100W amp: Leach amp or P101 ?

[pwan]

Hello,


I currently have 40-0-40 480VA and 6x 6800UF, I wonder which one ( Low-tim Leach amp, and P101) is suitable for my 88 db/w/m speaker and classic/pop music?

Thanks.

 

[Leolabs]

Depend on your DIY experience.

 

[pwan]

Depend on your DIY experience.

P101 seems to be simpler, however, I found Leach kit available at reasonable price. As far as sonically concerns, which one is your recommendation?

 

[AndrewT]

Hi,
you are short of smoothing capacitance.
You will need a minimum of +-10mF/channel for 8ohm speakers. i.e. 4off 10mF or 8off 6m8F
If you have 4ohm speakers, you need to double the minimum requirement. This will also apply to 4 to 8 ohm speakers since it is the bass unit that tends to be the 4ohm part. 4ohm bass units need 8off 10mF or 12off 6m8F.

There are three ways to arrive at smoothing caps:
1. 2mF/Apk output current. (based on nominal impedance or DCR)
2. 1mF/10W output power. (40Vac will give about 140W)
3. PSU RC time constant >1.4*NFB>1.4*input hiPass. (aim for 1 to 2Hz on 4r or 8r)

 

[pwan]

Hi,
you are short of smoothing capacitance.
You will need a minimum of +-10mF/channel for 8ohm speakers. i.e. 4off 10mF or 8off 6m8F
If you have 4ohm speakers, you need to double the minimum requirement. This will also apply to 4 to 8 ohm speakers since it is the bass unit that tends to be the 4ohm part. 4ohm bass units need 8off 10mF or 12off 6m8F.

My friend just offer to trade his 4x 10,000UF 63V with my 4x 6,800UF 80V. With 40-0-40 transfer produce ~ 58Vdc, Is it safe to use with 63V cap?

 

[AndrewT]

Hi,
allowing +5% for transformer regulation and a further +-6% for mains supply variation brings 40Vac right up to the 63Vdc limit.

So the answer is yes, use 63Vdc on 40Vac.

That gets you in the ballpark of about 130W to 140W into 8ohm.

 

[pwan]

I see. I will use 4x 10,000UF 63V for 40-0-40Vac traf then

Andrew, Many thanks.!

 

[still4given]

Actually Rod Elliot recomends 6X4700uf 80V for the P101.

I asked him when building mine if using 6X15000 whould improve things and he told me no. I used them anyway since that is what I had.

I think the Leach is a little more HiFi sounding than the P101 but it needs more heatsink than the P101. At least mine does.

Link to the PSU schematic at the bottom of the page.

Blessings, Terry

 

[pwan]

still4given,

Thanks for your comment. BTW, you might consider removing the schematic above as it's Rod's intelectual property.

PS: I sending you an email. Could you check it out? Thanks.

 

[djk]

"you might consider removing the schematic above as it's intelectual property"

Looks like any other power supply to me.

 

[AndrewT]

Hi,
I do not recommend the PSU schematic in post8.
There is too little capacitance after the R of the CRC.
This tends towards excessive modulation of the rails.

Still4given,
why do you say the Leach needs more heatsink than the ESP?
Surely since both need similar Iq and since both will run on the same Vrail that equates to same Pq.

Or did you find that different Iqs were required to get the best out of the two amps??

 

[still4given]

Hi,
I do not recommend the PSU schematic in post8.
There is too little capacitance after the R of the CRC.
This tends towards excessive modulation of the rails.

Still4given,
why do you say the Leach needs more heatsink than the ESP?
Surely since both need similar Iq and since both will run on the same Vrail that equates to same Pq.

Or did you find that different Iqs were required to get the best out of the two amps??

Hi Andrew,

I say that because my P101, which is three channel, has smaller heatsinks than my two channel Leach. And while the P101 get barely warm when driving it pretty hard, the Leach feels very warm under normal load. The Leach is built using the boards designed by Jens Rassmussen and runs 3 pair or BJT output devices per channel, while the P101 is built using Rod Elliots's boards and uses two pair of MOSFETs per channel. I used a single 45-0-45V 800vA toriodal tranformer for the P101 and a single 45-0-45V 300vA E-core for the Leach. Both amps were biased per the designers recomendations. I'm not savy enought to tell you why the Leach runs som much hotter, it just does. I was just sharing what I experienced with the two amps.

Blessings, Terry

 

[Upupa Epops]

Terry, reasons can be two : 1) bias isn't the same. 2) hotter amp is oscilating....

 

[jacco vermeulen]

PWAN,

you could also consider constructing one of Pavel's designs, if you have the stomach for it.

 

[JensRasmussen]

Terry, reasons can be two : 1) bias isn't the same. 2) hotter amp is oscilating....

Even with the same bias current the Leach will be warmer as it has 6 transistors vs. the P101s 4.

This means that the Leach will dissipate 1.5 times more idle power than the P101 amp. (The ratio of 6 to 4 on the number of output devises)

\Jens

 

[Upupa Epops]

If will be summary bias the same, dissipation will be the same.... I meant, that was the same, not the same " per device " ...

 

[still4given]

I believe the Leach is biased a little higher than the P101, but they are both set at the recomended bias.

Blessings, Terry

 

[Upupa Epops]

Be concrete, Terry : which is recomended bias of both ?

 

[HiFiddle]

Have you considered a greatmodern MOSFET design -

http://members.dodo.com.au/~gregball/guru_004.htm

This amplifier (the SKA) is a great value and performance kit.

I'm building mine at present to replace a dated old Leach.

 

[rolandong]

now its Leach vs. P101 vs. SKA