Retro PeeCeeBee inspired by Juma.

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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
 

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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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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.
 
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
 
The limit of my design skill is changing resistor values to adapt known topologies to different power supply voltages without melting parts. I'm a builder & copier of SS designs, not an originator. One main goal in diyaudio being to cut a very productive dictatorship out of supplying my entertainment wants.
The one criticism I can offer, is how does two 1n4148 provide enough gate drive split for fets? I thought they had about a 5 v turn on point, not 0.6 v.
Besides I'm busy this week trying to adapt a $35 automobile remote unlock/lock accessory to turn on & off a pipe organ blower. The donated pipe organ drive system is not communicating; costs $x000 to replace.
Glad you have your supplies. I will be watching to see how your experiment turns out.
 
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...
The one criticism I can offer, is how does two 1n4148 provide enough gate drive split for fets? I thought they had about a 5 v turn on point, not 0.6 v...

A single look at the datasheet would help you realise what's true. Many types of MOSFETs are out there and they differ much.
And it's not the gate drive (usually referred with parasitic capacitances and previous stage impedance) - it's the voltage between Gate and Source (Vgs) that controls any MOSFET's Drain current (Id).
 
Whereas the fairchild fet datasheets are pretty clear about miminum turn on voltage, the only indication I can find on the hitachi datasheet of no revision date, but copyright 1999, is a chart of drain to source voltage versus gate to source voltage, no temperatur specified. 2sj162 shows a 1 amp line vertical from Vds -10 to -2 of Vgs -2.4.
2sk1058 shows the 1 amp line from Vds 10 to Vds 2 of Vgs 2.5.
I'd have to say 10 v Vds (max charted for turn on point) is not very useful for driving 8 ohm speakers, 1 amp is pretty wimpy speaker drive, and 2.5 v Vgs is better than the 5 v fairchild "logic qualified" nfets but not much. At 2 amps current the Vgs of the vertical line is more like 4 v.
These datasheets were what I got from datasheetcatalog 7/11/2010, same place as I get everything else.
Without special knowledge gained by experience, I would say the diode stack of output transistor gate drive should include a 10 v zener, plus a parallel pot to adjust voltage separation down from 10.6 to minimum for good crossover distortion performance.
For my actual experience with fets, I've used them to turn on or off fans to cool heat sinks, driven by a 15k ntc resistor and a pull down resistor. For that purpose salvage fets out of dead switcher power supplies work fine.
 
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Hitachi datasheet, 2sk1058, first link in google search (datasheetcatalog.com).
Transfer characteristic clearly shows an Id of bit over 100mA for Vgs = 0.6 V
Okay, thanks. That chart was there, I just missed the meaning of it. 100 ma of cross conduction idle should be plenty.
So lateral Fets are quite different than the switcher fets, that have a chart showing less than 250 ua of sd current until gate voltage gets up to 4 or 5.
 
I had finalized the voltage values of the main capacitors in the diagram. Please advise whether those voltage values as minimum are OK. The front and output section will be on a small board. Assembling of resistors started.
Kindly advise !
--gannaji
 

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35 v electrolytic caps should work. Watch the 1 uf cap, the ones I keep in stock are rated 25 v.
50 v costs pennies more, and if you find a sale going on for out of shelf life caps, often less. I charge up caps with a meter ohms scale anyway, that reforms them enough. Shelf life spec is for pick & place machine assembly with no test until mains voltage hits the power supply.
For me the pennies are trivial; just getting a box in from the warehouse several states away is $8 or more. I buy some caps @ 25 v & others @ 80 or 100. Big size change between 25 & 80, & I use 25 v caps by the hundred in organ key sustain boards.
 
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