Volume and balance controls
Previously in this thread I asked about volume controls, which got me thinking about balance controls. After poking around the internet regarding balance controls, I've learned they can be complicated and degrade the signal. A dual volume control is one work around, however another idea which I did not find in my internet searches was dual volume controls + master volume. I'm guessing if the volume devices, be they pots or stepped attenuators were connected in series to accomplish this, there would be additive degradation of the signal. However, if they connected in parallel, wouldn't that diminish the degradation down to close to the amount produced by a single volume control? Am I missing something very important here?
Please let me know if this belongs in another area, perhaps it's own thread.
Cheers, Jim
Previously in this thread I asked about volume controls, which got me thinking about balance controls. After poking around the internet regarding balance controls, I've learned they can be complicated and degrade the signal. A dual volume control is one work around, however another idea which I did not find in my internet searches was dual volume controls + master volume. I'm guessing if the volume devices, be they pots or stepped attenuators were connected in series to accomplish this, there would be additive degradation of the signal. However, if they connected in parallel, wouldn't that diminish the degradation down to close to the amount produced by a single volume control? Am I missing something very important here?
Please let me know if this belongs in another area, perhaps it's own thread.
Cheers, Jim
Puzzles
Wayne,
I can't let a puzzle go either
. I will see if I can find some time over the weekend to resolder the LEDs and diodes. If there is a problem, is it likely to be the 7815 side that takes over 2 minutes for the LED to go out, or the 7915 side that takes 17 seconds to go out ?
Wayne,
I can't let a puzzle go either
. I will see if I can find some time over the weekend to resolder the LEDs and diodes. If there is a problem, is it likely to be the 7815 side that takes over 2 minutes for the LED to go out, or the 7915 side that takes 17 seconds to go out ?
Wayne,
I can't let a puzzle go either
17 seconds seems about what I see.
Puzzles
jwjarch,
The amp sounds fine, but like Wayne I can't let an unsolved puzzle go. I will certainly post if I find any questionable components. Wayne reckons he sees about 17 seconds till the LED is out, so it looks like the 7815 side of my amp is 'wrong'. I would be grateful if you could take your amp out of its case and time the LEDs and let me know how long your LEDs take to go out. It would help me to confirm whether one or both halves of my amp are 'wrong', which would avoid de-soldering stuff I don't need to.
jwjarch,
The amp sounds fine, but like Wayne I can't let an unsolved puzzle go. I will certainly post if I find any questionable components. Wayne reckons he sees about 17 seconds till the LED is out, so it looks like the 7815 side of my amp is 'wrong'. I would be grateful if you could take your amp out of its case and time the LEDs and let me know how long your LEDs take to go out. It would help me to confirm whether one or both halves of my amp are 'wrong', which would avoid de-soldering stuff I don't need to.
Puzzle
6L6,
I lifted the end of the diode in front of the 7815 and it measures the same as one of other 5 unused identical ones I bought. I soldered it back in and the time to LED out is still way more than the other LED. I therefore conclude it’s not the diode.
I replaced the LED and the time to LED out is still way more than the other LED. I therefore conclude it’s not the LED.
I originally fitted an MC7815CTG per the BOM. I don’t remember any noticeable difference between the LEDs extinguishing. I shorted this accidentally and replaced it with a MC7815CTG from a small UK supplier because RS only sell them in a pack of 50. Either I damaged it, or this supplier could be selling Chinese copies, so I don’t want to go back there.
RS sells the MC7815ABTG in a pack of 5 at a sensible price. It has an identical spec to the MC7815CTG, except that the line and load regulation are better (see attached comparison table). Is this going to cause a problem ?
Alternatively, does anyone in the UK have a surplus MC7815CTG from a reputable supplier they would be willing to sell me ?
Do you have one of the protection diodes in backwards? Or maybe not a good solder connection?
At this point I'm back to thinking it's a problem in the reg circuit.
6L6,
I lifted the end of the diode in front of the 7815 and it measures the same as one of other 5 unused identical ones I bought. I soldered it back in and the time to LED out is still way more than the other LED. I therefore conclude it’s not the diode.
I replaced the LED and the time to LED out is still way more than the other LED. I therefore conclude it’s not the LED.
I originally fitted an MC7815CTG per the BOM. I don’t remember any noticeable difference between the LEDs extinguishing. I shorted this accidentally and replaced it with a MC7815CTG from a small UK supplier because RS only sell them in a pack of 50. Either I damaged it, or this supplier could be selling Chinese copies, so I don’t want to go back there.
RS sells the MC7815ABTG in a pack of 5 at a sensible price. It has an identical spec to the MC7815CTG, except that the line and load regulation are better (see attached comparison table). Is this going to cause a problem ?
Alternatively, does anyone in the UK have a surplus MC7815CTG from a reputable supplier they would be willing to sell me ?
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I might have a spare l7815cp i Can send you if that has any interest. It is from ST micro, but specs look very similar.
https://www.mouser.dk/datasheet/2/389/l78-974043.pdf
It will take a bit of time to reach you from Denmark, so a UK source may still be more attractive, but let me know.
https://www.mouser.dk/datasheet/2/389/l78-974043.pdf
It will take a bit of time to reach you from Denmark, so a UK source may still be more attractive, but let me know.
Wayne,
I can't let a puzzle go either
I notice that the 7915 side also comes on faster and stronger than the 7815 at start-up.
Listened to several other opamps in the Whammy besides opa627: AD8620, opa2107, opa227. All but the 8620 sounded terrific in slightly different ways. Am ordering the opa1611 and 1612.Any reason the BOM indicated the single rather than the dual opamp?
Silasmellor,
That's very kind of you, but I am hoping Wayne/6L6 will OK the MC7815ABTG as a replacement for the MC7815CTG in the BOM, because I can get 5 of those for about £2.50 from RS in the UK which is a lot easier than putting you to the trouble of posting one from Denmark ! However the MC7815ABTG seems to have better spec than the MC7815CTG, so I don't want to create an 'imbalance', and then have to go looking for a 7915 to match !
7815s
I thought all 7815s were equal till I looked at the specs. Some have 10x better load and line regulation than others. Some are +/- 4%, some are better at +/- 2%. Whether you can hear the difference of course is another thing. However, I would have thought it makes sense to use a 7915 and a 7815 with similar specs.
The MC7815CTG I have may be a fake, and may be why it takes more two minutes for the LED to go out, or it may be something else. That's why the next one will come from a major (UK) supplier.
I thought all 7815s were equal till I looked at the specs. Some have 10x better load and line regulation than others. Some are +/- 4%, some are better at +/- 2%. Whether you can hear the difference of course is another thing. However, I would have thought it makes sense to use a 7915 and a 7815 with similar specs.
The MC7815CTG I have may be a fake, and may be why it takes more two minutes for the LED to go out, or it may be something else. That's why the next one will come from a major (UK) supplier.
