Please comment my pcb P3a

[mastertech]

amplifierguru forget about bass concentrate on distortion with
soft bass

cheers mate

 

[chicco_36]

Hi Greg,
It’s 3 and something A.M. here, and tomorrow is Sunday (actually it’s raining all day), so perfect time for couple of beers. Four one was the last one!
Capacitors, never-ending story… r!sc! Will get headache from us. He just want to construct P3A with our help.
Greg,
Last time I checked your design was top secret and you didn’t like to share schematic with us. Any change in your policy?
Link will be useful too.
Best regards,
Chicco

 

[Fritzell]

Don't forget to mount the Vbe multiplier termally together with the drivers if its a CFP output. This is essential if you don't want the Iq to drift away and eventually blow the output

 

[MidnightLamp]

I think it's lookin' great, and would like to test it as soon as you and everyone else is satisfied with it!

Cheers,

Nish

 

[fixation]

I made one!! and i can tell it sounds great!

no oscillation or what so ever...

here is a little picture of the sweet thing without the output transistor they will come underneath the board

its made of:
decoupling:
100nf 63V MKT caps
1000uf nichicon caps

amp:
Panasonic FC serie caps
Rubycon XYF serie caps
Vishay 4,7 uf 100v mkt input caps
silver Mica caps
MJE 150XX drivers
MJL2119X output
1% metal film resistors

 

[KBK]

One more comment. If you expand some of your poly areas to take up more of the black space, you could really cut down on the amount of etching you would have to do. Make your acid go a little longer for you as well.

I always liked it when my acid went a little longer. Two days is a bit much, though.

 

[gmphadte]

Chicco
The filter caps of the power amp gets loaded according to the music, especially with
the demanding lows. This creates varying supply voltage which is ok for the pwer transistors but are not good for the preceding stages. In order to improve the performabce of the VAS and other stages, just isolate their supply by using RC.
R should be a low value resistor.

This issue has been discussed lately in another thread. Just don't recollect....

Enjoy
Gajanan Phadte

 

[gmphadte]

Read here

Gajanan Phadte

 

[dexter]

my p3a, weak bass and veiled sound

hello folks,

I just finished my P3a amplifier similar to r!sc! designed pcb. thank you for sharing.

I'm using
philips BD139/140 and toshiba 2SC5200/2SA1943
Philips BC 546A.

all Metal fim resistors, except the collector resistor: 2w metal oxide paralled.

evox poly capacitor for pf value
wima input and psu bypass caps
nichicon gold tune for electrolytic capacitor

dual transformer (22-0-22V) 180VA
nichicon Gold tune 4X4700uf perchannel

dc offset : under 15mV for both channel
bias: 150mA

my listening impression:
the amplifier sound is not good.,
it's lack transparancy, weak and poorly defined bass and flat iamging.

the good part is only a slight hum and no hiss.

is there any suggestions for improving the sound?

I'm thinking of:
increasing the value of feedback capacitor to get more kick, increasing the value of input capacitor to 10uf (currently, 3.3uf )

best rgds,

 

[jaycee]

Are you sure it isn't oscillating? What transistors do you use for the drivers? If you are using BD139/140 for this then they are probably not up to the job of driving the Toshibas.

Also try putting 470uF electrolytics on the rails, on board close to the output transistors. I have found that this helps a lot with stopping oscillations due to insufficient decoupling.

 

[dexter]

I;m not quite sure about the oscilation, I don't have a scope to check it.

I'll change the driver tr from BD 139/140 to SA968/SC2335
hopefully in this coming weekend.

any other suggestions are welcome

 

[beboni]

I;m not quite sure about the oscilation, I don't have a scope to check it.

I'll change the driver tr from BD 139/140 to SA968/SC2335
hopefully in this coming weekend.

any other suggestions are welcome

greetings dexter,i have just built p3a amp with that pcb layout and bd139/140 drivers and mjl4281/mjl4302, and i could say that i am preety disapointed because the sound is the same as you described.

no bas,no dinamic{flat/not interesting}muudy or no details,iam sure the problem lies in bd139/140.did you changed these driver tranies,any changes in sound?

 

[tcpip]

greetings dexter,i have just built p3a amp with that pcb layout and bd139/140 drivers and mjl4281/mjl4302, and i could say that i am preety disapointed because the sound is the same as you described.

no bas,no dinamic{flat/not interesting}muudy or no details,iam sure the problem lies in bd139/140.did you changed these driver tranies,any changes in sound?

I have built the P3A on Rod Elliott's PCB (a friend had bought a couple from Rod) and using the parts Rod had listed in his notes for the P3A. I am using 1943/5200 OPS devices. The rest of the devices are all as per his notes. I am most certainly using BD139/140, and I'm happy with the sound.

On a related note, it's a bit difficult to understand what "I'm happy" or "the sound is muddy" means.... it's all subjective opinion. I don't know how to tackle this problem, however. We all just have words to interact with, on these forums.

BTW, if I remember right, your input cap is a little smaller than what Rod had recommended, and your quiescent current is a lot higher than what he recommends. So, maybe you could try fixing those before replacing devices?

 

[adey]

Can anybody tell me the value of C8 and C9 of ESP P3a?