Separate transformer is done in a lot of commercial designs. A lot of times it is so the designers can 'stage' start up. Something like the small transformer turns on relay that kicks in the main transformer after the fans are going. Of course if your fans draw less then an amp, a cheap LM7812 will be good enough on one of the supply rails. Another full wave bridge just using the center tap and one or the other taps, single diode doing the same, lots of options depending on what you feel like doing.
then what about startup delay, because its making "bump" sound from speaker when started, its not that loud but it annoying any schematic for that?
and i thinking to add small transformer because that lm7xxx regulator will heat up a bit and will be heating tda too if i put him on same heatsink as tda7293 even if fan current draw is 0.14A it still be more dropped from 35v to 12v (23v)
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Once again, it is up to you as IMHO any design is an expression of the builder as much as a painting would be.
That being said, I kind of lean toward a second transformer, maybe 12.6V center tapped at 6.3V, 1-3 amps would be plenty of current, or something in that range. For first round you could just ignore the center tap and just use a full wave bridge to get ~17-18V to work with. If you do get one with a center tap you will be set for any future expansion with things like preamps or tone controls. Of course if you don't have/can't find a center tapped transformer now, you could always swap it in later. 9 VAC are real common and would work just fine for a fan.
There's probably a 1,000,001 ways of doing a soft start. One of the oldest was just a relay with a resistor and capacitor. You choose the resistor such that it produces the minimum holding current for the relay and wire a fairly large capacitor across the relay.
I believe you are using a TDA7293 or something close? They have built in mute pin and standby pin. Lots of schematics/boards just tie them to be "Instant On" because it is cheaper. It is major surgery to add the parts to a finished board, involves cutting traces and adding the missing parts. It would make for a nice amp to do it as per the manufacturer's recommendations but kind of scary when you start cutting up working circuits. Anyway, if you don't have it yet, download the PDF for the TDA7293 and compare it to what you built. At least then you can tell if you have a design with soft start built in and it isn't working or if it was left out.
That being said, I kind of lean toward a second transformer, maybe 12.6V center tapped at 6.3V, 1-3 amps would be plenty of current, or something in that range. For first round you could just ignore the center tap and just use a full wave bridge to get ~17-18V to work with. If you do get one with a center tap you will be set for any future expansion with things like preamps or tone controls. Of course if you don't have/can't find a center tapped transformer now, you could always swap it in later. 9 VAC are real common and would work just fine for a fan.
There's probably a 1,000,001 ways of doing a soft start. One of the oldest was just a relay with a resistor and capacitor. You choose the resistor such that it produces the minimum holding current for the relay and wire a fairly large capacitor across the relay.
I believe you are using a TDA7293 or something close? They have built in mute pin and standby pin. Lots of schematics/boards just tie them to be "Instant On" because it is cheaper. It is major surgery to add the parts to a finished board, involves cutting traces and adding the missing parts. It would make for a nice amp to do it as per the manufacturer's recommendations but kind of scary when you start cutting up working circuits. Anyway, if you don't have it yet, download the PDF for the TDA7293 and compare it to what you built. At least then you can tell if you have a design with soft start built in and it isn't working or if it was left out.
preamp is already in there you can see little tl072 chip from texas instruments and button next to volume,that button is for gain - off/x5 gain,on/x10 gain
found transformer like this Transformer 9V 667mA HAHN, W*HTR609-1 - "EVITA" in my country and this Transformer 9V 166mA HAHN, W*HTF3209-1 - "EVITA" only for one fan or this Transformer 9V 334mA HAHN, W*HTF4809-1 - "EVITA" for two but i'm not sure because they are sealed, not had sealed before but i need smaller size so i selected sealed
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just searched all catalog and found some cheap and small transformer's witch can put 9Vac 2000mA Transformer 9V 2000mA MINWA, W-T2579200 - "EVITA" or 2x9Vac 2x2000mA Transformer 2x9V 2x2000mA MINWA, W-T2579200CT - "EVITA" so witch should i buy? the price is about the same, and size of both perfectly fits in the space left were i want to put transformer - for fan and also for AN6884 vu meter or for this speaker output protection from dc:
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Since you already have opamps on the board, less likely you will ever need another split supply => either transformer would be fine.
The mute and standby pins are as I feared, they are just tied to the power supply so instant on w/o delay. That is a nice protection circuit you posted but may be overkill. If it was me, I would consider some alternatives. If you want to do it manually, you could just add a switch that puts R4 & R5 at either the V+<as it is now> or ground.
*IF* you want it to be automatic, consider wiring a ~10 uF capacitor between the pin 9 and ground. Maybe the same for pin 10. It may take some playing around with values, like switching the values for R4 & R5 to 100k or the capacitor to ~50 uF. Hard to say unless you find someone who has done it already.
I would pick up the trace at the 22k resistor. You should be able to do it with just test leads or alligator clips. Hook one lead to the side of the resistor that goes to pin 10 of the IC and another to ground, then tie them to the capacitor. Repeat for pin 9.
The mute and standby pins are as I feared, they are just tied to the power supply so instant on w/o delay. That is a nice protection circuit you posted but may be overkill. If it was me, I would consider some alternatives. If you want to do it manually, you could just add a switch that puts R4 & R5 at either the V+<as it is now> or ground.
*IF* you want it to be automatic, consider wiring a ~10 uF capacitor between the pin 9 and ground. Maybe the same for pin 10. It may take some playing around with values, like switching the values for R4 & R5 to 100k or the capacitor to ~50 uF. Hard to say unless you find someone who has done it already.
I would pick up the trace at the 22k resistor. You should be able to do it with just test leads or alligator clips. Hook one lead to the side of the resistor that goes to pin 10 of the IC and another to ground, then tie them to the capacitor. Repeat for pin 9.
then what about speaker protection circuit from dc?
i think that speaker is protected in my schematic witch friend gave me with two diodes
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Just sort of. The two diodes are IC protection from the speaker! Speaker => powerful magnet with copper coil => generator. The suspension returning it to center, after say a base drum beat, generates a voltage that can exceed your power supply. For that matter, the speaker will pick up sounds from the room or the other speaker just like a microphone feeding generated voltage back into the amp.
I've never used anything but fuses on my speakers. I will never try to talk someone else out of being safer then me! The bar is set pretty low. If you want to add an extra level of protection then good for you.
The 10 uF caps I was talking about were a guess to remove the start up bump you were hearing. They would of course do nothing to protect your speakers should your amp burn out.
The two diodes are IC protection from the speaker! Speaker => powerful magnet with copper coil => generator. The suspension returning it to center, after say a base drum beat, generates a voltage that can exceed your power supply. For that matter, the speaker will pick up sounds from the room or the other speaker just like a microphone feeding generated voltage back into the amp.I've never used anything but fuses on my speakers. I will never try to talk someone else out of being safer then me! The bar is set pretty low. If you want to add an extra level of protection then good for you.
The 10 uF caps I was talking about were a guess to remove the start up bump you were hearing. They would of course do nothing to protect your speakers should your amp burn out.
1A 3mm glass fuse, with wire thread - blown at second start - moment then caps charge and tda make "bum" sound from speaker...also on fuse is written 6T
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This blowing during start up seems to indicate that your soft start is not working properly.
