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Old 18th October 2013, 03:22 PM   #31
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If I was to use a 28+28vac (56vct) transformer and a single set of MJL21193/4 outputs, what resistor values may be changed/optimized for the 40+40vdc rails?
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Old 18th October 2013, 04:28 PM   #32
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Quote:
Originally Posted by danielwritesbac View Post
If I was to use a 28+28vac (56vct) transformer and a single set of MJL21193/4 outputs, what resistor values may be changed/optimized for the 40+40vdc rails?
Different amp topology , Dan.
This one can scale from 30V to 100V rails because
of the independent regulated differentials and level shifter. At 80V and above
you might have to use 47-68K to feed the Zener's like in the badger cascode.

Sansui uses the same circuit for the Z- 3900 (40V) , 4900 (50V) , 5900 (65V).

You can also add AS MANY outputs as you like. Unlike the S. American amps ,
The triple OPS + the NJW0281/0302 could easily do a 20 device output stage.
Designing a 800 watt /2R capable sub amp is as easy as buying more transistors.

My two reasons for this endeavor is the great sound/ultra low S/N of this amp
and the fact it "survived" 32 years of college use only needing a re-cap.
One EXCELLENT circuit !

One more slight change - use a KSC3503/BD139 for the positive zener regulator,
at 6mA , wahab was correct to use a more robust device here. The small
KSA992 can stay for the negative reg. (only 2.8ma).

OS
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Old 19th October 2013, 11:41 AM   #33
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6ma, bd139? Okay to use 2n5551?
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Old 19th October 2013, 12:51 PM   #34
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Quote:
Originally Posted by danielwritesbac View Post
6ma, bd139? Okay to use 2n5551?

The recomendation of a TO126 was for 50V rails but even with 40V
it would be cautious to use this package for reliability purposes.

Voltage drop around the positive regulation being 25V ,

6ma x 25V = 150mW.

2N5551 junction/ambiant thermal resistance is 200C/W ,
hence the junction will be 200 x 0.15 = 30C over ambiant ,
a BD 139 is 100C/W , differential temp would be just 15C.
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Old 19th October 2013, 02:15 PM   #35
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Default Power circuit hack question. :D

Quote:
Originally Posted by ostripper View Post
The amp also exhibits the best clipping behavior
I have a weird affinity for the LM1875, but rather this way (Schematic for LM1875 Turbo II). The clipping pattern is tame and the dynamics blockbuster. It does use an offboard dc supply. See what I did to the amp board power circuit there? As far as I know, that schematic is unique, it blocks some of the crosstalk of a stereo pair and it promotes more interesting dynamics (vibrates the whole house).
Meanwhile, the power circuit. . .

See the crazy diodes?
Is it applicable (with 6a1, 10a1)? Or is it best reserved for small amplifiers?
Would take only minutes to test this, except that you'll need at least 220u//220u per each rail at the amp board because that trick won't show off with just 220u.
Anyway, that VDM diode trick doesn't cost much and it could be fun! For Dual Mono with only one transformer, this way to "individualize" the amplifier boards with diodes is cheaper than regulators.
What do you think?

Practically, play Zac Brown's "Jump Right In" long enough to get past the opening drum hit. . . add the 220u caps (to get your 440u), add the 6a1's (or the 6a05's from the radio shack--that 4 pack is just right--2 per amp board) located onto the amp boards, series to the power cables, and play the song again.
That should make the difference between just a bump or rolling thunder. So, does it work on discrete amplifiers? May be really fun if it does!
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Last edited by danielwritesbac; 19th October 2013 at 02:27 PM.
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Old 19th October 2013, 06:07 PM   #36
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Dan , if you use 2 bridges with 2 separate capacitor banks you essentially have
each amp "isolated" by diode (like your schema).

Both on my two Badger's and when I do two of these amps , I will use 25A
bridges for EACH channel and 4 X 8200uf caps for each.

The GLA already has very good psrr (below 1). I wondered how it could even
play music at low volumes with total capacitor failure !

Add a simple CRC (8200uf -.47R/10W-8200uf - below 2) , and this amp is
effectively a dual mono (spec wise - BELOW 3 !)

2- 10W/1R for R in parallel would most likely handle a 100-200W amp.

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Attached Images
File Type: jpg nativePSRR.jpg (36.1 KB, 377 views)
File Type: jpg CRC.jpg (17.4 KB, 363 views)
File Type: jpg CRC-PSSR.jpg (44.3 KB, 363 views)
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Old 19th October 2013, 06:12 PM   #37
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Quote:
Originally Posted by apexaudio View Post
Nice amp, this is my favorite old amp Pioneer A70.
All new Marantz amps are clone of old Pioneer amps, symetrical CFA are clone of Pioneer A400.
Regards
The A-70 is indeed interesting ... is it "stepped" (dynamic power supply) ?

The VAS is different , too ! Must simulate it ...

OS
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Old 20th October 2013, 04:52 PM   #38
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Quote:
Originally Posted by ostripper View Post
The A-70 is indeed interesting ... is it "stepped" (dynamic power supply) ?

The VAS is different , too ! Must simulate it ...

OS
It's 'stepped' and there is 'non switcing' circuit
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Old 22nd October 2013, 02:36 AM   #39
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Hi Ostripper
greetings i am interested in buildilng this GLA amp scalable to 800 watts using
10 output pairs at 70 volts dc rails i cant find KSA 992 TRS so can i use 2sa970 as i have these trs just need your confirmation and guidance to make this amp before i start designing this pcb
warm regards
andrew lebon
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Old 22nd October 2013, 01:51 PM   #40
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Quote:
Originally Posted by andrewlebon View Post
Hi Ostripper
greetings i am interested in buildilng this GLA amp scalable to 800 watts using
10 output pairs at 70 volts dc rails i cant find KSA 992 TRS so can i use 2sa970 as i have these trs just need your confirmation and guidance to make this amp before i start designing this pcb
warm regards
andrew lebon
2SA970 would be a good substitute. This device is used in many a vintage amp
such as this.
Q1-4 on this amp form a extreme high gain quad differential , best to keep the
Hfe 200-300 (970 grade- ? - "GR"). I have only simulated a Zetex high gain pair for
Q1-4 (1200Hfe) - no issue.

The Q5 and 6 regulators should be high voltage to-126 devices , R15-16 should be
47K for 70V rails. ABSOLUTELY use output devices for the drivers and
even a more robust device for predrivers (mje340/350 or 2sa1381/sc3503).

.asc (below) for 70V rails - all is good !!
EDIT - Bob Cordell once advised to keep the drivers as the highest Ft devices for the ultimate
stability in a triple. mje340/350 - Ft 10mhz , NJW0281/0302 - Ft 30mhz , and a "slow" output pair MJL21193/4 - 4 mhz ....
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Last edited by ostripper; 22nd October 2013 at 02:00 PM.
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