Hi,
I am a novice with big amps and I just have completed my first one.
Its a 2x100W using 4 tda7294 b.t.l. two for each channel
plus a preamp-tone control, and a speaker protection circuit all of which I want to put in the same chassis.
Each component is individually tested and working properly, but when I put them in the box and wire them, speaker protection kicks-in all the time when I try to feed the output signal of the preamp to the main amp.
I attach a drawing of the wiring. Is there any problem with the grounding?
The transformer is a 500VA dual 25V /AC dual 15V /AC torroid. Are their -0- ground common for both voltages?
Amps output is BTL +/- so L- and R- are not common ground I think
Any ideas what might I 've been doing wrong?
amplifier board
TDA7294 BTL Amplifier Board DIY Kit HiFi 10000uF 50V AC Dual 25V | eBay
preamp
NE5532 Volume Tone Control Board 10 Times Pre Amp DIY Kit New | eBay
Speaker protection
1pcs New Audio Speaker Protection Board Components Kit DIY for Stereo VC Best | eBay
I am a novice with big amps and I just have completed my first one.
Its a 2x100W using 4 tda7294 b.t.l. two for each channel
plus a preamp-tone control, and a speaker protection circuit all of which I want to put in the same chassis.
Each component is individually tested and working properly, but when I put them in the box and wire them, speaker protection kicks-in all the time when I try to feed the output signal of the preamp to the main amp.
I attach a drawing of the wiring. Is there any problem with the grounding?
The transformer is a 500VA dual 25V /AC dual 15V /AC torroid. Are their -0- ground common for both voltages?
Amps output is BTL +/- so L- and R- are not common ground I think
Any ideas what might I 've been doing wrong?
amplifier board
TDA7294 BTL Amplifier Board DIY Kit HiFi 10000uF 50V AC Dual 25V | eBay
preamp
NE5532 Volume Tone Control Board 10 Times Pre Amp DIY Kit New | eBay
Speaker protection
1pcs New Audio Speaker Protection Board Components Kit DIY for Stereo VC Best | eBay
Attachments
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Some photo's would help. I can see a fault in the schematic. The L/R outputs are switched after the speaker protection and normally you would use two speaker posts per channel.
And probably the speaker protection needs the grounds connecting to something.
And probably the speaker protection needs the grounds connecting to something.
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your wiring is shown as pairs. well done.
I can see pairs for:
Input to pre-amp.
Output from pre-amp.
input to power amp.
power to spk prot.
Mains to transformer.
triplet to :
Power to pre-amp
Power to power amp.
BUT !!!!!!
You have NOT used pairs for the power amp output.
Use twisted pairs for every Flow and Return circuit. No exceptions.
I can see pairs for:
Input to pre-amp.
Output from pre-amp.
input to power amp.
power to spk prot.
Mains to transformer.
triplet to :
Power to pre-amp
Power to power amp.
BUT !!!!!!
You have NOT used pairs for the power amp output.
Use twisted pairs for every Flow and Return circuit. No exceptions.
I would connect the purple and green lines together at some point as the protection board does need to be referenced to the same 0V as the amp....
Your protection board will not really work with a BTL anyway as a fault on the other side of the load will not be detected.
Regards, Dan.
Your protection board will not really work with a BTL anyway as a fault on the other side of the load will not be detected.
Regards, Dan.
An even more important reason to take the PAIR of outputs as a PAIR all the way from amp to terminals.
It appears you are missing the "ground " reference for the speaker protection circuit. As AndrewT said, connect the outputs for complete "send and return" pairs between amp and output jacks, with the speaker protection in between of course.
Mike
Mike
Hi, thank you all for the replies.
I've been troubleshooting the wiring and searching through the internet. Apparently, I will be needing two speaker protection circuit boards, since the outputs are B.T.L., L/R + /- and are all "hot" so none of them could be connected to the ground.
So each channel should have its own board. and use the input left/ right terminals of the board as one channel +/-.
Trying to connect only one channel to see if it works, there is something faulty and I can measure DC 6.1V between protection "L in" and ground, and the same DC voltage between "R in" and ground. The sum of these voltages is the Voltage across the voltage regulator that supplies the board.
And so, connecting the speaker ground of the board, to the physical ground of the amp there is a short circuit, detected both by the hum of the toroid, as well as, by the heating of the cable that goes to the ground (tested only for seconds).
The board supply is only half of the 15-0-15 AC of the transformer (15-0).
Until I figure out what to do I have omitted the protection board and connected normally the amplifier's outputs to the terminal posts. And it works perfectly, I've been testing it for hours measuring with the multimeter and listening to several kinds of music and the sound is fine no "hums" or "hisses" or clipping.
Has anyone used before the affore mentioned speaker protection circuit board? Any suggestions? An other protection board that it works b.t.l.?
I have connected mains earth to the chassis, and I have the rest grounded"floating" as suggested by Rod Elliot ( http://sound.westhost.com/p127-f3.gif )
It's just a drawing mistake. Me bad
The problem is how to ground the spk protection since it has voltage flowing through its ground.
As I mention above I cannot use pairs from the amp to the spk prot. board since the output of the amp is not L/ground - R/ground but L+/L- R+/R- since it works btl for each channel.
Any ideas?
I' did that, but still the protection circuit cannot be connected to the common ground ( DC voltage problem)
Any suggestion for a protection board or a soft start that works on a btl output?
Thank you all for your replies.
Regards, Kostas
I've been troubleshooting the wiring and searching through the internet. Apparently, I will be needing two speaker protection circuit boards, since the outputs are B.T.L., L/R + /- and are all "hot" so none of them could be connected to the ground.
So each channel should have its own board. and use the input left/ right terminals of the board as one channel +/-.
Trying to connect only one channel to see if it works, there is something faulty and I can measure DC 6.1V between protection "L in" and ground, and the same DC voltage between "R in" and ground. The sum of these voltages is the Voltage across the voltage regulator that supplies the board.
And so, connecting the speaker ground of the board, to the physical ground of the amp there is a short circuit, detected both by the hum of the toroid, as well as, by the heating of the cable that goes to the ground (tested only for seconds).
The board supply is only half of the 15-0-15 AC of the transformer (15-0).
Until I figure out what to do I have omitted the protection board and connected normally the amplifier's outputs to the terminal posts. And it works perfectly, I've been testing it for hours measuring with the multimeter and listening to several kinds of music and the sound is fine no "hums" or "hisses" or clipping.
Has anyone used before the affore mentioned speaker protection circuit board? Any suggestions? An other protection board that it works b.t.l.?
I have connected mains earth to the chassis, and I have the rest grounded"floating" as suggested by Rod Elliot ( http://sound.westhost.com/p127-f3.gif )
It's just a drawing mistake. Me bad
The problem is how to ground the spk protection since it has voltage flowing through its ground.
As I mention above I cannot use pairs from the amp to the spk prot. board since the output of the amp is not L/ground - R/ground but L+/L- R+/R- since it works btl for each channel.
Any ideas?
I' did that, but still the protection circuit cannot be connected to the common ground ( DC voltage problem)
Any suggestion for a protection board or a soft start that works on a btl output?
Thank you all for your replies.
Regards, Kostas
The spk protection has been left out and everything is in pairs.
Now I have to find what is wrong with the speaker protection board or a another spk protection circuit that works and is dependable. Any suggestions?
the speaker protection relay contacts are isolated from the protection detection circuits.
You can run the speaker Flow and Return into the relay contacts and out from the contacts as a pair. The Flow side uses one pair of contacts the Return side uses the other pair of contacts. Just use a double pole single throw relay or a double pole double throw relay.
Now to the detection.
The input to the detection SHOULD be a twisted pair. Remember EVERY circuit has a Flow and Return to complete the CIRCUIT !
That pair trigger the detection when the detection threshold is exceeded for a long enough duration.
If the circuit board does not have an isolated detection circuit, then throw it in the bin.
You can run the speaker Flow and Return into the relay contacts and out from the contacts as a pair. The Flow side uses one pair of contacts the Return side uses the other pair of contacts. Just use a double pole single throw relay or a double pole double throw relay.
Now to the detection.
The input to the detection SHOULD be a twisted pair. Remember EVERY circuit has a Flow and Return to complete the CIRCUIT !
That pair trigger the detection when the detection threshold is exceeded for a long enough duration.
If the circuit board does not have an isolated detection circuit, then throw it in the bin.
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