This is a project that started a litte over year ago.
Plenty of brainstorming (mainly with designer Salo who seems to write in here also) and any many prototypes later there is a 10 tube riaa with quite nice performance.
I was about to create a blog about the riaa in here but I do not find a way to make it so I just start a new thread.
The amp has four stages for voltage gain and a cathode follower as last stage to lower output impedance. RIAA filtering is made in separate stages. Voltage gain at 1kHz is over 1000 an is adjustable to match cartridges of different output levels.
Plenty of brainstorming (mainly with designer Salo who seems to write in here also) and any many prototypes later there is a 10 tube riaa with quite nice performance.
I was about to create a blog about the riaa in here but I do not find a way to make it so I just start a new thread.
The amp has four stages for voltage gain and a cathode follower as last stage to lower output impedance. RIAA filtering is made in separate stages. Voltage gain at 1kHz is over 1000 an is adjustable to match cartridges of different output levels.
Let's take a look of screenshot taken of LT-spice simulation.
Sweep is 5Hz to 30kHz and y scale only 0.1dB
Sweep is 5Hz to 30kHz and y scale only 0.1dB
An externally hosted image should be here but it was not working when we last tested it.
It seems that iCloud is not willing to share the picture of simulation here so I try Google.
An externally hosted image should be here but it was not working when we last tested it.
Fed with accurate inverse-riaa voltage source the output stays in +-0.05dB in simulation.
6S3P-EV tube has about 0.75uV noise on gate compared to other high-gain triodes like 12AX7 ... 1.5uV. The amp is very quiet and works just fine with Benz micro silver cartridge ... nominally 2mV ... without a step-up transformer.
The first prototype has been running since march 2020 and I assume most of of the troubles .. mainly heat-related have been found and fixed.
I will assemble another one and as proceeding ... provide step-by step instructions how to make one.
6S3P-EV tube has about 0.75uV noise on gate compared to other high-gain triodes like 12AX7 ... 1.5uV. The amp is very quiet and works just fine with Benz micro silver cartridge ... nominally 2mV ... without a step-up transformer.
The first prototype has been running since march 2020 and I assume most of of the troubles .. mainly heat-related have been found and fixed.
I will assemble another one and as proceeding ... provide step-by step instructions how to make one.
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This week I'm putting together the powersupply for RIAA.
It has two pieces Meanwell LRS-75-12 .. the first one is adjusted to 12.6V to feed heaters. The other one is connected to non-isolated step-up transformer to make 250V for anodesupply.
It has two pieces Meanwell LRS-75-12 .. the first one is adjusted to 12.6V to feed heaters. The other one is connected to non-isolated step-up transformer to make 250V for anodesupply.
You won't be able to filter those high frequency distortions from the Meanwell switching power supply out of your circuit. This will massively worsen the results in sound.
I would never put such a bad thing into any of my analog tube amps.
The only advantage I see is in the low price. But for that, I wouldn't choose to put the energy and effort in realisation of such a project. If you want it cheap, buy a cheap asian kit tube preamp. Thats real cheap. To design ones own tubeamp with much effort and to use cheap switching power supplies makes really no sense to me. But people are just different in their goals in audio. To me, good sound is the goal with such a project, that no other amp could provide.
I would never put such a bad thing into any of my analog tube amps.
The only advantage I see is in the low price. But for that, I wouldn't choose to put the energy and effort in realisation of such a project. If you want it cheap, buy a cheap asian kit tube preamp. Thats real cheap. To design ones own tubeamp with much effort and to use cheap switching power supplies makes really no sense to me. But people are just different in their goals in audio. To me, good sound is the goal with such a project, that no other amp could provide.
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Then further ... tested dcok- circuit with adjustable voltage source before mounting it in actual powersupply. The purpose of dcok is to provide tubes 45sec to heat up before opening the output-shorting relay on riaa pcb. If voltage is suddenly dropping the outputs of riaa are quickly shorted to avoid damaging power-amp and/or speakers.
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Heater supply is adjusted 12.65V and step-up converter's poor quality trimmerpot is replaced with suitable resistor ... I chose 3500ohms to get 244V. The step-up and clc/lcl filters are found in ebay. The filter for heaters must be checked to withstand needed current without overheating. Some filters promise 6A but are actually boiling with 1.5A
No connection between heater-negative and anodesupply-negative is made here. They must go with separate wires all the way to riaa pcb where heaters are connected to gnd.
No connection between heater-negative and anodesupply-negative is made here. They must go with separate wires all the way to riaa pcb where heaters are connected to gnd.
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...and pretty uneconomical, too. Passive EQ most often sounds pretty lame. Not my cup of tea circuit. Could be done much smarter.
Hi Depanatoru
The riaa has four stages of amplification ... but cathode resistors are not passed with capacitor so gain ain't so astronomical as expected. .. max gain at 1 kHz is 1250.
Before the last voltage gain stage .. there is a 47k potentiometer to adjust gain.
This passive-stage riaa can be used with cartridges outputting 1mV to at least 6,5 mV (tested). It is good to have plenty of gain to match the outputlevel of cdplayers and DAC's.
The riaa has four stages of amplification ... but cathode resistors are not passed with capacitor so gain ain't so astronomical as expected. .. max gain at 1 kHz is 1250.
Before the last voltage gain stage .. there is a 47k potentiometer to adjust gain.
This passive-stage riaa can be used with cartridges outputting 1mV to at least 6,5 mV (tested). It is good to have plenty of gain to match the outputlevel of cdplayers and DAC's.
Ready to be tested. I wanted to have a potential-free input to have same situation as with cartridge ... so the test signal is fed with Mac/HRT musicstreamer.
Then accurate inverse riaa by Reg Williamson ... improved by Jung and Lipshiz .. built to -60dB attenuation at 1kHz.
Musicstreamer is ouputting 2.30V so the RIAA stage is fed with 2.30mV at 1kHz when testing.
Audio analyzing is done with PC / Esi Juli / Right Mark Audio Analyzer at 96kHx sampling rate.
RIAA's gain is adjusted to about -1dB when setting levels for RMAA.
Then accurate inverse riaa by Reg Williamson ... improved by Jung and Lipshiz .. built to -60dB attenuation at 1kHz.
Musicstreamer is ouputting 2.30V so the RIAA stage is fed with 2.30mV at 1kHz when testing.
Audio analyzing is done with PC / Esi Juli / Right Mark Audio Analyzer at 96kHx sampling rate.
RIAA's gain is adjusted to about -1dB when setting levels for RMAA.
