I have a feeling that the filter caps should be replaced, and so should the rectifier diodes along with CR49 and CR50. Basically rebuild the power supply. Regardless, I'm going to be doing recap.
-3Vdc on that rail sound like a shorted or leaky diode.
You can lift one end of it to check it but DO NOT turn the amp on while it is out of the circuit.
As this will over voltage the opamps and they won't like that at all and will blow them
!!!
jer 🙂
You can lift one end of it to check it but DO NOT turn the amp on while it is out of the circuit.
As this will over voltage the opamps and they won't like that at all and will blow them
!!!
jer 🙂
No need to replace the rectifiers unless they are bad.
Filter Caps, Yes, This is a good idea for an amp with this age.
jer 🙂
Filter Caps, Yes, This is a good idea for an amp with this age.
jer 🙂
CR50 measures.025V when out of circuit on diode test. Its .025 EITHER polarity. So sounds like thats a problem. Should read open in one direction.
CR49 (out of circuit) measures infinite in one direction, and .739V in the other
CR49 (out of circuit) measures infinite in one direction, and .739V in the other
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Yep. it sure looks like it is a bad diode
Shorted!!!
Replacing it would be the simplest and cheapest way to go or you can mod it and put a pair of 3 terminal regulators in it as well.
A LM7815 for +15V and a LM7915 for -15V.
jer 🙂
Shorted!!!
Replacing it would be the simplest and cheapest way to go or you can mod it and put a pair of 3 terminal regulators in it as well.
A LM7815 for +15V and a LM7915 for -15V.
jer 🙂
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What confuses me, is where did the AC come from? AC goes through a rectifier CR45-CR48, and this takes the AC and spits out DC. Then this DC goes into the filter caps C92 and C93, then it goes through someother caps and resistors, and lastly the diodes CR49 and CR50. But the AC was supposedly converted into DC back at CR45-CR49. So why did I measure AC ripple?
And why does my meter go crazy when measuring AC ripple on both the preamp's filter caps AND the amps's 4700mfd 63V caps?
Also, CR49 and CR50 are 40102 diodes (well SZG-40102) 15V, 1W 5% ZENER diodes. Peavey states that a 1N4744 is a sub. So I'll just buy some of these when I purchase some caps..
1N4744A_T50R Fairchild Semiconductor | Mouser
I'll also stock up on some OP amps for this and for my other devices with 4558 OP amps, as it seems from what I hear, the TL082CP is superior than the 4558, and there is no issues (except in rare circumstances) replacing 4558s with TL082CPs.
EDIT: The diodes have 1N4744 printed on them, so I wouldn't be subbing. It appears that SZG-40102 is a Peavey house part number
And why does my meter go crazy when measuring AC ripple on both the preamp's filter caps AND the amps's 4700mfd 63V caps?
Also, CR49 and CR50 are 40102 diodes (well SZG-40102) 15V, 1W 5% ZENER diodes. Peavey states that a 1N4744 is a sub. So I'll just buy some of these when I purchase some caps..
1N4744A_T50R Fairchild Semiconductor | Mouser
I'll also stock up on some OP amps for this and for my other devices with 4558 OP amps, as it seems from what I hear, the TL082CP is superior than the 4558, and there is no issues (except in rare circumstances) replacing 4558s with TL082CPs.
EDIT: The diodes have 1N4744 printed on them, so I wouldn't be subbing. It appears that SZG-40102 is a Peavey house part number
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The A.C. comes from the increased ripple voltage on that line do to the excessive current draw from the short diode.
Basically it was feeding the -15V rail with -3V half sine wave pulses!!
Your meter was going nuts becuase it is an autoranging type and it didn't know what it was looking at.
A couple of times it did stabilize and that was the ripple voltage.
Use you should use no less than 1 watt types as specified more is good.
But a 1/2 watt zener would just blow out and short due to due to being over the rated current that flows through it while it is clamping at 15v.
jer 🙂
Basically it was feeding the -15V rail with -3V half sine wave pulses!!
Your meter was going nuts becuase it is an autoranging type and it didn't know what it was looking at.
A couple of times it did stabilize and that was the ripple voltage.
Use you should use no less than 1 watt types as specified more is good.
But a 1/2 watt zener would just blow out and short due to due to being over the rated current that flows through it while it is clamping at 15v.
jer 🙂
I love the TL082/72 series and still use them today!!
There are better ones these days but all they do is cost more.
Some say that they can hear the difference and that is okay.
They sound fine to me.
They were the state of the art that every one had to beat back then.
I have been using them since they first came out in like 1979 or so.
I used to make some very very high gain fuzz boxes with them and they were dead quite when the guitar was turned off.
Now you can get them for about 30 cents a piece and radio shack still has them if I ever need one in a pinch!
jer 🙂
There are better ones these days but all they do is cost more.
Some say that they can hear the difference and that is okay.
They sound fine to me.
They were the state of the art that every one had to beat back then.
I have been using them since they first came out in like 1979 or so.
I used to make some very very high gain fuzz boxes with them and they were dead quite when the guitar was turned off.
Now you can get them for about 30 cents a piece and radio shack still has them if I ever need one in a pinch!
jer 🙂
When I turn my amp up to play it,it sound like I am at the beach the hiss is so bad!!!
I can imagine how quiet that thing must must be with some TL072/82 in it!!!
jer 🙂
I can imagine how quiet that thing must must be with some TL072/82 in it!!!
jer 🙂
It seems the TL072 is actually better than the TL082
So I will replace them all with this
TL072CPE4 Texas Instruments | Mouser
So I will replace them all with this
TL072CPE4 Texas Instruments | Mouser
Yes, I like them better.
They have the lowest noise voltage of the series.
They claim that the TL082's were for audio but the differences were just that they where acceptable for audio and the TL072 had even less noise.
The differences are very small and is more about the lower frequency's.
I think the TL072's sound better with less change of the character to the sound.
jer 🙂
They have the lowest noise voltage of the series.
They claim that the TL082's were for audio but the differences were just that they where acceptable for audio and the TL072 had even less noise.
The differences are very small and is more about the lower frequency's.
I think the TL072's sound better with less change of the character to the sound.
jer 🙂
When I do get in to it, I am going to try the NE5532's as well they have an even lower noise level.
jer 🙂
http://www.mouser.com/ds/2/405/slos075i-121972.pdf
jer 🙂
http://www.mouser.com/ds/2/405/slos075i-121972.pdf
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I think someone already mentioned earlier that NE5532's will draw considerably more current and recommended against it.
Incidentally, congrats for nailing down a shorted diode!
Incidentally, congrats for nailing down a shorted diode!
Yes, Very good point.
The data sheet indicates nearly 4 times as much at 8ma vs 2.5ma per chip.
I would consider doing the regulator mod or use a much higher wattage zener diode when using the NE5532's.
I got to thinking about that when I realized that it is using only a 1 watt zener per rail to power 8 dual opamps!!
jer 🙂
The data sheet indicates nearly 4 times as much at 8ma vs 2.5ma per chip.
I would consider doing the regulator mod or use a much higher wattage zener diode when using the NE5532's.
I got to thinking about that when I realized that it is using only a 1 watt zener per rail to power 8 dual opamps!!
jer 🙂
I mentioned the 5532 increased current draw. It all depends on what you want to do. A couple of them added into a circuit won;t hurt anything, the power supplies are not that marginal as to be affected. But if you had a mixer with 50 of them in there, it would be a different story. In this amp, U6 and U1 are the input stages, so changing them to lower noise should have the most effect. Later stages have higher signal levels and so should be a lot higher above the noise floor.
Think again about the zener. The zener regulates the voltage, NONE of the load current flows through the zener. The zener is parallel to the load, not in series with it. You want the current through the zener - and thus its wattage - to be enough that variations in the load won;t make the dropping resistor make the load voltage drop below the zener voltage. Well, these loads don't vary much anyway.
I don't even keep TL082 in my drawer, The TL072 is a better choice in about any situation, so why have both? Perhaps someone had access to 082s at some point, otherwise they are an odd choice. Maybe it was what the local Radio Shack had in stock. The 4558 may not be the lowest noise of op amps, but it works fine in this circuit. More modern types like 4560 and 4580 probably work even better. But it is really not critical at all, I'd stick an LF353 in there if I had to. I keep 2068s in my drawer, and wouldn't hesitate to use them here. And i am sure the hifi guys have some OPA numbers they like.
Think again about the zener. The zener regulates the voltage, NONE of the load current flows through the zener. The zener is parallel to the load, not in series with it. You want the current through the zener - and thus its wattage - to be enough that variations in the load won;t make the dropping resistor make the load voltage drop below the zener voltage. Well, these loads don't vary much anyway.
I don't even keep TL082 in my drawer, The TL072 is a better choice in about any situation, so why have both? Perhaps someone had access to 082s at some point, otherwise they are an odd choice. Maybe it was what the local Radio Shack had in stock. The 4558 may not be the lowest noise of op amps, but it works fine in this circuit. More modern types like 4560 and 4580 probably work even better. But it is really not critical at all, I'd stick an LF353 in there if I had to. I keep 2068s in my drawer, and wouldn't hesitate to use them here. And i am sure the hifi guys have some OPA numbers they like.
That's correct that Radio Shack carried the TL082. (I have no idea if they still carry it.)
I believe I've read before that the TL082 chips come off the TL072 manufacturing line, but they may label some chips as TL082 because one chip from a TL072 batch didn't test up to the noise standard of the TL072 spec. I don't believe anyone actually intentionally manufactures a TL082, my understanding is that they are 072 chips that can't be guaranteed for 072 performance, but that people who have tested the noise floor of random 082 chips against 072 chips often find no actual difference, and it is quite common for the 082 to perform exactly the same as the 072 spec.
That being said, if you're buying chips for amp use, you might as well just buy the TL072, the cost can only be a few cents more.
I believe I've read before that the TL082 chips come off the TL072 manufacturing line, but they may label some chips as TL082 because one chip from a TL072 batch didn't test up to the noise standard of the TL072 spec. I don't believe anyone actually intentionally manufactures a TL082, my understanding is that they are 072 chips that can't be guaranteed for 072 performance, but that people who have tested the noise floor of random 082 chips against 072 chips often find no actual difference, and it is quite common for the 082 to perform exactly the same as the 072 spec.
That being said, if you're buying chips for amp use, you might as well just buy the TL072, the cost can only be a few cents more.
The difference I heard was in a very high gain fuzz circuit I made swapping out a TL074 with a TL084, But I could never tell the difference in a regular clean line level signal.
I even used them to invert video signals just to see if it would work and it did.
Great little chip!!!
Yes RS still has them for about $2.49.
TL082/TL082CP Wide Dual JFET Input Op Amp (8-Pin DIP) - RadioShack.com
jer 🙂
I even used them to invert video signals just to see if it would work and it did.
Great little chip!!!
Yes RS still has them for about $2.49.
TL082/TL082CP Wide Dual JFET Input Op Amp (8-Pin DIP) - RadioShack.com
jer 🙂
TL072s look to be about 60 cents at Mouser. About 25 cents at Jameco. 47 cents at Digikey.
Mouser also sells the NJM2068 for 40 cents. And NE5532 for 90 cents.
Jameco sells 5532 for 49 cents,
Mouser also sells the NJM2068 for 40 cents. And NE5532 for 90 cents.
Jameco sells 5532 for 49 cents,
Well I ordered all the parts, and new electrolytic caps on Sunday. They will be here this coming Monday.
Pictures and details to come when I start on it.
Pictures and details to come when I start on it.
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