+/- 90v smps looking for simple design

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I think its to powerfull and needs too much external components,my transformer is only as big as a roll of tape. arond 8cm diameter and 3-4 cm tall.Its a toroid which only says 18 0 18 on it
The amplifier which came with that trafo was 2x45w but i doubt it since it was a cheap one
it had 2sd1047 outputs quasi complementary
 
What can i say,i built my 2x tda2003 amp for my laptop.I was blown away,this time not by power,but by sound quality.
The best ever sounding amp ever.Better than thoe you buy from the shop.
For the equivalent of one american 1$ this amazes me,better than even the high end stuff which is like 1000$,of course in combination with theyr speakers
 
Hi,
Here's a link to the service manual of a bass amp I worked on. http://skycrash.net/gear/docs/GK/400RB-III_SM.PDF The THD is quite low and it's really well protected. It has a nice soft clip if you over drive it. It's based on Harman Kardon's Signature Series power amplifiers. It's very simple for a discrete amplifier. The 2SA1380 and 2SC3502 may be hard to find. MPSW06 and MPSW56 may work in a low power design. You really want a complementary pair of transistors with low Cob (output to base capacitance). Q18 needs to be near all the big output transistors on the heat sink or it (the amplifier) will blow up a lot.
The manual even gives you the layout of the board. Pay special attention to how the grounds are hooked up.

Good luck,

Marshall
 
a few photos more to come. th art work and schema are for the revised version it works well.

the pics and art work
 

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Hi Steve,
...thanks for adding the link to your newer version with larger creepages.

@ All:
Safety is a hot topic in offline SMPS.
No matter which country you live in and which rules/standards are applied there - all safety standards require large creepages between primary and secondary which feds your amp. Typical safety standards have a lot of similarities and require double or reinforced isolation of the secondary side audio supply vs primary.

In Europe EN60065 is the relevant standard.
Depending on the very details of your circuit most offline SMPS for audio power amplifiers end up in a min creepage requirement in the range between 5mm and 8mm.
- These creepages also must be realized inside the transformer design.
- Furtheron there are requirements on the min thickness of isolation or min number of layers. Heavily simplified rules of thumb:
Min thickness in case of single layer isolation is 0.4mm. If mechanically or thermally stressed go for 0.5mm at least.
If the material is thinner (i.e. isolation tapes), use at least three layers.

P.S:
With high rails on the secondary such as +/-90V you are again in the dangerous zone, even with perfect isolation vs. primary, because the amp can deliver high voltages at the speaker terminals ==> using isolated speaker connectors alike the Speakon connectors from Neutrik becomes necessary for a safe installation.

Disclaimer:
These informations are a rough simplification and not sufficient for a fully safety compliant design.
Careful study of the safety standards is necessary.
Besides the obvious safety standard (like EN60065), further special standards for safety relevant components like transformers and optocouplers may apply.
No guarantee on potential errors.
In case of doubts, consult a specialized safety engineer or test house.
 
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