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Retro PeeCeeBee inspired by Juma.
Retro PeeCeeBee inspired by Juma.
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Old 22nd October 2017, 01:58 PM   #1
gannaji is offline gannaji  India
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Default Retro PeeCeeBee inspired by Juma.

Dearfriends,
Oftenthere is a requirement for a low power amplifier (<30 watts into 8 ohms).Providing such a low power amplifier with output DC protection is simple andeasy if Capacitor coupled output is used with Single power supply. Our dearestJuma has published a few circuits that suit this requirement. I was attractedto a design of his where he developed a Retro design from a Two power supplydesign.

TheFig 1 is a Lateral Mosfet adaptation of F5.
Whena requirement arose for a 5-10 watt amplifier, Juma modified the above circuitto a retro circuit, as in Fig 2.

If,in the First circuit, Q3 & Q4 are replaced with BJT and Lateral mosfet combination, the now well-knowncircuit of PeeCeeBee will result, as in Fig 3:

Thiscan be converted to Retro style as in fig 2 above as in Fig 4.

Frankly,I do not know whether the circuit in fig 4 will work properly ! I requestdearest Juma to help in finalizing the above design.
My immediate doubts:
  • Is the HTrail filtering adequate or it requires modification? Are R9, D5, C13 & C12required or they can be removed?
  • Whatshould be the current in VAS ( Q3 & Q4)?
  • Is theStability OK with C1 & C6 at 22pf ?
  • The valueof R2 in the original is 10k. Will increasing it to 47k cause any problem ?
    Iam attaching the .asc file for the final circuit. My knowledge of LTspice islimited to using it for making drawings and sometimes to DC analysis. Any helpin analysing the above circuit to make it workable is welcome.
    Thetransistors used in the last diagram are the ones I am having ! I am having apair of PCBs supplied by Shaan, ver 1, which can be modified to adopt to theabove circuit.
    Thankingyou !
    --gannaji
Attached Images
File Type: gif 1 - f5lat.gif (7.4 KB, 749 views)
File Type: gif 2 - 5-10w-amp-#8-f5-bjt-lat-sr24.gif (9.4 KB, 749 views)
File Type: png 3 PeeCeeBee.png (28.5 KB, 740 views)
File Type: gif 4 - Retro PeeCeeBee inspired by Juma R1.gif (28.4 KB, 744 views)
Attached Files
File Type: asc Retro PeeCeeBee inspired by Juma R1.asc (7.4 KB, 32 views)
File Type: txt Cordell Models.txt (22.2 KB, 15 views)
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Old 26th October 2017, 01:24 PM   #2
gannaji is offline gannaji  India
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Is the idea of a retro amp so bad ? Bump !
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Old 26th October 2017, 01:55 PM   #3
juma is offline juma  Serbia
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Basically you just want to use the working circuit from 2nd attachment with 50V PSU, right ?
Sorry, don't have time to study all the details...
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Old 26th October 2017, 05:23 PM   #4
indianajo is offline indianajo  United States
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Quote:
Originally Posted by gannaji View Post
Is the idea of a retro amp so bad ? Bump !
Renardson mjr-8 is already out there, a capacitor output single supply amp. MJR-8 Mosfet Audio Power Amplifier
also has a thread here on diyaudio ss.
If you're going to use the unicorn like lateral fets, may as well use something that works already. Yeah, I know, there is a guy in California that sells them here, six at a time. This amp uses 2 of each for stereo.
Personally, I like the stupid proof speaker protection of single supply, but the parts required to move the operating point to 1/2 supply to avoid 2nd harmonic distortion are always left off the schematic. Up to the builder to make that circuit up. The one I came up with works at one temperature (room) and after zero power use to warm things up.
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Old 27th October 2017, 02:53 AM   #5
gannaji is offline gannaji  India
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Dear Juma,
My idea was essentially to have a retro mod to the simple PeeCeeBee, ie. apply the same transformation you did to fig 1 to obtain fig 2. I applied the same transformation to fig 3 to get fig 4. Is it workable ?
--gannaji
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Old 27th October 2017, 02:58 AM   #6
gannaji is offline gannaji  India
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Dear indianajo,
You are the champion of Retro amps on this forum.
Will not R21, R22 , R2 & C4 do the job of holding the mid point of output steady?
--gannaji
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Old 27th October 2017, 08:15 AM   #7
juma is offline juma  Serbia
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Dear Gannaji,
PeeCeeBee is not my design so please contact the author for the changes you have in mind.
Regards
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Old 28th October 2017, 03:15 AM   #8
gannaji is offline gannaji  India
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I have been a regular at Diyaudio for around 6 years. This is the first time I saw a retro mod to a "current feed back topology" amplifier like in fig 1 to fig 2 above ! There are many single transistor input and a few LTP style retros.
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Old 28th October 2017, 12:52 PM   #9
indianajo is offline indianajo  United States
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That npn-pnp input stucture is certainly unique. I guess that is "current feedback topology" If you build it, let us know what the center voltage turns out versus the supply, ie half or not. One certainly has to fool around with the resistors on single input transistor amps to get one to center the output idle voltage. Distortion level would also be interesting.
You've posted enough designs I'm surprised you haven't run a sim on it yet.
I'm certainly not building one in single sourced 2sj162 2sk1058 , and the input bc550/560 are 45 v transistors and are useless on any normal 50 w project containing a >=50 v supply. Moderately priced transformers are 24 v 1A doorbell type from the home store, or 55, 60,65, 70v dual winding from antek.inc ****, the freight on a UPS box from California containing only 2sj162 2sk1058 costs more than a couple of MJ15024/25's from a full line supplier that can ship the rest of my needs in one box.
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Old 28th October 2017, 02:14 PM   #10
gannaji is offline gannaji  India
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Dear Indianajo,
I have six pairs of Laterals with me. I have BC 546B/556B also with me.
So far I could learn making schematics in LT spice. If no help is forthcoming, I will have to visit Mooley's thread and sweat it out.
If you do not like laterals due their cost, can you give me a Retro scheme in CFB topology with BJTs? That will be the first in DIY audio.
--gannaji
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