to dreamth
Excuse but I can't understand the diagram you sent
they are of another era.
I have done something with EMT phono and, for the time, they were very good.
But now is possible to get better results with different circuit.
At that time, due the use on broadcasting and the noise generated by turnatable, some aspect weren't considered in a phono circuit.
Now with the help of a very good quality of components we can reach a much better perfomances.
Walter
Excuse but I can't understand the diagram you sent
they are of another era.
I have done something with EMT phono and, for the time, they were very good.
But now is possible to get better results with different circuit.
At that time, due the use on broadcasting and the noise generated by turnatable, some aspect weren't considered in a phono circuit.
Now with the help of a very good quality of components we can reach a much better perfomances.
Walter
Thanks everyone for the comments. It's clear that I knew little about RIAA pre-amps when I started this post, and that it's a "shades of grey" topic with competing requirements and some pretty strongly held opinions.
I need to go away and think about it, but I think I can come up with a single board design that will allow most of the recommendations to be implemented. Nothing like actually building them. I'll update this post as I go.
I need to go away and think about it, but I think I can come up with a single board design that will allow most of the recommendations to be implemented. Nothing like actually building them. I'll update this post as I go.
There's alo true that you only need maybe 8 of them for a lifetime...They' don't get easily damaged unless some mechanical shock are applied, but you'd need more of them because you can hardly find two of them with close enough parameters.Usually people build more than just one phono preamp as you get different results with different tubes and topologies so you only need to start doing something.
The COVID lockdown in Sydney had given me plenty of time to think about RIAA circuits to go with the RedRoo SE amplifier at Tube - Valve Stereo Amplifier to Build Yourself | RedRoo Kits
I'm working on a pcb design where the input tube is mounted on a plug-in module, so I can easily try a number of different tube options.
* Each module can be configured for a number of similar tubes using solder links.
* Each module contains part of the input resistance to the RIAA network, so it can be trimmed to take into account the Ra of the tube used.
* I'm using an LED in the cathodes of the input tube to simplify the bias set-up.
* I'm using the passive RIAA calculator at Passive RIAA equalization network response calculator - diyAudio
I've attached the idea circuits below but the component values are best guesses at this stage. There are some things I'm not too sure about, like using the SMPS power supply - will the radiated noise at 40kHz be a problem? Time will tell.
Anyway, thought you might be interested. It may just workout...
I'm working on a pcb design where the input tube is mounted on a plug-in module, so I can easily try a number of different tube options.
* Each module can be configured for a number of similar tubes using solder links.
* Each module contains part of the input resistance to the RIAA network, so it can be trimmed to take into account the Ra of the tube used.
* I'm using an LED in the cathodes of the input tube to simplify the bias set-up.
* I'm using the passive RIAA calculator at Passive RIAA equalization network response calculator - diyAudio
I've attached the idea circuits below but the component values are best guesses at this stage. There are some things I'm not too sure about, like using the SMPS power supply - will the radiated noise at 40kHz be a problem? Time will tell.
Anyway, thought you might be interested. It may just workout...
you may wanna choose some resonant or semi resonant supplies, but your main contender will be mains hum comming from the turntable mains transformer or motor itself if not carefully shielded and you'll always need good iron shielding no matter what you do for supply when you deal with tubes and their relatively large spread area circuit so maybe a good toroid or R-core transformer and good shielding may actually be a simpler and better option : https://www.diyaudio.com/forums/tub...s-regulated-stabilized-psu-7.html#post6718948
If it was just for me, or just skilled people building it, I wouldn't hesitate using a transformer supply but commercial kitsets can be built by anyone with any skill level. I don't really fancy myself in a courtroom inquest having to explain the reason for someone getting fried.
The SMPS inverter only needs 12VDC into the equipment and a benchtop 12V DC power supply takes care of all the mains power safety and regulatory issues. Naturally the HT supply is still an issue but not as much as mains power entering the equipment.
Maybe I'm being overly cautious but I was in the electronics manufacturing business for over 40 years and know how the law works when things go wrong.
Very different if you're just building something for yourself.
The SMPS inverter only needs 12VDC into the equipment and a benchtop 12V DC power supply takes care of all the mains power safety and regulatory issues. Naturally the HT supply is still an issue but not as much as mains power entering the equipment.
Maybe I'm being overly cautious but I was in the electronics manufacturing business for over 40 years and know how the law works when things go wrong.
Very different if you're just building something for yourself.