| pete.a |
Iv'e been making the Carlos buffer, and during testing found the pos reg getting very hot ? Only happens when connected to the buffer, and i think i may have contributed to it when my dvmeter was on the wrong setting...durrr.
When opperating found a difference at the output when no signal applied, 0.700mv left and .0330mv right..wonder if something is mismatched. Put an audio signal from my MD player and all soundedwell on both channels into a pair of headphone's. Just that reg fault, any ideas anyone..will change the opams and buffer's at some time this week, but ive ran out of time now due to parent hood ! |
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| Nuuk |
What voltages are we talking about here Pete? IOW - how many volts are droped across your regulators?
I doubt having your meter set to the wrong range has done any damage. ;) |
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| pete.a |
Hi Nick,
Tx is a 18v dual secondary , so its kicks out around 22v or there about. So were only looking at 7v to drop , but i can't think why that pos reg is getting so hot , to the point where it hurts to touch ! But the buffer still works ok, or so it would seem |
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| Nuuk |
Neither can I then Pete if it only drops 7 volts.
Is there anybody more knowledgeable that can suggest a reason? |
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| carlosfm |
Hi Pete,
Some questions to see if we can help:
1. What op-amps are you using with the BUF634?
2. At what gain?
3. What voltage do you have before and after each reg, under load?
4. Check the polarity of all the electrolythic caps.:hot:
5. Do you have a cap immediately before and after each reg (close to it)?
6. What regulators are you using? For LM317/337, check the orientation of the protection diodes (if any).:hot: |
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| Nuuk |
| Carlos - you forgot his inside leg measurment! :D |
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| pete.a |
Hi Carlos,
Op amps are 627 , and iv'e used your design. The voltage before the regs is around 22v and after is , 17v neg and 13v pos , under no load, under load its 14.99neg and 14.97 pos. All the caps are correctly orientated and the regs are the 1a / 15v fixed aka lm7815 and lm7915.
Just one thing Carlos what voltage did you get on the output of your audio buffer , was it around 300mv dc ? this would be at idle no signal....
Nick ..just for you..33inside and 34 waist 5" 10 and 13st..of pure power...:) :D :D :D |
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| carlmart |
| quote: | Originally posted by pete.a
what voltage did you get on the output of your audio buffer , was it around 300mv dc ? this would be at idle no signal....
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Is that DC offset, that is at the output of the BUF634? You shouldn't have that high a value, only a few mV.
Carlos |
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| Nuuk |
| quote: | | Nick ..just for you..33inside and 34 waist 5" 10 and 13st..of pure power... |
I suggest you do less hi-fi DIY and more jogging! :D :D :D |
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| carlosfm |
| quote: | Originally posted by pete.a
Op amps are 627 , and iv'e used your design. The voltage before the regs is around 22v and after is , 17v neg and 13v pos , under no load, under load its 14.99neg and 14.97 pos. |
:eek:
There's something very wrong there.
After the regs you should have the same voltage, loaded or not loaded.:confused:
It's a regulated PSU...
You have less voltage not loaded?:confused:
| quote: | Originally posted by pete.a
Just one thing Carlos what voltage did you get on the output of your audio buffer , was it around 300mv dc ? this would be at idle no signal.... |
0.2mv one channel and 0.3mv the other one.:D
Wait...
Check the pinout of the regs!:bawling: |
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| PMA |
Some of the 78XX/79XX (depends on manufacturer) exhibit strange behavior: under no load they supply more voltage than Vref. For example not mentioned Korean producer made 7805 with some 7V output under no load. When loaded everything was fine, 5V. The cure was to use load resistor at the output of the regulator to assure load current at least 5mA (i.e. 1kOhm resistor for 5V regulator).
And - do you have center point (0V) defined?. |
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| carlosfm |
| Pavel, he has less voltage under no load than connected to the circuit.:confused: :eek: |
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| pete.a |
Iv'e scrapped the whole build ! I couldnt find out what was going on in that little circuit. :bawling: :bawling: :bawling:
I may try building the heaphone amp just using one op amp as per Carlos design, as i feel thats where i went wrong using zero links for different connections ! between op amps and buffer chips.
As i only had limited time to construct this project i may have overlooked a connection ..who knows..it happens.
But thanks for the help guys.
Carlos..regs gave out 14.98v under load and 18v off load until the circuit went ...Pop !
Pavel do have any pcb graphics for the head amp, as i have a friend how will make a pcb, but isn't that good at pcb design. Has the equipment but not the electronic discpline. |
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| PMA |
Pete,
probably I would release a PCB artwork for audio buffer, that can be used as a headphone amp (see my web). Send me an e-mail, if you are interested in it.
Rgds,
Pavel |
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| PMA |
Pete,
what was the buffer package you have used? DIP8, TO220-5 or another.
Thanks, Pavel |
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| pete.a |
| It was To220 -5 and i only got a couple as samples...now theve ran out |
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| pete.a |
Guys Ive found the fault...or at least i think so.
It would appear that i forgot to break the track underneath the board , on pin 5 of the op amp. Due to the orientation of components and links, it connected pin5 op amp to pin 3 buffer ..ouch..
Take a look at the image, it may explain a little more, this is only prototype board. Finnished will look a whole lot neater and bare legs will be sleeved.
Just a thought , could i use slightly smaller rated regs , ie, 500Ma as apposed to 1A as seen before the smoothing caps.
Anyone got a spare Buf634T out there in diy land, cant get anymore for another 14weeks !!:bawling: :bawling: : |
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| PMA |
| Pin 5 of OPA627 is connected very close to +Vs (in the inner structure), pin 3 of BUF634T is -Vs .... the faults are usually like this. |
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