these posts remind me that once i hooked mine up and started listening, i forgot to come back and give my comments
it's great!
i think it sounds superb with both my old Shure V15 MR and AT-440MLa catridges
thanks, PMA!
mlloyd1
Michael, thanks for your feedback. I am glad you are satisfied.
i will eventually, but i have other projects in the fire for the near future.
in spite of it's age and comments to the contrary in the last several years, the OPA627 is still after all these years a very good op amp when correctly applied.
i suspect the OPA827 is also. but i think in my application, lower noise than OPA627 is lower priority.
mlloyd1
in spite of it's age and comments to the contrary in the last several years, the OPA627 is still after all these years a very good op amp when correctly applied.
i suspect the OPA827 is also. but i think in my application, lower noise than OPA627 is lower priority.
mlloyd1
Thanks Marra, up close it looks like a bit of a dog's breakfast! 
When testing and setting up the regulators I think I used a 100R load, though it's been a while. I might have started with twice that just to get the voltage set, then increased the current draw for more realistic conditions. I spent quite a bit of time adjusting the CCS current-setting resistors to get the same shunt current on both rails. I started with 10R, then added 15R in parallel, which got the positive supply to about 280mA. To get the negative rail to the same shunt current I had to add a third resistor of 8R2.
The raw DC supply uses a 6A filtered power inlet (because I could get them cheap, not because I thought I needed 6A!). That feeds a 36V center-tapped 56VA transformer. The bridge is made from 4 MUR820's (bolted to the chassis). Each rail goes through a 0R2 wirewound resistor to the first 4700uF cap, then a 10R wirewound to the next 4700uF cap, then out. The center tap is connected to the grounded chassis via 2 diodes, and to the caps and output through a heavy solid copper wire. A shielded cable carries the raw DC to the preamp chassis. It suplies a little over +/-20V, I don't remember the exact voltage. One nice thing about the shunt regulator is that it always consumes the same amount of current, no matter what the load, so the voltage drop over the supply filter resistors is consistent.
The chassis are anodized, but I ground off the anodizing on each end, and on the inside edges of the end plates, so they are electrically continuous.
Where the DC enters the regulator boards I have another 0R2 resistor, then another 4700uF cap. I guess it's all a bit over-built. The shunt MOSFETS run warm. I sort of had it in mind that I could use the raw supply, even in different configurations, for other projects, but it's all working so well I don't know if I can do that. The preamp is very quiet, and I have no doubt that the PSU contributes to that. The Salas SSLV regulator has been measured to have a very low output impedance throughout the audio band and beyond, and very low noise.
When testing and setting up the regulators I think I used a 100R load, though it's been a while. I might have started with twice that just to get the voltage set, then increased the current draw for more realistic conditions. I spent quite a bit of time adjusting the CCS current-setting resistors to get the same shunt current on both rails. I started with 10R, then added 15R in parallel, which got the positive supply to about 280mA. To get the negative rail to the same shunt current I had to add a third resistor of 8R2.
The raw DC supply uses a 6A filtered power inlet (because I could get them cheap, not because I thought I needed 6A!). That feeds a 36V center-tapped 56VA transformer. The bridge is made from 4 MUR820's (bolted to the chassis). Each rail goes through a 0R2 wirewound resistor to the first 4700uF cap, then a 10R wirewound to the next 4700uF cap, then out. The center tap is connected to the grounded chassis via 2 diodes, and to the caps and output through a heavy solid copper wire. A shielded cable carries the raw DC to the preamp chassis. It suplies a little over +/-20V, I don't remember the exact voltage. One nice thing about the shunt regulator is that it always consumes the same amount of current, no matter what the load, so the voltage drop over the supply filter resistors is consistent.
The chassis are anodized, but I ground off the anodizing on each end, and on the inside edges of the end plates, so they are electrically continuous.
Where the DC enters the regulator boards I have another 0R2 resistor, then another 4700uF cap. I guess it's all a bit over-built. The shunt MOSFETS run warm. I sort of had it in mind that I could use the raw supply, even in different configurations, for other projects, but it's all working so well I don't know if I can do that.
The preamp is very quiet, and I have no doubt that the PSU contributes to that. The Salas SSLV regulator has been measured to have a very low output impedance throughout the audio band and beyond, and very low noise.Thanks nezblue I;ve just to change a resistor in the adjust part of the regulator and I can get it set to 15/17v ready to use.As I have an 19ins case that I recently picked up for a good price I'll build in one chassis with the traffo at one end and the Openamp1 at the other.Guess I need to download the bom and place an order with Farnell.
I don't want to make this about voltage regulators, but I made a mistake in my last post. I reviewed my notes, and I used an initial 5R resistor for the current-setting resistors in the regulators, not 10R. So for the positive regulator R101 was 5R||15R, and for the negative rail R201 was 5R||8R2||15R. I wouldn't want anyone to try building it based on what I wrote above. Notice that that means a current-setting resistor for the negative rail around 2R5.
Yes, this regulator could safely power 3 of those boards! Some folks say that when the shunt MOSFETs are passing a considerable amount of current, the output impedance is lower and it "sounds better". So I have the constant current source set at about 280mA per rail. The regulator circuit itself will consume a few tens of milliamps, I'm not sure how much. The rest is shunted to ground less whatever is used by the Openamp board. It runs a little warm, but not too bad. Certainly the Openamp isn't putting any strain on it!
BOM, prices etc.
For those who are sending me requests to provide them with documentation, BOM, prices etc. - please consider that all this info is accessible from my webpage, Pavel Macura audiopage
Documentation and BOM is here:
Preamplifier for MM cartridge
prices:
http://web.telecom.cz/macura/pricelist.pdf
Thanks,
Pavel
For those who are sending me requests to provide them with documentation, BOM, prices etc. - please consider that all this info is accessible from my webpage, Pavel Macura audiopage
Documentation and BOM is here:
Preamplifier for MM cartridge
prices:
http://web.telecom.cz/macura/pricelist.pdf
Thanks,
Pavel
Labeling of this distributor:
CF3-1M0/J | GM electronic
You may use the caps as in the pdf attachment.
CF3-1M0/J | GM electronic
You may use the caps as in the pdf attachment.
Hi all, sorry I probably have forgotten to mention board dimensions. They are 100 x 134 (135) mm. Thanks Marra for posting the information here.
The boards dimensions should be measurable from manual, page 9, if it is printed as 1 : 1 (no scale for printer).
Unfortunately, all boards are sold out at the moment. I hope to repeat the production and distribution sometimes in future, when I get some time to do it again.
The boards dimensions should be measurable from manual, page 9, if it is printed as 1 : 1 (no scale for printer).
Unfortunately, all boards are sold out at the moment. I hope to repeat the production and distribution sometimes in future, when I get some time to do it again.