Hi everyone,
I built this TDA7294 amp several weeks ago and I've got some questions indirectly related to it.
1. I'm using a 500VA (2X30V) toroidal tranformer to feed two of these modules. When I switch it on, my fuse keeps blowing up so I replaced them by a Slo-Blo one but is that normal that I must use an 8A/250V one ? Is 2X30V too much considering that the TDA7294 is rated at +-40V ? (I'm simply using the transformer and a diodes bridge connected to two amp modules.)
2. Do TDA7294 have tendencies to blow up or explode for unknown reasons ?
3. I blew up a speaker because I had DC on one of my Output. Do you have any idea on how to protect my speaker from DC ?
(At least, my blown speaker was a test speaker retrieved from my car hehehe)
Well, thanks in advance for your help !
I built this TDA7294 amp several weeks ago and I've got some questions indirectly related to it.
1. I'm using a 500VA (2X30V) toroidal tranformer to feed two of these modules. When I switch it on, my fuse keeps blowing up so I replaced them by a Slo-Blo one but is that normal that I must use an 8A/250V one ? Is 2X30V too much considering that the TDA7294 is rated at +-40V ? (I'm simply using the transformer and a diodes bridge connected to two amp modules.)
2. Do TDA7294 have tendencies to blow up or explode for unknown reasons ?
3. I blew up a speaker because I had DC on one of my Output. Do you have any idea on how to protect my speaker from DC ?
(At least, my blown speaker was a test speaker retrieved from my car hehehe)
Well, thanks in advance for your help !
Attachments
More & Better Information, PLEASE ...
The Layout of Cicuit + Power Supply.
How the parts are placed. Is a PCB-card used?
This is just as Important for function
of an IC AMP.
--------------------------------
So it is not easy answering your questions
by only a schematic.
Better some pictures
and some PCB-layout daiagram.
THen I promise you will get more answers,
that CAN adress your problem
/just a little hint
from halojoy
The Layout of Cicuit + Power Supply.
How the parts are placed. Is a PCB-card used?
This is just as Important for function
of an IC AMP.
--------------------------------
So it is not easy answering your questions
by only a schematic.
Better some pictures
and some PCB-layout daiagram.
THen I promise you will get more answers,
that CAN adress your problem
/just a little hint
from halojoy
How to protect loudspeakers ?
As you can see the Amp is far from finished !
So if you have any comments or suggestions on :
1. How to protect loudspeakers connected to this (or any amp), from DC or any damageable signals
2. Anyone aware of good softstart circuits ? (not a delay for speakers)
3. Is it "normal" that I must use a 8A/250V fuse on the transformer primary? Otherwise, the fuse blow when the amp is powered up. (transformer is 2X30V, 500VA)
4. Finally, should I connect my Amp's ground to the case and consequently to Earth ? (Yeah, I know newbie question !)
Thanks for your help !
As you can see the Amp is far from finished !
So if you have any comments or suggestions on :
1. How to protect loudspeakers connected to this (or any amp), from DC or any damageable signals
2. Anyone aware of good softstart circuits ? (not a delay for speakers)
3. Is it "normal" that I must use a 8A/250V fuse on the transformer primary? Otherwise, the fuse blow when the amp is powered up. (transformer is 2X30V, 500VA)
4. Finally, should I connect my Amp's ground to the case and consequently to Earth ? (Yeah, I know newbie question !)
Thanks for your help !
One way to protect the speakers from DC is a cap on the output, it's seen in many Class-A amps, but with your IC it shouldn't be needed. You said you blew a speaker, what did you change after it blew?
There's a softstart circuit over at sound.au.com .
Usually it's normal to use a slowblow fuse, try using the smalest value that doesn't blow. Charging caps takes alot of current, so switching on causes the most current to be drawn, although a soststart circuit would help that. Maybe use a thermistor like in the pass designs.
There's a softstart circuit over at sound.au.com .
Usually it's normal to use a slowblow fuse, try using the smalest value that doesn't blow. Charging caps takes alot of current, so switching on causes the most current to be drawn, although a soststart circuit would help that. Maybe use a thermistor like in the pass designs.
Thanks !
A cap on the output ? Any idea of which value should I use ?
What will happen upon failure ? The cap will charge until the fuse blow up ?
Also, I'd like to know how to get rid of the little "hum" that I hear from the speaker when there's no input signal. Looks like it's 60Hz (Canada).
How can it be filtered ? Another cap ?
Thanks again !
A cap on the output ? Any idea of which value should I use ?
What will happen upon failure ? The cap will charge until the fuse blow up ?
Also, I'd like to know how to get rid of the little "hum" that I hear from the speaker when there's no input signal. Looks like it's 60Hz (Canada).
How can it be filtered ? Another cap ?
Thanks again !
Well, I'd only use the cap if you're excessively paranoid about DC getting to your speakers. The cap will act as a highpass filter, so you want it to be a high enough value so as not to attenuate frequencies you want, somewhere around 5000uF would be fine. DC won't flow through a cap, so your speaker would be protected from it. Again, some say that a cap in the signal path can degrade sound quality, keep that in mind.
As for a 60Hz hum, it could be a ground loop. I'd check there first.
As for a 60Hz hum, it could be a ground loop. I'd check there first.
a Ground Loop ?
Thank you for your help !
A ground loop ?
What can be the causes of a ground loop ?
If I take a look at my picture previously posted, the two module's ground (Green Wires) are connected to my transformer secondaries (Blue & Grey wires) at one point.
Should I connect my speakers' (-) at this point too ? Could it be the cause ?
Thanks again !
Thank you for your help !
A ground loop ?
What can be the causes of a ground loop ?
If I take a look at my picture previously posted, the two module's ground (Green Wires) are connected to my transformer secondaries (Blue & Grey wires) at one point.
Should I connect my speakers' (-) at this point too ? Could it be the cause ?
Thanks again !
Hi!
Yeah, normally I would connect speaker's - to the star grounding point...
As for connecting amp-ground to chassis: Put a MKP between ground and chassis (I always use Wima MKP 10 0.47 uF, 630 V DC), again this prevents humming
As for DC offset, I can tell you I have the same prob with a gainclose I tried... but this one blew up my "real" speaker...
Greetings,
Arndt
Yeah, normally I would connect speaker's - to the star grounding point...
As for connecting amp-ground to chassis: Put a MKP between ground and chassis (I always use Wima MKP 10 0.47 uF, 630 V DC), again this prevents humming
As for DC offset, I can tell you I have the same prob with a gainclose I tried... but this one blew up my "real" speaker...
Greetings,
Arndt
Vivek said:
Can't help you with 7293s.
I have however a good source for 7294. Last I checked, they were 140 bux each. Cheap!!
Want some by courier?
Or, you can pick up the kits (550 bux each, AFAIK) in SJP Road. First shop on the left.... Can't remember the name, though. Sells Elektor-kits...
Hi Vivek,
If you can live with slightly less power, why not use an LM3886 in place of the TDA chip? Don't know if you can buy it in blr, but that's no problem... just ask National (hint, hint!). I've built some LM3886 amps, blew some up, too (by powering them from +/-40V, even tho the spec claims they go up to +/-48V). Transformer was an E-I type custom wound at Universal Transformers. I'm still looking for Toroids. Any ideas? Miracle, Inc. is v. expensive.
You can find a good circuit for DC protection on Rod Elliot's "ESP" site
If you can live with slightly less power, why not use an LM3886 in place of the TDA chip? Don't know if you can buy it in blr, but that's no problem... just ask National (hint, hint!). I've built some LM3886 amps, blew some up, too (by powering them from +/-40V, even tho the spec claims they go up to +/-48V). Transformer was an E-I type custom wound at Universal Transformers. I'm still looking for Toroids. Any ideas? Miracle, Inc. is v. expensive.
You can find a good circuit for DC protection on Rod Elliot's "ESP" site
there is for
sure a serious absense of knowledge to proceed properly with this .....
you need to make sure
- pcb is correct
-construction has no errors
-no short circuits between traces and or other error
-missplaced parts
-proper power connected
-proper ground set up ( wrong one will cause the ground loops )
if you havent made any mistake to all this your amp will work perfectly BUT !!!!!!!!!!!!!!!!! it will be not easy from forum members to advice you sine from the way you post it looks that you are a rooky .... ( everybody has been one )
the think is that with this circuit and this power sup everything will work fine with very little or no dc at all in the out
so for sure you have some construction error ..... to find it you need to read a lot ..... a wild guess by me or any other forum member has one chance in amillion to solve the problem ....
sure a serious absense of knowledge to proceed properly with this .....
you need to make sure
- pcb is correct
-construction has no errors
-no short circuits between traces and or other error
-missplaced parts
-proper power connected
-proper ground set up ( wrong one will cause the ground loops )
if you havent made any mistake to all this your amp will work perfectly BUT !!!!!!!!!!!!!!!!! it will be not easy from forum members to advice you sine from the way you post it looks that you are a rooky .... ( everybody has been one )
the think is that with this circuit and this power sup everything will work fine with very little or no dc at all in the out
so for sure you have some construction error ..... to find it you need to read a lot ..... a wild guess by me or any other forum member has one chance in amillion to solve the problem ....
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