Hi Bob and others,
the MOXlite PCB is configured for u20 7815 and u21 7915.
check the track layout as follows.
-ve supply to j2 bottom pin.
-ve to r27.
r27 to -ve c27.
-ve c27 to u21 middle pin.
mid pin u21 has a diode to left (out) terminal. When looking at the back of u21 heatsink, PCB oriented with u21 r27 labels facing right way up.
mid pin u21 has a cap to right (com) terminal.
Now compare that pin layout to a diode protected To220 7915 and you will find it fits.
It is the schematic that has the wrong label on u21, although the schematic wiring is correct.
Somebody, have another careful look and come back and confirm.
the MOXlite PCB is configured for u20 7815 and u21 7915.
check the track layout as follows.
-ve supply to j2 bottom pin.
-ve to r27.
r27 to -ve c27.
-ve c27 to u21 middle pin.
mid pin u21 has a diode to left (out) terminal. When looking at the back of u21 heatsink, PCB oriented with u21 r27 labels facing right way up.
mid pin u21 has a cap to right (com) terminal.
Now compare that pin layout to a diode protected To220 7915 and you will find it fits.
It is the schematic that has the wrong label on u21, although the schematic wiring is correct.
Somebody, have another careful look and come back and confirm.
AndrewT - you're right. I made the novice mistake of assuming that the 7815 and 7915 pinouts would be the same. That will make it easier when I build the next ones.
I ended up cutting some traces to allow resistive setting of Q for my subwoofer sections, and others to allow bypassing unused filter sections. I don't think that the board could accommodate another pair of resisters per filter section unless many went to vertical mounting. The board size looks like the maximum allowed by the free version of Eagle (again without actually checking)
I ended up cutting some traces to allow resistive setting of Q for my subwoofer sections, and others to allow bypassing unused filter sections. I don't think that the board could accommodate another pair of resisters per filter section unless many went to vertical mounting. The board size looks like the maximum allowed by the free version of Eagle (again without actually checking)
discrete opamp assembly photos
Hi all,
Tiroth linked a series of 10 pics of the discrete opamp into his www showing the detail of various stages of assembly.
Since his computer went down and work pressure he has been unable to link in these detailed pics (which were of very good quality).
Does anyone have some/any similar opamp assembly pics they could post?
Hi all,
Tiroth linked a series of 10 pics of the discrete opamp into his www showing the detail of various stages of assembly.
Since his computer went down and work pressure he has been unable to link in these detailed pics (which were of very good quality).
Does anyone have some/any similar opamp assembly pics they could post?
Bob posted:
There is, I think, a relavent discussion taking place in the "Lovoltech LU1014D power JFETs" thread beginning here:
http://www.diyaudio.com/forums/showthread.php?s=&postid=893103#post893103
edit: insert "quotes"
There is, I think, a relavent discussion taking place in the "Lovoltech LU1014D power JFETs" thread beginning here:
http://www.diyaudio.com/forums/showthread.php?s=&postid=893103#post893103
edit: insert "quotes"
Hi,
not much activity lately.
I have just built up my first 4pole L-R crossover.
I set the buffer resistors to 10k, with 47pF for RF filter and feedback.
Used PMI op275gp, in sockets, for the opamps.
I wired it for Low Pass @ 156Hz (15k & 48nF/96nF)
High pass @ 156Hz (15k/30k & 48nF).
I have not used any EQ, these locations are empty.
I had intended using 7k5/15k and 100nF/200nF but did not have enough stock to get a matched set of 10 within 1%
DC output offsets:- hipass 9.1mV, lowpass 3.9mV.
Powered up with shorting plug in the crossover input.
At the power amp outputs the DC offset is virtually the same as when the amp is tested with a shorted input.
The AC noise measurements are very different.
LowPass into power amp remains at 0.0mVac at output,
but HiPass into power amp jumps from 0.0mVac to 0.7mVac.
I connected up to the speakers and the bass is completely silent, but the passive mid/bass and the treble both produce noticeable noise.
Switched off and connected the source into the crossover and listened to some music (bass is far too strong) and during quiet or muted source I can just hear the noise that I had measured earlier.
What have I done wrong?
Where will I get the best improvement in reducing the high pass noise?
Different opamps (all three duals)?
Lower value buffer resistors?
Lower value crossover resistors and higher value caps?
Quieter PSU?
or something else?
Help!
not much activity lately.
I have just built up my first 4pole L-R crossover.
I set the buffer resistors to 10k, with 47pF for RF filter and feedback.
Used PMI op275gp, in sockets, for the opamps.
I wired it for Low Pass @ 156Hz (15k & 48nF/96nF)
High pass @ 156Hz (15k/30k & 48nF).
I have not used any EQ, these locations are empty.
I had intended using 7k5/15k and 100nF/200nF but did not have enough stock to get a matched set of 10 within 1%
DC output offsets:- hipass 9.1mV, lowpass 3.9mV.
Powered up with shorting plug in the crossover input.
At the power amp outputs the DC offset is virtually the same as when the amp is tested with a shorted input.
The AC noise measurements are very different.
LowPass into power amp remains at 0.0mVac at output,
but HiPass into power amp jumps from 0.0mVac to 0.7mVac.
I connected up to the speakers and the bass is completely silent, but the passive mid/bass and the treble both produce noticeable noise.
Switched off and connected the source into the crossover and listened to some music (bass is far too strong) and during quiet or muted source I can just hear the noise that I had measured earlier.
What have I done wrong?
Where will I get the best improvement in reducing the high pass noise?
Different opamps (all three duals)?
Lower value buffer resistors?
Lower value crossover resistors and higher value caps?
Quieter PSU?
or something else?
Help!
Andrew,
What board are you using?
I suspect you are talking about the mox lite as you refer to an EQ section - Is this right?
Lets start by getting a signal through on all channels, then we can start looking at noise later.
Can you post a schmatic of your setup, it would make the debugging a lot easier.
\Jens
What board are you using?
I suspect you are talking about the mox lite as you refer to an EQ section - Is this right?
Lets start by getting a signal through on all channels, then we can start looking at noise later.
Can you post a schmatic of your setup, it would make the debugging a lot easier.
\Jens
Hi Jens,
I have a music signal through both halves of one MOXlite.
I have now added another opamp (u3a+b) and a bass level control to reduce that bass.
u1a=input buffer with 10k resistors for r20, 21, 22 & 26 inverting input grounded via input cable.
u4ba=hp + u4ca=hp = 4pole, Q=0.5
u4bb=lp + u4cb=lp = 4pole, Q=0.5
u3a=bass output buffer
u4cb feeds 10kpot into u3a
u1b & u3b unused and all component locations empty. i.e. no loading to keep them @0v.
I have a music signal through both halves of one MOXlite.
I have now added another opamp (u3a+b) and a bass level control to reduce that bass.
u1a=input buffer with 10k resistors for r20, 21, 22 & 26 inverting input grounded via input cable.
u4ba=hp + u4ca=hp = 4pole, Q=0.5
u4bb=lp + u4cb=lp = 4pole, Q=0.5
u3a=bass output buffer
u4cb feeds 10kpot into u3a
u1b & u3b unused and all component locations empty. i.e. no loading to keep them @0v.
Hi,
has anyone else found this?
I'm getting ready to assembe the second MOXlite and could use a few pointers to keep my speakers from hissing.
I found an earlier reference to muting the unused halves of the opamps. I plan to do this on the first MOXlite and measure again.
has anyone else found this?
or taken steps to avoid it?
I'm getting ready to assembe the second MOXlite and could use a few pointers to keep my speakers from hissing.
I found an earlier reference to muting the unused halves of the opamps. I plan to do this on the first MOXlite and measure again.
Hi,
I changed the frequency setting R & C from 15k/47nF to 7k5/100nF (with some values doubled for the unity gain Q=0.7)
I removed the two 10k balanced inverting input resistors and reduced 10k hot input to 750r, increased the fourth 10k to ground to 100k. Now it is unbalanced. Zin=100k//1nF.
The high pass noise after the power amp is now down to 0.2mV (8db quieter than before).
But, at least 12db noisier than the power amp alone.
0.2mV is about -85dbW and will be just above audibility with normal speakers at 1m.
I would like to activate my Tannoys.
Bass/Mid is about 94db/W and treble about 105db/W. That puts treble noise at about 20db above audibility.
I just found Ben Duncan's HFN&RR 1981 article on active filters.
He claimed -101dbm for upper and lower mid outputs and -95dbm on treble output filtered @ 4kHz upwards, all measured bandpass 20Hz to 20kHz.
He used a mix of tl071 as S&K (R=10k) and ne5534 as buffers. Seems I am getting close to the 25year old opamp standard.
I wonder how far my DMM is under-reading?
Getting close, but can I expect any/much better?
Has anyone found a similar noise output from the crossover?
I changed the frequency setting R & C from 15k/47nF to 7k5/100nF (with some values doubled for the unity gain Q=0.7)
I removed the two 10k balanced inverting input resistors and reduced 10k hot input to 750r, increased the fourth 10k to ground to 100k. Now it is unbalanced. Zin=100k//1nF.
The high pass noise after the power amp is now down to 0.2mV (8db quieter than before).
But, at least 12db noisier than the power amp alone.
0.2mV is about -85dbW and will be just above audibility with normal speakers at 1m.
I would like to activate my Tannoys.
Bass/Mid is about 94db/W and treble about 105db/W. That puts treble noise at about 20db above audibility.
I just found Ben Duncan's HFN&RR 1981 article on active filters.
He claimed -101dbm for upper and lower mid outputs and -95dbm on treble output filtered @ 4kHz upwards, all measured bandpass 20Hz to 20kHz.
He used a mix of tl071 as S&K (R=10k) and ne5534 as buffers. Seems I am getting close to the 25year old opamp standard.
I wonder how far my DMM is under-reading?
Getting close, but can I expect any/much better?
Has anyone found a similar noise output from the crossover?
Noise update
Hi,
I have cleaned the pins of the opamps & reinserted them in the sockets a few times. It was when swapping between tl072 and op275 and opa2134 that I discovered that each swap made the crossover sound quieter. Even reverting to the original op275 was much quieter than the first try. Dirty or tarnished pins sockets?
Noise is now much lower on both.
The original with 15K and balanced input is now producing 0.3mV (T) 0.1mV (B) after the buffer but varies slightly with attenuation.
The newer with 7k5 and unbalanced input produces 0.1mV(T) 0.0mV (B) no attenuator.
Both are completely silent on the bass speaker.
The low resistor value version is almost silent. You have to listen close up.
The high resistor version is slightly noisy but inaudible from about 2feet.
I will have to invest in some switch cleaner or de-oxit, until I have settled on the final opamp complement.
Hi,
I have cleaned the pins of the opamps & reinserted them in the sockets a few times. It was when swapping between tl072 and op275 and opa2134 that I discovered that each swap made the crossover sound quieter. Even reverting to the original op275 was much quieter than the first try. Dirty or tarnished pins sockets?
Noise is now much lower on both.
The original with 15K and balanced input is now producing 0.3mV (T) 0.1mV (B) after the buffer but varies slightly with attenuation.
The newer with 7k5 and unbalanced input produces 0.1mV(T) 0.0mV (B) no attenuator.
Both are completely silent on the bass speaker.
The low resistor value version is almost silent. You have to listen close up.
The high resistor version is slightly noisy but inaudible from about 2feet.
I will have to invest in some switch cleaner or de-oxit, until I have settled on the final opamp complement.
Hey Vince,
Old thread ;-). I asked Jens a few questions last, including info on the filters. He was so kind to direct me to his site:
DELTA AUDIO - Active Filter one
All design files, manuals, etc. can be dowloaded from there.
He does not sell any PCB's anymore, so far as I know. So if you want one, you probably should have one made. Or somebody must still have one lying around..
Maarten
Old thread ;-). I asked Jens a few questions last, including info on the filters. He was so kind to direct me to his site:
DELTA AUDIO - Active Filter one
All design files, manuals, etc. can be dowloaded from there.
He does not sell any PCB's anymore, so far as I know. So if you want one, you probably should have one made. Or somebody must still have one lying around..
Maarten
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