Mmmm - your maths differs to mine! 😵
0.34mV (340 uV, as you say) is a typical LOMC output. But 0.34mV x 1000 x 10 (for HFs) x 10 (for transients) = 34v.
And passive RIAA loss is 20dB (ie. reduced to 1/10th) in my experience - not 40dB (1/100)??
You usually have a level control somewhere in the signal chain. The important thing is to ensure the stages before the level control never overload and that is a relatively easy problem to solve, especially with all-active RIAA where >30 dB ref 5 mV is achievable, but even active- passive will get you 15 dB O/load at HF.
Sure, "somewhere in the signal chain" - but when do you have a volume control in a phono stage?
Sure in a preamp - but the phono stage preceeds this and generally just amplifies the cart input signal ... without any attenuation.
Hello,
Our maths are same, you just added x10 overload margin 🙂.
Look, I'm using this https://www.diyaudio.com/community/...eded-with-motor-and-drive.412984/post-7688045 for 25 years, no problem.
This is because there is no full signal recorded at such high frequencies. Even 60db gain allows to record it fully, but not for overload margin of 10.
If there would be such signal, imagine what would happen? Can you imagine maximum possible system signal in last octave, same power as in mid bass??? Burning tweeters, ears, birds falling dead, dogs running away in agony 🙂 🙂 Tinitus for everybody 😎
Here the math did not work. Look closely; RIAA 0 level is at 1khz, all ok. Highs are recorded 20db over that, so +20db (they need 20db cut to equalize). Lows are recorded -20db (so they need boost of 20db to equalize).
Now, in passive Riaa equalizer, we cannot boost, only cut..... So we must bring everything back to bass octaves level. In our case of 0.34 mV output at 1000hz that is just 0.034 mV.
So highs are cut with 40, and mids with 20db, so all is equalized on bass level... does it help?
A phono stage almost never passes on to a line preamp and then power amp without some sort of level control in the signal chain - normally on the input to the line level preamp. The recording I put up the other day was with the volume control at max and the gain from the MC input to the power amp output was 94 dB. I cannot imagine listening to music with that much signal chain gain without a level control, can you?
Hi Bonsai,
I think Andy is talking about overloading preamp in HF before RIAA cut, (which in theory is possible, but in practice not really....)
I think Andy is talking about overloading preamp in HF before RIAA cut, (which in theory is possible, but in practice not really....)
Regarding testing preamp, continuation from yesterday post #115:
I contemplated on this bit more, and my conclusion is that it will not be neither easy neither faithful to try to copy signal coming from cartridge by whatever signal generator. I think measurements should be done by using TT as signal generator, and soundcard like RME that I have is good for other (receiving ) end.
So the test record is needed! As side effect that will also help with cart-arm setup.
Quickly I stopped at my favorite hifi shop and they only had Ortofon test LP, this record has sweep and 1kHz spot frequencies, but doesn't have pink noise , neither other spot frequencies. I think that all is needed to get picture complete.
What is your recommendation for test record, I am going to get one, but witch one? CH precision one mentioned earlier I cannot find.....
Another off subject, I was looking for test LP and returned back with this.... Discussion started immediately as I entered the shop, as usual, 5 min become 30 min and guy that was in the shop sold me them, 400€, me being sucker on vintage audio couldn't refuse. If I don't come back on this post, it means wife shoot me dead (and I deserve it!)
I contemplated on this bit more, and my conclusion is that it will not be neither easy neither faithful to try to copy signal coming from cartridge by whatever signal generator. I think measurements should be done by using TT as signal generator, and soundcard like RME that I have is good for other (receiving ) end.
So the test record is needed! As side effect that will also help with cart-arm setup.
Quickly I stopped at my favorite hifi shop and they only had Ortofon test LP, this record has sweep and 1kHz spot frequencies, but doesn't have pink noise , neither other spot frequencies. I think that all is needed to get picture complete.
What is your recommendation for test record, I am going to get one, but witch one? CH precision one mentioned earlier I cannot find.....
Another off subject, I was looking for test LP and returned back with this.... Discussion started immediately as I entered the shop, as usual, 5 min become 30 min and guy that was in the shop sold me them, 400€, me being sucker on vintage audio couldn't refuse. If I don't come back on this post, it means wife shoot me dead (and I deserve it!)
55-60 dB is the normal gain range for an MC input to phono stage output. The MC amp is usually flat and the EQ stage follows that (most designs are like this). 60 dB on 500uV is 500mV. But, it’s very easy to have some gain adjustment in the phono MC+MM part before you get to the level control.
Yes on 1kHz, on 20kHz is 5V. But as i tried to elaborate earlier, also that is neither a problem, neither ever happens 🙂
I prefer
Isobarik clones by KEF!... ouch!....nice!... This reminds me of the time I purchased stacked Quad 57's that blocked out the sun from our living room. I had to promise my wife I would attend regular meetings of "Audio Addictions Anonymous".
I am currently using a single stage multiple feedback loop active RIAA feedback network, this being fed from the GyroHead. This was specifically designed for the Denon 103R, producing maximum signals around 8V RMS when playing records. This "single" stage consists of three cascaded operation amplifiers in an overall feedback loop, an input integrator addressing the need for a 2122 Hz pole, followed by ~x10 amplifier and a unity gain buffer with overall loop feedback controlling the gain and the 50/500Hz pole.
What this means is that the output of the input stage (although an open loop integrator on its own) ultimately has flat frequency response with feedback applied, having an output of ~1/10 of the overall output, hence about 800mV RMS. This supports good input overload as well as high frequency filtering (RF) (because of the direct input integration) beyond frequencies produced by the cartridge alone, and a reasonable compromise between noise and distortion being around 800mV RMS. A triple stage network also provides an ability to regulate down and clean the input stage supplies (currently an LT1115 device). In practice from +/- 15 volts to +/- 12 volts.
Supplies are critical to performance. This is why I began with floating Lithium Manganese Dioxide batteries (very low noise) in a differential amplifier configuration (suppressing battery noise further by CMR), being coupled to an input amplifier with zener shunt supply being fed from LM317LM337 based supplies. As the signal level increases by successive stages the absolute noise becomes less critical, rather the focus becomes more of noise management. This is particularly the case for high frequencies and instabilities that may not appear on measurement instruments.
What this means is that the output of the input stage (although an open loop integrator on its own) ultimately has flat frequency response with feedback applied, having an output of ~1/10 of the overall output, hence about 800mV RMS. This supports good input overload as well as high frequency filtering (RF) (because of the direct input integration) beyond frequencies produced by the cartridge alone, and a reasonable compromise between noise and distortion being around 800mV RMS. A triple stage network also provides an ability to regulate down and clean the input stage supplies (currently an LT1115 device). In practice from +/- 15 volts to +/- 12 volts.
Supplies are critical to performance. This is why I began with floating Lithium Manganese Dioxide batteries (very low noise) in a differential amplifier configuration (suppressing battery noise further by CMR), being coupled to an input amplifier with zener shunt supply being fed from LM317LM337 based supplies. As the signal level increases by successive stages the absolute noise becomes less critical, rather the focus becomes more of noise management. This is particularly the case for high frequencies and instabilities that may not appear on measurement instruments.
Hi,
Due to the RIAA preemphasis the highs are up to almost 20dB higher than the nominal signal level which is referenced to 1khz.
About +40-+50dB should be maximum for a first linear gain stage.
This should leave enough overhead to prevent the stage from clipping due to scratches, etc.
Then a passive filter might follow.
I prefer the 2120Hz LP only, but some like a full passive EQ here.
A second linear gain stage with a gain of +40dB (for a fully passive EQ-network) may follow ...
or a +20db@1kHz gain stage with the 50/500Hz EQ in the feedback ... which I prefer, as the splitting of the filters allows to optimize the filters for higher RIAA-precision and lower noise.
btw. John Lindsay Hood wrote a paper in the early 80s about this topology and came to the conclusion, that if the first gain stage can meet the criteria for noise and signal overload, than the split filtering --half passive - half active-- resulted in optimal signal conditioning.
jauu
Calvin
That is exactly the right thing for Pono playback. +60dB of linear gain is way too high.
Due to the RIAA preemphasis the highs are up to almost 20dB higher than the nominal signal level which is referenced to 1khz.
About +40-+50dB should be maximum for a first linear gain stage.
This should leave enough overhead to prevent the stage from clipping due to scratches, etc.
Then a passive filter might follow.
I prefer the 2120Hz LP only, but some like a full passive EQ here.
A second linear gain stage with a gain of +40dB (for a fully passive EQ-network) may follow ...
or a +20db@1kHz gain stage with the 50/500Hz EQ in the feedback ... which I prefer, as the splitting of the filters allows to optimize the filters for higher RIAA-precision and lower noise.
btw. John Lindsay Hood wrote a paper in the early 80s about this topology and came to the conclusion, that if the first gain stage can meet the criteria for noise and signal overload, than the split filtering --half passive - half active-- resulted in optimal signal conditioning.
jauu
Calvin
John Lindsay Hood had some nice designs and sold several kits back in the day (this was largely before those nasty op-amps came into universal being... though the SSM2019 looks really cool to try... and available at Digikey in a Dip8 too!... and just ordered... ).
Anyway, if you begin with an amplifier capable of 100dB open loop gain and set gain at 40dB the feedback is 60dB, meaning that for input signals from a MC in the order of 300uV this reduces the differential input signals to 300nV with feedback. For smaller input signals 60dB below 300uV this results in 300pV input differential. In contrast for an amplifier set for 60dB gain, the feedback is 40dB resulting in 3nV input differential for signals 60dB down.
The point being that there can exist significant extraneous circumstances that can influence the corruption of the differential signals across the inputs in high feedback ratio networks, hence can require extensive engineering prowess to gain advantage in doing so.
Anyway, if you begin with an amplifier capable of 100dB open loop gain and set gain at 40dB the feedback is 60dB, meaning that for input signals from a MC in the order of 300uV this reduces the differential input signals to 300nV with feedback. For smaller input signals 60dB below 300uV this results in 300pV input differential. In contrast for an amplifier set for 60dB gain, the feedback is 40dB resulting in 3nV input differential for signals 60dB down.
The point being that there can exist significant extraneous circumstances that can influence the corruption of the differential signals across the inputs in high feedback ratio networks, hence can require extensive engineering prowess to gain advantage in doing so.
Hi, so I'm still alive, got some moderate passive aggression about new old boxes, so far so good, but next days I must behave as she might come back to it.
But back to subject; trying to wrap up on the first stage gain, linear part before any EQ:
But back to subject; trying to wrap up on the first stage gain, linear part before any EQ:
- I see lot of disagreement on 60db (even I use it for quarter of century , but will not push more) . 40 to max 50db seems acceptable. I'm ok with that.
- I see no disagreement that first stage should not be "MC head" with just x10 gain, feeding complete MM preamp.
- I see no disagreement on completely passive EQ, might be just to take LF pole in second stage active. But this can still be left open.
On SSM mic preamps subject, I can say that I like SSM2017 very much, used in above mentioned 60db gain stage. SSM2019 has slightly worse characteristics on paper than predecessor (probably typical corporate improvement of manuf costs) but probably negligible.
Also I'm using PMI (Precision Monolithic INC) product, don't even have datasheet of that, just younger AD variation.
One more notice, before I got first real MC cartridge, I also tried SSM2017 (single unit, differential in - single ended out) on MM and high output MC. Frankly I think relic of NE5534 is better here. SSM is suited for lower source Z-s, but not for high...
I never used SSM2019, still I would recommend it as really good and quick way to the goal, very almost the same as 2017.
Regarding some short feedback discussion, these are not opamps. Whatever gain is set, differential signal on inputs will remain the same, as given by the source, pls check internal diagram:
But finally, I think earlier it was concluded they are not optimum, ever very very good, so I think we move on with discrete or hybrid first stage.
The above is a hybrid circuit used in the Rotel_rq970 dedicated phono stage. It has a passive 2122Hz interstage lowpass filter feeding a second stage active 50/500 network. If you are going with a hybrid it shows some frequency compensation components both in the forward and feedback paths. Somewhere there is a mod that replaces the input AD744 with an AD743. I believe they are both FET devices. It might give you some ideas in how you want to proceed.