PeeCeeBee

[shaan]

Based on VSSA, possibly the simplest discrete symmetrical CFB Class-AB amp design with only six transistors in total, popularized by the Slovenian builder Andrej Lackner of diyAudio.

-3dB bandwidth is about 1.3MHz for my boards, can be extended to stable 3MHz. High slew rate, at least 100V/us for the simplest version shown here. Stable without miller compensation, only RF filtering at input. No zobel in my boards. Hitachi LATFET pair as output devices.

Sound is plain natural, i.e. no apparent signature, nothing added nothing removed.

cheers...

diyAudio build thread link- PeeCeeBee



shaan

 

[keith_correa]

Is this the one that LC says sounds better with an SMPS powering it? I remember reading about it once in DIYA - not sure if it is this amp though.

 

[doors666]

hi shaan,

could u please provide some basic info about the amp.. kinda difficult to go thru the 100 page thread...


output power into 4/6/8 ohm loads
approximate heatsink requirements
transformer, caps needed
any particular components that give better sound with better than average parts.
are u selling these, cost for a pair of boards
can the parts be gotten locally.... transistors mainly...

 

[omishra]

Shaan! Nice one.

Please find in inbox PM sent.

 

[bhaskarcan]

Hi Shanti,

Nice PCB. Waiting eagerly to listen to this small wonder. Great review in DIYA, must be sounding great.......:clapping::clapping:

Regards,

Bhaskar

 

[har297]

hi Shaan,

a bit of info on RMS output power into 4/8 ohm loads would be helpful..

thanks for the post

regards
Harsha

 

[shaan]

Is this the one that LC says sounds better with an SMPS powering it? I remember reading about it once in DIYA - not sure if it is this amp though.

It is, almost. LC uses and recommends SMPS for his VSSA modules which use CCS as current source. These boards shown here uses exactly six active devices in the whole circuit and resistors as current sources. PSRR, even with resistor current source remains very high as there is only silence in the speaker when the amp is turned on and the sound doesn't show a hint of hum, this with my unregulated Linear PS. I don't use or recommend SMPS only because I haven't used one with any of my amps.

output power into 4/6/8 ohm loads...

With +/-35V supplies you can expect about 60W into 8R and 90W-100W into 4R load. I am using +/-28V and this provides about 40W into 8R.

approximate heatsink requirements

It's a Class-AB amp with low idle dissipation. A 0.5degC/W or 1degC/W[with fan] heatsink will be enough.

transformer, caps needed

Transformer should be 200VA for two channels when load is 8R, 300VA for 4R. PS caps should be at least 15000uF or more per rail per channel.

are u selling these, cost for a pair of boards

Please PM me if you are interested to buy my boards.

can the parts be gotten locally.... transistors mainly...

I found all the transistor in the most deserted place on earth called Kolkata. :lol:

Well, all the transistors are OLD chips and should be available where you live. If not, especially the Laterals, I can arrange.

Hi Shanti,

Nice PCB. Waiting eagerly to listen to this small wonder. Great review in DIYA, must be sounding great.......:clapping::clapping:

Regards,

Bhaskar

Thanks a lot Bhaskar da.

My exam will be over this month, so I hope I'll have the luck to meet you before you set sail, and to run my amp with your blessed open baffle wonders. They look super pro. :clapping:

shaan

 

[shaan]

...any particular components that give better sound with better than average parts...

As 'better' sound IMO is a subjective area that varies from one person to the next, all I can say is that you will forget the need for 'better' parts after hearing this amplifier.

Being a CFA and using a robust split feedback technique this amp makes 3MHz with those 'old' BD pair. Of course bandwidth alone is not an indicator for low distortion.

The feedback node, having a low impedance load for the feedback signal and the input device itself as the subtraction node, has it's HF roll-off pole at least 100 times higher than our highest frequency of interest. This results into an ultrafast feedback mechanism which virtually eliminates possibilities of intermodulation distortion below 100KHz.

With shown input BJTs of hFE more than 500, the OLG is static 80dB, but extends to more than 20KHz, which ensures there is no 'run out of gain' anomaly at the far highs when running closed-loop, resulting into effortless HF reproduction and zero audible crossover distortion at HF. You can read reviews in the diyAudio build thread, all praise its magic on the highs. Loud when you want it, yet crystal clear.

The output impedance is tested to be in the micro-ohms range, again for the efficient feedback technique. Ensuring superb control for the speaker cone if subwoofer is in your mind. Output impedance is, again, static even at 20KHz.

Transient reproduction of this amp is excellent thanks to the high slew rate which is scalable with resistor variation in the feedback and input collector load nodes.

This amp is three stage, and keeps itself oscillation-free without any extra capacitive compensation in VAS or anywhere. Just limit the input lowpass to say 1MHz and all's fine. That said, Miller compensation might be necessary with lower value feedback resistor. The 2K2/100R config doesn't need this.

Finally the output devices are chosen so that the amp is immune to thermal runaway and allows simply two 1N4148 diodes to bias the FETs well near ideal Iq. The diodes will also protect the LATFETs at the moment of an over-curent condition in the VAS stage, reason to eliminate a resistor in the bias node. The FETs incorporate integrated zener diodes in the package which needs no external Vgs limiter on-board.

More can be said about this circuit that uses old transistors and claims to be hi-fi. But I'll stop here. If you build this you will know the rest.

 

[shaan]

My prototype stereo system using these boards.

 

[Hiten]

Nice DIY work shaan.
Regards

 

[shaan]

Thanks Hiten.

 

[kaushik]

This is nice , active diy from shaan all the time is inspiring .

 

[shaan]

Thanks Kaushik.

My jobs are still not that good IMO, but it's more fun to share the fun.

shaan

 

[shaan]

Now cooking -

This baby is going to drive my 40W DIY spherical sub. The heatsink is a bit small... but will be fan cooled.

cheers
shaan

 

[sarith]

This baby is going to drive my 40W DIY spherical sub

cheers
shaan

A pic of the sub too (for sake of curiosity )

 

[shaan]

Here it is...

Stay tuned...

 

[sarith]

Here it is...

Stay tuned...

Reminded me of my first speaker cabinets. Clay pots big enough to accommodate me when I was a kid and two 8" delhi stuff. The bass was cool

 

[shaan]

This one's bass isn't just 'cool'. This ugly half-globe has beaten each and every commercial sub in the 30-50Watt range from my local friends. The latest was an isobaric from Altec-Lansing 5.1 system costing 14000/- or so. hehe

Naturally all of them asked me how much for it. All rejected.

They have no idea that there is also an Amp that drives the sub, and needs to be good. Also, there is the sub-processor, tweaked to bring the best from this sub.

The enclosure is made of twin sheet of copper+brass, weighing less than 2Kg in total. It's actually the 'Bayan' of the Tabla pair I used to play 10 years ago. My left hand no longer fits the surface. So it was left unused for, say, 8 years. Until...

FYI, the driver is only 4". And makes 30Hz easy. No math was used in the whole build. Thanks to the port of course, and my luck.

Stay tuned...
shaan

 

[prosenjit]

great work guru...
really great..

 

[sarith]

Sounds good . I used 8" 40W 'fullrange' speakers and the clay pots are actually 'ghatams'. Back in 1998, these pots cost me around Rs.200-300 each. It was hell of a task to bring them home few km away by myself. I was in 8th std. Brought it home in a rickshaw. I still remember rickshawala's smile.

Mom was furious for spending all this money on a pair of clay pots. Also it's no space saver. It was more elliptical in shape than round (like an egg). The mouth of the pot was perfect fit for 8". The height of the pot was 3' I remember.

In short, the tallest clay pot I have seen. If you hit it, it produced 'ding' sound like a bell. The finish of the pot wasn't smooth. They said they made it by hand unlike other pots that were made on potter's wheel (I bought it directly from the kiln).

I used a uPC1230H power board and pre from a sony amp. Sound was amazing. The bass was so well defined. My neighbours with their imported sony hifi inquired me about my new 'system' and told me it sounded pretty impressive.

I always played cross of changes by enigma in that. The feeling still lingers in my mind like yesterday. Few months ago I thought of buying a pair of pots for old time sake, but there was no kiln or potters. I checked out some huge aluminium pots fit for 12", but lost my interest in them.

The clay pot and the diy amp (my first serious diy) ended up on my friend's posh apartment who gave me a pair of BS and some money in exchange.

That BS was part of his Sony hifi. Only mod we made was painting the pot so as to look like a show piece vase or else his mom would have thrown it out for it being a mere clay pot (unfit for their status). Sorry for exaggerating. Shaan bhai's 'pot' brought back a flood of good old memories.