Official 33609 builder's tread. See 1st page for updates.
- Thread starter Igor
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RuudNL
Well-known member
What did you do to get the voltages to 4V? For some reason the buffer amplifier is still drawing too much current!
Did you lower the value of R37/R38? Doing so, this will only reduce the voltage drop, but not the current! A better way is to reduce the value of R55 and R56 slightly.
Do you mean that the BC184C (TR2) in the BA640 gets overheated? The collector resistor is 47 K, so there is no significant collector current. It should not get warm at all. Are you sure all components around TR2 do have the right values?
(Always difficult to troubleshoot from a distance....)
Did you lower the value of R37/R38? Doing so, this will only reduce the voltage drop, but not the current! A better way is to reduce the value of R55 and R56 slightly.
Do you mean that the BC184C (TR2) in the BA640 gets overheated? The collector resistor is 47 K, so there is no significant collector current. It should not get warm at all. Are you sure all components around TR2 do have the right values?
(Always difficult to troubleshoot from a distance....)
audiovisceral
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- Mar 25, 2008
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- 150
Igor, is there any plan to revise the PCBs or offer an optional side-PCB with an official 'fix' for the limiter LF distortion?
promixe
Well-known member
Before there will be an "official fix" there should be an "official acknowledgement" of the problem, which isn't there yet. Because the majority of people who built the 33609 haven't reported the LF distortion problem, it is still in the air as of why exactly (not engineering wise, which RuudNL has explained pretty well, but assembly/component-mismatch wise) the rest of us have the problem.
It would be very interesting, however, to see what Igor comments on RuudNL's circuit and the problem at hand in general. People should also test their units with the LF distortion test proposed a page or two back in this thread to see if they REALLY don't have the issue. It seems that a lot of people are not evaluating their units to a full extent to find out where the issue may pop up. For example running drums through the unit will NOT reveal the LF distortion in an apparent easy to hear way... A few pages back I have explained what kind of material exposes the problem in the ugliest way. =)
It would be very interesting, however, to see what Igor comments on RuudNL's circuit and the problem at hand in general. People should also test their units with the LF distortion test proposed a page or two back in this thread to see if they REALLY don't have the issue. It seems that a lot of people are not evaluating their units to a full extent to find out where the issue may pop up. For example running drums through the unit will NOT reveal the LF distortion in an apparent easy to hear way... A few pages back I have explained what kind of material exposes the problem in the ugliest way. =)
sorry tr7 gets hot it is the bc441. the voltages got to 4v on one start up but subsequently i have not been able to reproduce it. still consistently the same voltage no matter whether the op amp is installed or not or the switch elcos. I will triple check the resistors in this section.RuudNL said:
So I plugged in the other channel without the op amp and everything read with voltages too high or low by about 20-30%. when i put the op amp in it blew the 10ohm resistor that you are supposed to measure the current draw across. ???
As far as the build, I can't find a resistor that is the incorrect value or a backwards cap or diode. All the transistors are functional they are just not producing the right voltage for some reason. I checked the switch wiring against some of the build pics and everything looks ok. the only thing that is questionable for me is the audio transformer hookup. I think i have it right but i am not positive. Could this be the cause of the issue? All the voltages read the same with or without the transformers plugged in.
Thanks for the help
As far as the build, I can't find a resistor that is the incorrect value or a backwards cap or diode. All the transistors are functional they are just not producing the right voltage for some reason. I checked the switch wiring against some of the build pics and everything looks ok. the only thing that is questionable for me is the audio transformer hookup. I think i have it right but i am not positive. Could this be the cause of the issue? All the voltages read the same with or without the transformers plugged in.
Thanks for the help
RuudNL
Well-known member
No. The way the transformers are connected will never change the DC voltages.
You could get and output level of +6 dB, -6 dB or nothing at all, but even without transformers the DC voltages should be correct.
The only thing that is strange (in the original Neve design!) is that the gates of the FET's are 'floating' for DC; without a control voltage they don't have a ground reference other than the leak current through the diodes.
I once discussed this with a Neve designer, but he could not explain it. "At least, we know that it works!", was his conclusion...
How did you set RV1? You should start with the wiper set at minimal resistance between base and collector of TR5.
This will cause the lowest current. If R44 burns out, the current drawn is far too high!
You could get and output level of +6 dB, -6 dB or nothing at all, but even without transformers the DC voltages should be correct.
The only thing that is strange (in the original Neve design!) is that the gates of the FET's are 'floating' for DC; without a control voltage they don't have a ground reference other than the leak current through the diodes.
I once discussed this with a Neve designer, but he could not explain it. "At least, we know that it works!", was his conclusion...
How did you set RV1? You should start with the wiper set at minimal resistance between base and collector of TR5.
This will cause the lowest current. If R44 burns out, the current drawn is far too high!
I Think that may have been the issue for the blown resistor. I still cant figure out why the voltages are off. I cannot find any issues on the board, i don't know where to start looking for issues or why the switches seem to have no effect.
RuudNL
Well-known member
Did you measure the resistance of the limit and compress threshold switches? The resistance will vary from 0 ohm up when you turn them, but you should always measure some resistance.
If you get an infinite resistance here (=interruption!), this would mean the compress and/or limit side chains don't receive anything. On the opposite: there might be a form of oscillation in the compress and/or limit side chain.
This could explain the 6 dB signal loss and the permanent meter deflection. Without an input signal, the Control Voltage to the diode bridge should be 0 Volt. (Although personally I don't really believe in oscillations; the sidechains were always very stable here.)
If you get an infinite resistance here (=interruption!), this would mean the compress and/or limit side chains don't receive anything. On the opposite: there might be a form of oscillation in the compress and/or limit side chain.
This could explain the 6 dB signal loss and the permanent meter deflection. Without an input signal, the Control Voltage to the diode bridge should be 0 Volt. (Although personally I don't really believe in oscillations; the sidechains were always very stable here.)
RuudNL
Well-known member
That will make a difference! ;D
ok, better now meter pops up and returns to zero when i power it up , however the 10r resistor that measures the current of the op amp keeps blowing. It has between 4-7 volts on it when i have been able to measure it. I have tried the op amp trimpot at both extremes and in the middle and the 10r resistor blows every time. HELP!
RuudNL
Well-known member
What is the voltage between the bases of TR7 and TR8? By setting RV1 (base of TR5 to collector) you should be able to get this voltage lower than 1,2 V. because TR5 will conduct.
I would check TR5, (the right position of) D1 and D3, and the values of R9, R10, R11 and R12.
Four to seven volts over 10 ohms means a current of 400 to 700 mA, causing a dissipation of 1,6 to 4,9 Watt in the 10 ohms resistor, so it will act as a fuse!
I would check TR5, (the right position of) D1 and D3, and the values of R9, R10, R11 and R12.
Four to seven volts over 10 ohms means a current of 400 to 700 mA, causing a dissipation of 1,6 to 4,9 Watt in the 10 ohms resistor, so it will act as a fuse!
ok that is solved, turns out one of my bc441s was bad, Now I get the current draw correct but the voltage at Tp D is 8.2v and the audio is extremely quiet when engaged. i cant get any of the switches to do anything. other voltages are in the +- 15% area.
I don't think i have ever had a project with so many issues. I prey for the pay when this thing works.
I don't think i have ever had a project with so many issues. I prey for the pay when this thing works.
danjpiscina
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- Joined
- Aug 27, 2008
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I can't seem to find any info on the power transformer here. 24 volts. does anyone have a recommendation for a good quality toroid? Preferably something that can be purchase in the US? Or maybe farnell since I'll need VU meters too.....
Thanks!
Thanks!
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