Hi,
I'm sure you know the huge phonoclone-Thread http://www.diyaudio.com/forums/showthread.php?s=&threadid=57398&highlight= concerning the fabulous design of rjm.
A few weeks back, I gave it a try and build it on veroboard. I noticed two things immediatly:
1) Resolution was quiet average.
2) Rhythm (be it transient response or whatever) was very, very good.
So I decided to squeeze some more performance out of this nice little circuit. The result, however, is not that simple (and not that cheap to build) as before.
Every now and then, I made some sims or put a scope at the circuit, but every step off from the original design was confirmed by close listening for a week minimum with various kinds of music, and most steps were taken back one or more times to confirm my listening impressions. Not all were beneficial, of course.
But let me describe the steps I took, at least the major ones.
1) Imagine my first version is rjm's original circuit, but build on veroboard and fired with lead acid batteries (+/- 12V)
My first change was to use the famous jung/didden super regulator with the AOS-boards.
What a difference! The soundstage was much more focussed, instruments have a defined and narrow place at the 'stage', the overall sound is much cleaner with tight and fast bass response. Going back to batteries made the sound muddy and fluffy.
2) Replacing the output cap with a servo loop needed a bit of tweaking. The shown values give the best results, I could only find them through listening, since the sim showed only very minor differences were the sound changed substantly (from unusable to very good) with different values for R9/R6. The bass sounds more tight and deeper, even compared to an 47uF foil cap from mundorf.
The mids and highs 'de-sweetened' with the servo, I found them much more real then. Overall, a big step forward.
3) Then I tried some fancy mod with a 'frozen cartridge', that is injected in the feedback path of the AD811, see
http://www.diyaudio.com/forums/showthread.php?s=&threadid=32318&highlight=
At first, I thought to hear a big increase of resolution, but several switches back and forth assured me that I most probably was fooling myself with wishful thinking. So, it stayed out.
4) Op-amp choice. That was the most surprising task, never would I have thought of the shown combination (AD811 as first stage, AD797 as second) as best possible! Which did I try?
At first, the OP27 of the second stage stayed. The AD811 was indeed the first I tried (due to the above linked thread), but I wasn't so sure, a bit better, but lacking something. The second best was the OPA627, which I found surprising as well (in this configuration). Very sweet highs, but a bit muddy in the lower mids.
I tried OPA604 (baaad...), LT1028 (doesn't work, just fancy noises), AD797 (Ok, but not without radio broadcast, and beneath OPA627 and AD811) and AD8761 (?) (nothing special). At this point, I would probably have stayed with the op27.
Then I checked 2nd stage (all of the mentioned ones in the first).
OPA627: boring! Somewhat extended highs, but fluffy. No punch either. OP27 is better here.
LT1028: way better, but way too soft as well. Choice between OP27 and 1028 would be a matter of taste.
OPA604: simply bad.
AD797: A true winner by a far margin! Endless Resolution, and rhythmycally involving. What a chip!
The first stages op-amp choice was a match between AD811 and OP627 then, because they were both good, but very differently sounding (not surprising, they are very different topologywise).
While the OPA627 has nicer trebles, the AD811 is more complete and a 'groove monster', so it was the winner after two weeks. Only thing I have to try is the AD844, but it hasn’t arrived yet. There are other CF-amps, but nearly all have way too much offset (and cancelling did affect the sound, if possible at all).
5) Class A biasing. The shown 4k are better than higher values, I did not go lower as the chip gets hot enough after a few hours. A more elaborate solution with res+FET sounded worse, so I did not try more fancy solutions with two FETs. The shown decoupling scheme for the AD811 lowers noise significantly when cart is connected and may sound a bit better, too.
I have attached the actual circuit and am looking forward to rebuild it nicely (groundplane, without IC-sockets and the like).
Feel free to comment or point me to a mistake if you see one.
thanks for reading,
Rüdiger
I'm sure you know the huge phonoclone-Thread http://www.diyaudio.com/forums/showthread.php?s=&threadid=57398&highlight= concerning the fabulous design of rjm.
A few weeks back, I gave it a try and build it on veroboard. I noticed two things immediatly:
1) Resolution was quiet average.
2) Rhythm (be it transient response or whatever) was very, very good.
So I decided to squeeze some more performance out of this nice little circuit. The result, however, is not that simple (and not that cheap to build) as before.
Every now and then, I made some sims or put a scope at the circuit, but every step off from the original design was confirmed by close listening for a week minimum with various kinds of music, and most steps were taken back one or more times to confirm my listening impressions. Not all were beneficial, of course.
But let me describe the steps I took, at least the major ones.
1) Imagine my first version is rjm's original circuit, but build on veroboard and fired with lead acid batteries (+/- 12V)
My first change was to use the famous jung/didden super regulator with the AOS-boards.
What a difference! The soundstage was much more focussed, instruments have a defined and narrow place at the 'stage', the overall sound is much cleaner with tight and fast bass response. Going back to batteries made the sound muddy and fluffy.
2) Replacing the output cap with a servo loop needed a bit of tweaking. The shown values give the best results, I could only find them through listening, since the sim showed only very minor differences were the sound changed substantly (from unusable to very good) with different values for R9/R6. The bass sounds more tight and deeper, even compared to an 47uF foil cap from mundorf.
The mids and highs 'de-sweetened' with the servo, I found them much more real then. Overall, a big step forward.
3) Then I tried some fancy mod with a 'frozen cartridge', that is injected in the feedback path of the AD811, see
http://www.diyaudio.com/forums/showthread.php?s=&threadid=32318&highlight=
At first, I thought to hear a big increase of resolution, but several switches back and forth assured me that I most probably was fooling myself with wishful thinking. So, it stayed out.
4) Op-amp choice. That was the most surprising task, never would I have thought of the shown combination (AD811 as first stage, AD797 as second) as best possible! Which did I try?
At first, the OP27 of the second stage stayed. The AD811 was indeed the first I tried (due to the above linked thread), but I wasn't so sure, a bit better, but lacking something. The second best was the OPA627, which I found surprising as well (in this configuration). Very sweet highs, but a bit muddy in the lower mids.
I tried OPA604 (baaad...), LT1028 (doesn't work, just fancy noises), AD797 (Ok, but not without radio broadcast, and beneath OPA627 and AD811) and AD8761 (?) (nothing special). At this point, I would probably have stayed with the op27.
Then I checked 2nd stage (all of the mentioned ones in the first).
OPA627: boring! Somewhat extended highs, but fluffy. No punch either. OP27 is better here.
LT1028: way better, but way too soft as well. Choice between OP27 and 1028 would be a matter of taste.
OPA604: simply bad.
AD797: A true winner by a far margin! Endless Resolution, and rhythmycally involving. What a chip!
The first stages op-amp choice was a match between AD811 and OP627 then, because they were both good, but very differently sounding (not surprising, they are very different topologywise).
While the OPA627 has nicer trebles, the AD811 is more complete and a 'groove monster', so it was the winner after two weeks. Only thing I have to try is the AD844, but it hasn’t arrived yet. There are other CF-amps, but nearly all have way too much offset (and cancelling did affect the sound, if possible at all).
5) Class A biasing. The shown 4k are better than higher values, I did not go lower as the chip gets hot enough after a few hours. A more elaborate solution with res+FET sounded worse, so I did not try more fancy solutions with two FETs. The shown decoupling scheme for the AD811 lowers noise significantly when cart is connected and may sound a bit better, too.
I have attached the actual circuit and am looking forward to rebuild it nicely (groundplane, without IC-sockets and the like).
Feel free to comment or point me to a mistake if you see one.
thanks for reading,
Rüdiger
Attachments
I have never thought of a cartridge as a current generator, some MM types might approximate that, but no MC types do. I would reconfigure as a normal non-inverting voltage amplifier. Note that the cartridge is being loaded into a virtual earth and I wonder what that is doing to the frequency response of the cartridge, not to mention its electromechanical damping. I assume this would seriously affect the Q of the mechanical system. I am not sure that is a good or bad thing, but different from what the cartridge designer had in mind.. 
MC typically have very low dcr so you would get a lot more gain, but the system would almost certainly be highly mechanically overdamped as the coils would be looking into a short circuit. This might not matter much in very low output mc due to their very low source impedances, but again I am not totally sure about this... Rationally speaking it seems like this might be appropriate for very low output mc types, perhaps better than some other possibilities.
It is generally not a bad idea to provide some voltage gain in the first stage as this helps to establish a good noise figure before you apply equalization using potentially noisy passive components.
I'm not too comfortable with the quality of this design, but I admit I design with op-amps all day long for ATE applications, no longer do audio design professionally, and use tubes for my own designs. This design strikes me as far from optimum, but YMMV.
One possible thought is you might want to try a two pole integrator in your dc servo. I have not had good results in the past with the single pole type. Stagger the values by about an order of magnitude, both poles can be relatively to extremely close together, try to taste.
Also I would use smaller value resistors in the servo divider back to the AD797, don't change the ratio..
The 2.21K resistor(s) contribute(s) almost as much noise as the input voltage noise of the AD797. The signal level at the output of the AD811 is going to be on the order of millivolts, certainly less than 100mV even at 20kHz with a typical MM cartridge with a dcr of say 600 ohms, so even a 221 ohm input resistor at the AD797 is not going to result in excessive currents and linearity problems.
I would scale the resistors and capacitors in the feedback network with an eye to reducing resistor johnson noise within reason. A 750K resistor will generate almost 100nVrtHz, and even though shunted at high frequencies it will generate low frequency noise. I would scale by at least an order of magnitude for low noise, but be cognizant of quality issues in the equalizer network capacitors.
edit: additional thoughts added
MC typically have very low dcr so you would get a lot more gain, but the system would almost certainly be highly mechanically overdamped as the coils would be looking into a short circuit. This might not matter much in very low output mc due to their very low source impedances, but again I am not totally sure about this... Rationally speaking it seems like this might be appropriate for very low output mc types, perhaps better than some other possibilities.
It is generally not a bad idea to provide some voltage gain in the first stage as this helps to establish a good noise figure before you apply equalization using potentially noisy passive components.
I'm not too comfortable with the quality of this design, but I admit I design with op-amps all day long for ATE applications, no longer do audio design professionally, and use tubes for my own designs. This design strikes me as far from optimum, but YMMV.
One possible thought is you might want to try a two pole integrator in your dc servo. I have not had good results in the past with the single pole type. Stagger the values by about an order of magnitude, both poles can be relatively to extremely close together, try to taste.
Also I would use smaller value resistors in the servo divider back to the AD797, don't change the ratio..
The 2.21K resistor(s) contribute(s) almost as much noise as the input voltage noise of the AD797. The signal level at the output of the AD811 is going to be on the order of millivolts, certainly less than 100mV even at 20kHz with a typical MM cartridge with a dcr of say 600 ohms, so even a 221 ohm input resistor at the AD797 is not going to result in excessive currents and linearity problems.
I would scale the resistors and capacitors in the feedback network with an eye to reducing resistor johnson noise within reason. A 750K resistor will generate almost 100nVrtHz, and even though shunted at high frequencies it will generate low frequency noise. I would scale by at least an order of magnitude for low noise, but be cognizant of quality issues in the equalizer network capacitors.
edit: additional thoughts added
Hi Kevin,
thanks for sharing your thougts. Let me respond to some of them.
1) lower load resistor for U1: I thought about it previously, and I will possibly try that later on. The feedback network of U2 would as well be lowered then to achieve the same gain. On the other hand, the light feedback loading may be one reason for the good sound. We'll see.
2) two pole integrator for servo: do you have an example? Are you simply talking of dividing up R9 and insert an additional cap? What benefit would you want?
3) Of course, I use a MC cart here. Though one with a low Z would probably be optimum, I use a Denon DL103 (~40Ohm) at the moment. When it comes to inverted topo, people say that carts that perform well with input transformers might perform well with this design. See my links for experiences of other people with this topology.
Rüdiger
thanks for sharing your thougts. Let me respond to some of them.
1) lower load resistor for U1: I thought about it previously, and I will possibly try that later on. The feedback network of U2 would as well be lowered then to achieve the same gain. On the other hand, the light feedback loading may be one reason for the good sound. We'll see.
2) two pole integrator for servo: do you have an example? Are you simply talking of dividing up R9 and insert an additional cap? What benefit would you want?
3) Of course, I use a MC cart here. Though one with a low Z would probably be optimum, I use a Denon DL103 (~40Ohm) at the moment. When it comes to inverted topo, people say that carts that perform well with input transformers might perform well with this design. See my links for experiences of other people with this topology.
Rüdiger
Hi Rudiger,
Just add a 100K resistor and 1.0uF cap ahead of the existing bias servo integrator and that should do the trick. Tweaking of values (aka tc's) might be necessary to retain the tight bass response you are looking for, overall subsonic behavior will be a lot better due to the steeper slope the 2nd order network gives you.
I have since looked at the other thread where the virtues of this approach are discussed so I have a better feel for the intent at least.
The DL-103 I suspect is a good match for this design, and probably any comparable transformer matched cartridges would work pretty well.
I am still curious about the effect of the virtual earth input (transimpedance amplifier) on the damping of the mechanical system. I wonder whether it tames the typical ultrasonic peak in the transfer function of mc type cartridges, I would assume it does..
I would also recommend taking a look at a combination of passive and active equalization in your next go around. The basic transimpedance concept is an interesting one, and suitable enough for low output mc cartridges..
Lots of interesting audio ideas have come out of MIT over the years, this phono stage concept, lightbulb based speaker protection (read simple compressor) and of course Dr. Bose
Just add a 100K resistor and 1.0uF cap ahead of the existing bias servo integrator and that should do the trick. Tweaking of values (aka tc's) might be necessary to retain the tight bass response you are looking for, overall subsonic behavior will be a lot better due to the steeper slope the 2nd order network gives you.
I have since looked at the other thread where the virtues of this approach are discussed so I have a better feel for the intent at least.
The DL-103 I suspect is a good match for this design, and probably any comparable transformer matched cartridges would work pretty well.
I am still curious about the effect of the virtual earth input (transimpedance amplifier) on the damping of the mechanical system. I wonder whether it tames the typical ultrasonic peak in the transfer function of mc type cartridges, I would assume it does..
I would also recommend taking a look at a combination of passive and active equalization in your next go around. The basic transimpedance concept is an interesting one, and suitable enough for low output mc cartridges..
Lots of interesting audio ideas have come out of MIT over the years, this phono stage concept, lightbulb based speaker protection (read simple compressor) and of course Dr. Bose
Hi Kevin,
1) The question of mechanical damping and its relevance to freq. response or other domains is behind my capabilities (I'm no EE or the like). What effects would you expect are present, at least potentially?
2) I sim'ed an elaborate servo loop, yes, the slope is steeper, but there is also a resonance area, don't know if it would affect the sound.
I think I have to try...
(don't mind different opamps here, they are just present to get the sim running)
1) The question of mechanical damping and its relevance to freq. response or other domains is behind my capabilities (I'm no EE or the like). What effects would you expect are present, at least potentially?
2) I sim'ed an elaborate servo loop, yes, the slope is steeper, but there is also a resonance area, don't know if it would affect the sound.
I think I have to try...
(don't mind different opamps here, they are just present to get the sim running)
Attachments
Hi Rudiger,
Your servo circuit is not quite what I had in mind when I suggested the change. Basically what you now have is an op-amp with an inverting gain of 2 and some frequency response shaping inside the loop.
I can well see why there is a huge resonance in the pass band and I expect the servo won't really work at all, overall gain including the attenuation at the op-amp input is far less than unity, for effective servo operation you want fairly high voltage gain.
Refering to your current schematic I would remove R10, this will restore the integrator loop gain.. Change R4 to 100K, C2 to 1.0uF, remove C5, and replace R9 with a short. This will give you the classical 2nd order integrator I was talking about, and should have very good subsonic behavior.
You don't need to use a laplace source to model the cartridge, just a simple voltage generator with a 40 resistor in series, unless you want to do eq which appears to be the case here.
I still recommend scaling the components in the feedback network to reduce johnson noise, reduce resistors to 0.1X current values, increase caps 10X for a worthwhile reduction in noise.
Your servo circuit is not quite what I had in mind when I suggested the change. Basically what you now have is an op-amp with an inverting gain of 2 and some frequency response shaping inside the loop.
I can well see why there is a huge resonance in the pass band and I expect the servo won't really work at all, overall gain including the attenuation at the op-amp input is far less than unity, for effective servo operation you want fairly high voltage gain.
Refering to your current schematic I would remove R10, this will restore the integrator loop gain.. Change R4 to 100K, C2 to 1.0uF, remove C5, and replace R9 with a short. This will give you the classical 2nd order integrator I was talking about, and should have very good subsonic behavior.
You don't need to use a laplace source to model the cartridge, just a simple voltage generator with a 40 resistor in series, unless you want to do eq which appears to be the case here.
I still recommend scaling the components in the feedback network to reduce johnson noise, reduce resistors to 0.1X current values, increase caps 10X for a worthwhile reduction in noise.
Hi Kevin,
Most probably, this fiddling with the servo is a bit overkill, but:
according to the sim, R10 dampens the 'spike' of the pole. The output network (R9/C5) should filter any potential audability of the servo further, but the integration is indeed affected above 1k, so I leave it out.
I will try other values for the riaa, but I have to order some parts first.
The plot is taken without R9/C5 but with R10, green is freq. response at output, blue is output of the servoamp
Rüdiger
Most probably, this fiddling with the servo is a bit overkill, but:
according to the sim, R10 dampens the 'spike' of the pole. The output network (R9/C5) should filter any potential audability of the servo further, but the integration is indeed affected above 1k, so I leave it out.
I will try other values for the riaa, but I have to order some parts first.
The plot is taken without R9/C5 but with R10, green is freq. response at output, blue is output of the servoamp
Rüdiger
Attachments
Hi Rudiger,
R10 reduces the loopgain to 2 which is why it damps the resonance, if this is a concern a very small amount of resistance in series with the integrator cap(s) will perform the same function and preserve the dc gain required for good servo operation. Squashing down that peak you see by using R10 is actually killing the dc response required for good servo action. Your FFT does not go down to dc, but essentially at 0 Hz an integrator provides gain equivalent to the open loop gain at dc. (Say > 100dB depending on op amp type)
A properly functioning servo loop is going to have what looks like a first or second order step in the response at the very bottom end near dc - this is actually necessary in order to have the high dc gain required for the servo, the integrator topology limits gain above dc as a function of the rc time constant. If you are having audible effects from the servo this means the overall time constant is too short. I think a tc upward of >1 sec is acceptable here.
The integrator time constant should be long enough to keep you out of trouble in the warp frequency range which means it should probably be 1Hz or less.
I understood the purpose of the additional low pass section on the output of the integrator, in this situation I don't believe you really need it, but it can't hurt either. What you want is a low noise op-amp in this location.
An OPA177 might be an ideal device for the servo integrator.
R10 reduces the loopgain to 2 which is why it damps the resonance, if this is a concern a very small amount of resistance in series with the integrator cap(s) will perform the same function and preserve the dc gain required for good servo operation. Squashing down that peak you see by using R10 is actually killing the dc response required for good servo action. Your FFT does not go down to dc, but essentially at 0 Hz an integrator provides gain equivalent to the open loop gain at dc. (Say > 100dB depending on op amp type)
A properly functioning servo loop is going to have what looks like a first or second order step in the response at the very bottom end near dc - this is actually necessary in order to have the high dc gain required for the servo, the integrator topology limits gain above dc as a function of the rc time constant. If you are having audible effects from the servo this means the overall time constant is too short. I think a tc upward of >1 sec is acceptable here.
The integrator time constant should be long enough to keep you out of trouble in the warp frequency range which means it should probably be 1Hz or less.
I understood the purpose of the additional low pass section on the output of the integrator, in this situation I don't believe you really need it, but it can't hurt either. What you want is a low noise op-amp in this location.
An OPA177 might be an ideal device for the servo integrator.
First, big thank you to onvinyl for going the extra mile to check out so many different ideas. Even the frozen cartridge. Wow... somebody actually went and did that! I hope we can now lay that myth to rest.
If the AD797 works for you, that's great. My only concern would be that the opamp is adequately bypassed at high frequencies. As it is a lot faster than the OP27 its probably going to need small ceramics in addition the electrolytics. See the AD797 datasheet for examples. You can also try decompensating it, again as per the datasheet.
The rest - superregs, servo and class A biasing - are all standard upgrades, they can be added on at will since the basic circuit isn't modified. If the sonic benifit is worth the expense and/or complexity, mod on!
Of the various points Kevinkr raised this is the only one of interest, as electrically the input stage is - or more correctly can be thought of as - an inverting voltage amplifier with the cartridge source impedance as the inverting resistor. It is not - or more correctly should not be analyzed as - an I/V converter. Refer to the Phonoclone homepage for more explanation on this point.
For the record the noise of the RIAA components as configured is too small to contribute anything to the total output noise. All the output noise comes essentially from the voltage noise of the first stage op-amp.
Mechanically, though, I admit that the cartridge is performing under rather different conditions than is usual. Its not a short circuit per se, as the internal impedance of the cartridge coils still act as a load. On average, I suppose its about 3 times smaller than the typical recommended load. (For the DL103, 40 ohms rather than 100+40=140 ohms) Note that in the case of the Denon, 100 ohms is only a minimum recommended value below which the rated voltage output is not obtained, not an absolute dictum from on high.
I have found that reducing the cartridge load used with the DL103 from 47k to 1k to 470 ohms, 100 ohms, and finally zero ohms (phonoclone), generally tended to fill in the bass and soften the treble. So yes, it could be that an ultrasonic peak is increasingly damped. That's complete speculation on my part, though, and to be fair the frequency reponse data that came with the cartridge showed no indication whatsoever of any rise up to 20kHz with a 1kOhm load.
The input configuration of the phonoclone is unconventional, but by removing the voltage divider implicit in the use of a load resistor it does fufill the claim made by the designer of "amplifying all the cartridge output without loss", while offering the lowest possible noise.
-rjm
If the AD797 works for you, that's great. My only concern would be that the opamp is adequately bypassed at high frequencies. As it is a lot faster than the OP27 its probably going to need small ceramics in addition the electrolytics. See the AD797 datasheet for examples. You can also try decompensating it, again as per the datasheet.
The rest - superregs, servo and class A biasing - are all standard upgrades, they can be added on at will since the basic circuit isn't modified. If the sonic benifit is worth the expense and/or complexity, mod on!
Of the various points Kevinkr raised this is the only one of interest, as electrically the input stage is - or more correctly can be thought of as - an inverting voltage amplifier with the cartridge source impedance as the inverting resistor. It is not - or more correctly should not be analyzed as - an I/V converter. Refer to the Phonoclone homepage for more explanation on this point.
For the record the noise of the RIAA components as configured is too small to contribute anything to the total output noise. All the output noise comes essentially from the voltage noise of the first stage op-amp.
Mechanically, though, I admit that the cartridge is performing under rather different conditions than is usual. Its not a short circuit per se, as the internal impedance of the cartridge coils still act as a load. On average, I suppose its about 3 times smaller than the typical recommended load. (For the DL103, 40 ohms rather than 100+40=140 ohms) Note that in the case of the Denon, 100 ohms is only a minimum recommended value below which the rated voltage output is not obtained, not an absolute dictum from on high.
I have found that reducing the cartridge load used with the DL103 from 47k to 1k to 470 ohms, 100 ohms, and finally zero ohms (phonoclone), generally tended to fill in the bass and soften the treble. So yes, it could be that an ultrasonic peak is increasingly damped. That's complete speculation on my part, though, and to be fair the frequency reponse data that came with the cartridge showed no indication whatsoever of any rise up to 20kHz with a 1kOhm load.
The input configuration of the phonoclone is unconventional, but by removing the voltage divider implicit in the use of a load resistor it does fufill the claim made by the designer of "amplifying all the cartridge output without loss", while offering the lowest possible noise.
-rjm
Yes, probably, but of course there *might* be other reasons why I did not found it superior after some time, e.g. degeneration of the frozen cart while fiddling with so many possibilities (but it measures still 39Ohms dc-wise, the onyl thing I can actually check), or that mod has only sense with low Z carts (but guess, I will not crack any Lyra or dynavector carts to tryrjm said:
)Yep, I use small additional foilcaps, the sound improves then (with the LT1028, I absolutley needed them, they oscillated without). I hope to get a small working function generation to crosscheck if i have any ringing before I put it all in a nice box...
However, AD811/797 *is* a great match, e.g. all the issues you posted some time ago concerning the little harshness in the heights are completly gone. We have resolution instead
Well, beware! Things are not that straight. It all depends on the systems balance. The AD811, for instance, has a comparably poor PSSR-rejection (about 60dB, if I recall correctly). When I first tried it, I still had the batteries, and the sound was not really better as a whole, but mainly different. The big difference emerged when I attached the superreg.
I thought it's mainly that cicken-and-egg issue wether to think of voltage or current but maybe I should check again...
I read that you originally had lower resistors in the network and changed it in favour to a lighter load to the first stage. Did you observe any changes in sound back then?
The damping issue: which other carts did you try with the clone? I'm going to upgrade soon and will probably try a dynavector (low Z), a Lyra, a Shelter and a Van den Hul
Thanks again, rjm, for digging me into the grooves of the phonoclone!
Rüdiger
No, that's basically it. An input voltage in series with the source impedance is a better model overall, though, since the source impedance is so low.
To answer your other questions, no, I haven't used any other cartridge that the DL-103, and no I didn't really notice any great change when I changed the RIAA values to higher impedances, though at the time I though it was a slight improvement. I did it mainly to get a more accurate RIAA response, keeping as many of the parts as possible in standard values.
/R
Some more tests...
Application Note 202
Figure 3c, p.3
And yes, the noise of the second stage is so much lower it probably won't make a difference at all.
Regarding the servo: To add the 2nd pole did not make things better in the longer run, the sound got more unstable (don't know how to say it better). But I raised R9 to 1000k, which made the lower regions even more transparent.
Meanwhile I checked the AD844 in the first stage. I couldn't make it work together with the AD797, so I switched back to the OP27 for testing. It's not better than the AD811, even when I tried the non-feedback-tweak with R1 omitted and pulled the TZ-node to ground via a resistor.
Rüdiger
Look Analog'srjm said:
Application Note 202
Figure 3c, p.3
And yes, the noise of the second stage is so much lower it probably won't make a difference at all.
Regarding the servo: To add the 2nd pole did not make things better in the longer run, the sound got more unstable (don't know how to say it better). But I raised R9 to 1000k, which made the lower regions even more transparent.
Meanwhile I checked the AD844 in the first stage. I couldn't make it work together with the AD797, so I switched back to the OP27 for testing. It's not better than the AD811, even when I tried the non-feedback-tweak with R1 omitted and pulled the TZ-node to ground via a resistor.
Rüdiger
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