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-   -   Class A? Really? (https://www.diyaudio.com/forums/solid-state/376461-class.html)

acampm 30th August 2021 10:46 PM

Class A? Really?
 
I've never been that interested in class A, the low power output, expensive ancillaries, static power consumption and roasting heat put me off.

This little unit looks quite promising for the active 3 way set up I have in mind though. 30 watts is juuuust enough, it's appealingly simple, and it's pleasingly chap. Also claims to be pretty robust and heat proof. Does it look OK to you?

It quotes perfectly acceptable distortion at 10w. Hmmm. Does that mean that, realistically, it's a 10w amp? 30 is tight, 10 is a non starter.

Assemble A30 FET Pure Class A Power Amplifier Board Stereo HiFi Audio Amp Board | eBay

Description:

The A30 power amplifier circuit is very compact. It consists of only 8 transistors and a few passive components in a single channel. There are no redundant components, which is in line with the HiFi concept of “simply supreme”.
The A30 power amplifier circuit is very stable. It can use a relatively small heat sink and the current is very large. When the heat sink temperature is 80 °C, the circuit can work very stably. There is no need to worry about overheating and damaging the transistor.
A30 installation and commissioning is very simple, only need to connect DC power, adjust the quiescent current and midpoint potential is OK. Where R17 regulates the midpoint potential and R16 regulates the quiescent current.
The A30's low cost and small size of the power amplifier board make it ideal for small HIFI or desktop amplifiers and multichannel amplifiers.
This project consists of two boards (two channels. one board = one channel)
Specifications:
Maximum output power: 30W/8 ohms 60W/4 ohms
Maximum Class A power: 30W
Maximum supply voltage: DC+ -33V
Harmonic distortion: <0.01% 10W/8 ohms
Frequency response: 0Hz-100KHz
Damping coefficient: >100
Signal to noise ratio: >96dB
Conversion rate: >30V/uS
Input sensitivity: 0.5V (effective value)
Input impedance: 10K
Gain: 31dB (34 times)
Size: 99mm × 53mm (mono PCB size)

OldDIY 30th August 2021 10:57 PM

Really! Maximum power consumption: <110W (single channel). (Nelson Pass) A30 . 200W loop cow power supply, the use of a 6 fever 10000uF capacitor filter, the total filter capacity is 60,000uF, uses about 2kg of heat sink.- expensive ancillaries, static power consumption and roasting heat :)
https://ae01.alicdn.com/kf/HTB141L7O...a0087875b841d4

acampm 30th August 2021 11:19 PM

Same case I'm looking at. How big is it roughly? Sounds like the same amp, how do you like the sound? How big a transformer did you pick? Would the case support two units?

OldDIY 30th August 2021 11:33 PM

What is "Pass A30?" Is it genuine? | Audiokarma Home Audio Stereo Discussion Forums

acampm 30th August 2021 11:36 PM

I doubt it's genuine. Follow the link on my post to see what is probably the board. What do you make of it?

acampm 30th August 2021 11:41 PM

Ah. I see. This is a knock off of a well known design which I recognise. The documentation on that makes a big fuss about the heatsink. This seems a bit... Relaxed on that front.

acampm 31st August 2021 12:07 AM

And this is what is being knocked off.
The Volksamp Aleph 30 SE Power Amplifier by Dick Olsher
I'd need three of these, they are a bit underpowered, they would send my electricity bill through the roof and, by the time you've added all the ancillaries, they are not that cheap.

wiseoldtech 31st August 2021 12:19 AM

You all can have that class A stuff.
I'll stick with my A/B and enjoy a lower electric bill and cooler house.

indianajo 31st August 2021 12:41 AM

You want simplicity, my AX6 is 6 transistors, class AB. 3 1/2"x5" board, single 68 v supply, I get 75 watts for 5 seconds out of mine on SP2-XT speaker. 2 1/2"x6"x1" heat sink.
AX6 - Page 42 -simresults- diyAudio
I have MJ15003 equivalent output transistors & MJE15028/29 drivers. Those are heat sinked, also the VAS which is another 30 mhz ft TO220 transistor. My input transistor was MPS8099.
The simulation guys say .06% HD. I don't have instruments, but it sounds the same at 1-75 w as my Peavey CS800s that boasts .02% HD @ 400 W. The Peavey has no capacitors in the sound path with XLR connectors, the AX6 has capacitors in & out. I typically run 1/8 W on pp passages, with 70 w peak on the cannon shot in 1812 overture.
Only problem, you can't buy boards. Prasi made me some, maybe you can ask him for another run.
I stuffed mine in a dynakit ST120 case, maligned on here as "the worst amp ever made". I think the sinclair probably lasted less long than the ST120, but I made a major upgrade in heat sink. The AX6 controls its OT idle current a lot better than OEM did. I have the bias diodes + pot on a terminal strip mounted over the OT's. The 6.75 A dynaco transformer & regulated PS allows the wattage quoted above with only a single 3300 uF mains cap. I regulate with 5 TO3P darlingtons controlled by a zener diode.

Ian Finch 31st August 2021 02:51 AM

I don't see any problem with building an A30 or any other related design offered for DIY with whatever suitable materials are available to you. If that means a kit of parts from China or anywhere else, then its a choice you make of low cost and simplicity V merchandising standards and integrity. It's often obvious from purchaser feedback whether a specific kit or its components is going to work properly when complete, so is there any good reason to buy the parts individually at much greater cost and still have to make the PCBs?

Generally, class A amplification is only necessary to drive the tweeters and 10-20W power is considered plenty for use there in domestic 3-way systems that could require 100W Bass/mid power. I know of a few impressive systems locally that use such active systems but the actual tweeter power levels have been estimated as surprisingly small, going by 'scope measurements, even at deafening, near destructive total 3-way SPLs.


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