[fkclo]

This is a multi-part post due to its length. It is about my own story of the first "all-out" custom amp project.

[size=medium]Intro[/size]

It all started 6 months ago, in June 2009. A casual check on Blue Circle Audio’s headphone amp offerings have turned out to be the first ever custom design project I commissioned. And it turned out to be an educational, fun filled and exciting experience.

[size=medium]Some Background [/size]

Blue Circle is not new to those who are at the high-end of the hi-fi hobby. They have been in the hi-fi business for over 20 years. The founder and chief designer Gilbert Yeung has been gaining a lot of attention by virtue of his unique design and universal praise of his products.

Ultra Audio Archives -- Searching for the Extreme: Gilbert Yeung of Blue Circle Audio -- Part One (7/2008)

Ultra Audio Archives -- Searching for the Extreme: Gilbert Yeung of Blue Circle Audio -- Part Two (8/2008)

For those who have not heard much about this company, you can have a quick glance at their website :

Blue Circle Audio

Browsing through the product offering of Blue Circle, one can easily notice that Blue Circle offers possibly the widest price range of audiophile products in the industry. If you want a US$20,000 power amp ? No problem. Want something even more exotic ? Gilbert will be happy to satisfy your wishes – as long as it is about the sonics, not extravagant case work, and as long as you have a deep enough pocket

. Budget constrained and want to get a no-frills audiophile component ? Blue Circle offers the “Shoe Box” series or even the “Thingee” series which present the some of the best values in hi-fi. It also creates its own line of interconnects, power cables, power conditioners and even surge protectors ! The very unconventional approach of its product line up gas made Blue Circle a class of its own in this industry.

But Blue Circle did not make its name out of its headphone amp offerings. It was not until an accomplished member of Head-Fi, Skylab, did a review of its only headphone amp product at that time – the SBH Headphone Amplifier (which is part of the Shoe Box series) that I started to take notice of what appeared to be a very capable headphone amp from Blue Circle.

For those interested in the review by Skylab, here is the link to the review.

http://www.head-fi.org/forums/f5/rev...ne-amp-248158/

There are other reviews of Blue Circle headphone amp products in this forum and they are just some search away.

[size=medium]The Beginning[/size]

At that time I was already in possession of some of the better amps in this hobby, including the Rudistor RP010B MKII, the Phonitor, my all time favourite Woo Audio 5 ( one can check my profile for a listing of the amps I currently own here My Stuff but I kept wondering what Blue Circle is really capable of in headphone amp design if budget is a lesser constraint and Gilbert is given more free hand in his design. Will Gilbert be able to come up with some hallmark design also in the headphone amp arena ?

So in June 2009 I wrote to Gilbert to inquire about his products. It all started with the Hat Peed Thingee, which I thought is a pretty interesting idea. The Hat Peed Thingee made me think of the “wolf in lamp’s skin”. I always like understated, low key design which is exactly how Blue Circle presents its products. After some warming up and exploring the possibility of customisation the dialogue with Gilbert didn’t take too long to evolve around the possibility of building a custom headphone amp to my own specification. At that time, I was suggesting a “BC” series of headphone amp. Gilbert wrote back and told me he have made several cost-no-object solid state headphone amp that uses SuperCap and solar power for the absolute minimum noise level. But he added that a headphone amp like that will not make its way into the mass market due to insane cost involved. Therefore instead of introducing a flag ship line of headphone amp Gilbert seemed to be scouting for interesting custom projects. To inspire him I started describing my wishes about my dream solid state headphone amp. The same day Gilbert wrote back “It is an interesting project. Give me a few days and I will get back to you on specs. and pricing.” With this reply I just passed the point of no return.

To be continued.....

 

[fkclo]

continued from above...

[size=medium]The Design and Feature Set[/size]

In the subsequently 2 months, we exchanged numerous emails about the music I like, my listening preference, and feature set of this custom headphone amp, which we later called it the “FLO Amp”. We then discussed the space requirements, case work and even colour of the chassis. Space has always been an issue for those of us city dwellers, and in Hong Kong the situation is even worse. I spent quite some time figuring out the space I can free up in my rig for this project.

For a custom headphone amp building a custom case will be prohibitively expensive (a custom made and engraved stainless steel face plate alone can cost over US$400 a piece! ) So, in search for better value we fell back to other options – including a plain metal box, decorations by Plexiglas, powder coating …. but none is as impressive as what I have seen on the BC109 preamp. (priced from US$4,295 onwards). Seeing how eager I was Gilbert looked around in his workshop and one evening he finally found a steel face plate which he can modify to suit my project. I was delighted.

In the beginning of September the specification and feature set were basically “frozen”, followed by some submission of the layout design and finalisation of minor details. Here is what I have specified for the FLO amp :

Sound Signature :

I want natural, articulated and balanced sound overall. Smooth and extended highs with minimum roll off. True to source, realistic, precise imaging and a holographic sound stage. By balanced and realistic I want music to be right-proportioned and portray a true picture of the performance ( I hate to see a ensemble being casted like an orchestra, or a cosy jazz pub to sound like a staged performance in a stadium…).

I do not want to be in the front row for the” in-my-face” music push, nor do I want to be sitting too far back to become detached from the performers. I realised it is not easy to convey my preference in words but luckily Gilbert is such an intelligent person that he knew what I wanted to have and echoed my words with something that he can translated into his design. This dialogue alone was indeed some experience and I learnt a lot from him.

Feature Set:

The main constraints are in determining the feature set is what can be accommodated within the space I can free up from my rig, and how to make the amp user friendly and intuitive to operate. Gilbert has been ultra flexible in the process and he basically took all that are technically feasible and that won’t compromise sound quality. We did discuss the optimum location for the power switch (to avoid hum), the need for separate battery on/off switch and how to strike a balance between user-friendliness and appearance. The discussion went into such details like spacing of the headphone jacks, fonts on the engraved panel, and even labels on the back..... It took us many rounds of emails to come up with the following:

1. Chassis : 445 mm (W) x 375 mm (D) and 96 mm (H)
2. Construction : 18g steel chassis with curved stainless steel face plate, engraved
3. Stainless steel volume control knob and source selection knob
4. Shallco volume port (47 steps with H/L internal switch giving 94 steps)
5. Gold plate Grayhill Selector Switch
6. Mains power on/off in the front (for ease of access)
7. Battery power on/off in the front (to preserve juice while I am traveling)
8. The classic black lit Blue Circle logo and of course a blue chassis

... To be continued.

 

[fkclo]

continued from above...

Power scheme :

We spent a lot of time discussing about the power supply arrangements for the FLO Amp, and finally ended up with the following :

1. Mains supply : 110 or 220-240V a.c. supply with internal user selector switch (complete with safety feature to avoid inadvertent operation)
2. 14 x AA size 2,500+ mAh Ni-MH batteries. ( The amp is designed to work best with battery but also works with direct AC in)
3. Power supply capacitance : 846,000 uF !! [ This is probably the biggest capacitor reserve for a headphone amp I have seen to-date
   
   ] using Panasonic 85 deg high speed switching caps, although in one of Gilbert “ultimate reference project” – the Pinkie, a total 2,800 Farads of capacitors were deployed so comparatively speaking what is on mine is very humble. The choice of caps is always a struggle between performance, space and affordability. This is an area I have to trust Gilbert because he has probably experimented with more caps that I can ever imagine
   

The power supply scheme proposed by Gilbert reflected one key design consideration of the FLO amp – putting as much power reserve as one can afford, and as best quality d.c. power supply as one can physically put into the case as the best assurance of black background and ultimate low noise floor.

The idea of having a lead-acid battery was also discussed. While lead-acid battery has better internal resistance it is just beyond the size constraints I have specified to be put inside the box. The capacitor bank will serve to ensure ultra power draw in quick transients and extreme dynamics while at the same time providing the best quality d.c. one can expect.

The FLO amp will be equipped with switches to allow use of either battery or mains power. It has a built-in charger and the batter voltage will be constantly monitored. The amp will cut itself off should the battery voltage falls below certain level. As long as the mains is on, the battery will be charged automatically.

In the final design Gilbert has added an extra 4-pin connector at the back to allow one to plug in an external battery source to further extent the run time of the FLO amp off-the-grid if one desires. I am grateful Gilbert did this, although I would expect with continual advancement in battery capacity the built-in battery pack should be capable for higher capacities in the future.

Input and Outputs :

Inputs - The FLO Amp can take 4 inputs :-

1. 1 pair balanced XLR input (back)
2. 2 pairs RCA SE inputs (back)
3. 1 pair RCA SE input (front) – especially provided to allow A/B comparison of sources

Outputs :

1. 1 pair balanced XLR headphone out (front)
2. 1 high impedance headphone out (front)
3. 1 low impendance headphone out (front)
4. 1 balanced XLR loop out (back)
5. 1 RCA SE loop out (back)

The the Blue Circle FLO amp is intended to be a single purpose machine – just for headphone listening. I add the loop outs just to allow sharing of the incoming signals by my other amps. So, it is NOT a pre-amp, period.

Attention to Details

While drilling down the design and the drawings we also touched on the parts to be used, from internal wiring, RCA plugs, type of finishing and of course the volume pot. Gilbert was a Shallco fan and he believed this is the only one that matches his expectation and so all high-end Blue Circle gears can be fitted with the Shallco ports, at a cost of course. Again it was a great lesson learnt from Gilbert, who openly shared with me his experience with different types of wiring and what plugs to use to suit different signal levels. I couldn’t thank him enough in correcting some of my previous mis-concepts about audio components and choice of materials.

.... to be continued.

 

[fkclo]

continued from above...

The Finished Product

So, after some 150 emails, and 6 months, my FLO Amp is finally done, tested and tweaked in early December. Gilbert put the amp through a few battery charge-discharge cycles to make sure everything works as expected. Gilbert told me he was extremely happy with the result. The FLO amp is capable for driving pair of AKG K240S for over 21 hours on battery while maintaining an almost flat frequency response all the way beyond 50kHz. Total distortion was less than 0.0045% across over 95% of the output range. Yes, he did the measurements specifically for this amp, although he seems to trust his own ears more than the figures

Here are a few photos that Gilbert took for me.

Front view showing all accessible features

Rear view showing inputs and loop outs

The monster capacitor bank, battery pack has taken up most of the space

Use of silicone has become a “signature” of Gilbert Yeung’s creations

Neat craftmanship and manual labour as another hallmark of Gilbert’s product

A close up of the Shallco stepped attenuator

Custom voltage selector, with safety latch, and auxiliary d.c. input

This 30lb+ monster is now on its long journey to its new home Hong Kong. If everything goes well I should be having it by end this week and I will be taking some more photos. I would expect it is going to take a while before those huge caps are properly formed and I would be glad to share some impression later.

That's all for now, and hope you enjoy this read.

F. Lo

 

[Skylab]

Wow - looks great. Congrats. Gilbert/BCA makes great stuff, to be sure.

 

[fkclo]

I am keeping my fingers crossed

Looking back this can be considered a "risky project" to most and all I am betting is the reputation of Gilbert / BCA.

F. Lo

 

[Skylab]

I look forward to reading about your thoughts on the sound!

 

[Kees]

Amazing amp! Congratulations! And thanks for the nice story.
I'm sure you're going to love it and I'm anxious to read about your impressions.

 

[AmanGeorge]

Looks great, can't wait to hear more about this one!

 

[Jodet]

That is one of the most amazing things I have EVER SEEN. ABSOLUTELY FRAKKING AMAZING.

Having owned an SBH I know how good BC stuff is. You're going to own a 'one in the world' headphone amp, congratulations!

 

[SoupRKnowva]

The question no one else has asked flo, how much did that beast set you back?

 

[Dan Millheim]

^ that's what i've been wondering too

 

[fkclo]

Quote:

Originally Posted by SoupRKnowva /img/forum/go_quote.gif The question no one else has asked flo, how much did that beast set you back?

Well, consider it is in the same price class as a Rudistor RB010B MKII, or a maxxed out Woo Audio 5. Yes, it does cost a fair amount of money given that Gilbert is not able to spread the cost spent in the design and preparation to multiple units.

F. Lo

 

[fkclo]

Just checked UPS that the boxes landed Hong Kong earlier today (16th). I should be able to have it in the next 24 hours

Really excited.....

F. Lo

 

[Jodet]

You've inspired me. I ordered an SBH this morning.