gswan
Well-known member
Could you get a signal between pins 2 & 3? That's the balanced output. Pin 1 is GND. If it's a transformer coupled output then the signal is likely to appear between pins 2 and 3.
All things G1176 - the new "repost" thread.
- Thread starter orson whitfield
- Start date
Help Support GroupDIY Audio Forum:
The signal on the digi002 output appears between pin 2 and 3, but since pin 3 in this case seems to be GND, I figure it may in fact be a impedance balanced output. As in this figure:
http://www.dself.dsl.pipex.com/ampins/balanced/balfig2.gif
Anyway, building Lundahls into the digi002 seems like a later project (and a new topic on The Lab!) :sam:
/F
http://www.dself.dsl.pipex.com/ampins/balanced/balfig2.gif
Anyway, building Lundahls into the digi002 seems like a later project (and a new topic on The Lab!) :sam:
/F
gswan
Well-known member
That's a fairly typical electronic balanced output. The ground itself is relatively unimportant, since operation relies on the difference between the hot and cold. You need to connect the hot and cold signal lines into transformer input of your compressor.
[quote author="gswan"]That's a fairly typical electronic balanced output. [/quote]
I don't agree. A typical electronic balanced output would look like this, with two active outputs and ground:
http://www.dself.dsl.pipex.com/ampins/balanced/balfig5b.gif
[quote author="gswan"]You need to connect the hot and cold signal lines into transformer input of your compressor.[/quote]
Read my previous posts. I didn't work. We can discuss the digi002 furher, but I suggest that we use PM's since this is a 1176 help thread.
I don't agree. A typical electronic balanced output would look like this, with two active outputs and ground:
http://www.dself.dsl.pipex.com/ampins/balanced/balfig5b.gif
[quote author="gswan"]You need to connect the hot and cold signal lines into transformer input of your compressor.[/quote]
Read my previous posts. I didn't work. We can discuss the digi002 furher, but I suggest that we use PM's since this is a 1176 help thread.
gswan
Well-known member
You are right.
I didn't look too closely. Impedance balanced simply means that the hot and cold lines see the same impedance, to maintain a good CMRR. It's not the same as a fully balanced system. Sorry for that.
As you rightly pointed out, the signal will be at the hot output.
I didn't look too closely. Impedance balanced simply means that the hot and cold lines see the same impedance, to maintain a good CMRR. It's not the same as a fully balanced system. Sorry for that.
As you rightly pointed out, the signal will be at the hot output.
Underthebigtree
Well-known member
Please pardon the crosspost - I've also posted this to the 1176 RevD Mnats thread, but figure that more people read this one, and the problem is quite possibly in part of the system that is common to both the straight G1176 and the Mnats rev D version:
So it appears that I was highly optimistic as to my success.
The unit is generating an incredible amount of output - like 21V with the output knob set to halfway. I've gone through the whole thing carefully, replaced Q4 (see below), checked for shorts, and so on. I just can't figure out what's going on.
To start with, here are my test settings:
Input signal: 260Hz sin wave at 0.69Vp-p (-10dBu, 0.448Vac)
Input knob set to 10 (on 0-10 scale), output 0, attack and release fully CW, ratio 1:4, meter knob: bypass
Now here are my readings going through the signal chain to the main board:
Input: 0.448Vac
Hi output of T600: 0.448Vac
(Hi output of T600 at midway setting of T600: .221Vac)
Hi input to Mnats input card: .447Vac
Either output of input trafo (Lundahl LL1540 on Mnats input card): 1.786Vac
So first of all, should the input signal be more than tripled in voltage coming out of the input transformer?
Now here are the readings at my transistors through the signal chain, with the output signal set at zero:
Signal preamp section:
Q1: G=1.62V, D=1.78V, S=1.78V
All the rest are in the order B, C, E:
Q2: 1.78V, 1.78V, 1.78V
Q3: 1.78V, 2.07V, 1.78V
Q14: 2.07V, 1.78V, 2.07
Signal line section:
Q4: 1.79V, 1.79V, 1.79V
Q5: 1.79V, 1.79V, 1.79V
Q6: (didn't measure - has to be done from underside of board)
Now if I set the output knob to 20%:
Q1: 2.6, 3.4, 2.9
Q2: 3.4, 1.7, 2.8
Q3: 1.7, 2.7, 3.0
Q14: 2.6, 3.0, 2.6
Q4: *** (80V?), 1.8, 1.8)
Q5: 1.8, 3.1, 2.1
*** at this setting, Q4 is off the charts when I touch the test probe to the Base pin, and I start to hear a buzzing, ticking sound in my output transformer, which makes me remove the test probe rapidly. WTF?
Now if I set the output knob to 50%:
Q1: 18.5, 21, 20
Q2: 21.6, 1.8, 21
Q3: 1.8, 19.6, 20.7
Q14: 20, 20.7, 19.1
Q4: ***, 14.8, 18
Q5: 16.3, 20.8, 3.6
The first thing I did after taking these measurements was to swap out Q4. No change.
In addition, as soon as I get the output up to about 20%, the sin wave starts distorting asymmetrically on my scope.
Here are the corresponding output voltages, measured at pin 2 of the output XLR, between my unit and a UA 1176 reissue:
Output knob My unit 1176 reissue
0 .001V .001V
2 2.8V .068V
5 21V .425V
Any help would be greatly appreciated. I've been banging my head against this for a couple of weeks, and don't know where to look next.
-Nick
So it appears that I was highly optimistic as to my success.
The unit is generating an incredible amount of output - like 21V with the output knob set to halfway. I've gone through the whole thing carefully, replaced Q4 (see below), checked for shorts, and so on. I just can't figure out what's going on.
To start with, here are my test settings:
Input signal: 260Hz sin wave at 0.69Vp-p (-10dBu, 0.448Vac)
Input knob set to 10 (on 0-10 scale), output 0, attack and release fully CW, ratio 1:4, meter knob: bypass
Now here are my readings going through the signal chain to the main board:
Input: 0.448Vac
Hi output of T600: 0.448Vac
(Hi output of T600 at midway setting of T600: .221Vac)
Hi input to Mnats input card: .447Vac
Either output of input trafo (Lundahl LL1540 on Mnats input card): 1.786Vac
So first of all, should the input signal be more than tripled in voltage coming out of the input transformer?
Now here are the readings at my transistors through the signal chain, with the output signal set at zero:
Signal preamp section:
Q1: G=1.62V, D=1.78V, S=1.78V
All the rest are in the order B, C, E:
Q2: 1.78V, 1.78V, 1.78V
Q3: 1.78V, 2.07V, 1.78V
Q14: 2.07V, 1.78V, 2.07
Signal line section:
Q4: 1.79V, 1.79V, 1.79V
Q5: 1.79V, 1.79V, 1.79V
Q6: (didn't measure - has to be done from underside of board)
Now if I set the output knob to 20%:
Q1: 2.6, 3.4, 2.9
Q2: 3.4, 1.7, 2.8
Q3: 1.7, 2.7, 3.0
Q14: 2.6, 3.0, 2.6
Q4: *** (80V?), 1.8, 1.8)
Q5: 1.8, 3.1, 2.1
*** at this setting, Q4 is off the charts when I touch the test probe to the Base pin, and I start to hear a buzzing, ticking sound in my output transformer, which makes me remove the test probe rapidly. WTF?
Now if I set the output knob to 50%:
Q1: 18.5, 21, 20
Q2: 21.6, 1.8, 21
Q3: 1.8, 19.6, 20.7
Q14: 20, 20.7, 19.1
Q4: ***, 14.8, 18
Q5: 16.3, 20.8, 3.6
The first thing I did after taking these measurements was to swap out Q4. No change.
In addition, as soon as I get the output up to about 20%, the sin wave starts distorting asymmetrically on my scope.
Here are the corresponding output voltages, measured at pin 2 of the output XLR, between my unit and a UA 1176 reissue:
Output knob My unit 1176 reissue
0 .001V .001V
2 2.8V .068V
5 21V .425V
Any help would be greatly appreciated. I've been banging my head against this for a couple of weeks, and don't know where to look next.
-Nick
gswan
Well-known member
1. Measure your supply rails (DC).
2. Measure the DC operating point of each of the devices (ie no signal).
3. I'm not sure how you are measuring your transformer ratio. Feed a sine wave into it and measure the output across the transformer. If it's a 1:1 transformer the voltages should be the same. If it's 2:1 it should be half or double (depending on which way you have it inserted).
4. Q4 base at 80V sounds like a problem, if that's really what it is. Q4-b should be the same as Q3-c (since they are connected together). If not then you have a problem there. Are these AC measurements you have taken?
5. Save yourself some time and check the signal (wrt GND) at the input pot, the output pot and the driver side of the output transformer. Disable the GR amp when doing this since it will only mask amplifier problems. It sounds like one of the feedback loops is not correct, which could be due to an open circuit or wrong value resistor somewhere. Locate whether it is in the pre-amp or driver amp section.
2. Measure the DC operating point of each of the devices (ie no signal).
3. I'm not sure how you are measuring your transformer ratio. Feed a sine wave into it and measure the output across the transformer. If it's a 1:1 transformer the voltages should be the same. If it's 2:1 it should be half or double (depending on which way you have it inserted).
4. Q4 base at 80V sounds like a problem, if that's really what it is. Q4-b should be the same as Q3-c (since they are connected together). If not then you have a problem there. Are these AC measurements you have taken?
5. Save yourself some time and check the signal (wrt GND) at the input pot, the output pot and the driver side of the output transformer. Disable the GR amp when doing this since it will only mask amplifier problems. It sounds like one of the feedback loops is not correct, which could be due to an open circuit or wrong value resistor somewhere. Locate whether it is in the pre-amp or driver amp section.
raysolinski
Well-known member
okay..so my 1176 with the electronic input went a little crazy (the 5532 was killing me with gain, turns out one of the 10k resistors had come loose)..SO I decided to put an input stepdown transformer in and bypass the electronically balanced section..I took out the 5532, disconected the input wires and ran the high side of the transformer secondary to the high side of the input pot...sounds great as a line amp with no fets in, input and output pots work, no distortion...put in the fets and my meter sits at zero in gr mode..the tracking pot does zilch while calibrating (zero pot works fine)....upon further experimentation my vu tracks perfectly with the meter fet in and callibrated...6 db reduction of a 1k sine wave reads -6db on the vu...put in Q1 and you can hear the compression but the meter sits at 0..doesn't matter what fet you put in there..matched, random etc. I did tests with 15 different fets in Q1 and the meter behaved the same way. I made sure the Q1 socket has continuity...I have been looking at the schematic but I am stumped..it as if Q1 is somehow shorting the meter in gr mode...
I know the meter works because it works without Q1 flawlessly and tracks the output perfectly as well in VU mode... and this unit worked for over a year....
...
Cheers,
Ray
I know the meter works because it works without Q1 flawlessly and tracks the output perfectly as well in VU mode... and this unit worked for over a year....
...Cheers,
Ray
gswan
Well-known member
[quote author="raysolinski"]okay..so my 1176 with the electronic input went a little crazy (the 5532 was killing me with gain, turns out one of the 10k resistors had come loose)..SO I decided to put an input stepdown transformer in and bypass the electronically balanced section..I took out the 5532, disconected the input wires and ran the high side of the transformer secondary to the high side of the input pot[/quote]
OK, sounds like the signal path's working fine.
[quote author="raysolinski"]...sounds great as a line amp with no fets in, input and output pots work, no distortion...put in the fets and my meter sits at zero in gr mode..the tracking pot does zilch while calibrating (zero pot works fine)....upon further experimentation my vu tracks perfectly with the meter fet in and callibrated...6 db reduction of a 1k sine wave reads -6db on the vu...put in Q1 and you can hear the compression but the meter sits at 0..doesn't matter what fet you put in there..matched, random etc. I did tests with 15 different fets in Q1 and the meter behaved the same way. I made sure the Q1 socket has continuity...I have been looking at the schematic but I am stumped..it as if Q1 is somehow shorting the meter in gr mode...[/quote]
Q1 is the signal attenuation FET, Q10 is the metering FET. Q1 has no effect on the metering.
The meter is hooked across the output signal in VU mode, so that's a good indication that the meter works and that the meter is a 'real' VU meter (with internal diodes).
When you say the meter 'sits at 0', do you mean it reads 0VU, or it is not reading anything at all?
Have a poke around Q10 and the TL071 op amp. Check the output voltage for different levels of compression. Also check that the tracking pot is OK.
[quote author="raysolinski"]I know the meter works because it works without Q1 flawlessly and tracks the output perfectly as well in VU mode... and this unit worked for over a year.... ...
Cheers,
Ray[/quote]
If it worked OK previously then you've probably either splashed some solder into the meter circuit or dislodged something when you put in the transformer.
OK, sounds like the signal path's working fine.
[quote author="raysolinski"]...sounds great as a line amp with no fets in, input and output pots work, no distortion...put in the fets and my meter sits at zero in gr mode..the tracking pot does zilch while calibrating (zero pot works fine)....upon further experimentation my vu tracks perfectly with the meter fet in and callibrated...6 db reduction of a 1k sine wave reads -6db on the vu...put in Q1 and you can hear the compression but the meter sits at 0..doesn't matter what fet you put in there..matched, random etc. I did tests with 15 different fets in Q1 and the meter behaved the same way. I made sure the Q1 socket has continuity...I have been looking at the schematic but I am stumped..it as if Q1 is somehow shorting the meter in gr mode...[/quote]
Q1 is the signal attenuation FET, Q10 is the metering FET. Q1 has no effect on the metering.
The meter is hooked across the output signal in VU mode, so that's a good indication that the meter works and that the meter is a 'real' VU meter (with internal diodes).
When you say the meter 'sits at 0', do you mean it reads 0VU, or it is not reading anything at all?
Have a poke around Q10 and the TL071 op amp. Check the output voltage for different levels of compression. Also check that the tracking pot is OK.
[quote author="raysolinski"]I know the meter works because it works without Q1 flawlessly and tracks the output perfectly as well in VU mode... and this unit worked for over a year....
...Cheers,
Ray[/quote]
If it worked OK previously then you've probably either splashed some solder into the meter circuit or dislodged something when you put in the transformer.
raysolinski
Well-known member
Sits at zero..well, it moves a tiny bit if you jam the compression up to 20 db..I did replace the opamp in the meter section... what stumped me was the fact that the meter works perfectly without Q1...I suspect the tracking trimmer...since I don't have a spare trimmer I will mount a 100k pot on the rear in one of the many holes for experimentation purposes...I will check the voltages around there as well...all ratios work as expected in relation to input voltage as confirmed witha dvm and DAW..like I said, every aspect of it works to spec except gr mode..and gr mode works without Q10...hmmmm :?
Ray
Ray
Jim50hertz
Well-known member
I have just completed my G1176 using mnats board with input transformer.
I'm just doing some preliminary testing and setup and have noticed a substantial High Frequency loss at all settings resulting in the unit sounding dull.
I think I have made the q bias adjustment fine, and the GR zero adjustment, but, when I switch to any setting other than 1:4 the meter pegs to the right and doesn't move
Also, there is little noticable compression going on!
Any ideas where to start guys?
I'm just doing some preliminary testing and setup and have noticed a substantial High Frequency loss at all settings resulting in the unit sounding dull.
I think I have made the q bias adjustment fine, and the GR zero adjustment, but, when I switch to any setting other than 1:4 the meter pegs to the right and doesn't move
Also, there is little noticable compression going on!
Any ideas where to start guys?
raysolinski
Well-known member
Solved my metering problem...everything seems to be hunky dory...thanks for all the help gswan!
Cheers,
Ray
Cheers,
Ray
raysolinski
Well-known member
[quote author="Jim50hertz"]I have just completed my G1176 using mnats board with input transformer.
I'm just doing some preliminary testing and setup and have noticed a substantial High Frequency loss at all settings resulting in the unit sounding dull.
I think I have made the q bias adjustment fine, and the GR zero adjustment, but, when I switch to any setting other than 1:4 the meter pegs to the right and doesn't move
Also, there is little noticable compression going on!
Any ideas where to start guys?[/quote]
What input transformer? How is it connected? Do you have the termination and zobel (if needed) right?
Ray
I'm just doing some preliminary testing and setup and have noticed a substantial High Frequency loss at all settings resulting in the unit sounding dull.
I think I have made the q bias adjustment fine, and the GR zero adjustment, but, when I switch to any setting other than 1:4 the meter pegs to the right and doesn't move
Also, there is little noticable compression going on!
Any ideas where to start guys?[/quote]
What input transformer? How is it connected? Do you have the termination and zobel (if needed) right?
Ray
gswan
Well-known member
[quote author="Jim50hertz"]I have just completed my G1176 using mnats board with input transformer.
I'm just doing some preliminary testing and setup and have noticed a substantial High Frequency loss at all settings resulting in the unit sounding dull.
I think I have made the q bias adjustment fine, and the GR zero adjustment, but, when I switch to any setting other than 1:4 the meter pegs to the right and doesn't move
Also, there is little noticable compression going on!
Any ideas where to start guys?[/quote]
Quantify it. Use 100Hz, 1kHz and 10kHz tones to measure the unit's gain (set for unity with 1kHz) with no compression. First verify the operation of your signal path before adding compression. Check for distortion as well.
Measure the DC bias changes on the compression FET at different ratio settings to make sure you have the correct ratio resistors. Check your -10V supply rail.
I'm just doing some preliminary testing and setup and have noticed a substantial High Frequency loss at all settings resulting in the unit sounding dull.
I think I have made the q bias adjustment fine, and the GR zero adjustment, but, when I switch to any setting other than 1:4 the meter pegs to the right and doesn't move
Also, there is little noticable compression going on!
Any ideas where to start guys?[/quote]
Quantify it. Use 100Hz, 1kHz and 10kHz tones to measure the unit's gain (set for unity with 1kHz) with no compression. First verify the operation of your signal path before adding compression. Check for distortion as well.
Measure the DC bias changes on the compression FET at different ratio settings to make sure you have the correct ratio resistors. Check your -10V supply rail.
Underthebigtree
Well-known member
[quote author="gswan"]1. Measure your supply rails (DC).
2. Measure the DC operating point of each of the devices (ie no signal).
3. I'm not sure how you are measuring your transformer ratio. Feed a sine wave into it and measure the output across the transformer. If it's a 1:1 transformer the voltages should be the same. If it's 2:1 it should be half or double (depending on which way you have it inserted).
[/quote]
Thanks for the advice - now we are getting somewhere. Sadly, nowhere great.
The supply rails appear to be the culprit. When I first built up the board and wired it to the power transformer, I read -10VDC and +30VDC at the appropriate test points, so I moved on.
Checking them now, I read nearly 0VDC at either point, but 43VAC at both places, plus many others across the main board! I don't see any burnt components or smell any smoke - nothing has given any hint of problem. Could it be the voltage regulator?
And just to confirm that I have my power transformer wired correctly, I have 30VAC between either of the AC inputs and the center tap, and 60VAC when measuring between the AC inputs.
The input transformer clue was a red herring. Turns out I was measuring the voltage with respect to ground, not across the output of the input transformer. When measured correctly, it is properly behaving as a 2:1 stepdown transformer.
2. Measure the DC operating point of each of the devices (ie no signal).
3. I'm not sure how you are measuring your transformer ratio. Feed a sine wave into it and measure the output across the transformer. If it's a 1:1 transformer the voltages should be the same. If it's 2:1 it should be half or double (depending on which way you have it inserted).
[/quote]
Thanks for the advice - now we are getting somewhere. Sadly, nowhere great.
The supply rails appear to be the culprit. When I first built up the board and wired it to the power transformer, I read -10VDC and +30VDC at the appropriate test points, so I moved on.
Checking them now, I read nearly 0VDC at either point, but 43VAC at both places, plus many others across the main board! I don't see any burnt components or smell any smoke - nothing has given any hint of problem. Could it be the voltage regulator?
And just to confirm that I have my power transformer wired correctly, I have 30VAC between either of the AC inputs and the center tap, and 60VAC when measuring between the AC inputs.
The input transformer clue was a red herring. Turns out I was measuring the voltage with respect to ground, not across the output of the input transformer. When measured correctly, it is properly behaving as a 2:1 stepdown transformer.
gswan
Well-known member
[quote author="underthebigtree"]
The supply rails appear to be the culprit. When I first built up the board and wired it to the power transformer, I read -10VDC and +30VDC at the appropriate test points, so I moved on.
Checking them now, I read nearly 0VDC at either point, but 43VAC at both places, plus many others across the main board! I don't see any burnt components or smell any smoke - nothing has given any hint of problem. Could it be the voltage regulator?
[/quote]
Sounds like you don't have the 0V connected from the power supply. Are you sure you are measuring these at the right points?
What PSU are you using and how have you got the transformer connected?
How have you connected the outputs, particularly the 0V/GND reference?
The supply rails appear to be the culprit. When I first built up the board and wired it to the power transformer, I read -10VDC and +30VDC at the appropriate test points, so I moved on.
Checking them now, I read nearly 0VDC at either point, but 43VAC at both places, plus many others across the main board! I don't see any burnt components or smell any smoke - nothing has given any hint of problem. Could it be the voltage regulator?
[/quote]
Sounds like you don't have the 0V connected from the power supply. Are you sure you are measuring these at the right points?
What PSU are you using and how have you got the transformer connected?
How have you connected the outputs, particularly the 0V/GND reference?
Underthebigtree
Well-known member
[quote author="gswan"]
Sounds like you don't have the 0V connected from the power supply. Are you sure you are measuring these at the right points?
[/quote]
On the Mnats Rev D board, there are labels that read -10V on one side of diode CR6, and +30V where R87 connects to the output of the voltage regulator. Those are the locations I was measuring.
[quote author="gswan"]
What PSU are you using and how have you got the transformer connected?
[/quote]
I'm using the Mnats PS onboard the main board. The power transformer is an Avel Lindberg Y236106 30VA with 2 115V windings on the primary side, and 2 25V windings on the secondary. I have the primaries wired in parallel (I'm in the US, with 110V wall power), and the secondaries wired in series, with a center tap. The two AC outputs of the transformers go to the AC inputs on the power supply board, and the center tap goes to the center tap input, right in between the AC inputs, on the board. I did find it interesting that I'm measuring 30V between either AC input and the center tap, not 25V, but wasn't sure what it meant, if anything.
[quote author="gswan"]
How have you connected the outputs, particularly the 0V/GND reference?
[/quote]
I had heard that ground was a big issue with this unit, so I experimented with overdoing it. I have a thick piece of solid copper romex soldered to the power inlet's ground input, which stretches across the length of the back panel to near the XLR input, where it is attached to the chassis with lock washers and a wing nut. Pin 1 of XLR input and output are soldered via very short wires to the copper bar.
But thinking about your question more, it dawns on me that there is no connection between the main board and chassis ground. It is being used as a telescoping ground for the connection from the XLR input and the T600 input and output, and it connects pins 1 of XLR in and out together, but they are not connected to the ground connection on the main board. :roll:
Sounds like you don't have the 0V connected from the power supply. Are you sure you are measuring these at the right points?
[/quote]
On the Mnats Rev D board, there are labels that read -10V on one side of diode CR6, and +30V where R87 connects to the output of the voltage regulator. Those are the locations I was measuring.
[quote author="gswan"]
What PSU are you using and how have you got the transformer connected?
[/quote]
I'm using the Mnats PS onboard the main board. The power transformer is an Avel Lindberg Y236106 30VA with 2 115V windings on the primary side, and 2 25V windings on the secondary. I have the primaries wired in parallel (I'm in the US, with 110V wall power), and the secondaries wired in series, with a center tap. The two AC outputs of the transformers go to the AC inputs on the power supply board, and the center tap goes to the center tap input, right in between the AC inputs, on the board. I did find it interesting that I'm measuring 30V between either AC input and the center tap, not 25V, but wasn't sure what it meant, if anything.
[quote author="gswan"]
How have you connected the outputs, particularly the 0V/GND reference?
[/quote]
I had heard that ground was a big issue with this unit, so I experimented with overdoing it. I have a thick piece of solid copper romex soldered to the power inlet's ground input, which stretches across the length of the back panel to near the XLR input, where it is attached to the chassis with lock washers and a wing nut. Pin 1 of XLR input and output are soldered via very short wires to the copper bar.
But thinking about your question more, it dawns on me that there is no connection between the main board and chassis ground. It is being used as a telescoping ground for the connection from the XLR input and the T600 input and output, and it connects pins 1 of XLR in and out together, but they are not connected to the ground connection on the main board. :roll:
ChrioN
Well-known member
underthebigtree:When you measure voltages, you should measure from the secondary "0" of your power transformer.
Underthebigtree
Well-known member
OK, massive improvement!
GSwan, you are a Jedi master. I bow to your freakish powers of insight and getting to the heart of a problem.
I simply connected the main board ground to chassis ground with an alligator clip wire, and the system stabilized. Power supply is fine, much less distortion and crazy non-linear behavior with the output knob, etc.
However, it *still* outputs a gargantuan signal. Is this normal? Feeding it a -10dBU signal (0.25VRMS), in bypass mode, with input and output set to 5, I'm reading 1VAC at the output. If I turn them both to 10, the output reads 22VAC. Can this possibly be right? That translates to 29dBU!
GSwan, you are a Jedi master. I bow to your freakish powers of insight and getting to the heart of a problem.
I simply connected the main board ground to chassis ground with an alligator clip wire, and the system stabilized. Power supply is fine, much less distortion and crazy non-linear behavior with the output knob, etc.
However, it *still* outputs a gargantuan signal. Is this normal? Feeding it a -10dBU signal (0.25VRMS), in bypass mode, with input and output set to 5, I'm reading 1VAC at the output. If I turn them both to 10, the output reads 22VAC. Can this possibly be right? That translates to 29dBU!
gswan
Well-known member
Doesn't sound right. Check the gain at each stage (ie signal preamp and line driver stages). You may find that one of your gain setting components is the wrong value or not installed correctly.
Similar threads
