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Old 1st March 2013, 08:56 AM   #241
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Default I've made the "plunge",too!!

Now that I have these awesome boards, all will be easy..... my experience in sourcing the right "stuff" at the lowest price will be valuable.(I will share)

My first impressions are that these boards are top quality. The resulting amp will dependent on what components are chosen for it.

The gain match of the 1381 and the 3503 is futile. the 3503's are just doing "CCS work". The 1381 is the "star player" .. It's gain (along with it's driver) , is what you hear. 10K gain + (close to) no load on the cascode is the "trick" that the "blameless" topology utilizes to achieve near zero distortion.

PS - on a current sourced amp , the CCS is a fully separate entity . You could use lamearse devices for the CCS , as long as the darlington- active (1381-ksa992) pair is there. 10K+ of gain +NFB is what makes the" blameless" rock!!
OS
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Last edited by ostripper; 1st March 2013 at 09:05 AM.
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Old 1st March 2013, 12:21 PM   #242
bkevin is offline bkevin  United Kingdom
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Quote:
Originally Posted by ostripper View Post
Now that I have these awesome boards, all will be easy..... my experience in sourcing the right "stuff" at the lowest price will be valuable.(I will share)
Excellent! That’d be a great help to amateurs such as myself in identifying the best quality components. Look forward to seeing the outcome.
Quote:
My first impressions are that these boards are top quality. The resulting amp will dependent on what components are chosen for it.
Good to hear – I’m now close to pushing the “buy button”

Quote:
The gain match of the 1381 and the 3503 is futile. the 3503's are just doing "CCS work". The 1381 is the "star player" .. It's gain (along with it's driver) , is what you hear. 10K gain + (close to) no load on the cascode is the "trick" that the "blameless" topology utilizes to achieve near zero distortion
"
Thanks for that. So for the 1381 you’d recommend the highest gain available? SA1381E (hfe 100-200) is best I can find - is that good enough? Or would the MJE340/350 combo (hfe 30-240) be a better bet?[/COLOR]

Quote:
PS - on a current sourced amp , the CCS is a fully separate entity . You could use lamearse devices for the CCS , as long as the darlington- active (1381-ksa992) pair is there. 10K+ of gain +NFB is what makes the" blameless" rock!!
OS

Last edited by wintermute; 1st March 2013 at 12:27 PM. Reason: fix quoting.
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Old 1st March 2013, 03:51 PM   #243
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Quote:
by Bkevin -Thanks for that. So for the 1381 you’d recommend the highest gain available? SA1381E (hfe 100-200) is best I can find - is that good enough? Or would the MJE340/350 combo (hfe 30-240) be a better bet?[/COLOR]
Either a high gain 1381 OR a high gain 992 will suffice. The ideal is for BOTH Hfe's to be as high as possible.
200(1381-F or E) x 400(ksa992-F or E)=80k. 8ma/80k = about a .1 uA(.0000001A) load on the current mirror. In real life this might be higher, (flux ,the board,or loading by the drivers).

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Old 1st March 2013, 05:27 PM   #244
naf is offline naf  Indonesia
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Quote:
Originally Posted by ostripper View Post
Either a high gain 1381 OR a high gain 992 will suffice. The ideal is for BOTH Hfe's to be as high as possible.
200(1381-F or E) x 400(ksa992-F or E)=80k. 8ma/80k = about a .1 uA(.0000001A) load on the current mirror. In real life this might be higher, (flux ,the board,or loading by the drivers).

OS
Thank you for explanation
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Old 2nd March 2013, 01:03 AM   #245
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Default Proposed updated schematic?

OStripper,
What do you think of this proposed and minor collection of updates?:
http://www.diyaudio.com/forums/attac...oneybadger.gif
There's a few different devices, much easier matching, one different cap value (for cleaner deeper bass) and hopefully non-explosive, constrained trimmer settings. Are there any errors on that schematic? Can we indeed dial the potentiometers shown to Any setting and not burst the outputs, or do those potentiometer variables need reworked again?
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Old 2nd March 2013, 03:43 AM   #246
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Question OOPS! did I already make a bad decision?

Daniel's updated schematic says "no ON Semi small or medium signal devices -- Please use Fairchild and/or Toshiba." for 4R loads. I'd like to be able to drive 4R loads. My speakers are rated as "6 ohms nominal, 4 ohms minimum". I already purchased the ON Semiconductor NJW0302G and NJW0281G, both rated at 150W. My transformer is 800VA, 35V secondaries, so I could potentially drive them beyond their 450 watt (150 X3) rating. But then, I don't play music very loud. Is it worth getting higher rated output transistors?
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Old 2nd March 2013, 10:53 PM   #247
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That representation of what the footnote says is definitely a misquote.
For small signal and medium signal (driver) transistors, there is currently a production problem with OnSemi's purchase of a new fab plant, and this is causing gross mismatch when big vendors stock compliments from differing production. And, they did!
Fairchild would be more predictable for small signal.
So far, OnSemi large output devices are not affected, so don't be confused. The OnSemi output devices work just fine.
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Originally Posted by ByronInLawrence View Post
I already purchased the ON Semiconductor NJW0302G and NJW0281G, both rated at 150W. My transformer is 800VA, 35V secondaries, so I could potentially drive them beyond their 450 watt (150 X3) rating. But then, I don't play music very loud. Is it worth getting higher rated output transistors?
In this case, the triple parallel outputs should work fine when the transformer has 35v secondaries.

The combination looks just fine for home replay. Basically, the fuses protect the amp; however, your oversize transformer doesn't protect the fuses.

The only error I can see is if it was used for a music production amplifier, you'd need to choose a lower VA transformer in order to prevent the fuses from breaking a concert.
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Old 2nd March 2013, 11:46 PM   #248
AJT is offline AJT  Philippines
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Quote:
Is it worth getting higher rated output transistors?
of course, having a 150 watt rating by itself means nothing, you have to look at SOA at the operating point and derate with temperature, this why we parallel devices...

another thing to consider is beta droop at higher currents, we want a trannie that maintains beta flat with current...
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Old 7th March 2013, 01:56 PM   #249
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What I'd like to know is: Did I successfully alter the schematic trimmer values to remove explosion settings but retain useful settings?
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Old 8th March 2013, 02:00 PM   #250
chunek is offline chunek  Singapore
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Hi Daniel,

The complementary pair for MJL1302 should be MJL3281 as in
http://www.onsemi.cn/pub_link/Collateral/MJL3281A-D.PDF

I am using 3 pairs of NJW1302/NJW3281 with driver of 2SC5171/2SA1930 pairs on 4 ohms speakers with 800VA toriod and 20kuF capacitor on each line. They are running fine. I just burnned a few fuses due to the bias current set more than 35mV on 0.22ohm resistor. (I think the the amp can handle more power if the fuse can set higher.) Currently the bias current is set to 22mV on 0.22ohm resitor without any failure on fuse for few months. I had bad experience only on the mouting of the transistors even with aluminium bar clamp on top. If they are not totally contacted or in parallel with heatsink, the amp still had surged in current. Luckily, the transistors didn't cook as I offed the amp instantly.

MJL version definitely will have better power control as compare to NJW version in my opinion.



James
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