PLAYMASTER 40/40 - schematic needed

[brett-ballarat]

Hi all,
I have been digging in the shed and found my part built Playmaster 40/40 amp. It was an Electronics Australia design from the late 70's.

It has a quasi complimentary output (4*2N3055) and quite a few parts missing on board -- never did finish it.
I am hoping someone out here may have a schematic for this project, it has been sitting waiting in my shed for at least 18yrs and the mice have already had their way with the diagrams and things.
Anyone help?

Brett

[glennb]

Contact me via email and we can arrange something. I have every issue of Electronics Australia ever published.

[quasi]

Hi Glenn,

Do you mind if I can get a copy of the schematic as well. I've been looking for this one myself. I'll send an email and if you can reply at your convenience I would be most grateful.

Cheers
Quasi

[glennb]

If anyone is interested, I've scanned the articles for the Playmaster Forty Forty amplifier from the Dec 1976 and Jan 1977 issues of Electronics Australia and they are available as a 12 page PDF file (1.37MB) at http://au.geocities.com/glennbaddele...ster-40-40.pdf

The Forty Forty is a fairly pedestrian and typical differential input pair - VAS - Complementary symmetry BJT power amplifier. It uses garden variety 2N3055 output transistors. It included a phono stage based on the LM741 and a 3 transistor bass / treble controls stage.

The precedessor to the Forty Forty was the Playmaster Twin 25, which was featured in the April, May, June and September 1976 issues. There were several popular solid-state power amps prior to that in the early 1970s, the Playmaster 136, 140 and 143. I built both the Twin 25 and the 136 at the time they came out.

These amplifiers were superceded in the late 70's by the Playmaster 50W MOSFET amp, which was followed by other more powerful MOSFET amps, such as the series 200 and 300 over the following years. I built my own variation of the series 200, as a 3 channel version for stereo plus a sub woofer. This featured pairs of Toshiba MOSFETS (which are now unavailable) and could pump 150W into 8Ohm and 200W into 4 Ohm.

All of these power amplifiers were all available as kits in Australia during the 1970s-1980s and they sold by the tens of thousands.

[glennb]

Originally posted by glennb
...The Forty Forty is a fairly pedestrian and typical differential input pair - VAS - Complementary symmetry BJT power amplifier...

Oops, I meant quasi complementary. ie. NPN devices in both + and - sections of the output stage.

[RichieRich]

Hi Glennb,

I have a Playmaster 50W MOSFET amp that I built when I was at school. My son uses it now (!) but it recently died.

Do you have a copy of the circuit diagram so I can troubleshoot it?

Cheers,
Richard.

[Jonathan Bright]

And that pair of amps (the 25/25 and 40/40) had a couple of nice features. I remember the power amp' compensation was unusual and I suspect the 25 Watt edition may have been the first published circuit with the Neville Thiele dual purpose sabilization and RFI rejecting network at the output.
BTW that network only gave a 1st order rejection. In his JAES paper there are further developements with values for 2nd and 3rd order networks........but not for those who don't like chokes on their outputs!

[MosfetOwner]

I also built a Playmaster 40-40 when I was at high school in the 70's, and managed to blow it up at first switch on by turning it on before I'd completely finished building it! The impetuosity of youth. I had to learn quickly about fault finding after that, although the burnt out resistors were a clue, and luckily, the only fault. I still have it gathering dust in a spare room, although I haven't used it for years.

The preamp stages used 741 op amps, and a cheap upgrade was to use TLO71 op amps, which were used on the later Playmaster Twin 50 Mosfet amp. I found that out from a fellow Telstra trainee a few years later - thanks Spider.

-Don

[Jonathan Bright]

Richard your email is denied. I'm closer than glennb. Drop us an email and I'll get send you a copy.
Jonathan

[pheralfill]

hi all,

I have just unearthed my Playmaster 40 40. Itwould appear to be still OK, although it has only been out of service for about 2 1/2 years.

I was wondering if anyone out there still has the connector diagram as supplied in the DSE kit? I would like to put this amp back into service but am unable to remember what connects to what (input wise).

Thanks in anticipation.