Panasonic fc, fm works great with filtering any high slew rate op-amp...I actually use lots of old capacitors from scrapped industrial electronics and i had no problem with caps used for 10 years in heavy duty equipment if the capacitance value was within 5% -10% if the written value on them.
There are lots of other capacitors suitable for this project.
Nichicon muse kz, bp, ....fine gold are available and they are the best for signal coupling or low frequency filtering but honestly, i remember of not being able to hear any difference between some transistor based tone control Off or On coupled through usual Nippon Chemicon capacitors. in an old Realistic tuner with 40 years old capacitors...Then i read the technical review done in Holland on that particular Realistic and they were't able to measure any distortion caused by the entire tone section, let alone the coupling capacitors...
Myths have been debunked on a regular basis and that is why i love Diy audio.
Thanks for your suggestions, Dreamth
!The datasheets of these transistors don't either show that ominous rbb' parameter of the 2SD786 originals. Doesn't this matter?
Best regards!
The original 2sa1038 rohm datasheet shows 0.2db NF though...somebody measured them a while ago finding something like 2..10 ohms rbb.Thanks for your suggestions, Dreamth
The datasheets of these transistors don't either show that ominous rbb' parameter of the 2SD786 originals. Doesn't this matter?
Best regards!
The smd versions are indicated as replacements for the old 2sa1038, except the power handling.I had the old 2sa1038 which i found to be fantastic.Hopefully the newer ones are at least as good as the older ones.
Usual bc337/40 bc327/40 have about 40 ohms rbb...which doesn't sound bad at all...
Hi Guys, Although the Hifi World mod is widely known - I am not about to change components as I have no confidence in my soldering ability - at least not to the extent I would need to carry this out successfully. Instead I was considering maybe converting the RQ to a DC feed from a Low noise PSU or maybe changing the Transformer for a better quality toroidal. Has anyone done this? If so could they pass on their experience - Many Thanks
The toroidal transformer is supposed to be lower noise because the form contains magnetic flux better. I have used it successfully in many projects. Where did you read the statement you quote? Any link?
However, not all toroidal are created equal. I once got 2 toroidal on e-bay from a Chinese seller. It hums terribly. I have good luck with the toroidal, many of them, that I got from American manufacturer, Antek. All of them are quiet.
In the case of the Rotel RQ-970BX, the OEM transformer is already shielded and has plenty of space to the phono circuit. I do not see any reason to change it.
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I have no coomparative data myself, but I beleive the argument goes like:
The toroid transformer does contain the magnetic field better, so less risk of magnetic fields inducing noise in the electronics. Toroids also has a much greater frequency bandwidth thereby allowing more mains borne noise from other appliances in the house onto the internal supply rails of your amplifier.
Think electric motor brush-noise, hi frequency noise form SW mode PSUs etc.
In fact, over on the "Valves" forum you will find people using toroids as output transformers for small PP-amplifiers!
John Curl talks about it here on pages-8/9
https://www.parasound.com/pdfs/JCinterview.pdf
He makes an argument for EI-transformers with primary and secondary wound on separate separate bobbins for pre-aps and toroids for power amps.
The toroid transformer does contain the magnetic field better, so less risk of magnetic fields inducing noise in the electronics. Toroids also has a much greater frequency bandwidth thereby allowing more mains borne noise from other appliances in the house onto the internal supply rails of your amplifier.
Think electric motor brush-noise, hi frequency noise form SW mode PSUs etc.
In fact, over on the "Valves" forum you will find people using toroids as output transformers for small PP-amplifiers!
John Curl talks about it here on pages-8/9
https://www.parasound.com/pdfs/JCinterview.pdf
He makes an argument for EI-transformers with primary and secondary wound on separate separate bobbins for pre-aps and toroids for power amps.
Now, where did I find that...(?)
Hey Keilau, Yes, I hear you and at one time would have believed likewise but lately I have been looking at what makes the design of the preamp as a complete unit give the best result.
I am sure it was a recent thing I read, so i'll go back through my browsing history in the hope of finding it.
I'm doing mine up just now too.
Stay Safe,
Steve
Hey Keilau, Yes, I hear you and at one time would have believed likewise but lately I have been looking at what makes the design of the preamp as a complete unit give the best result.
I am sure it was a recent thing I read, so i'll go back through my browsing history
in the hope of finding it. I'm doing mine up just now too.
Stay Safe,
Steve
Thank you for the reference. I am in the process of building Wyn Palmer's MC phono stage. My plan calls for a toroidal based PSU in a separate box. I will need to change plan if it is not the right approach. However, in the John Curl interview you quoted, It seems to me that John believe toroidal has lower hum noise, but he worries about RFI in toroidal.
In the case of the Rotel RQ-970BX, the OEM transformer is already shielded D-core transformer and has plenty of space to the phono circuit. I do not see any reason to change it.Parasound John Curl Interview said:
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Agree
One beauty of DIY is that we can do whatever we want with whatever parts we have at hand! Transformer is only one part, there ere also input filtering/IEC sockets, Diode types, snubbers, regulator quality etc so nothing is carved in stone!
As for the HiFi-World upgrades: I would go ahead with replacing the output electrolytic as proposed and maybe put the decoupling capacitors on the reference diodes for the CCS of the input LTP.
For op-amps, I'm not sure the AD743/AD745 devices are still available in 8 pin DIP. Maybe OPA627 or OPA132 could be alternatives?
Also, at first glance, I see no reason for the input amp to be FET type as the input is already buffered by the LTP. Makes me wonder how for example an LT1115 would fare in this position. I guess High CMRR and low 1/f are important parameters here. Second stage Op-Amp is probably best served by J-FET type with low current noise and bias current due to the high 75K value of the series resistor forming the 2122 Hz LPF filter.
I am not convinced that increasing the current in the input LTP is a good idea if one is using an MM pickup. It may improve linearity and voltage noise spesifikasjons, but I suspect that the claimed S/N improvements for MM is with shorted inputs (not taking current noise in real life MM pickups into account).
Sorry that I did not make it clear. I am building Wyn Palmer's MC phono stage to replace the Rotel RQ-970BX which is a perfectly fine phono preamp.
The Rotel RQ-970BX input stage uses a pair of 2SD786 NPN bipolar which is an ultra low noise device designed specifically for head amp. It gives Rotel RQ-970BX very good noise performance in MC mode. I agree with you on not changing current on the input stage.
Replacing the AD744 with AD743 makes sense in the RIAA stage. AD744 is an improved 711 in settling time. But it is still not a good choice for audio application. A L1115 or LME49710 will be even better. But the SQ improvement is very subtle.
I absolutely again replacing the NE5534 with AD744. It will be a step backward. LME49710 is a good choice if you must substitute.
LJT - ThankYou! for that link to John Curl Interview. There are some really good design strategies in there! I will print that one out and put it with my library of other printout papers!
Keilau, Haven't been able to find where I saw the information on the Toroid. You building a MC Stage, that should be able to be fed into a MM Pre if you are building what I think you are..(?) When you get to Phono Stages, you aren't dealing with a very high powered signal. When you use a MC Cartridge, That signal becomes even more complex where any noise from your cables to power supply [why some prefer batteries!] to the layout of the PCB can all ruin your day! Just now looking at the Wyn Palmer project you've selected. Will try and have a good look over it! Enjoy your build! I am looking forward to see how it goes for you!
Keilau, Haven't been able to find where I saw the information on the Toroid. You building a MC Stage, that should be able to be fed into a MM Pre if you are building what I think you are..(?) When you get to Phono Stages, you aren't dealing with a very high powered signal. When you use a MC Cartridge, That signal becomes even more complex where any noise from your cables to power supply [why some prefer batteries!] to the layout of the PCB can all ruin your day! Just now looking at the Wyn Palmer project you've selected. Will try and have a good look over it! Enjoy your build! I am looking forward to see how it goes for you!
The Rotel RQ-970BX is a excellent phono preamp that outperforms the later offers from Parasound or NAD. In early 2019, I was looking for a DYI phono stage to build.
The Nelson Pass Pearl2 is very attractive but the complexity is not for beginner. The selection of parallel input transistors can be expensive and challenging. I found HynpoToad's AD797 based design but was disappointed that he would not share an schematic. I was looking for an op-amp based approach that is easy to build and have a high chance of success. But, as an principle, I will not build anything that the designer would not release the schematic for a DYI project. I almost gave up until I saw some comments by Wyn Palmer. He suggested some improvements of the AD797 based board. After some pledge, Wyn agreed to complete a new design with his upgrades and published it on AudioKarma. The thread is a joy to read. It already has many success build.
High gain opamp based preamp for low output MC cartridges. | Audiokarma Home Audio Stereo Discussion Forums
I started a thread here to alert people of Wyn's design.
https://www.diyaudio.com/forums/analogue-source/341287-gain-opamp-based-preamp-low-output-mc-cartridges.html#post5886653
Wyn Palmer and Scott Wurcer (Scott designed the AD797.) are both retired Senior Technical Fellow from Analogue Device. They are considered the pioneers of high performance op-amp for audio application. We are very lucky to have them on DIYAudio.
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Hey Kielau, I recommend some good reading of a design done here in Australia by a not too well known designer that has some fantastic kits 'with' schematics and lots of explanation and interesting things! Have a look: Project 187 As you scroll down the first page there is a very interesting list of common [to us!] IC's and the qualities we're after... some surprises there! Enjoy!!
Steve
Steve
The ESP (Elliot's Sound Project) is a well known and well respect website among DIYers. Their design varies from basic to very complex, but are always well engineered. Some project have PCB design and some do not. ESP was mentioned a lot on this forum.
The Project 187 is a head amp design. It confirmed the advantage of high end op-amp with a transimpedance input design (AD797 or LT1115) which are quite expensive in Australia. The NJM2068 is suggested as a lower cost alternative. Elliot tried other older op-amp too with limited success.
The NJM2068 is an excellent candidate for the Rotel RQ-970BX op-amp upgrade too. It is $0.60 per piece from Mouser in US.
I wanted to build a full Moving coil phono stage with RIAA equalization. Wyn Palmer's design is what a modern design should be. He shares a lot of design information that others do not offer. Besides the schematic, detail component BOM, build instruction, LTspice input file and detailed performance measurement are all readily available. Wyn Palmer's post on AudioKarma is a DIYer's dream come true.
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