The power of Leach

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Scented audio gear (on explosion)

Sorry, but couldn't resist commenting on the spelling of sentence. I am sure that an exploded filter cap might ... excite the olfactory senses. No toying with filter caps though (an experiment in my childhood jumps to mind, 220V AC + 16V electrolytic = :yikes: ), results with filter caps might be ... well :wchair:. The bigger rated caps shouldn't be too expensive and in comparrison to other parts of the amps don't push up the price too much. Then again I get caps from a wholesaler which ends up being a third as expensive as in the electronics shops at those voltages.

Martin
 
so I think I've got 4 options for my filter caps:

- go with 63v which janneman does NOT recommend
- buy 100v caps which is more than twice the price
- put 40v caps in series to obtain 80v (?)
- order 75v or 80v caps from over seas, which means they're not the easiest to get (and I don't know what the shipping will cost)

what should I do? I feel that the 100v caps are unnecessary expensive.

-truls
 
I would go for the 63 V caps if yu already have them. You will be at rougly 58 V if you have one bridge per winding. Of course it would be preferable to have higher ratings but IMHO it is within limits.

Don't put any caps in series. You loose half the capacitance (if the caps are the same) and most likely you end up with the same price as 100V or close.

/UrSv
 
My Caps

I'm looking forward to building my first Leach, and what i've got so far are 2 9800 uF @100V just to ensure that surges wont mess up my capacitors. May be a little underpowered, but i've got a 1200VA transformer to help out.

How picky are the ONsemi guys about sample's being returned or payed for after a while? Eg, are these essentially free transistors?



Chris Martens

Oh, Btw, anyone know any nice PCB makers in BC Canada?
 
BrianGT said:
Which transistors did you get? Did you go for the MPS-A06/56 combo, or did you manage to get the obsolete MPS8099/8599? or some other set?

--
Brian

The MPS8099 and MPS8599 are apparently in production, I bought a reel of them which is the only way they could be had at the time. They are on tape. If anyone cares, check out <p> www.tech-diy.com/store.htm
 
Re: My Caps

sirtiff said:
I'm looking forward to building my first Leach, and what i've got so far are 2 9800 uF @100V just to ensure that surges wont mess up my capacitors. May be a little underpowered, but i've got a 1200VA transformer to help out.

How picky are the ONsemi guys about sample's being returned or payed for after a while? Eg, are these essentially free transistors?


There really aren't any "surges" that you'll have to worry about such severe overvoltage on the secondary side of a transformer. That's also a really big transformer with too little capacitance, IMO, for a 125W per channel stereo amplifier PSU.

I ordered the drivers and the output (I used MJL21193/4) as samples from OnSEMI, and the 2N's from MultiCOMP (I think - that was a year ago) as samples, too. I paid for the MPSA parts, and bought a hundred of each (they're something like 6 cents US each for a hundred) so I could match them well.

Regards,

Mark Broker
 
MPS8099/8599

I am building a Leach amp to drive the bass for my biamp system using SA1302/2SC3281 for the output stage. For the input, can I replace the MPS transistors with the Toshiba low noise matched pair 2SA1349 and 2SC3381 which incidently I have many?

Some parameters:-

Vceo 80V
Ic 100ma
hfe 200-700 @ Vce 6V & Ic 2ma
casing - dual transistor in 1 chip

thanks

ckt
:confused:
 
Hi all,

What a great thread! I am working on an amp that requires MJL21193/4 parts and I finally got a place to get them from this thread!!!! My problem is that I have 84VDC rails and I need 40,000uF of filtering per rail, according to the design. With all of the talk about capacitors, Have any of you ever put 2 identical caps in series, to get a higher voltage rating? Is this a good idea? I realize that the capacitance will be half but at 68,000uF, 34,000uF after series-ing will be close enough for me... Any suggestions or comments will be greatly appreciated as I have boards coming next week. :eek:

Thanks in advance,

Chris
 
BrianGT said:
Dr. Leach has been using 50v caps with his leach amp everyday for the last 25 years.

--
Brian


True, but this amp was his original amp - the one appearing on the cover of Audio Magazine - which used a lower voltage power supply putting out just 48 volts. Thus, a 50V capactor was just right. (I use this same transformer in my own leach amp.

I mention this primarily so people won't think Dr. Leach is stupid or in any way implying that it is ok to use a 50V cap in a 63V circuit. I do agree with Brian that if a 50V cap has a surge voltage of 75V it will probably be ok in a 63 V circuit, bu it will be less able to successfully deal with line voltage surges and this could lead to early capacitor failure.
 
Jeff R said:



True, but this amp was his original amp - the one appearing on the cover of Audio Magazine - which used a lower voltage power supply putting out just 48 volts. Thus, a 50V capactor was just right. (I use this same transformer in my own leach amp.

I mention this primarily so people won't think Dr. Leach is stupid or in any way implying that it is ok to use a 50V cap in a 63V circuit. I do agree with Brian that if a 50V cap has a surge voltage of 75V it will probably be ok in a 63 V circuit, bu it will be less able to successfully deal with line voltage surges and this could lead to early capacitor failure.
Be carefull guys.

How much a cap can withstand is very much dependent of brand! This can be tested rather easily. Just put a resistor in series and measure the leakage, which increases rapidly over a certain point.
 
peranders said:

Be carefull guys.


Indeed. I did not mean to imply it was a wise thing to do and if one expects to save money by using an under-rated capacitor, as I said, it may work for a while, but the life of the device will be reduced and you will end up spending more. A LOT more if the cap explodes and catches something on fire. Do it right the first time and you will never have any regrets.
 
Diode:

Putting caps in series will raise the ESR and series inductance;
better to get a suitably rated single capacitor or parallel a couple
of lower value capacitors with the right voltage rating. Two
series caps also need equalization resistors to prevent an
unequal charge from building up on a single cap and exceeding
the voltage rating.
 
Actually, ESL is quite low in good Electrolytics. From the Cornell-Dubilier Electrolytic Application Guide, "Inductance is the equivalent series inductance, and it is relatively independent of both frequency and temperature. Typical values range from 2 to 8 nH for SMT types, 10 nH to 30 nH for radial-leaded types, 20 to 50 nH for screw-terminal types, and up to 200 nH for axial-leaded types. These low values are achieved by tab location and intrinsic, low inductance of the dielectric contact geometry. The capacitor element has typical inductance of less than 2 nH."

For a comparison, a straight wire in free space has an intrinsic inductance of approximately 1.2uH/m, somewhat regardless of diameter. (That's 4*pi*10^-7 H/m).

I would argue that the ESR is the important attribute to keep as low as possible, and therefore agree that series capacitors should be avoided in power supplies. If that's the setup used, bleeder resistors across each cap should be used, which will also act as equalization resistors.

Good Luck,

Mark Broker
 
Thanks for the info guys....

I just hit the jackpot. I asked my boss if he'd sell me some caps from junk boards and he said that I could just have them. I ended up getting 6 10,000uF/100V and 4 7,500/100V!!!!!!!! I don't know what I did right but I can now build my power supply!!! It will be +/- 74VDC with 37,500uF per rail. Close enough to 40,000uF for me.

I don't know about using a 50V cap in a 63V circuit. I'd never do it. I've had small electrolytics blow up and one hit me in the forehead and paper, electrolyte and foil went into my eye. I can't imagine one of these big filter caps doing the same. I'd imagine I'd be completely blinded and fighting for my life. If you look at most designs, they go to within 10% of the rated voltage NOT the surge voltage, ie 75V on a 80V cap. Yes, doing a foolish thing like the 50V thing would destroy a cap pretty quickly. Putting 2, like, under voltage caps together, in series, will work and has been done in most tube type guitar amps for years and they last for at least 20 years. For Hi-Fi, I guess it's different, but I can't see the big deal, personally. Oh well, it worked out for the best anyway. Tanks for the information.

Can anyone lead me to a company who carries this kind of capacitor for a good price? Peavey wants 31.00 for 10,000uF/100V. I will assume Crown will be even more.

Thanks again!

Chris
 
"if a 50V cap has a surge voltage of 75V it will probably be ok in a 63 V circuit"

Absolutely not!!!

Surge voltage ratings are for choke input filters ONLY, the surge only lasts 8.3mS on 60hz.

Anyone that runs a capacitor input supply with 63V on a 50V cap deserves whatever happens.
 
Diode said:
Can anyone lead me to a company who carries this kind of capacitor for a good price? Peavey wants 31.00 for 10,000uF/100V. I will assume Crown will be even more.

Good score!!

All the standard electronics catalogs will have big eletrolytics: Newark, Digikey, Allied Electronics, Mouser, etc. Your local electronics shop will likely have the common sizes in stock, or can order them. Brand doesn't matter too much, just look for low ESR and high quality construction.

Regards,

Mark Broker
 
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