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 Post subject: LeMonstre 15W.
PostPosted: 07 Nov 2017, 18:42 
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Joined: 27 Aug 2009, 15:19
Posts: 243
Location: Sweden
Hi guy's ,
i just woke up a old project and i just got a 160VA , 2x9V transformer and 8 pcs of 22000uF caps for the powerboard
and this weekend i was thinking to power'it up but one issue is between that ,
i've been reading a lot of material about this amp but one thing i don't get is how to set bias or Dc offset .
If i need to run that with a load i have a 4 Ohm's dummyload that can handle 200W if that helps and now i hoping
you guy's can explain for a another (dummy) how to perform a correct adjustment for this.
I took a picture of one the boards.


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 Post subject: Re: LeMonstre 15W.
PostPosted: 07 Nov 2017, 19:18 
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Joined: 27 Aug 2009, 15:19
Posts: 243
Location: Sweden
Sorry but i did a mistake about filtering board it's the boards for my other amp that have 22000uF caps ,
for this i have 8x15000Uf for each channel and i should be OK with 240000uF or do i need more ?


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 Post subject: Re: LeMonstre 15W.
PostPosted: 08 Nov 2017, 00:36 
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Joined: 08 Aug 2009, 03:11
Posts: 2229
Location: Chilliwack, BC
Nah, I'd not worry about more. It's a complimentary circuit, right? PSRR is high. You could probably get away with 4700uF if the transistors are matched for hfe.

Cheers!

_________________
-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


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 Post subject: Re: LeMonstre 15W.
PostPosted: 08 Nov 2017, 03:17 
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Joined: 27 Aug 2009, 15:19
Posts: 243
Location: Sweden
Hi Gregg,
the power transistors that i know to 100% are original (0302 & 0281) are with'in 3mA matched and
the 716 & 756 are matched to 2mA,
the other i'm not sure if they are org or fake but they are very close to each other (with'in 4mA ) on all and of the other
i bought in pack of 50 so it was a lot of measuring before i was satisfied.
So what is my biggest concern now ? is that to set DC offset ? or is it bias to set in a class A ?


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 Post subject: Re: LeMonstre 15W.
PostPosted: 08 Nov 2017, 03:48 
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Joined: 23 Feb 2017, 02:02
Posts: 204
tjolle62 wrote:
the other i'm not sure if they are org or fake but they are very close to each other (with'in 4mA ) on all and of the other

To check if a transistor is real, the only way is to put it at about 70% of maximum rated voltage and about 70% of rating power disipation with resonablly large cooling, also should be directly connected to heatsink with heat sink grease for large transistors.

For to-92 transistors about 300-400mW of load is a good target.
I can share my transistor testing schematic if your interested


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 Post subject: Re: LeMonstre 15W.
PostPosted: 08 Nov 2017, 03:58 
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Joined: 27 Aug 2009, 15:19
Posts: 243
Location: Sweden
Hi, that testing schematic sounds very interesting and yes please share that valuable info to me.


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 Post subject: Re: LeMonstre 15W.
PostPosted: 08 Nov 2017, 06:43 
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Joined: 08 Aug 2009, 03:11
Posts: 2229
Location: Chilliwack, BC
Hi,

tjolle62 wrote:
So what is my biggest concern now ? is that to set DC offset ? or is it bias to set in a class A ?


If you are having DC offset issues, the attached is how I'd handle it.
(not affiliated with URL on image, I retained it for the (C) of the image)

You can use a film for the 10uF bypass cap... I just have parts drawers full of Nichicon MUSE bipolars and think that way ;)

The 470K to ground across the cap is if the trimmer wiper lifts due to contamination or age, you won't lose a speaker.

As for the class-A bias, the key here is use a BIG heatsink, because you have no thermal feedback :hot:

Bipolars are interesting devices like this.... they can runaway even though they're within their running temp. and SOA of operation, if they're above their manufacturers recommended constant Iq bias.

Alas, the *only* manufacturer I know to specify this in their datasheets in ON Semi.

Cheers!


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_________________
-= Gregg =-
* Ratings are for transistors - tubes have guidelines*
Home: GeeK ZonE
Work: Classic Valve Design


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 Post subject: Re: LeMonstre 15W.
PostPosted: 08 Nov 2017, 06:59 
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Joined: 27 Aug 2009, 15:19
Posts: 243
Location: Sweden
Thank you ! now is that issue solved ....
oh yes heatsink !! i have 2pcs for each board and they weigh around 1.7 kg combined so it's 850gr for each
transistor which should be fairly ok i think.


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 Post subject: Re: LeMonstre 15W.
PostPosted: 08 Nov 2017, 21:46 
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Joined: 23 Feb 2017, 02:02
Posts: 204
viewtopic.php?f=5&p=52028#p52028


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