Hi - I purchased an Eagle 7a new back in 1986. It's been a great amp, but by the late 90s the right channel stopped working. I recently got together with an electronics friend and we took a look at it. Besides several cold soldered joints, we found that the bar attached to Q16 had become unsoldered. We resoldered it and checked the voltages. We got 75V for left and 88V for the right. Searching some more we found that zener diode ZD1 has a crack through it. The schematic online here doesn't say, but we're wondering what is the voltage and wattage of the ZD1 zener diode in the power supply so we can get a replacement. Attached is a pic of the subsection of the schematic we're referring to.
My friend also emailed me the following...
"I still have not figured out exactly how the grounds can swing around without affecting the input ground. There may really be isolation that does not show on the schematic. The output stage is kind of like a complementary bridged configuration. I have not figured out the deep meaning of the common mode circuit in the middle of the schematic.
It is so complicated that I would not be surprised if it needed bias adjustment after 27 years. If you see anything on the web how to check that we should do it."
Thanks in advance for any help on this!
My friend also emailed me the following...
"I still have not figured out exactly how the grounds can swing around without affecting the input ground. There may really be isolation that does not show on the schematic. The output stage is kind of like a complementary bridged configuration. I have not figured out the deep meaning of the common mode circuit in the middle of the schematic.
It is so complicated that I would not be surprised if it needed bias adjustment after 27 years. If you see anything on the web how to check that we should do it."
Thanks in advance for any help on this!
Attachments
Yes, that's the schematic I'm referring to and extracted my image from. That diode is not labeled with the voltage or wattage in that schematic so I'm looking for something else that may have it listed or specified. The diode is located on the little pcb located near the front right of the amp (when viewed from the front). It's shown in your schematic in the section just above all the text in the lower right corner of the image. Not that it makes a difference, but the schematic has Rev B at the bottom right and my amp's pcb's say Rev D. Thanks
When we started the left channel worked and the right channel was dead. We measured the large FV+ 80V filter caps in the center of the amp. The one for the left channel had 75 volts and the right channel cap had a fraction of a volt.
We traced the problem to a cold solder joint on the bus bar on Q16. After soldering that we had clear audio on the right side (good news!).
We measured the large FV+ 80V filter caps in the center of the amp. The one for the left channel had 75 volts and the one for the right channel read 88 volts (kind of high).
While troubleshooting the power supply I was measuring the zener diode and when I pushed on it with the test probe to measure the voltage the voltage dropped. I did not have extra hands for accurate measurements, but I did see the right filter cap drop to a voltage similar to the left side while pushing on the zener. The zener has a crack through the center, so we know that is bad.
Questions:
What should the voltage be on the large FV+ 80V filter caps in the center of the amp? The Rev B schematic says 80 volts, but our left channel power supply has 75 volts on an amp with Rev D printed on the circuit board.
What wattage and voltage is used for ZD1 on the 80 volt regulator card?
Does anyone have a layout diagram that shows the location of the components with reference to the names on the schematic?
Does anyone have an adjustment procedure for things like bias and offset? I see some notes on the bottom right of the schematic, but I need more details.
Has anyone written a “theory of operation”? There appears to be some interesting tricks with floating grounds for power supplies and speaker negative leads and I have not figured out how the common mode section in the middle of the schematics works.
Thanks.
We traced the problem to a cold solder joint on the bus bar on Q16. After soldering that we had clear audio on the right side (good news!).
We measured the large FV+ 80V filter caps in the center of the amp. The one for the left channel had 75 volts and the one for the right channel read 88 volts (kind of high).
While troubleshooting the power supply I was measuring the zener diode and when I pushed on it with the test probe to measure the voltage the voltage dropped. I did not have extra hands for accurate measurements, but I did see the right filter cap drop to a voltage similar to the left side while pushing on the zener. The zener has a crack through the center, so we know that is bad.
Questions:
What should the voltage be on the large FV+ 80V filter caps in the center of the amp? The Rev B schematic says 80 volts, but our left channel power supply has 75 volts on an amp with Rev D printed on the circuit board.
What wattage and voltage is used for ZD1 on the 80 volt regulator card?
Does anyone have a layout diagram that shows the location of the components with reference to the names on the schematic?
Does anyone have an adjustment procedure for things like bias and offset? I see some notes on the bottom right of the schematic, but I need more details.
Has anyone written a “theory of operation”? There appears to be some interesting tricks with floating grounds for power supplies and speaker negative leads and I have not figured out how the common mode section in the middle of the schematics works.
Thanks.
Crown used this "theory of operation" in many of their amplifiers. In a "normal" amplifier you have a positive and a negative supply both referenced to ground. In this amplifier there is only one supply with the low side of the amplifier being the reference. Both the high and low sides are the same but run output of phase. When a positive going signal is input the positive output transistors conduct on the high side and the negative output transistors conduct on the low side. Since the output or would be output of the low side is grounded FV-, the negative side of the main supply capacitor, is pulled toward ground leaving FV+ for use by the high side. A negative going signal does just the opposite, FV+ is pulled towards ground leaving FV- for use by the high side.
As far as the bad zener goes there should be another just like it in the other channel. Just measure across it to find the voltage. The wattage can be determined by the physical size. The triac does the regulating, should be open when off, check to be sure it's not shorted. Could be the reason the zener went. According to the Eagle site the regulator was eliminated later on and the power went up due to the higher unregulated voltage.
I'm sure everything is clear as mud now.
Craig
As far as the bad zener goes there should be another just like it in the other channel. Just measure across it to find the voltage. The wattage can be determined by the physical size. The triac does the regulating, should be open when off, check to be sure it's not shorted. Could be the reason the zener went. According to the Eagle site the regulator was eliminated later on and the power went up due to the higher unregulated voltage.
I'm sure everything is clear as mud now.
Craig
did you try the phone number on the website? Contact Eagle. not sure if he still has that number. havent spoken to him in a while. he made my 2c abput 8 years ago. not to mention he upgraded a friends 7 after the ups driver literally rolled it off the truck cuz he couldnt pick it up.
These amps are strange beasts, and with the complete disappearance of Jon Iverson in recent years (original designer and defense-contractor-genius-of-sorts) your best and only source for knowledge is Russell Sherwood at http://www.eagle-audio.com/upgrades.htm. Russ worked along side Jon for many years and understands much about these Eagle amps.
Russell is a great guy and helped me rebuild and improve my Eagle2 with circuit mods that brought it up to the latest version, correcting errors (!) in the original circuit board layout and disconnecting several diodes in a 'protection circuit' that were better off removed. His email is russ@eagle-audio.com
Below is a link with some background on designer, Jon Iverson of Electron Kinetics and his disappearance, if interested:
Audio Asylum Thread Printer
Russell is a great guy and helped me rebuild and improve my Eagle2 with circuit mods that brought it up to the latest version, correcting errors (!) in the original circuit board layout and disconnecting several diodes in a 'protection circuit' that were better off removed. His email is russ@eagle-audio.com
Below is a link with some background on designer, Jon Iverson of Electron Kinetics and his disappearance, if interested:
Audio Asylum Thread Printer
Exactly how do I remove the voltage regulators from my Eagle 7A? Both have become noisy and I can hear them BUZZ inside the AMP and it also bleeds through to the speakers.
I was then going to put the input side of the power transformers in series and run the amp at 1/2 voltage but after looking I do not think that will be possible as there are 2 outputs from the power transformer and one runs the +/- 15V circuit which will prevent me from performing my trick. Looks like I will have to get some 100V caps instead. Anyway, please some tell me exactly what I have to do to remove my noisy voltage regulators. Please.
I was then going to put the input side of the power transformers in series and run the amp at 1/2 voltage but after looking I do not think that will be possible as there are 2 outputs from the power transformer and one runs the +/- 15V circuit which will prevent me from performing my trick. Looks like I will have to get some 100V caps instead. Anyway, please some tell me exactly what I have to do to remove my noisy voltage regulators. Please.
Hi LineSource,
I am looking for an Eagle 7A. I had one (#103) and it was stolen from me. One of the worst things to be honest in my life. I loved that amplifier. I had a pair of respons Grand loudspeakers from around 1984 - crazy good speakers running dynaudio drivers when dyn was only making drivers.
The amp never made it from new york to vegas. It wasn't on the moving truck. Recouped some funds from the insurance but that doesn't replace an amp like this.
I'm sure you don't have yours anymore - but if you did I would be interested. I saw you're still an active member here.
I just picked up a pair of McIntosh XRT 24s and am just missing that piece of gear. I still have a crazy custom power cable I had built for the amp.
Let me know what you think!
-Kronos
I am looking for an Eagle 7A. I had one (#103) and it was stolen from me. One of the worst things to be honest in my life. I loved that amplifier. I had a pair of respons Grand loudspeakers from around 1984 - crazy good speakers running dynaudio drivers when dyn was only making drivers.
The amp never made it from new york to vegas. It wasn't on the moving truck. Recouped some funds from the insurance but that doesn't replace an amp like this.
I'm sure you don't have yours anymore - but if you did I would be interested. I saw you're still an active member here.
I just picked up a pair of McIntosh XRT 24s and am just missing that piece of gear. I still have a crazy custom power cable I had built for the amp.
Let me know what you think!
-Kronos
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