I afraid the OPA 2227 is not the optimum choice, because it has fairly low slew rate. For the purposes, where the final gain is higher or equal to 5 the OPA 2228 is definitely better - in fact this is an undercompensated - and so far not unity gain stable - version of the 2227. The AD 8671 (in fact AD 8672 as dual) lies somewhere between - it has similar (or lower) noise, the SR is lower than 2228 but higher than 2227 and it is unity gain stable, so it is definitely better than OPA 2227 for the low gain applications.
Even substantially better should be the OPA 2827, but this is only planned for now.
Even substantially better should be the OPA 2827, but this is only planned for now.
Hi from a new member.
I too would also like to get a gopy of the circuit for the SE and possibly the SE"2".
Having recently aquired the SE version of the Pro-ject and noticed it has 3 NE5532s and 1 JRC opamp inside.I pressume it has been repaired sometime..
I was initially a bit unhappy at the performance until I opened up the box ,I am considering certain improvements , some of which have been discussed here .
The first thing I have started is replacement of the resistors with Vishays. Already 8 random replacements due to instant availabilty from my workshop have resulted in a better sonic.2 Schottky diodes helped.
Firstly the Wallwart power supply gets fairly ward and I suspect the quality of sound drops. Has anyone tried a better torroid power supply with improved results.
I intend to try the following as I need a bit more out of this unit.
1)Snubber caps accros the schottky diodes
2)Larger value smoothing caps and better quality.I dont realy want to use Blackgates if possible as I find their sonic signature un musical.I have used thm in many mods for nearly 15 years.
Im looking t 1000 for 470mfs and 100 for 47mfs.Im assuming I can use 25v type as this is only single rail.I prefer Slmics.
3) Bypass caps on Electrolytics.Possibly under the board.
4)Possibly increase gain by a smidgeon.
5)Quieter nicer op amps.Ive tried many in varying mods in the last 40 years .Some nice suggestions already picked up in this thread.
6)Continue upgrade to Vishay resistors.
7) Upgrade some ofthe smaller caps.I do have a range of esoterics from previos designs spare.
8)Anything anyone else suggests..
Ive even considered dual/seerate power supplys as a possibilty.
Thanking all those who have already posted I look forward to any helpfull comments and advice.
I too would also like to get a gopy of the circuit for the SE and possibly the SE"2".
Having recently aquired the SE version of the Pro-ject and noticed it has 3 NE5532s and 1 JRC opamp inside.I pressume it has been repaired sometime..
I was initially a bit unhappy at the performance until I opened up the box ,I am considering certain improvements , some of which have been discussed here .
The first thing I have started is replacement of the resistors with Vishays. Already 8 random replacements due to instant availabilty from my workshop have resulted in a better sonic.2 Schottky diodes helped.
Firstly the Wallwart power supply gets fairly ward and I suspect the quality of sound drops. Has anyone tried a better torroid power supply with improved results.
I intend to try the following as I need a bit more out of this unit.
1)Snubber caps accros the schottky diodes
2)Larger value smoothing caps and better quality.I dont realy want to use Blackgates if possible as I find their sonic signature un musical.I have used thm in many mods for nearly 15 years.
Im looking t 1000 for 470mfs and 100 for 47mfs.Im assuming I can use 25v type as this is only single rail.I prefer Slmics.
3) Bypass caps on Electrolytics.Possibly under the board.
4)Possibly increase gain by a smidgeon.
5)Quieter nicer op amps.Ive tried many in varying mods in the last 40 years .Some nice suggestions already picked up in this thread.
6)Continue upgrade to Vishay resistors.
7) Upgrade some ofthe smaller caps.I do have a range of esoterics from previos designs spare.
8)Anything anyone else suggests..
Ive even considered dual/seerate power supplys as a possibilty.
Thanking all those who have already posted I look forward to any helpfull comments and advice.
Schottkys don't need snubbers, that's the whole point of using Schottkys...
I think using a toroid instead of the wall wart will hurt sonics as they will let much more noise and spikes through. Just because the wall wart gets a bit warm does not mean it's bad in any way. It's mostly due to the magnetising current.
I think using a toroid instead of the wall wart will hurt sonics as they will let much more noise and spikes through. Just because the wall wart gets a bit warm does not mean it's bad in any way. It's mostly due to the magnetising current.
Originally posted by Calvin (long ago, i know)
If You just want to use MMs -which mostly are no symmetrical generators because of internal grounding of the coils- You´d be better of with devices like LT1028 or AD797!
That to me is not clear: I always thought that a mm pickup is as symmetrical as a mc one, at least in principle.
Where is the grounding done? Inside the pickup or the turntable? Always or only with some/many MM pickups? And why? I ask because i can not detect any grounding in a Shure V15 III i have here in a Dual tt. At least to me it appears perfectly symmetrical.
Maybe someone can shed some light for me on this matter, or point me to the right direction, because i found nothing (yet) about this on the net.
Thanks, Clemens
Hi,
You´re right..MMs are symmetrical by nature too. But a lot of MMs are desymmetrized by the manufacturers by simply connecting one pin to ground. You can often see this connection from the outside as a small band of metal at one of the pins going to the pickups casing. You could try and break this node to have a symmetrical pickup again, or use a MM that is not connected to gnd.
jauu
Calvin
You´re right..MMs are symmetrical by nature too. But a lot of MMs are desymmetrized by the manufacturers by simply connecting one pin to ground. You can often see this connection from the outside as a small band of metal at one of the pins going to the pickups casing. You could try and break this node to have a symmetrical pickup again, or use a MM that is not connected to gnd.
jauu
Calvin
Hi Calvin,
thanks, that clears up some things but brings up more questions
Do you know how important the grounding of the casing is? I guess it's grounded because of shielding issues. But why are the cases of MC pickups not grounded then (making them symmetrical)? They should be equally susceptible to em fields.
And what would or could happen if i just connect an mm pickup symmetrically to a symmetric preamplifier, without breaking the connection between the cold line and the casing? The casing at least with my pickup is completely isolated from everything else, with the exception of that node directly at the cold pin (i think it's rg). Could i pickup interference because of that? I guess that leads back to my first question.
Does that mean that without modifying most of the mm pickups it's a bad idea to connect them to a symmteric preamplifier?
As i see it now there are some options to connect a magnetic pickup to a preamplifier:
1. Just the standard, asymmetrical way to an asymmetric preamplifier.
2. Do just some recabling and connect it symmetrical to an appropriate preamplifier without modifying the cartridge. That will most often lead to a pickup case that is connected to one cold signal line.
3. Similar as 2 but break the connection of the case and the cold. The case now is not connected to anything, so maybe shielding issues could arise.
4. Similar as 3, but now connect the case to ground. Now everything should be fine, the sky will open up, the sun will shine and everyone will live happily ever after.
I definitely can see an advantage in going symmetric, that being common mode signal rejection, less capacitance of the cabling, maybe other things as well. But how far down the line would one have to go? Point 4 will be a bit awkward because it will make the changing of pickups much harder. Point 3 will damage (change) the pickup permanently. Maybe 2 would be enough?
Thanks, Clemens
thanks, that clears up some things but brings up more questions
Do you know how important the grounding of the casing is? I guess it's grounded because of shielding issues. But why are the cases of MC pickups not grounded then (making them symmetrical)? They should be equally susceptible to em fields.
And what would or could happen if i just connect an mm pickup symmetrically to a symmetric preamplifier, without breaking the connection between the cold line and the casing? The casing at least with my pickup is completely isolated from everything else, with the exception of that node directly at the cold pin (i think it's rg). Could i pickup interference because of that? I guess that leads back to my first question.
Does that mean that without modifying most of the mm pickups it's a bad idea to connect them to a symmteric preamplifier?
As i see it now there are some options to connect a magnetic pickup to a preamplifier:
1. Just the standard, asymmetrical way to an asymmetric preamplifier.
2. Do just some recabling and connect it symmetrical to an appropriate preamplifier without modifying the cartridge. That will most often lead to a pickup case that is connected to one cold signal line.
3. Similar as 2 but break the connection of the case and the cold. The case now is not connected to anything, so maybe shielding issues could arise.
4. Similar as 3, but now connect the case to ground. Now everything should be fine, the sky will open up, the sun will shine and everyone will live happily ever after.
I definitely can see an advantage in going symmetric, that being common mode signal rejection, less capacitance of the cabling, maybe other things as well. But how far down the line would one have to go? Point 4 will be a bit awkward because it will make the changing of pickups much harder. Point 3 will damage (change) the pickup permanently. Maybe 2 would be enough?
Thanks, Clemens
Hi bobolix,
pleas can you tell me something about clearaudio balanced reference?Or this is not your design?It´s look realy good.Two separate channel in two box and external power supply.Inside is some special topology?I still looking some phonopreamp.
Or what about Borbely MM/MC phono preamp?
pleas can you tell me something about clearaudio balanced reference?Or this is not your design?It´s look realy good.Two separate channel in two box and external power supply.Inside is some special topology?I still looking some phonopreamp.
Or what about Borbely MM/MC phono preamp?
I have just messed with a Phonobox 1 today. I think there are definately more then one version of even box 1. The firts I had in my shop a few years ago had a painted box, the one I have now looks more like it is powdercoated. Also, the first unit had cheap panel mount RCAs linked to the PCB with "wires"/leads, the newer one has PCB mounted RCA sockets. Board layout seems differnt too with all metal film resistors, the legends do not seem to correspond with data previously posted.
I have upped the PSU caps from 470 mfd to 1000 mfd and replaced diodes with BYT53. Also swapped out op amps TL01>OPA134 and 4580 > LM4562. I had these around...
What is the difference in operation when these devices are set to MC vs MM? Does an additional opamp section get used for MC or just the gain adjusted? I can figure out that the one set of links on the PCB brings in a 100 ohm resistor for MC loading. (I fitted cut up IC tulip socket here, so the link can be made with wire or a resistor that will be added to the 100 ohm allowing a bit more variance.)
Does the TL071 "cooling circuit" remain active for MC? What would be the best way to adjust load resistance for my Sumiko high output MC 2.5 mV? In previous set ups I got best sound when playing in to MM gain stages but set to a load of about 22K. Would I need to swap out the 47K resistor for a 22K one or can I add the MC load resistor + additional one as described above?
One thing nobody seems to have discussed is the silly PSU arrangement. I mean half wafe rectification for a device requiring clean smooth power. This imo seems to have been forced by wanting to use the std 16V project wall wart but still allow +/- 15V rails.
I suspect a serious upgrade for this unit would be an external DC supply with full wave rectifiers and say at least 4700 mfd smoothing per rail feeding the built in regulators.
I will probably also change the little 78L05 79L05 regulators for T0220 packages. In previous projects I have found these little regulators to restrict subjective dynamics. I may even run "zener set" 317/337 from a little extra vero board with short fly leads.
I have upped the PSU caps from 470 mfd to 1000 mfd and replaced diodes with BYT53. Also swapped out op amps TL01>OPA134 and 4580 > LM4562. I had these around...
What is the difference in operation when these devices are set to MC vs MM? Does an additional opamp section get used for MC or just the gain adjusted? I can figure out that the one set of links on the PCB brings in a 100 ohm resistor for MC loading. (I fitted cut up IC tulip socket here, so the link can be made with wire or a resistor that will be added to the 100 ohm allowing a bit more variance.)
Does the TL071 "cooling circuit" remain active for MC? What would be the best way to adjust load resistance for my Sumiko high output MC 2.5 mV? In previous set ups I got best sound when playing in to MM gain stages but set to a load of about 22K. Would I need to swap out the 47K resistor for a 22K one or can I add the MC load resistor + additional one as described above?
One thing nobody seems to have discussed is the silly PSU arrangement. I mean half wafe rectification for a device requiring clean smooth power. This imo seems to have been forced by wanting to use the std 16V project wall wart but still allow +/- 15V rails.
I suspect a serious upgrade for this unit would be an external DC supply with full wave rectifiers and say at least 4700 mfd smoothing per rail feeding the built in regulators.
I will probably also change the little 78L05 79L05 regulators for T0220 packages. In previous projects I have found these little regulators to restrict subjective dynamics. I may even run "zener set" 317/337 from a little extra vero board with short fly leads.
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