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Old 13th June 2009, 05:37 PM   #101
jaycee is offline jaycee  United Kingdom
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This wasn't a particularly heavy duty PA amp by the looks. It was also designed to run from a car battery, so the power supply was 13.8V and the speaker connected via a transformer (with 8 ohm and 100V taps), and a feedback winding! Rather odd... I'd have thought it cheaper to use an SMPS than an output transformer!

Anyway, 30W should be adequate for me. I have a 2xLM3886 based amp which is on 25V rails, and that produces plenty of sound The only reason Im building this, is because I want to build a discrete amp
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Old 13th June 2009, 07:50 PM   #102
jaycee is offline jaycee  United Kingdom
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I might have a better case candidate now. I got a Technics SU-Z55 from freecycle. The original owner said it wouldn't power on. Well, it powered on but the right channel was heavily distorted. After a poke about and investigating a quite warm 2SD592A - no sound at all
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Old 13th June 2009, 10:14 PM   #103
anatech is offline anatech  Canada
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Hi jaycee,
Wow, I didn't realize that 60 W PA amp .... wasn't.

Still, I imagine you would be doing no worse than most of the commercial product out there. I don't read you as a head banger either.

Allow me one comment though. Joy may be found with systems around 150 wpc (+3 dB headroom also) and a pair of large speakers. This is an occasional thing, but satisfying. Puts a grin on one's face when the music is up to the job. I'll admit that most times, a 30 ~ 50 wpc system would do very well.

I would suggest that you also build a SymAsym at some point. That is one very good sounding little amplifier. I used MJW0281A and MJW0302A for outputs and Japanese transistors for everything else. My bias current for lowest THD ended up lower than most. There are several variants of that basic circuit now, my next build will use J-Fets for the diff pair. It will work well anywhere from 25 to 35 volt supplies. I would recommend tending towards the 35 V end as that was what it was really designed for.

Check out the threads for this amplifier if you have time. Poke around past the middle and closer to the ends.

-Chris
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Old 30th July 2013, 11:24 PM   #104
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Default Back To The Future 50 (BTF50)

Actually I was looking for Frugalamp/Symasym schematics and then then found another OStripper project, the BTF50!

Does anyone have the simulator files for BTF50?

Fortunately, it was possible to find the schematics and layout examples, so those are in the attachment.
Attached Files
File Type: zip BTF50.zip (319.0 KB, 105 views)
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Old 31st July 2013, 08:26 AM   #105
gannaji is offline gannaji  India
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Default Simulation file.

I think this is the simulation file.
--g annaji
Like to thank Daniel for uploading old missing files.
Attached Files
File Type: asc BTF50.asc (14.9 KB, 45 views)
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Last edited by gannaji; 31st July 2013 at 08:28 AM. Reason: Added thanks
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Old 31st July 2013, 08:32 AM   #106
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Quote:
Originally Posted by ostripper View Post
Looking recently for information to construct a simple set of amplifiers to complete my HTPC amp , I attempted to discuss the issue on the DX thread.
Since I was forced to modify the layout because of my application (stealth amp retrofit) , I could not use the DX board. I also have a surplus of 2sa992's , mje/ and other on- semi devices.

The amp in question was originally an RCA application note (1972)...

amplifiers
Click the image to open in full size.

As most of us know , this is the "original" .. skillfully upgraded and modified by "uncle charlie" , aksa , and too many others to count.
Also very interesting is that on the other pages (link above), many of our DIY SS amps found their beginnings in these RCA designs.

This thread is to address ALL modifications that are possible to this simple topology (even minor ones). In other threads it was suggested
that the use of new high Ft devices would render both the sound and stability of this amp unusable AND that if a constructor does modifications,
strays from the path,or asks questions, they will learn nothing !!

I know this to be false , as many clones of the RCA exist of world class performance that DO use modern parts. (I already have 2 that are 1 year old )
Who can upload the genuine datasheet from RCA of this diode (1N3754):
http://www.radiomuseum.org/images/tu...ein/1n3754.jpg
thank you therefore.
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Old 31st July 2013, 10:44 AM   #107
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Quote:
Originally Posted by tiefbassuebertr View Post
Who can upload the genuine datasheet from RCA of this diode (1N3754):
http://www.radiomuseum.org/images/tu...ein/1n3754.jpg
thank you therefore.
No problem. Attached is the genuine RCA datasheet for 1N3754.
The forward voltage drop is unusually large. That one was popular in radios for a "clamp diode" so 1n4007 doesn't replace it.
See also ebay item # 400329897502 for the 1N3754 hangout in Bonner Springs, KS, USA.

Substitutes?
A "1/2w" rated blue-white ingan led ~3v may (or may not) work instead of the series three 1N3754 on that schematic. High voltage zeners used as ordinary diodes may (or may not--check datasheet) have a Forward voltage drop as large as 1N3754. About twice as many of the smallest FR diodes may (or may not) do it. Even BA159 might work. Or there's the option of using transistors as diodes. Unfortunately, it looks like we'd have to physically measure the real unit and compare to the real replacement if an exact mach is wanted.
Attached Files
File Type: pdf 1N3754_RCA.pdf (86.4 KB, 47 views)
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Last edited by danielwritesbac; 31st July 2013 at 11:10 AM.
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Old 31st July 2013, 12:58 PM   #108
gannaji is offline gannaji  India
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Dear Daniel,
I found two more files in my BTF folder.
--gannaji
Attached Files
File Type: asc 20 - RCA 1972 Basic amplifier.asc (9.5 KB, 28 views)
File Type: asc BTF50.asc (14.9 KB, 13 views)
File Type: asc Noobworx50.asc (13.8 KB, 22 views)
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Old 31st July 2013, 07:21 PM   #109
Bigun is online now Bigun  Canada
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Wow, this thread is a blast from the past - from the days when the bootstrap amp was king on this forum, before the CFA amp took it's crown (for the time being).

We had AKSA, DX, my TGM1, OS amps, MJL2119's amps - there was a flurry of stuff going on back then.
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Old 31st July 2013, 11:21 PM   #110
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Quote:
Originally Posted by gannaji View Post
Dear Daniel, I found two more files in my BTF folder. --gannaji
Thank you very much!
Quote:
Originally Posted by Bigun
Wow, this thread is a blast from the past - from the days when the bootstrap amp was king on this forum, before the CFA amp took it's crown (for the time being). We had AKSA, DX, my TGM1, OS amps, MJL2119's amps - there was a flurry of stuff going on back then.
I think that this thread and the BTF50 is really great for showing a place to start.

On first glance, there seems to be a few places where higher performing active parts cost same or less. And I see some probable locations in the power circuit that could make use of a diode drop, either at small signal like Hafler DH220 or at large signal like my TDA7293 project which doesn't need any topology changes (it uses one external CRC power supply). Those sorts of little mods (transistor selection and virtual dual mono power) could probably get it, sonically very competitive.
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