Shot down in flames
Chris, after the op amp there must be some small mid sized transistors prior to current amplification? I've seen Tip 31/32s substituted here and it totally messed up the gain of the amp. I've seen it more than once! Especially where high voltage pre drivers are used that are supplied ~50 volts or more but rated at 650mW, stick a tip 31 in there and you got big time hfe/gain problems man?
I didn't say go out and purchase ECG transistors but the book, IMHO, is a great reference. But now that you criticize it, I wonder if it is just a printed piece of propaganda to sell their own devices? With that said. What do you suggest as an off the shelf transistor cross companion?
Thank you for you knowledge!
anatech said:
Chris, after the op amp there must be some small mid sized transistors prior to current amplification? I've seen Tip 31/32s substituted here and it totally messed up the gain of the amp. I've seen it more than once! Especially where high voltage pre drivers are used that are supplied ~50 volts or more but rated at 650mW, stick a tip 31 in there and you got big time hfe/gain problems man?
I didn't say go out and purchase ECG transistors but the book, IMHO, is a great reference. But now that you criticize it, I wonder if it is just a printed piece of propaganda to sell their own devices? With that said. What do you suggest as an off the shelf transistor cross companion?
Thank you for you knowledge!
Sorry guys, i was talking 8mv difference
this test is run with a frequency generator
1st reading 400hz
left channel led indicator off and voltmeter reading 6.86vac
right channel led indicator reading 12db and voltmeter reading 6.98vac
2nd reading 300hz
the left channel led indicator is at 9db and shows 12.23vac
the right channel led indicator is at 6db and shows 12.43vac
this test is run with a frequency generator
1st reading 400hz
left channel led indicator off and voltmeter reading 6.86vac
right channel led indicator reading 12db and voltmeter reading 6.98vac
2nd reading 300hz
the left channel led indicator is at 9db and shows 12.23vac
the right channel led indicator is at 6db and shows 12.43vac
The gain is fine.With 6.86 Vrms vs. 6.98 Vrms (@ 400Hz), you'r talking 0.15dB imbalance. These power LED's are using a window comparator with at least a 3 dB granularity. For one channel you might be at the top of an LED segments window, while the other channel might be at the low side of the next window up. You might want to check the meter calibration itself. The voltage measurements indicate that the amp channel to channel gain is fine.
....don't even think of adjusting the bias to adjust gain.
....don't even think of adjusting the bias to adjust gain.
Hi Shawn,
The transistor beta doesn't make much difference in a Carver unless it's way out of spec. Then you have other problems as well. For people who just throw other devices into amps - well. They should not be servicing unless they know what they are doing. The opposite argument is that consumers refuse to pay for proper technicians.
There are small transistors between the op amp and the outputs. They are many in number. They only do what they are told to do as the open loop gain is extremely high with an op amp acting as the error amp. Individual hFE variations don't matter (within reason) for the circuit gain to be considered.
My problem with the ECG / NTE book is that they quote specs for an unknown part number that they say will replace the number you have looked up. The only truth is to look up the actual device spec. I know of many repair shops that take this a step further. They cross in what they need. They then cross other parts in to see what comes up as the part that crosses to the same number. I call it crossing in and crossing out. Stupid. Those manuals should be burned as they have guided more poor service to be done than is realized. The cost is always passed on the the set owner.
-Chris
The transistor beta doesn't make much difference in a Carver unless it's way out of spec. Then you have other problems as well. For people who just throw other devices into amps - well. They should not be servicing unless they know what they are doing. The opposite argument is that consumers refuse to pay for proper technicians.
There are small transistors between the op amp and the outputs. They are many in number. They only do what they are told to do as the open loop gain is extremely high with an op amp acting as the error amp. Individual hFE variations don't matter (within reason) for the circuit gain to be considered.
My problem with the ECG / NTE book is that they quote specs for an unknown part number that they say will replace the number you have looked up. The only truth is to look up the actual device spec. I know of many repair shops that take this a step further. They cross in what they need. They then cross other parts in to see what comes up as the part that crosses to the same number. I call it crossing in and crossing out. Stupid. Those manuals should be burned as they have guided more poor service to be done than is realized. The cost is always passed on the the set owner.
-Chris
Hi, Thanks But i still find it weird, unless i am getting too old at low volumes you can hear the right channel playing louder, and yes i have switched over the boxes just to be sure , for the vu meter is there a way i could calibrate it then ? i just the schematics for it, and apparently it's all drivent by the output of the amps...
like written in the manual
d10 will light up at 7vrms
d9 will light up at 10vrms
d8 will light up at 13vrms
d7 will light up at 21vrms
d6 will light up at 28vrms
The Seventh Led is amber and indicates distortion in excess of 1%, and it will "accurately" indicate clipping at any frequency regardless of load impedance or line voltage,
so if my problem are at the transistors that drives the input board it should be easy to check and replace, the display board on my pm-1200 works fine, so i will try to use that one on my pm 1.5 and see if i have the same results,
Thanks
worse comes to worse i'll disable the leds....
, for the vu meter is there a way i could calibrate it then ? i just the schematics for it, and apparently it's all drivent by the output of the amps...like written in the manual
d10 will light up at 7vrms
d9 will light up at 10vrms
d8 will light up at 13vrms
d7 will light up at 21vrms
d6 will light up at 28vrms
The Seventh Led is amber and indicates distortion in excess of 1%, and it will "accurately" indicate clipping at any frequency regardless of load impedance or line voltage,
so if my problem are at the transistors that drives the input board it should be easy to check and replace, the display board on my pm-1200 works fine, so i will try to use that one on my pm 1.5 and see if i have the same results,
Thanks
worse comes to worse i'll disable the leds....
Hi pjaneiro,
I'd start with meter calibration. It sounds like the metering is inaccurate. Are there no pots to adjust the input level of the meter circuit?
Other things to check.
Your attenuator volume tracking ability.
Volume controls have a logarithmic taper. They are very hard to manufacture with excellent channel to channel tracking. Many people have turned to stepped attenuators with fixed resistors to cure this problem.
The source material.
The source material may be imbalanced, although I don't think all of the source material could be biased to the same channel all of the time.
Room effects.
One speaker's position in the room may give it greater acoustic gain.
You can take one preamp channel, "Y" it into the Carver, Listen, then just swap the speaker connections and see if the greater volume exits the same speaker, or the other speaker. If it stays with the same speaker, it's the room effect. If it moves to the other speaker, it's the amp gain. ....although I'm not expecting it to be amp gain judging from your measurements.
I'd start with meter calibration. It sounds like the metering is inaccurate. Are there no pots to adjust the input level of the meter circuit?
Other things to check.
Your attenuator volume tracking ability.
Volume controls have a logarithmic taper. They are very hard to manufacture with excellent channel to channel tracking. Many people have turned to stepped attenuators with fixed resistors to cure this problem.
The source material.
The source material may be imbalanced, although I don't think all of the source material could be biased to the same channel all of the time.
Room effects.
One speaker's position in the room may give it greater acoustic gain.
You can take one preamp channel, "Y" it into the Carver, Listen, then just swap the speaker connections and see if the greater volume exits the same speaker, or the other speaker. If it stays with the same speaker, it's the room effect. If it moves to the other speaker, it's the amp gain. ....although I'm not expecting it to be amp gain judging from your measurements.
Hi mrshow4u,
The manual refers to the references for the meter switch points as "approximate values". There are no adjustments.
There are two level controls on the Carver. They should be set at maximum, or some other measured value. Volume controls will typically mistrack greater that this. Don't worry as this is the way things are. Not too much you can do about it. Not that is reasonable anyway.
In short. Nothing is perfect although there are some steps you can take to make them better. At this point we are talking about things outside of the amplifier.
-Chris
The manual refers to the references for the meter switch points as "approximate values". There are no adjustments.
There are two level controls on the Carver. They should be set at maximum, or some other measured value. Volume controls will typically mistrack greater that this. Don't worry as this is the way things are. Not too much you can do about it. Not that is reasonable anyway.
In short. Nothing is perfect although there are some steps you can take to make them better. At this point we are talking about things outside of the amplifier.
-Chris
Hi, Thanks But i still find it weird, unless i am getting too old at low volumes you can hear the right channel playing louder, and yes i have switched over the boxes just to be sure , for the vu meter is there a way i could calibrate it then ? i just the schematics for it, and apparently it's all drivent by the output of the amps...
like written in the manual
d10 will light up at 7vrms
d9 will light up at 10vrms
d8 will light up at 13vrms
d7 will light up at 21vrms
d6 will light up at 28vrms
The Seventh Led is amber and indicates distortion in excess of 1%, and it will "accurately" indicate clipping at any frequency regardless of load impedance or line voltage,
so if my problem are at the transistors that drives the input board it should be easy to check and replace, the display board on my pm-1200 works fine, so i will try to use that one on my pm 1.5 and see if i have the same results,
Thanks
like written in the manual
d10 will light up at 7vrms
d9 will light up at 10vrms
d8 will light up at 13vrms
d7 will light up at 21vrms
d6 will light up at 28vrms
The Seventh Led is amber and indicates distortion in excess of 1%, and it will "accurately" indicate clipping at any frequency regardless of load impedance or line voltage,
so if my problem are at the transistors that drives the input board it should be easy to check and replace, the display board on my pm-1200 works fine, so i will try to use that one on my pm 1.5 and see if i have the same results,
Thanks
Hi pjaneiro,
Let's not get confused.
Please understand that you measured the gain balance and it's well within spec. You could never hear this level shift. Ever.
Most volume controls track at their worst at low levels. It is a normal "feature" of most controls. If there is a -20 dB mute button on your preamp, use it. You are now chasing issues that are outside your amplifier. Put the covers on it and enjoy the music.
-Chris
Let's not get confused.
No, see ....
from my previous post.
No, that will not affect the meter reading or the output level.
Please understand that you measured the gain balance and it's well within spec. You could never hear this level shift. Ever.
Most volume controls track at their worst at low levels. It is a normal "feature" of most controls. If there is a -20 dB mute button on your preamp, use it. You are now chasing issues that are outside your amplifier. Put the covers on it and enjoy the music.
-Chris
Ok, Ok , Ok , I'll live with it, it's just annoying to always see the right channel light up higher and even blink amber once in a while..., i just tried using the display from my pm 1200 and it still does the same thing, but when installed on the pm 1200 it does not, i can understand that just that little extra mv on the right channels might trigger the led earlier...so i'll just learn to accept it...
Thanks everyone for your help in fixing my fan, bias and led issues
once again this site and it's members "SPECIAL MENTION" to >>Anatech<< have proven me that there are competent people out there...
There should be a way to get Bob Carver to send something to Chris for all the help he provides us in here...
, I'll live with it, it's just annoying to always see the right channel light up higher and even blink amber once in a while..., i just tried using the display from my pm 1200 and it still does the same thing, but when installed on the pm 1200 it does not, i can understand that just that little extra mv on the right channels might trigger the led earlier...so i'll just learn to accept it...Thanks everyone for your help in fixing my fan, bias and led issues
once again this site and it's members "SPECIAL MENTION" to >>Anatech<< have proven me that there are competent people out there...
There should be a way to get Bob Carver to send something to Chris for all the help he provides us in here...
Hi pjaneiro,
If the led meters bother you that much, there is something you can do. It is DIY after all.
Take both meter units out. Replace all the scaling resistors with 1% metal film types. The meter tracking should be better. I haven't looked, but there are some resistors on the power supply board as well that feed the meter unit. Replace those with 1% metal film also.
At this point the meters should both respond more accurately and be the same for the two amplifiers. You will notice that the same value will not be available for 1 % resistors. Just choose close values. They will be within the tolerance range of the originals.
Thanks and glad to help.
-Chris
If the led meters bother you that much, there is something you can do. It is DIY after all.
Take both meter units out. Replace all the scaling resistors with 1% metal film types. The meter tracking should be better. I haven't looked, but there are some resistors on the power supply board as well that feed the meter unit. Replace those with 1% metal film also.
At this point the meters should both respond more accurately and be the same for the two amplifiers. You will notice that the same value will not be available for 1 % resistors. Just choose close values. They will be within the tolerance range of the originals.
Thanks and glad to help.
-Chris
I will do that as soon as i get home, But as i stated earlier, the meter on my pm-1200 works fine but when i tested it on my pm 1.5 the right channel still lit up sooner, when i used the meter of my 1.5 on my pm-1200 both channels were acting correctly, so the "problem" lies within my pm 1.5....but i will try changing the resistors on my pm 1.5 display...
Thanks,,,
Thanks,,,
pjaneiro
It is not unusual to have a situation where as both displays do not track 100% with each other. I have taken many amplifiers out of the box and rack mounted them and have sent signal thru them. I have found that over 60% will not jive with each other.
With a given signal input into both channels of an amplifier you will find that they will not produce the same spot on amount of power. They will be close but not identical with each other.
Your "problem" as you put it is normal tolerance that one may experience with any amplifier. It is NOT off enough that you would experience any difference in level. My advice would be to put a piece of duct tape over the display and sit back with a nice glass of wine and relax.
It is not unusual to have a situation where as both displays do not track 100% with each other. I have taken many amplifiers out of the box and rack mounted them and have sent signal thru them. I have found that over 60% will not jive with each other.
With a given signal input into both channels of an amplifier you will find that they will not produce the same spot on amount of power. They will be close but not identical with each other.
Your "problem" as you put it is normal tolerance that one may experience with any amplifier. It is NOT off enough that you would experience any difference in level. My advice would be to put a piece of duct tape over the display and sit back with a nice glass of wine and relax.
Chris,
You know as well as I do the meters and led's are too slow. The amp already has clipped before the peak light comes on. So why bother? The meters and led's are a joke. I have seen/repaired more amps because someone just had to see how hard he could push his/her amp.
My favorite piece of music to destroy an amp has to be the 1812 overture with canon blasts. That has always been a money maker for me.
What is the point in meters and led's anyway? Is the program material going to be the same level for each channel? Well, in mono it is but then again who listens to a mono source anyway?
Dial in a FM station and see what happens. Unless you purchase/make a special cut antenna for the station the multipath isn't going to be correct.
You know as well as I do the meters and led's are too slow. The amp already has clipped before the peak light comes on. So why bother? The meters and led's are a joke. I have seen/repaired more amps because someone just had to see how hard he could push his/her amp.
My favorite piece of music to destroy an amp has to be the 1812 overture with canon blasts. That has always been a money maker for me.
What is the point in meters and led's anyway? Is the program material going to be the same level for each channel? Well, in mono it is but then again who listens to a mono source anyway?
Dial in a FM station and see what happens. Unless you purchase/make a special cut antenna for the station the multipath isn't going to be correct.
Hi Joe,
I'll agree with you that peak light junkies have given me a lot of business. However, I have seen the peak lights come on now and then. I have turned the volume down in those cases. I do believe that power indicators are useful.
Yes, there are no predictive peak lights out there. Add human reaction time + other events in the chain and it may be too late.
"Were the peak lights on?" How many times did you ask that?
-Chris
I'll agree with you that peak light junkies have given me a lot of business. However, I have seen the peak lights come on now and then. I have turned the volume down in those cases. I do believe that power indicators are useful.
Oh yeah!
Yes, there are no predictive peak lights out there. Add human reaction time + other events in the chain and it may be too late.
"Were the peak lights on?" How many times did you ask that?
-Chris
I'll give you that one, Chris.
I was always told there was plenty left because they only had the volume up 1/2 way.
Actually Chris, I repaired a heck of a lot of Ampzilla's and SAE's do to the 1812 piece of music thanks to Mr. Bongiorno's inferior output stages. It kept the Wolf from the door.
Hi Joe,
I can't disagree one bit. Dead sets used to line the walls in the mid 80's and up. The earlier sets not so much. It was dead speakers more than anything.
"Why does the volume control go to ten if you can't turn it up that far?"
Don't even try to reason with them. I've had some success by comparing the volume control to the accelerator in the car.
Hmmmm. Maybe that's why some of them didn't come back.
-Chris
I can't disagree one bit. Dead sets used to line the walls in the mid 80's and up. The earlier sets not so much. It was dead speakers more than anything.
"Why does the volume control go to ten if you can't turn it up that far?"
Don't even try to reason with them. I've had some success by comparing the volume control to the accelerator in the car.
Hmmmm. Maybe that's why some of them didn't come back.
-Chris
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