Hi there..... for those interested..Since it has been published.........D Self wrote an interesting article in the J Audio Eng Soc Vol 35; No 11; 1987 Nov........ <Ultra low noise Amps and granularity distortion>. I don't have anywhere fast enough web connex to retrieve the material.
The servo loop biassing and multiple input tranny low noise building approach is technically the bestway...for a very low front end input...
rich
The servo loop biassing and multiple input tranny low noise building approach is technically the bestway...for a very low front end input...
rich
I have just built one of the LM833 app. note preamps, and it sounds just fine to me. I used OP275 op. amps., as they were the only low noise type I had. You can see a picture of my almost complete board here: http://stiftsbogtrykkeriet.dk/~mcs/Phono1_PCB_small.jpgSoundadvice said:
I did manage to get all the resistors in E-24 values and all the caps in E-12. The schematic with my values is here: http://stiftsbogtrykkeriet.dk/~mcs/Phono1_sch.gif
If anybody wants the PCB drawings (or a PCB) let me know.
Best regards,
Mikkel C. Simonsen
RJM Phono Preamp
Hi,
I built two of these about 1 year ago, one for MC and one for MM. The MC version has 40dB gain per buffer stage, battery powered. Don't claim they are best ever, but sound nice for the complexity and effort. Beats most commercial ones at the US$200 price tag.
http://www.geocities.com/rjm003.geo/rjmaudio/pho_a6.html
Opamps I used are AD797 for front, OPA637 for the rear, both biased in class A with a 2mA constant current diode between output and -ve rail. RIAA capacitors are MKP1837 1%, values recalculated from the Lipwitz paper.
Also built the version 3 of the Rod Elliot "Phono Preamp for All', which came originally from S. Bateman. Have more gain than the one above and actually sounded better for some cartridges. But I like the Buffer-Filter-Buffer configuration, rathar than RIAA on the feedback loop.
The next I am going to build would be JFET Class A, balanced output, no feedback, also buffer-filter-buffer. But many other projects planned before than (including turntable).
Patrick
Hi,
I built two of these about 1 year ago, one for MC and one for MM. The MC version has 40dB gain per buffer stage, battery powered. Don't claim they are best ever, but sound nice for the complexity and effort. Beats most commercial ones at the US$200 price tag.
http://www.geocities.com/rjm003.geo/rjmaudio/pho_a6.html
Opamps I used are AD797 for front, OPA637 for the rear, both biased in class A with a 2mA constant current diode between output and -ve rail. RIAA capacitors are MKP1837 1%, values recalculated from the Lipwitz paper.
Also built the version 3 of the Rod Elliot "Phono Preamp for All', which came originally from S. Bateman. Have more gain than the one above and actually sounded better for some cartridges. But I like the Buffer-Filter-Buffer configuration, rathar than RIAA on the feedback loop.
The next I am going to build would be JFET Class A, balanced output, no feedback, also buffer-filter-buffer. But many other projects planned before than (including turntable).
Patrick
Attachments
djaleksei said:
Hi there.....I doubt you will find the ideal transformer you are looking for....a low flux EI type(or toroid).....no-one really makes them anymore although a custom one-off wouldn't come cheap.
The drawback with the AES & R.I.A.A eq is it requires +18dB bass boost at 50Hz and poor layouts with bad wiring layout will find the stray 50/60Hz from elsewhere and not from the pickup. Ideally the juice should come from within the amp you are using via additional pass regulators so common mode intererence signals are cancelled out as part of equipment case and wiring. I found some time ago that a separate power supply put in a box just for mag or MC pickup eq's will create interference charge capacitive injection clicks through transformer windings or via earth returns. Remember ic regulators have a good ripple rejection spec....(better than discrete) and this is a good starting point....however these require short pcb layouts, thick tracks and short earths to obtain the full ripple rejection. So many designs go wrong due to excessive pcb track length.
I'm not a great believer in interwinding screens although for safety compliance they maybe required.
If you have to design with discretes....avoid toroid transformers.....high magnetising flux can create problems with ajacent wiring. Any transformer has to be some distance away from sensitive input circuitry.
rich
Re: lm833 phono
All the files are mirrored for printing on transparancies.
Regarding the transformer. I use a 12V AC wall wart transformer placed about 25cm away from the unshielded preamp board - and I have no hum problems...
Best regards,
Mikkel C. Simonsen
Thanks! You can find PCB files here (PDF): http://stiftsbogtrykkeriet.dk/~mcs/Phono1_PCB.zipbucurb said:
All the files are mirrored for printing on transparancies.
Regarding the transformer. I use a 12V AC wall wart transformer placed about 25cm away from the unshielded preamp board - and I have no hum problems...
Best regards,
Mikkel C. Simonsen
Transformer for Phono
My 2 cents' worth :
Don't waste time (and money). Just get yourself 4x 8.4V 250mAH NiMH's and done. Sufficient for 10 hours for most opamp circuits.
I have tried them all -- remote Cap Multipliers, LM317's, Jung Super Reg, Current sourced shunt regulator, .....
You saw what I am using after all that.
Patrick
My 2 cents' worth :
Don't waste time (and money). Just get yourself 4x 8.4V 250mAH NiMH's and done. Sufficient for 10 hours for most opamp circuits.
I have tried them all -- remote Cap Multipliers, LM317's, Jung Super Reg, Current sourced shunt regulator, .....
You saw what I am using after all that.
Patrick
I think this will be very difficult to do something better than Thorsten Loesch phono preamp. http://www.users.nac.net/markowitzgd/phonopre.html
I built one 2 weeks ago using exactly the components he recommends and 2 1.2 AH 12V lead batteries and it is just wonderful. The sound is great ! It makes wonders with my modfified TD 125 MKII.
Give it a try and I am sure you will not be disappointed.
And go for batteries. I can't see any reason not to use it. The sound is clearly better than with AC and it does not cost more.
It costs me around 30 € for the 2 batteries and the charger and for the value that is the best investment you can make.
I built one 2 weeks ago using exactly the components he recommends and 2 1.2 AH 12V lead batteries and it is just wonderful. The sound is great ! It makes wonders with my modfified TD 125 MKII.
Give it a try and I am sure you will not be disappointed.
And go for batteries. I can't see any reason not to use it. The sound is clearly better than with AC and it does not cost more.
It costs me around 30 € for the 2 batteries and the charger and for the value that is the best investment you can make.
Thorsten Loesch phono
For any phono preamp with the RIAA filter on the feedback loop, the gain tends to 1 instead of 0 at infinitely high frequency as stated in the RIAA correction. One can argue whether it makes a difference sonically or not. There are enough examples of both, so I am sure both can sound good.
For example the Pass DIY phono (Pearl), which is a later but simplified version of the Pass Aleph Ono, uses the Buffer-Filer-Buffer configuration, so does the Thel Phono preamp. The original Borbely phono uses filter on the feedback loop, but his latest design (starters kit) also offers the buffer-filter-buffer option.
Just an observation. The only way to find out is to try both and see what appeals to you sonically. (I did, of course.)
Patrick
For any phono preamp with the RIAA filter on the feedback loop, the gain tends to 1 instead of 0 at infinitely high frequency as stated in the RIAA correction. One can argue whether it makes a difference sonically or not. There are enough examples of both, so I am sure both can sound good.
For example the Pass DIY phono (Pearl), which is a later but simplified version of the Pass Aleph Ono, uses the Buffer-Filer-Buffer configuration, so does the Thel Phono preamp. The original Borbely phono uses filter on the feedback loop, but his latest design (starters kit) also offers the buffer-filter-buffer option.
Just an observation. The only way to find out is to try both and see what appeals to you sonically. (I did, of course.)
Patrick
Re: Re: lm833 phono
I'm kinda confused about how to get a V+ & a V- from the wall wart. I don't understand how to get the equivilent of dual secondaries from the wall wart.
Do I just take the wall wart output & let the regulator make the v+ & v-, am I just making this too hard??
thanks
Brett
mcs said:
I'm kinda confused about how to get a V+ & a V- from the wall wart. I don't understand how to get the equivilent of dual secondaries from the wall wart.
Do I just take the wall wart output & let the regulator make the v+ & v-, am I just making this too hard??
thanks
Brett
Re: Re: Re: lm833 phono
Best regards,
Mikkel C. Simonsen
You don't need two secondaries. Look at the schematic I posted. You use the positive halfwaves for V+ and the negative for V-.dieselpower said:Do I just take the wall wart output & let the regulator make the v+ & v-, am I just making this too hard??
Best regards,
Mikkel C. Simonsen
While reading threads at this forums I found this:
http://www.diyaudio.com/forums/showthread.php?postid=257653#post257653
"Op amps like AD797, LT1028 and LT1115 have very low voltage noise. However, they are all bipolar input op amps so they have a much higher current noise than, for instance, JFET input op amps. For MC, the source impedance is usually so low that the voltage noise is dominant, but for MM the source impedance is much higher so the current noise can cause a noise voltage many times higher than the op amps own voltage noise. Basically, check the current noise of the op amp and multiply with the source impedance and compare it to the voltage noise. That is somewhat simplified, but gives you the idea of how a particular op amp will perform."
So after looking into many datasheets I realised that the OPA627 has low voltage noise and a very low current noise, and I guess that this one will do just fine for my phono preamp (for MM pickup with 47Kohms)... but then I also found that many people say that this op amp does not sound nice... what do you think? Or maybe I could use the OPA627 as an input buffer without the RIAA eq. on the feedback, and then use just a very low voltage noise op amp like the LT1115 or AD797 for RIAA equalization? Thanks.
http://www.diyaudio.com/forums/showthread.php?postid=257653#post257653
"Op amps like AD797, LT1028 and LT1115 have very low voltage noise. However, they are all bipolar input op amps so they have a much higher current noise than, for instance, JFET input op amps. For MC, the source impedance is usually so low that the voltage noise is dominant, but for MM the source impedance is much higher so the current noise can cause a noise voltage many times higher than the op amps own voltage noise. Basically, check the current noise of the op amp and multiply with the source impedance and compare it to the voltage noise. That is somewhat simplified, but gives you the idea of how a particular op amp will perform."
So after looking into many datasheets I realised that the OPA627 has low voltage noise and a very low current noise, and I guess that this one will do just fine for my phono preamp (for MM pickup with 47Kohms)... but then I also found that many people say that this op amp does not sound nice... what do you think? Or maybe I could use the OPA627 as an input buffer without the RIAA eq. on the feedback, and then use just a very low voltage noise op amp like the LT1115 or AD797 for RIAA equalization? Thanks.
best phono preamp on ICs
Hi All,
One more design for consideration. Almost 20 years ago I built ETI-468MM two stage phono preamp. Although I built a number of other RIAA preamps afterwards (and before) I think the old ETI-468 has not yet still reached its potential.
The attached zipped MS Word file contains its schematics and design comments with my small modifications. It has been designed to minimise noise, impedance interaction between a cartridge and the preamp, and interaction between RIAA components. Anyway, as I said before it still can be tweaked but to make the best of this concept one must have a fully equipped electronic workshop (which I do not have except for the basics) and a lot of spare time and experience which I do not have either.
Consequently my economic mind (I am economist although I studied enginneering before I found how I would like to earn my everyday crust) tells me that all the sophisticated calcs and experiments are better left to electronic engineers and those with more equipment and experience.
So, here it is - the ETI-468MM design. See for yourself and say what you think about it and how one to tweak this design to the max.
Cheers,
Hi All,
One more design for consideration. Almost 20 years ago I built ETI-468MM two stage phono preamp. Although I built a number of other RIAA preamps afterwards (and before) I think the old ETI-468 has not yet still reached its potential.
The attached zipped MS Word file contains its schematics and design comments with my small modifications. It has been designed to minimise noise, impedance interaction between a cartridge and the preamp, and interaction between RIAA components. Anyway, as I said before it still can be tweaked but to make the best of this concept one must have a fully equipped electronic workshop (which I do not have except for the basics) and a lot of spare time and experience which I do not have either.
Consequently my economic mind (I am economist although I studied enginneering before I found how I would like to earn my everyday crust) tells me that all the sophisticated calcs and experiments are better left to electronic engineers and those with more equipment and experience.
So, here it is - the ETI-468MM design. See for yourself and say what you think about it and how one to tweak this design to the max.
Cheers,
zip file does not open
Hi Brett,
I have just unzipped it and opened the MS Word file and it's exactly the same as the original. Maybe your unzip program does not work properly. I have MS Windows 2000 and use WinZip to zip and unzip. If you do not succeed in opening it I can email you the original MS Word file. So if you need the original email me on:
janusz.pradzynski@dpi.wa.gov.au
It's my work place address. I'm going home in four hours and be back on Monday.
cheers,
Hi Brett,
I have just unzipped it and opened the MS Word file and it's exactly the same as the original. Maybe your unzip program does not work properly. I have MS Windows 2000 and use WinZip to zip and unzip. If you do not succeed in opening it I can email you the original MS Word file. So if you need the original email me on:
janusz.pradzynski@dpi.wa.gov.au
It's my work place address. I'm going home in four hours and be back on Monday.
cheers,
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