well i hope post #171 isn't like what my kids used to do when they made a mess or broke something; they would point off in the distance and say "hey what's that over there!" hoping to divert your attention.
i'm sure he's taking a 'round about way to teach us both something valuable that i can't seem to grasp.
i'm sure he's taking a 'round about way to teach us both something valuable that i can't seem to grasp.
I was hoping JMFahey would answer post 171. He knows a lot more than either turk or I. Or andrew T, or Mooly, or some other senior circuit expert.
The tone controls if the wiper oxidizes IMHO have the possiblity of throwing U1b and U2b into ultrasonic oscillation which could suck too much current from +-15 and also blow your tweeters. Wiggling the potentiometer to get the wipers to connect, is a nice temporary solution. Open op amp inputs can throw the output of an op amp to either rail, or oscillation. The .01 cap to ground parallel to the wiper inputs on the op amps I suggested Chiauna buy could solve the oscillation, but also affect the sound, so that may not be a good solution.
Is the +14 -11 v you measured on the power board only or is the op amp board connected? If power board only where is the current going? Where exactly is the +14 -11? On the output pins of the board? on the output pins of the 7815 7915? On the outside terminals of the post regulator filter caps?
When you were at the store did you get the 47 uf cap for the op amp board?
On post 171 There are ways to detect ultrasonic oscillation. I use a Simpson 260 VOM on 2.5 VAC scale with a 390 pf cap in series with one lead. Farnell still sells Simpson 270's. You can use an oscillloscope. I have a small collection of broken ones, the used ones are full of expired e-caps so I don't recommend buying one of them used. I use the VOM on 20 VAC scale or 2.5 VAC scale to trace music through amps using a .047 cap in series with the probe. Rock music, the meter is fast enough you can see the beats. Oscillations, you get a steady AC voltage. The smaller cap can prove the AC voltage is ultrasonic: music won't go through a 390 pf cap.
However if the current is being hogged on the power board alone, careful inspection, parts replacement, or board replacement are the only solutions. There are non-contact current probes, using the hall effect, but I don't see any for sale these days. You can build one out of a hall effect sensor, but they are all surface mount package anymore.
The tone controls if the wiper oxidizes IMHO have the possiblity of throwing U1b and U2b into ultrasonic oscillation which could suck too much current from +-15 and also blow your tweeters. Wiggling the potentiometer to get the wipers to connect, is a nice temporary solution. Open op amp inputs can throw the output of an op amp to either rail, or oscillation. The .01 cap to ground parallel to the wiper inputs on the op amps I suggested Chiauna buy could solve the oscillation, but also affect the sound, so that may not be a good solution.
Is the +14 -11 v you measured on the power board only or is the op amp board connected? If power board only where is the current going? Where exactly is the +14 -11? On the output pins of the board? on the output pins of the 7815 7915? On the outside terminals of the post regulator filter caps?
When you were at the store did you get the 47 uf cap for the op amp board?
On post 171 There are ways to detect ultrasonic oscillation. I use a Simpson 260 VOM on 2.5 VAC scale with a 390 pf cap in series with one lead. Farnell still sells Simpson 270's. You can use an oscillloscope. I have a small collection of broken ones, the used ones are full of expired e-caps so I don't recommend buying one of them used. I use the VOM on 20 VAC scale or 2.5 VAC scale to trace music through amps using a .047 cap in series with the probe. Rock music, the meter is fast enough you can see the beats. Oscillations, you get a steady AC voltage. The smaller cap can prove the AC voltage is ultrasonic: music won't go through a 390 pf cap.
However if the current is being hogged on the power board alone, careful inspection, parts replacement, or board replacement are the only solutions. There are non-contact current probes, using the hall effect, but I don't see any for sale these days. You can build one out of a hall effect sensor, but they are all surface mount package anymore.
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the voltage is lower than one would expect because it is running on the limiter.
your premise of ultra sonic oscillation is a distinct possibility but i still think it was a situation involving "feedback" from an open mic. i see this kind of thing in the many types of powered speakers i've repaired (Mackie JBL QSC)
i really need to understand how you arrive at a value of 1k for the protection resistors?
the fact that Chiunana measured the same resistors on the good board he has as being 1.2 ohms?
i have the utmost respect for your body of knowledge on these matters which is why i'm a little dismayed by the fact you seem to be withholding something.
and for the purpose of insuring that i'm not misguiding chiunana i'd rather be schooled on the matter.
ultra sonic oscillations (any increase in current draw in the load would make the limiter lamp brighten! been there,done that,got the T-shirt)
your premise of ultra sonic oscillation is a distinct possibility but i still think it was a situation involving "feedback" from an open mic. i see this kind of thing in the many types of powered speakers i've repaired (Mackie JBL QSC)
i really need to understand how you arrive at a value of 1k for the protection resistors?
the fact that Chiunana measured the same resistors on the good board he has as being 1.2 ohms?
i have the utmost respect for your body of knowledge on these matters which is why i'm a little dismayed by the fact you seem to be withholding something.
and for the purpose of insuring that i'm not misguiding chiunana i'd rather be schooled on the matter.
ultra sonic oscillations (any increase in current draw in the load would make the limiter lamp brighten! been there,done that,got the T-shirt)
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The print chiauna gave me has 1 kohm for the series resistors. As much as I can read it. The blob has a definite tail on it.
That is why I suggested a long time ago 47 ohm protection resistors. I think 1 kohm is a little overkill, but what do I know? On my DIY +-8 v supply is used 5 w zener diodes for regulators, which required 22 ohm resistors between them and the transformer to not overheat the zeners. The RA88a only had 5 op amps, this Kempton has over a dozen. The question is, if the e-caps are not leaky, what blew the protection resistors? Op amps don't short often, only when the pins are shorted across. They do oscillate, see the thread "you checked your replacement op amps were stable, didn't you?
If the protection light bulb was limiting the +-15 supply, it would show up in the 16 vac before the bridge rectifier. I had to abandon light bulb limiting testing my PV-1.3k amp and use a room heater with a bad tip over switch for limiting, to get the +-15 supplies up to value, but keep the output transistors from blowing their dies through the steel case.
That is why I suggested a long time ago 47 ohm protection resistors. I think 1 kohm is a little overkill, but what do I know? On my DIY +-8 v supply is used 5 w zener diodes for regulators, which required 22 ohm resistors between them and the transformer to not overheat the zeners. The RA88a only had 5 op amps, this Kempton has over a dozen. The question is, if the e-caps are not leaky, what blew the protection resistors? Op amps don't short often, only when the pins are shorted across. They do oscillate, see the thread "you checked your replacement op amps were stable, didn't you?
If the protection light bulb was limiting the +-15 supply, it would show up in the 16 vac before the bridge rectifier. I had to abandon light bulb limiting testing my PV-1.3k amp and use a room heater with a bad tip over switch for limiting, to get the +-15 supplies up to value, but keep the output transistors from blowing their dies through the steel case.
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Well, i'm kinda waiting to know what to do, you know.. I've been thinkin about what you are discussing, but i can't really understand. And you surely know that, being something new for you as well.. So..
Only thing i can say is that these resistors were 1 ohm, the scheme i got is not only in bad risolution, but also not really accurate. For instance: there are just 2 e caps before the regulators and not 4 as showed in the scheme.
Only thing i can say is that these resistors were 1 ohm, the scheme i got is not only in bad risolution, but also not really accurate. For instance: there are just 2 e caps before the regulators and not 4 as showed in the scheme.
is it the same on both boards (as in both are missing the same components or one board has more cap's?)
it's not uncommon for changes to be made as to what gets loaded onto a pc board at the factory. some manufactures delete components to save costs or accommodate design changes.
it's not uncommon for changes to be made as to what gets loaded onto a pc board at the factory. some manufactures delete components to save costs or accommodate design changes.
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No, it's the same for both boards. On the scheme you just have a couple more capacitors (c31-c33 i think), the ones placed just before the regulators.
Strange, but true! Maybe there are even other flaws on the scheme, i've found just this until now..
Strange, but true! Maybe there are even other flaws on the scheme, i've found just this until now..
I see.. I suppose it wouldn't happen if i would had some Jbl's or superior quality stuff than these.. I dunno.
sounds like your giving up! despite quality they're what you have let's see if we can't get them to work for you!
Never ever taught of givin up! I am just... Stuck.
I was saying that with some better speakers MAYBE i would had a clearer and without flaws scheme.. Actually i'm not sure about it, but that was my statement.
Givin up? No way man, that's not me. I rather take a flight to Canada or Us and find you both.. 😀
I was saying that with some better speakers MAYBE i would had a clearer and without flaws scheme.. Actually i'm not sure about it, but that was my statement.
Givin up? No way man, that's not me. I rather take a flight to Canada or Us and find you both.. 😀
i'd love to meet you but save the airfare for "replacement parts" and "tequila".
at this point i'd try and see if adding the preamp board effects the supply in a bad way and if it doesn't i'd check to see if signal is making it through.
at this point i'd try and see if adding the preamp board effects the supply in a bad way and if it doesn't i'd check to see if signal is making it through.
You stopped me at the last minute, there is a flight tomorrow morning at 6 am.. Too bad Canada is quite big, but i do have relatives in Toronto. Shouldn't be too difficult to find you! 😀
Kidding apart, should i try with these 1k protection resistors?
Remember i got +14 and -11 on the rails.. Isn't it dangerous somehow for the op amps of the pre?
Kidding apart, should i try with these 1k protection resistors?
Remember i got +14 and -11 on the rails.. Isn't it dangerous somehow for the op amps of the pre?
i'm 8 hours drive from toronto and there's a foot and a half snow on the ground...
if the 1k's are on the board check the voltage before and after the regulator.
if the 1k's are on the board check the voltage before and after the regulator.
So, with the two 1k resistors, we have:
7815
Input +14.90
Output + 13.95
7915
Input -11.6
Output -11.0
The black probe of the DMM on the ground leg of each regulator.
7815
Input +14.90
Output + 13.95
7915
Input -11.6
Output -11.0
The black probe of the DMM on the ground leg of each regulator.
ok this is still with the preamp disconnected right.
i'd plug in the preamp board and see if the voltage drops (if it drops hard you have a short on the pre board. if not will it pass signal? keep things low volume for now if you get here)
i'd plug in the preamp board and see if the voltage drops (if it drops hard you have a short on the pre board. if not will it pass signal? keep things low volume for now if you get here)
Ok. We have, with the pre plugged (i tried with both of them, one of them has signal problems as you remember):
7815
In +3.49
Out + 2.18
7915
In -2.70
Out -0.73
7815
In +3.49
Out + 2.18
7915
In -2.70
Out -0.73
Sorry about the misunderstanding, If the print says 1 ohm protection resistors and the boards had 1 ohm protection resistors, put in 1 ohm protection resistors.
I thought the print said 1 K but it is fuzzy.
Dropping a volt or 0.6 volt across the 1 k resistors indicates there is not much problem now on the power board.
If you still cant get +-15, put a 100 w bulb in the light bulb limiter instead of the 60W. I couldn't get +-15 to work right in my PA amp on a light bulb either, but 100 W bulbs were banned from sale here at the time so I had to do something else.
I thought the print said 1 K but it is fuzzy.
Dropping a volt or 0.6 volt across the 1 k resistors indicates there is not much problem now on the power board.
If you still cant get +-15, put a 100 w bulb in the light bulb limiter instead of the 60W. I couldn't get +-15 to work right in my PA amp on a light bulb either, but 100 W bulbs were banned from sale here at the time so I had to do something else.
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