AB100 Class AB Power Amplifier

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osscar

osscar

Member
Joined 2009
DaveFred said:
I think this is the AB100,

Portal Audio Panache Integrated Amplifier


To me it looks like there was no "separate" capacitor bank, just the ones on the amp boards, fed by a dual output 425 VA toroidal transformer to two bridge rectifiers.

Original text,

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Why A Passive Preamp/High Gain Amp?

When we began to tackle the idea of a world-class, budget-priced integrated amp, the first ugly reality we faced was that you can't build an excellent-sounding active line stage on the cheap. Our answer was to build a passive line stage using the same level of parts you'll find in very high end preamps.

Although passive preamps are theoretically the most pure, many good free-standing designs just don't sound that good when connected to solid state amps. Most of them sound lifeless and lacking in dynamics. Reality is that the very high output impedance of the passive unit is being asked to drive the (generally) low input impedance of a solid state amp. Making the situation worse, is that the signal has to travel from preamp to amp over a length of reactive interconnect cable.

BUT...

What if you connected the output of this preamp directly to the input of a high-gain solid state amp designed expressly to receive that specific signal? That's the guiding design principle of the Portal Panache.

We're not claiming that the preamp section of this unit is perfect. It's just more perfect functionally than anything remotely in its price class. The input selector, balance control, and attenuator are Alps controls, each hand-selected for neutrality, lack of noise, and reliability. All point-to-point wiring - 14 gauge OFC with PE dielectric - is the shortest possible path. In other words, the signal only goes through the Alps controls and scant inches of pure copper before being delivered intact to the input of the amp.

Dual Mono Amplifier Section

The amplifier section is a dual mono design. The toroidal transformer, custom built for us in California, has separate windings and separate rectifier bridges for each channel. After the transformer, the two channels are completely separate, each with its own bank (40,000 MFD/ch) of filter capacitors, and each channel physically isolated to prevent interaction with its twin.

The transformer itself is rated at 425 va and is capable of producing twice its rated power for extended periods. With a potential 400 watts of power dissipation per channel - 4 pairs of high-speed bipolar output devices rated at 100 watts/12 amps per device - the rated 100 watts per channel into 8 ohms is very conservative. Operation is A/AB, with all stages before the output transistors operating in single-ended Class A mode.

MADE IN THE USA

To order call 1-888-737- HIFI

Description and Specifications

Click to Enlarge
The amp design is a classic complimentary symmetry A/AB design with a current source differential pair followed by a common emitter going to a Darlington configuration output stage.

Specifications:

Rated output: 100 watts/ch at 8 ohms;
200 watts/ch at 4 ohms
Click To EnlargeDistortion: 20 Hz-20kHz both ch driven
@ no more than 0.1% THD
Bandwidth:5 Hz to 100 kHz
Gain: 20 dB
Input impedance: 22 k Ohm
Slew rate: >20 v per microsecond

Specifications are subject to change without notice.
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Click to expand...

interesting - the gain is even much lower than the NP AB100 and than my lowered gain version AB 100 (26-27dB) :confused:
 
D

DaveFred

Member
Joined 2018
Paid Member
Boards showed up today!

NP AB100.jpg

2mm board, 2oz copper, ENIG coating.
 
T

thimios

Member
Joined 2009
DaveFred said:
Thank you Prasi for the reply.!

Does anyone know of a source for 63volt 8200uf caps that are 25mm in diameter other than Cornell Dubilier?

Cornell Dubilier 63v 8200uf 25mm

No one seems to have them in stock, and if they can order them, there are minimum order quantities.
Click to expand...

You don't need 8200uf here.
Use whatever 2200uf-4700uf, isn't the main caps bank!
Is a local decoupling.Use main caps bank direct after rectifier.
 
D

Dennis Hui

Member
Joined 2002
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You need not follow exact how the Panache was built. For example, it appears to
use a transformers with two sets of centre-tapped secondaries and you'll likely
not find something like that readily available.

You'll may find it to use what you like which fits on the main PCB and feed that from
another power supply board.
 
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DaveFred

Member
Joined 2018
Paid Member
Dennis Hui said:
You need not follow exact how the Panache was built. For example, it appears to
use a transformers with two sets of centre-tapped secondaries and you'll likely
not find something like that readily available.

You'll may find it to use what you like which fits on the main PCB and feed that from
another power supply board.
Click to expand...

Readily available no, but not impossible to get either,

----
Dear David.

Here's an updated export offer:

Audio grade transformers:
TS 600VA PRI: 2x115V SEC: 4x 35V (4,28A) - cost: 92,10 EUR/pc (0% VAT export price).

Our offer is valid for the 30 days.


In audio grade, noiseless transformer price You'll get transformer winded with with the largest possible inductance.
Core will be measured and selected, nominal induction will be lowered for the leakage flux minimalization
For a best noise reduction core and all the windings are impregnated.
Transformer will also has electric and electromagnetic shields and epoxy filled interior.
----

I ordered one last week :)

Looks like I will be adding additional capacitance, just not 100% sure how I will be doing that yet.

David.
 
prasi

prasi

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Joined 2014
sites.google.com/site/analogdesign1234/
Paid Member
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DaveFred

Member
Joined 2018
Paid Member
prasi said:
How about something like this?
LT4320 based active rectifier
Its compact CRC that can take up either dual secondary or CT transformer. Instead of rectifier, you can also fit my SMD LT4320 rectificer in the same place.

PCBway order link is in this post LT4320 based active rectifier
Click to expand...

These two files for the PS and active rectifier?

COMPT-CRC-95X100-CT_2020-06-07.zip

IDEAL BRIDGE-R3_TO-220 mosfets_2019-04-24.zip

And I don't need to bother with snubbers?
 
prasi

prasi

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Joined 2014
sites.google.com/site/analogdesign1234/
Paid Member
pl read the thread, i am selling lt4320 in various options there.
if you want to go with conventional SIP rectifier, this LT4320 based active rectifier can be used as stand alone OR along with an option fit my lt4320 smd rectifier instead of SIP rectifier.

Documentation and schematic of the compact crc psu linked above is quite comprehensive and should make things pretty clear.
 
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DaveFred

Member
Joined 2018
Paid Member
Are there any substantive differences between these various TIP142's?

tip142.jpg

Or is a TIP142 a TIP142?

There is the obvious differences of mounting hole placement, one is max 80v where the others are max 100v, one is max 15 amp where the others are max 10 amp and overall length.

I am leaning towards the STMicroelectronics TIP142T for the higher amperage and what look like longer legs which would allow more standoff from the heat sink.

(I did try Googling "TIP142 verations", "TIP142 differences", "best TIP142", etc., to no avail)
 
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D

Dennis Hui

Member
Joined 2002
Paid Member
You want the TO247 part for the pcb you have. Also, he last one in your list is
the TIP141G, which is not the part you want.

Of the two remaining, I don't see much to differentiate them. Note
the ST TIP147 TO247 part is current out of stock at mouser while the OnSemi
one is available, so that might influence your decision.
 
D

DaveFred

Member
Joined 2018
Paid Member
Hello,

I am completely unqualified to come up with a BOM for the Prasi Nelson Pass AB100 circuit board, but if anyone wants to take a look, I have attached a ZIP of a preliminary stab at it.

Every part has a link to Mouser so it is easy to see what each is.

There is some duplication with the input cap being several possible choices.

I would be interested in any feedback anyone would have to offer!

View attachment Prelim DaveFred Prasi NP AB100 BOMS.zip

Thank you,

David.
 
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