The simulator shows that you can try 7mA BL with no source resistor and 24V B+, 2K4 Rd. I did it because I know that people will not find GR as easy as BL, and the latter averages 7-8mA Idss. Use no higher!
The lower the Idss the more Vds on a given resistor, you can increase the Rd a little and go 11V as in the original, when using 4mA GR.
You can fine tune by ear, many options, depends on system and taste.
Also the nF value caps need measuring so to know their real value. Broad 1dB lifts or cuts are very audible.
Those things refer to the original Pacific.
The lower the Idss the more Vds on a given resistor, you can increase the Rd a little and go 11V as in the original, when using 4mA GR.
You can fine tune by ear, many options, depends on system and taste.
Also the nF value caps need measuring so to know their real value. Broad 1dB lifts or cuts are very audible.
Those things refer to the original Pacific.
Talking about the Salas Riaa now? If talking about the Mad-K, bigger cap is ok if that is your best quality, but changing the resistor changes the load impedance that the Riaa network sees. If not too drastic a change, say go down to 1Mega, that I recommend for stability with BLs, it will not change appreciably.
Re: ultrasimple mm/mc riaa preamp 2
Just finished and installed a discrete ouput stage on my CDP using fet´s.... sound is unbelievably good.... So I searched for a RIAA with fet´s and found your juicy thread.
Can you provide a PCB for this design ?
I would really apreciate this because I am not a electronics wizz and need all the help you can provide.
Best regards
Ricardo
Hi Mad KMad_K said:
Well, enough rambling; do yourself a favour and try this circuit!
Just finished and installed a discrete ouput stage on my CDP using fet´s.... sound is unbelievably good.... So I searched for a RIAA with fet´s and found your juicy thread.
Can you provide a PCB for this design ?
I would really apreciate this because I am not a electronics wizz and need all the help you can provide.
Best regards
Ricardo
Cascode
You guys really should try cascoding this thing. It really elevates this beatiful little pre to compete with most circuits out there. I agree, when doing the "simple version" P2P is the way to go! When you start cascoding and buffering etc it is often more convenient to have a pcb. I have previosly built versions with 10 transistors/channel. The current version uses 6 transistors/ch. If I should redesign it today, I would probably go with 4 transistors/ch (2 fet + 2 bipolar in cascode)
I was forced to try a new picup recently (My Clearaudio Virtuoso was killed). As a temporary solution I bought the Denon DL160 as it seemed a good value (about 4 times cheaper!) and good match for my Clearaudio Solution/RB250/JFET phono rig. And it works extremely well. It is not as hyper-detailed as the Virtuoso, but has a more balanced sound, with great musical enjoyment. The DL160 stays, and I'm spending all the $$$ saved on records instead!
You guys really should try cascoding this thing. It really elevates this beatiful little pre to compete with most circuits out there. I agree, when doing the "simple version" P2P is the way to go! When you start cascoding and buffering etc it is often more convenient to have a pcb. I have previosly built versions with 10 transistors/channel. The current version uses 6 transistors/ch. If I should redesign it today, I would probably go with 4 transistors/ch (2 fet + 2 bipolar in cascode)
I was forced to try a new picup recently (My Clearaudio Virtuoso was killed). As a temporary solution I bought the Denon DL160 as it seemed a good value (about 4 times cheaper!) and good match for my Clearaudio Solution/RB250/JFET phono rig. And it works extremely well. It is not as hyper-detailed as the Virtuoso, but has a more balanced sound, with great musical enjoyment. The DL160 stays, and I'm spending all the $$$ saved on records instead!
Re: Cascode
Hello Mad_K
I use it too. In my system 40 dB are OK for the Denon DL-160. Its 2.2mV actually. I agree with your subjective impression, a very potent cart, and in a really accessible price. No terrible fear for the odd tip destruction or wear.
What is your subjective impression for cascoding with bipolars? Makes it more precise with stronger upper bass? My impressions are mainly such, for tube+tube and Jfet + bip. But sometimes I perceive some ''mechanical'' stability too. Depends on details.
I simulated 2 cascoded versions. One 40dB for circa 2mV high MCs like Denon and the like, and one 52dB for the large normal MC group of 0.4mV to 0.6mV. What do you think that it must be done differently in your experience?
Thank you in advance
Mad_K said:You guys really should try cascoding this thing. It really elevates this beatiful little pre to compete with most circuits out there. I agree, when doing the "simple version" P2P is the way to go! When you start cascoding and buffering etc it is often more convenient to have a pcb. I have previosly built versions with 10 transistors/channel. The current version uses 6 transistors/ch. If I should redesign it today, I would probably go with 4 transistors/ch (2 fet + 2 bipolar in cascode)
I was forced to try a new picup recently (My Clearaudio Virtuoso was killed). As a temporary solution I bought the Denon DL160 as it seemed a good value (about 4 times cheaper!) and good match for my Clearaudio Solution/RB250/JFET phono rig. And it works extremely well. It is not as hyper-detailed as the Virtuoso, but has a more balanced sound, with great musical enjoyment. The DL160 stays, and I'm spending all the $$$ saved on records instead!
Hello Mad_K
I use it too. In my system 40 dB are OK for the Denon DL-160. Its 2.2mV actually. I agree with your subjective impression, a very potent cart, and in a really accessible price. No terrible fear for the odd tip destruction or wear.
What is your subjective impression for cascoding with bipolars? Makes it more precise with stronger upper bass? My impressions are mainly such, for tube+tube and Jfet + bip. But sometimes I perceive some ''mechanical'' stability too. Depends on details.
I simulated 2 cascoded versions. One 40dB for circa 2mV high MCs like Denon and the like, and one 52dB for the large normal MC group of 0.4mV to 0.6mV. What do you think that it must be done differently in your experience?
Thank you in advance
Attachments
Yes. Whose word is out? I'd like to see the comparison, though I'd have to admit that a biploar with a few mA through it may be a stiffer voltage source than a JFET due to the higher transconductance. The difference may not mean that much at the low signal levels involved in the first stage, where the cascode will really make a difference, especially with a high inductance MM cartridge. The fet doesn't seem to suffer too much in simulation, though I admit I haven't made a direct comparison between the FET and bipolar. One thing I will say, though - you need to select a top JFET most carefully. The PN4391 has a high enough IDSS and pinch-off voltage such that the 2SK170 below it isn't voltage starved, and has a Vd of 4-5V. This may not be true of other JFETs tried this way.
In old threads, Werner, and Thorsten said that the bipolar on top sounded better in their circuits. If I remember correctly.
I would be preferring the all Jfet solution aesthetically too, but I trust those guys. Mad_K said BP in his above comment too. Maybe he will enlighten us further.
If I will be tweaking some Riaa I would like to do the comparison myself too.
I don't know about PN parts in Europe, have to look. The part you suggested has very strong Idss and high Vp, probably works like a high Beta bipolar, plus simpler (no resistors like in bp's base) but not really something good can be done with parts like 2N5459 on top of BL, with 2-3V Vp and 6mA Idss average...
I also wonder if the voltage divider for biasing the bipolar adds noise, especially in first stage.
I would be preferring the all Jfet solution aesthetically too, but I trust those guys. Mad_K said BP in his above comment too. Maybe he will enlighten us further.
If I will be tweaking some Riaa I would like to do the comparison myself too.
I don't know about PN parts in Europe, have to look. The part you suggested has very strong Idss and high Vp, probably works like a high Beta bipolar, plus simpler (no resistors like in bp's base) but not really something good can be done with parts like 2N5459 on top of BL, with 2-3V Vp and 6mA Idss average...
I also wonder if the voltage divider for biasing the bipolar adds noise, especially in first stage.
For grins, I did a simulation of a simple cascoded common source stage using a 2SK170 set up for a gain of about 40X, what I would use as the front end for a MM preamp. I tried a JFET cascode and a bipolar cascode, making sure that the drain voltages for the 2sK170 were similar for the two cases. The results are interesting. THD is about the same, but the harmonic distributions are different. Attached are the JFET cascode results:
Attachments
Next is the bipolar simulation. One could quibble all day long about the validity of the precise values for the harmonic spectrum and come out no wiser. I find it interesting that the two results were different, and wonder if there is any real-world impact. I've also been doing some simulations lately with Werner's folded cascode circuit, and found that it was important to allow proper breathing room (read sufficient VDS) for the input JFET. When properly implemented, the results go from a lackluster 0.4% THD to 0.002%. Maybe that's the lesson here, as well.
Attachments
wrenchone said:
In my two circuits posted above, I have allowed just a touch lower than 8V VDS for the 2SKs. Just ok for them I have concluded by experience. Enough working frame, & steady operation just before their drain gate leakage onset. Can use high input impedance for the second stage that way with a highish Riaa impedance so there is no appreciable strain that leads to buffers usage. I keep it simple.
It may be very tempting to patch everything up to best measures on the sim, but in real life I could clearly hear just one 100 Ohm gate stopper on first stage damping the dynamics of a low Z, low out Ortofon MC, in my Riaa. Its just a stopper? Arguably no, if it dwarfs the tiny Z of the source. In a tube line stage is innocuous by comparison. Such Riaa circuits must be made tight and with lowest part count possible, judged step by step by ear IMHO.