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PeeCeeBee V4H GB
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Old 8th January 2018, 06:15 PM   #1
shaan is online now shaan  India
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Default PeeCeeBee V4H GB

Hello everyone.

The PeeCeeBee V4H is finally here. As promised, PCBs will be available through group buys arranged in this thread.

Since the introduction of PeeCeeBee V4 early last year I have been receiving emails/PMs on a continuous basis with requests for a higher power version of the same amplifier. While most of the default components allowed for the use of a higher voltage PSU and more power would be readily available by paralleling the MOSFETs, it appeared to me that the amplifier's sonics can still be improved without using additional active devices in the signal chain or biasing the MOSFETs to 1A or 2A and turning the setup into a miniature furnace that would dramatically increase its requirements in every accompanying segment from Transformer rating to heatsink size. This is to say that much of V4's unused potential has been attempted to put to use. As a result, we now have PeeCeeBee V4H, the high power PeeCeeBee that won't need to be a furnace to deliver pleasant music. (However, the option for manual bias trimming remains available, very handy in the chilly winter nights IMO!)

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A bit of detail: (it doesn't go too deep. )

The original PeeCeeBee V4 upto Rev1, uses emitter follower VAS and simple miller compensation at VAS stage that gives us a stable Class-AB "current feedback" amplifier with more than enough speed and much lower THD than any of its previous versions. Many members bought the PCBs, assembled them, listened to the amplifier and sent me more encouraging emails than I could imagine. While most of the comments I received on V4's sonics were positive, a few members who bought the PCBs in the group buys reported excellent sonics but only at 500mA or higher MOSFET bias.

V4's distortion at low frequency is very low and its LF performance with music input directly reflects that, with THD level being very low up-to around 2KHz with 100mA MOSFET bias. At gradually higher frequencies THD tended to gradually rise, as it normally would. However, while 500Hz to 5KHz THD measured low, level of higher-order harmonic content at 100mA bias wasn't as low as measured with 500mA/1A bias, resulting in a "thin" sound at low bias. It is a well known fact that higher order harmonics can be annoying at a lower magnitude than lower order harmonics. The output stage crossover distortion with its spiky and subtle nature was naturally the primary suspect and I was absolutely against building an amplifier with 1000V/uS slew rate (so to speak). Experiments followed.

Meanwhile, I stumbled upon online and printed resources that illustrate "tricks" which, when properly applied, make use of the available negative feedback in a standard closed loop amplifier much more efficiently and effectively. After switching between a few of those "tricks" and measuring/listening to the setup for a few weeks I decided on one arrangement that is simple, has a visible improvement in the THD plot, most stable, sounded best, and noticeably better at HF than the vanilla V4 Rev1, at the same 100mA per MOSFET bias. It is a very simple modification of the miller compensation network that corrects HF distortion at output node and further attenuates higher order harmonics by forming a semi-local feedback network between the output and the VAS stage. The original simple miller compensation used just two capacitors. For this mod we need four additional passive components - two resistors and two more capacitors - R31, R32, C7, C8 as seen in the layout and schematic below. The idea is courtesy of the late Peter Baxandall, kindly made available for everyone by Douglas Self in his website. It is a very flexible technique and after much experimentation a combination of the involved components struck my setup, that had the best effect on sonics of this amplifier, and I went along.

The technique is called "Output Inclusive Compensation", some call it "Transitional Miller Compensation". Whatever we call it, the mod is very simple and cheap, but its effect on sound is grand. The most elegant nature of this technique is that it helps the amplifier exactly where it is needed most. It has little effect on total distortion amount for frequencies below 5KHz but works on the crossover spikes and reduces higher order harmonic considerably, leaving THD to be consisting of almost entirely of second and third harmonic which are way less disturbing than say 5th and 7th and are already very low. At HF it works equally effectively reducing higher order harmonics even better and also having more effect on lowering second and third harmonics - for example check the increase in second+third harmonic levels in the 1KHz 10W and 1KHz 100W spectrum shots below. Compare that to the same in the 10KHz 10W and 10KHz 100W spectrum shots.

---------------------------------------------

All in all, PeeCeeBee has yet again been improved in a key segment of its performance, harmonic distribution. The V4H is just as stable as the V4 and it provides not only more power headroom but has much less crossover distortion and sonics that are perceptibly more balanced throughout the octaves. The modification in compensation has also been incorporated in the lower power V4 Rev2 amplifier and it shows the same improvements in both measurement and sonics.

As shown, each of the feedback resistors have been divided into two 4K7 resistors to result into about the same total resistance in parallel but double the total dissipation limit. This will prevent these resistors from overheating during high power output. The 0.1R resistors allow for using unmatched MOSFETs. If your MOSFETs are matched, replace these resistors with wire links (use thick wire).


The PeeCeeBee V4H layout looks like this:

Click the image to open in full size.

Click the image to open in full size.

Schematic: (>full size<)

Click the image to open in full size.

THD Plots: (1KHz - 0.001% source THD, 10KHz - 0.002% source THD, 100mA per MOSFET, 10mA VAS bias, no matching for any transistor pair except Q1 and Q2.)

1KHz 1W into 5R

Click the image to open in full size.

1KHz 10W into 5R

Click the image to open in full size.

1KHz 100W into 5R

Click the image to open in full size.

10KHz 1W into 5R

Click the image to open in full size.

10KHz 10W into 5R

Click the image to open in full size.

10KHz 100W into 5R

Click the image to open in full size.


Specs:
Power - 150W/250W into 8R/4R load with +/-56V PSU (0.1% THD)
Frequency response(simulated) - ~2Hz to ~800KHz (-3dB)
Slew Rate - 80V/uS
Offset variation - +/-10mV
SNR - >110dB
AC gain - 24.5 (28dB)
DC gain - Unity
Input level for 250W into 4R - 1.5VRMS (~4V P-P)
THD:
100Hz 10W - 0.0005%, 100Hz 100W - 0.001%
1KHz 10W - 0.002%, 1KHz 100W - 0.003%
10KHz 10W - 0.002%, 10KHz 100W - 0.005%

BOM uploaded >Here<

Setup Guide Link >Here<

Drill Template >Here<

---------------------------------------------

Group Buy Information:

The layout is 150mm x 61mm Dual Layer.
Batch of 50, 75 or 100 PCBs will be printed depending on interest. The boards will be 2.4mm thick with FR4 material, 60micron copper, HASL finish, white silkscreen and black solder mask.

> The default price of PCBs is US$16 for 50 confirmed PCBs, decreasing to US$15 for 75 confirmed PCBs and US$14 for 100 or more confirmed PCBs.
> Two forms of shipping are available.
1. International Air Parcel (recommended, 15-20 days delivery time, but a bit expensive. Covers most countries).
2. Registered Post (cheaper, 30-40 days delivery time. Available for all countries)
> After GB list is full, first invoice for PCB price will be sent to each GB member's email address. After payment GB order will be confirmed for the member and PCB batch will be ordered to fab shortly afterwards. After I receive the PCB batch, second invoice for preferred mode of shipment (International Air Parcel or Registered Post) will be sent to each member.
> International payments are accepted through PayPal only and payments from within India are accepted through bank account transfer/deposit, NEFT, IMPS etc.
> Delay between placing the batch order to PCB plant and delivery of the boards to me will be 18-20 days.

---------------------------------------------

Thanks.
shaan
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V4 GB! | V4H GB!! | PSU GB!!!

Last edited by shaan; 6th May 2018 at 03:56 PM.
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Old 8th January 2018, 06:43 PM   #2
rajesh is offline rajesh  India
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Great news Shaan, pl count me in for a stereo set along with whatever components are part of this Group Buy
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Old 8th January 2018, 06:49 PM   #3
rogerneiva is offline rogerneiva  Portugal
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Join Date: Sep 2011
Location: Between Madrid (Spain) and Lisbon (Portugal)
PeeCeeBee V4H GB
Default Components

Hi, congrats for the project. Two questions:

1. Can we have the components BOM ?
2. Are you considering send everything (PCB + components) ?

Thank you and regards

Roger
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Old 8th January 2018, 07:06 PM   #4
shaan is online now shaan  India
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Location: Kolkata
Quote:
Originally Posted by rajesh View Post
Great news Shaan, pl count me in for a stereo set along with whatever components are part of this Group Buy
Hi Rajesh. Sure will do. Thanks for starting it

Quote:
Originally Posted by rogerneiva View Post
Hi, congrats for the project. Two questions:

1. Can we have the components BOM ?
2. Are you considering send everything (PCB + components) ?

Thank you and regards

Roger
Hi Roger.

1. BOM isn't ready yet but you can get an idea from the schematic.
2. I supply full kit with all components only within India. Outside India I can ship the MOSFETs along with the PCBs.

Thanks.
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V4 GB! | V4H GB!! | PSU GB!!!
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Old 8th January 2018, 07:20 PM   #5
rogerneiva is offline rogerneiva  Portugal
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Join Date: Sep 2011
Location: Between Madrid (Spain) and Lisbon (Portugal)
PeeCeeBee V4H GB
Hi Roger.

1. BOM isn't ready yet but you can get an idea from the schematic.
2. I supply full kit with all components only within India. Outside India I can ship the MOSFETs along with the PCBs.

Thanks.[/QUOTE]

OK, please keep me posted for additional news as soon as you have the complete BOM.
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Old 8th January 2018, 07:22 PM   #6
vgeorge is offline vgeorge  Greece
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Location: poros island
PeeCeeBee V4H GB
I' m in for a stereo set!
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Old 8th January 2018, 07:41 PM   #7
gwrskien is offline gwrskien  Norway
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Join Date: Feb 2014
Location: skien
PeeCeeBee V4H GB
rajesh 2pc
vgeorge 2pc
gwrskien 4pc

Thank`s
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Old 8th January 2018, 08:21 PM   #8
bambadoo is online now bambadoo  Norway
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Join Date: Feb 2003
Location: West Coast of Norway
At last. In for this:
rajesh 2pc
vgeorge 2pc
gwrskien 4pc
bambadoo 4pc
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Old 8th January 2018, 08:32 PM   #9
smartx21 is offline smartx21  Brazil
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Location: Santiago, RS/ Brasil
Send a message via MSN to smartx21 PeeCeeBee V4H GB
What would be the price for a pair of boards and 4 pairs of MOSFETS, plus shipping to Brazil (cheapest mode, pls)? Thanks.
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Max.
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Old 8th January 2018, 08:42 PM   #10
Medisinmannen is offline Medisinmannen  Norway
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Join Date: Jan 2015
Location: North
rajesh 2pc
vgeorge 2pc
gwrskien 4pc
bambadoo 4pc
medisinmannen 2pc + mosfets
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