, film caps are better for the environment when disposed of.

Cons of GreenForce might be that many electrolytic capacitors have a warming effect on sound quality, which a listener could miss when moving to a more accurate power supply.

tonyb wrote: »

What discovery pointed you in this direction....and when did that "ah-ha" moment happen for you ?

Over the years I tried a few things that allowed me to remove more and more of the fingerprint of the capacitors in the power supply by taking capacitance more and more out of the picture. But the specific design that we stuck with came to me at breakfast that morning. It wasn't exactly an ah-ha moment, more like, "maybe this would work."

tonyb wrote: »

Maybe a little background on yourself so we get an idea where your coming from tech wise, gear wise.

After completing courses in electronics, radio, and television in the late 1950s I learned to repair amplifiers, preamps, speakers, tuners, reel-to-reel tape decks, cassette decks and turntables throughout the 1960s. Through the ‘70s and ‘80s I became more senior in various retail operations managing audio and video repair, and during those years I started getting the itch to design circuits myself. As I have often done in my life, I asked the Lord for help and inspiration in coming up with ideas for designing new circuits. The ideas began to flow shortly thereafter, and in the late ‘80s I began designing and modifying circuits, primarily for preamps and power amps, with a focus on tube circuits. In the ‘90s I started my modding business, and in the 2000s my son Gary joined me. I came up with the GreenForce power supply in late 2010 and began incorporating it in mods for my clients in 2011 – Andy was one of the first ones to receive it. He called me up after listening and was fairly excited, suggesting that I should patent it, which hadn’t been on my mind at all. I decided to give it a try, and from there we began working together and filed, obtaining the patent in 2012. That year we began designing a product that would use the power supply. It took over two years and used circuits I had been working on for over a decade. In 2014 we came out with our first preamp, the Rhythm 1.1.

As for equipment I try to stay mainstream, we use CD for source usually, with a mid-fi Rotel CD player that I like because it uses BlackGate capacitors rather than typical electrolytics, and a high end Marantz SACD player. As for power amps we alternate between vintage and modern designs, using mostly solid state. For speakers, we stick with Usher towers and a variety of bookshelf speakers. Cables are by a local gentleman who used gold-coated silver.

footwedge

Big thanks to @tonyb for starting this thread and big thanks to Bob for his informative response.

Moose68Bash

footwedge wrote: »

Big thanks to @tonyb for starting this thread and big thanks to Bob for his informative response.

Ditto!

Very interesting reading.

breal74

Thanks goes toTony for the questions and Bob for taking the time to answer.

Bob, you do very fine work and can not wait to enjoy the fruits of your labor for years to come!

-Brian

tonyb

Thank you for the responses Bob. The warmer characteristic of the Rhumba is a welcome attribute to older sets of ears. It certainly retains all the details without clouding some frequencies other warmer sounding gear seems to do.

I understand Gary is quite the designer himself. Do either of you plan on taking that power supply design and incorporating it into other pieces such as CDP's, Dacs, etc. ?

Any glimpse of future products on the drawing board....or napkin ?

You guys have certainly created something special in my view. Many blessings for continued success.

tonyb

In addition, as Bob also suggests and we keep spouting about, the power supply is a very important part of any piece. That's just not some old audiophile adage, spoken from the lips of a bunch of old deaf guys on the couch like Al Bundy.

If you look at all the sought after brands, known for their sound quality, you'll see no matter what the design, a well built power supply is key to the sound they portray. Keep that in mind when looking for your next piece.

Which brings up yet another question I have for Bob.

Are you familiar with Chord ? Specifically their Dacs ? We both know about the importance of power supplies, but Chord has come up with "gates", a different version of getting the signal across.

Now, I haven't had an ear on them yet, but by all accounts a very analog sounding dac. I'm just wondering if technology at some point will render power supplies, least as we view them today, practically useless and an outdated design.