Ultrasimple mm/mc RIAA preamp 2

[ra7]

I have the AN 8 drivers, >95 db, 2.5 W Miniwatt tube amp.

Cartridge is an old ADC QLM III... i don't know anything about that cartridge. I got it with the turntable. Is it time to upgrade?

I've heard better setups (my Dad has a nice Project turntable), and I don't think this cart sounds bad at all.

[ra7]

I tried measuring the Vds, but I can't get any sensible reading on the meter. Is there something I'm missing while making the measurements?

I'm measuring directly in the circuit, without any signal.

[Salas]

You look for DCV under 2k4 to earth. Is that ADC having something like 30, or 32, before MKIII? If yes then a 3g tracking force 7.8mV MM cartridge. Tell me, can you turn all volume up without clipping or not?

[Salas]

Originally Posted by ra7

I have the AN 8 drivers, >95 db, 2.5 W Miniwatt tube amp.

Cartridge is an old ADC QLM III... i don't know anything about that cartridge. I got it with the turntable. Is it time to upgrade?

I've heard better setups (my Dad has a nice Project turntable), and I don't think this cart sounds bad at all.

Hmm lets see. Right now you got 71dB system gain with 53dB phono and 18dB amp, you need 4.5V for 2.5W on 8 Ohm, 60dB would do with 5mV cart. Lets use 65dB to allow for peaks and quiter records. The changes in the attachment will get you there, will let THD calm down with the cart you have and help other matters too. Trimmer R9 to get 7.5V drain to ground. Trimmer R1 for the best sound you like in your system. You will not need output matching trimmers anymore.

[ra7]

Salas,
I do not know much the cartridge... sorry! Also, I do not want to turn up the volume
coz it will become too loud. Right now, I have it at about 12 o'clock on the miniwatt.
Guess that means the pre is giving too much gain. The miniwatt will deliver full 2.5W
for 500 mV input.

The circuit you are showing has a lot of differences from the one I am using.
I'm using the original circuit (attached).

I'll try yours and report back.

Btw, can you tell me how you measure Vds (simply stick the probes at the ends of the JFETS)? Also, what simulator are you using?

Thanks a million for your help.

[Salas]

So, you don't use the Madk? You use the one in the last pic above? Wait, I think I have it too. CM2000 is the sim. I am pretty sure about the models the betas etc I use for your circuit because I have ironed them out and comppared in practice for the many simplistics. Stay tuned.

[Salas]

Originally Posted by ra7

Salas,
I do not know much the cartridge... sorry! Also, I do not want to turn up the volume
coz it will become too loud. Right now, I have it at about 12 o'clock on the miniwatt.
Guess that means the pre is giving too much gain. The miniwatt will deliver full 2.5W
for 500 mV input.

The circuit you are showing has a lot of differences from the one I am using.
I'm using the original circuit (attached).

I'll try yours and report back.

Btw, can you tell me how you measure Vds (simply stick the probes at the ends of the JFETS)? Also, what simulator are you using?

Thanks a million for your help.

What you got right now is 51.2dB gain and about 1.8VRMS with 5mV average input. Too much for your amp, too much for a non degenerated Njfet second stage regarding THD. The MadK has better Riaa when fed by an accurate reverse Riaa model, yours is ''doctored''. It may be livening up your MM cart though. You must be having 4-5V Vds DC right now with 8mA Idss. Please check. Will see if we can soup up the one you use for your system. More in a while...

[Salas]

Originally Posted by ra7

I'll try yours and report back.

This one is based to what you got. I have used easy, standard values.
Much more compatible gain and output with 8mA Idss and MM, less thd, way to set the Vd to earth DC of your second stage between channels via R8 (also to match ACmV out), along some little Rs degeneration to bring it under control. Stage psu decoupling. Much better Riaa, better it not be doctored as in the original, use your input 100k trmmer load to find your preferable tone with MM carts. Its drastic and handy.

[ra7]

Salas,
thanks for all your time!!!!! Really appreciate it.

For some reason, the 9V battery stack had dropped a lot of voltage over the past three four days. They total voltage was at 20 V. With that, the Vds was about 1 V. I put new batteries and now the voltage is at 23.9V.
Vds for one channel reads 4.8V and for the other is 4.9V.

[Salas]

Originally Posted by Salas

You must be having 4-5V Vds DC right now with 8mA Idss. Please check.

Originally Posted by ra7

Vds for one channel reads 4.8V and for the other is 4.9V.

So we simulate well, be confident. Tune up to what I have given, its easy with what you got, and let us know. I consumes less battery life too. Next you make yourself a shunt reg.