Mullard SS power amplifier - Page 11

Nordic · 11th June 2008, 02:20 PM

I have all my parts ready, but so far have been stopped by realy bad weather, two developments came out bad enough to be wiped clear straight away... under exposed... !!! (thats the downside of useing the sun as a UV source... Oh well, I have some press 'n peel if it does not work this time.... (I have that sh^%#^%y Cremolin positive, could not get my usual brand).

Out of 5 pcbs I made only the 5A heater supply for another project came out right...
My sinks are about .5 to .6W/C by my estimation... think these are big enough?

I also have a 100W sink for the regulator... (third of the price of getting another transformer), I have some 300VA 26VAC ones... and a 250VA 25VAC...

Is going to be a sick amp dissipating 160W at idle... reg + amp.

Luckily it is freezing cold winter here now... probably about 15C today... ( I am wrapped around a hot water bag now).

linuxguru · 11th June 2008, 02:41 PM

Without the regulator, it's only about 60W quiescent/channel. You can drop that further with +/- 18V rails.

The simulation shows the PSRR at 60 dB - not very good. I could go back to the CCS on the LTP to ramp up the PSRR, but let me see how it sounds first before modding it again. With sufficient capacitance on the PSU rails, the PSRR may not be an issue in practice, and the sonics of a resistive current source on the LTP are superior to that of a CCS current source.

Nordic · 11th June 2008, 05:39 PM

unfortunatly that would just make the regulator put out the diffirence... I am useing the pedja rogic design... which basicaly looks like a combined Vreg and capacitance multiplier...

Nordic · 12th June 2008, 02:34 PM

Finaly a bit of weak sun.... I put on a thicker layer of photoresist and went for a 6 minute exposure... seems to do the trick OK...

Of course I put the logo upside down and exposed the damn thing upside down...and etched it... twice....!!!!!!!!

But that saves me drilling holes...

Stee · 12th June 2008, 07:49 PM

I have a dream

a bipolar amplifier clear and free like tube
but with a body-sound, with bass

see this solution

Nordic · 12th June 2008, 08:22 PM

Hey Stee, give me some alternatives for transistors on the outputs... TR7-10... I have stuff like bd139/140 c5200/a1943

What does the TEXT say about TR9 and 10?

What are the notes relateing to TR1, and the 470p cap?

TR5 on main heatsink?

You resolution is a bit low, so the pic is too small to see the numbers on the meters here.

kenpeter · 13th June 2008, 12:51 AM

Quote:

Originally posted by linuxguru
The simulation shows the PSRR at 60 dB - not very good.

You could take a clue from the past and inject a cancelling hum.
I'm struggling a bit to understand that technique myself...
Loftin White was the classic example.

If you want to discuss my unfinished circuit, another thread.
I'm only illustrating a quick and dirty way the Mullard PSRR
could be fixed, not wanting to derail the original topic.

Nordic · 13th June 2008, 07:53 AM

I think you are adding to the topic, not makeing it worse...

I am not sure what the symbol under the output fet is...

What kinda numbers are we looking for as values for those inductors?

would seperate supplies for the front end help?... thinking PCB mount trannies... or even just a bit of extra regulation for those parts a la DX style...

linuxguru · 13th June 2008, 08:46 AM

Nordic: The artwork image was laterally inverted? That's not a problem for any of the components except the output MOSFETs - you just have to rotate the the small signal devices by 180 degrees before mounting them. It does cause an issue for the output devices because of the heatsink orientation, but that can be resolved by mounting on the solder side, as you've done with all the other components.

Kenpeter: OK, I'll look at it in due course. For now, the quick and dirty solution is to use larger filter caps and maybe a pi-filter.

Nordic · 13th June 2008, 12:15 PM

Lol, yeah I was so stupid... so far soldering to the top seems to be fine... and actualy opened my eyes to the fact that we could butterfly the two output transistors to the sides, with a minor track adjustment.

You know, designing PCB's is a very good school at haveing to process each component's operation, how hot will it get...? how far will it radiate? And building it so far suddenly I realised that these two little transistors are constantly dissipating more than my HRII with big TO3P output packages, does at peaks...

(Sorry let me just move my soldering sponge, it dried out, and looks like a cookie... I'm hungry)

Arrangeing them as closely as I did may, very likely, be problematic... we'll see when we get there...

I guess if buying a transformer for the thing, I can settle for about 180-200VA per channel.

I am also playing in my spare time with a processor that connects to a USB stick for programming, that can be used to track temperature etc through the onboard ADC...

HOW can we add adjustable biasing?

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11th June 2008, 02:20 PM	#101
Nordic diyAudio Member Join Date: Sep 2005	I have all my parts ready, but so far have been stopped by realy bad weather, two developments came out bad enough to be wiped clear straight away... under exposed... !!! (thats the downside of useing the sun as a UV source... Oh well, I have some press 'n peel if it does not work this time.... (I have that sh^%#^%y Cremolin positive, could not get my usual brand). Out of 5 pcbs I made only the 5A heater supply for another project came out right... My sinks are about .5 to .6W/C by my estimation... think these are big enough? I also have a 100W sink for the regulator... (third of the price of getting another transformer), I have some 300VA 26VAC ones... and a 250VA 25VAC... Is going to be a sick amp dissipating 160W at idle... reg + amp. Luckily it is freezing cold winter here now... probably about 15C today... ( I am wrapped around a hot water bag now).

11th June 2008, 02:41 PM	#102
linuxguru diyAudio Member Join Date: Sep 2007	Without the regulator, it's only about 60W quiescent/channel. You can drop that further with +/- 18V rails. The simulation shows the PSRR at 60 dB - not very good. I could go back to the CCS on the LTP to ramp up the PSRR, but let me see how it sounds first before modding it again. With sufficient capacitance on the PSU rails, the PSRR may not be an issue in practice, and the sonics of a resistive current source on the LTP are superior to that of a CCS current source.

11th June 2008, 05:39 PM	#103
Nordic diyAudio Member Join Date: Sep 2005	unfortunatly that would just make the regulator put out the diffirence... I am useing the pedja rogic design... which basicaly looks like a combined Vreg and capacitance multiplier...

12th June 2008, 02:34 PM	#104
Nordic diyAudio Member Join Date: Sep 2005	Finaly a bit of weak sun.... I put on a thicker layer of photoresist and went for a 6 minute exposure... seems to do the trick OK... Of course I put the logo upside down and exposed the damn thing upside down...and etched it... twice....!!!!!!!! But that saves me drilling holes...

12th June 2008, 08:22 PM	#106
Nordic diyAudio Member Join Date: Sep 2005	Hey Stee, give me some alternatives for transistors on the outputs... TR7-10... I have stuff like bd139/140 c5200/a1943 What does the TEXT say about TR9 and 10? What are the notes relateing to TR1, and the 470p cap? TR5 on main heatsink? You resolution is a bit low, so the pic is too small to see the numbers on the meters here.

13th June 2008, 07:53 AM	#108
Nordic diyAudio Member Join Date: Sep 2005	I think you are adding to the topic, not makeing it worse... I am not sure what the symbol under the output fet is... What kinda numbers are we looking for as values for those inductors? would seperate supplies for the front end help?... thinking PCB mount trannies... or even just a bit of extra regulation for those parts a la DX style...

13th June 2008, 08:46 AM	#109
linuxguru diyAudio Member Join Date: Sep 2007	Nordic: The artwork image was laterally inverted? That's not a problem for any of the components except the output MOSFETs - you just have to rotate the the small signal devices by 180 degrees before mounting them. It does cause an issue for the output devices because of the heatsink orientation, but that can be resolved by mounting on the solder side, as you've done with all the other components. Kenpeter: OK, I'll look at it in due course. For now, the quick and dirty solution is to use larger filter caps and maybe a pi-filter.

13th June 2008, 12:15 PM	#110
Nordic diyAudio Member Join Date: Sep 2005	Lol, yeah I was so stupid... so far soldering to the top seems to be fine... and actualy opened my eyes to the fact that we could butterfly the two output transistors to the sides, with a minor track adjustment. You know, designing PCB's is a very good school at haveing to process each component's operation, how hot will it get...? how far will it radiate? And building it so far suddenly I realised that these two little transistors are constantly dissipating more than my HRII with big TO3P output packages, does at peaks... (Sorry let me just move my soldering sponge, it dried out, and looks like a cookie... I'm hungry) Arrangeing them as closely as I did may, very likely, be problematic... we'll see when we get there... I guess if buying a transformer for the thing, I can settle for about 180-200VA per channel. I am also playing in my spare time with a processor that connects to a USB stick for programming, that can be used to track temperature etc through the onboard ADC... HOW can we add adjustable biasing?