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Old 23rd December 2012, 03:25 PM   #131
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yes for thermally coupled and yes for 9 transistors on same heatsink.. But dont know if they have same temperature, i only test using my finger and looks like all 9 transistors have same temperature.



Thanks
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Old 28th December 2012, 01:52 PM   #132
tsip is offline tsip  Greece
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Greetings to all and congratulations for providing this project to the diy community.
I have received the boards and I am beginning to populate them. I have an issue though with the jumpers and particularly those at the driver stage transistors Q14 & Q15. The jumper from the transistors base to C18, C19 have no soldering pads. Does this mean that the wire will be soldered to the capacitor and then directly on the transistor base?
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Old 28th December 2012, 04:56 PM   #133
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Hi,

The boards already have the jumpers in place so no need for any jumpers. As for C18 and C19, it was highly recommended by the designer and iirc, a few other members, that they be installed as close to the transistors as possible.

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Old 28th December 2012, 05:43 PM   #134
tsip is offline tsip  Greece
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Thanks, good to have this clarified. Just to point out that you mean except the one next to the C1 cap(if a big size cap is used). I assume then that CRZ should be left as is as well.
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Old 28th December 2012, 08:12 PM   #135
clm811 is offline clm811  United States
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Question 4 ohms with 63vdc rails

Hi All.
Making monoblock amps with a similar circuit, but only 2 instead of 3 OPT's.

I have a pair of 300VA 45-0-45vac transformers(63vdc rails, measured), and will be using two each of the beefier ON Semi MJL4281-4302 transistors, mounted on large 350mmx150mmx50mm heatsinks (Conrad MF35-151.5).

My speakers are rated at 4ohms (Dynaudio Focus), and therefore present a lower impedance than most.

Any concerns or cautions?

Happy Holidays!

-Chas
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Old 2nd January 2013, 12:39 PM   #136
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Quote:
I have a problem with bias setting, i checked and follow the guide...dmm on tp1 and tp2, set voltage on R30 about 20mv, wait.for a few minutes for thermal stablize recheck again after half hour, tp1 - tp2 become 25.4mv. Turned it back to 20mv. check again for another 1 hour, tp1-tp2 become 27.7mv
This is the case with one of my AX's (larger badger -4 op devices). It finally does stabilize , but it takes longer. I did build a smaller amp like the badger and
extended the Vbe out on a short piece of flat cable to attach it directly to one of the output devices. This shortened the stabilization time considerably.
But both amps are thermally stable ... try to use an all plastic device for the Vbe .. use either a mje340 or 2sa3503 , the differences in Hfe/internal silicon structure will create a different temperature coefficient.

To go insane , one could even use a 2 device Vbe brought out to one of the output devices with a cable. This would not require reworking the board as one could design a small "daughtercard" with the 2 devices and a couple passive component quite easily. Read Doug Self's "Audio Power Amplifier Design Handbook" - thermal compensation and thermal dynamics... This is just a suggestion as I tried this for use with a "inadequate" heatsink - and it worked !The single vbe should be sufficient with most builds.

OS
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Old 5th January 2013, 06:34 PM   #137
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Quote:
Originally Posted by ostripper View Post
This is the case with one of my AX's (larger badger -4 op devices). It finally does stabilize , but it takes longer. I did build a smaller amp like the badger and
extended the Vbe out on a short piece of flat cable to attach it directly to one of the output devices. This shortened the stabilization time considerably.
But both amps are thermally stable ... try to use an all plastic device for the Vbe .. use either a mje340 or 2sa3503 , the differences in Hfe/internal silicon structure will create a different temperature coefficient.

To go insane , one could even use a 2 device Vbe brought out to one of the output devices with a cable. This would not require reworking the board as one could design a small "daughtercard" with the 2 devices and a couple passive component quite easily. Read Doug Self's "Audio Power Amplifier Design Handbook" - thermal compensation and thermal dynamics... This is just a suggestion as I tried this for use with a "inadequate" heatsink - and it worked !The single vbe should be sufficient with most builds.

OS

Thanks ostripper for your reply
Im using KSC1503, did try change one KSC1503 to another KSC1503, nothing change. Removed mica insulation on VBE and changed to thermal pad and still nothin changed. then i put KSC1503 directly on heatsink without mica or thermal pad, voltage on TP1 - TP2 still moving up. And finally i put VBE on top of Q12 and it does stabilize.
Now i set R30 to 44mv across TP1-TP2 and so far it stable, but i havent check it again since i went out for holiday since Christmas and just back home.

Thanks

Last edited by gundul; 5th January 2013 at 06:39 PM.
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Old 6th January 2013, 04:43 AM   #138
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Quote:
By CLM 811 - Any concerns or cautions?
use 3 pair @60+ V rails!!

Dynaudio focus's are sealed. Big impedance dips near the Fc of the bass driver might make the amp see 2-3R on occasion. These dips are small and close to resonance but with a strange source (my virtual synths) , I have seen my amp
load down.

This might possibly be a "doomsday" scenario , but it CAN happen.

BTW , what dynaudio (340/360/260)... nice speakers !!

OS
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Old 6th January 2013, 05:29 AM   #139
AJT is offline AJT  Philippines
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Quote:
Originally Posted by gundul View Post
Hi all

I have a problem with bias setting, i checked and follow the guide...dmm on tp1 and tp2, set voltage on R30 about 20mv, wait.for a few minutes for thermal stablize recheck again after half hour, tp1 - tp2 become 25.4mv. Turned it back to 20mv. check again for another 1 hour, tp1-tp2 become 27.7mv

It happen always all the time when i checked and tried to setting bias.
Basicly it always moving up slowly but sure.

Thanks
that is why it is important that when you do the bias adjustments, the heatsinks are already heated up and you set your bias accordingly...
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Old 6th January 2013, 08:47 AM   #140
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I'm looking at building an amp for my system, and this could be ideal. Have there been any reviews yet or any frequency plots?

Thanks!
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