Juma's Easy-Peasy Capacitance Multiplier

[xrk971]

Here is a photo. Of note, first time I ran across a fake BD140. Upon power up, I heard a pop and then no LED light. The positive rail was fine. To be safe, I replaced the BC860 and pulled the BD140 to test it on transistor tester and it was dead - appeared as a diode. I cracked open the case to find a teeny tiny die - no way 1.5amps can flow on that. I had some BD140’s from another vendor and looked carefully at package. Both laser inscribed with NXP BD140 and a date code. But good one has tiny numbers cast inside the little divets on the face whereas fake are plain. Can’t remember where I got these from...

After putting good BD140 in place it fired up and works fine. The voltage range is smoothly and finely adjustable. In a way, a great way to have a variable voltage low ripple PSU. It’s not regulated in the sense of feedback, but gives you choice of voltage setting for steady Class A loads.

These boards are really handy to have around and are proving to be very quick and easy to build. Definitely a nice PSU to have around for small preamp or HPA projects needed quiet dual rail service.

 

[prasi]

nicely done x, you are a very tireless builder

 

[BRN]

I was able to fix the shorting problem with one of the Cap-Mx in my FW M2C, and put everything together. I did purchase another transformer based on X’s recommendation, and I have no hum. I’m using 20v 400VA transformers, so I have no promblem providing the 23VDC recommended for the amp. The big caps are 33k uF that I had in my parts bin.

Thanks for everyone’s help. The DIYA forum is a great resource and the people are great.

 

[Skylar88]

Congratulations, BRN. That looks like a nice build. Seeing that I'll get to my own M2 clone build someday, I have a few questions and comments.

The case looks like a 3U or 4U 300. What is the temp like with lid on?
I suppose 2 x 200VA transformers will be more than adequate for the M2, don't you think (in hindsight)?

I'll definitely look into using 2 Cap Mx's as well.
It's really great to know that you have no hum. What is the sensitivity of your speakers?

 

[BRN]

I’m using the Deluxe 4U 300 steel chassis.

I would recommend 300VA transformers as the minimum rating. This is based on my reading in the forums.

I have not measured the temp, but I can touch the heat sinks and lid.

My speakers are 92db, and I’m running subs and sub amps off of the M2C speaker outputs.

 

[Skylar88]

Thanks for the answers, BRN. This should really go in the M2 thread, but I saw too late that you posted there too.

One 300VA toriod (preferably 400VA) is specified for a stereo M2. 2 x 200VA = 400VA combined.

It's easy to say 2 x 300VA is the minimum rating (if I understand you correctly), but cost is a problem for some builders.

 

[ernesternest]

As I remember a rule of thumb is: transformer should be rated at least twice the dissipation of the Amp. So I think 300W is minimum for M2. 400 W is not wrong. More might not be needed.

 

[BRN]

I’m no expert, but that makes sense since your only driving one channel. I already had the one transformer when I was going to build the amp with just one.

 

[Mercury99]

IRFZ44N to replace IRFP240

Would an IRFZ44N be a good substitute for IRFP240 in the original Juma design? It should have only around 2 volt drop. It is a logic level MOSFET.

 

[samoloko]

thx for review
seems very useful addition for first watt amps

would you please give us details about what are cap multiplier voltage drop and rail levels measured after cap multiplier when you are loading It with 1.27A
what Is max current / voltage drop that this cap multiplier can work reliable

I connected the Mjohnson Cap Mx to my 400VA 18v transformer fitted with dual square puck rectifiers, and then installed my old M2 amp into my 4U case. <snip>

 

[xrk971]

You can adjust voltage drop as low as 1.3v and I run mine at 2v. Note that drop has to be greater than levels of ripple you at trying suppress. So my voltage after cap Mx is about 22v.

 

[samoloko]

thx for reply

so It looks that you are better using It with few mF before cap multiplier Input

what Is ripple before and after cap multiplier for 1.27 A load and 2 V voltage drop (you have 24 V at Input)

can I use Mark Johnson cap multiplier feeding first watt amp rails at 24 Vdc / 4 Amp
what would be optimal spec for transformer secondaries 19 Vac or 20 Vac

 

[xrk971]

Size a C and bridge to get the ripple to a level below the dropout voltage. Let’s give it a factor of 2 margin so 1v ripple at 1.3amps. Know that the cap Mx will reduce ripple by up to -50dB. So the smaller you can get it before you go to the cap Mx, the better. You can run simulations to perfectly size it for your case, but use what you have and see how it works. For example, a 10mF cap before the cap Mx is a lot smaller than typical 4x33mF caps normally specified per rail. And even then, the ripple after the cap Mx is about 1mV vs maybe 100mV with a bunch of large caps in CRC alone.

 

[jwjarch]

I have a small batch PCB's for the smaller CapMx on the way from JLCPCB. Thanks for posting those gerbers Prasi! I'm planning to use these as future preamp supplies for a number of different preamps I want to try out. So ordering parts now. Is the value of R1/R5 critical? X, I noticed you used 10k. Is this basically a bleeder for the main caps? So 3k would be a minimum value?

 

[prasi]

if in bleeder position, value is not critical as long as dissipation is taken into account for safety. more clarity on "smaller cap-mx" would be useful, as i posted many designs in this thread.
use ohms law and calculate dissipation by V(squared)/R.

 

[jwjarch]

Hi Prasi. Referring to the CapMx that you posted gerbers for on post #626.

 

[prasi]

Hi jwjarch,
Ok. the Mark Johnson cap mx.
Yes, the bleeder can be any value as long as dissipation through it is taken into account.

lower value = quick bleed and high dissipation
higher value = long time to discharge the caps and lesser dissipation

play around with different values in excel for the voltage you plan to use.

regards
Prasi

 

[jwjarch]

Thanks Prasi. I will choose wisely.

 

[BRN]

I'm running the CapMx in my FW M2c and wanted to know if I should adjust the voltage with no load or with a load?

 

[xrk971]

With load as that will change the output of the transformer significantly. The cap multiplier adjusts a delta from the nominal input voltage under load.