It sounds good that performance can be very good. Du you have good suggestion for opamps? Are those discrete Burson moduls better than any opamp?
Do you have other suggestions for tweaks, than what is suggested in this article?
I am in a bit of a doubt if I should make all the modifications, what if I dont like the result! But I am also a bit lasy, so It would be easiest to make all upgrades when I am at it... What I really like about this Rotel phono is that it does not enhance siblince sounds, most other equipment does, but at the same time I would like a more transparent sound, more details, then I am afraid the other problems will come...
Do you have other suggestions for tweaks, than what is suggested in this article?
I am in a bit of a doubt if I should make all the modifications, what if I dont like the result! But I am also a bit lasy, so It would be easiest to make all upgrades when I am at it... What I really like about this Rotel phono is that it does not enhance siblince sounds, most other equipment does, but at the same time I would like a more transparent sound, more details, then I am afraid the other problems will come...
Put sockets in the op-amp positions and then you can tweak them to your liking. I really like OPA134's personally. They seem to be the most neutral to my ears. The Bursons added a depth and better imaging to the sound that the op-amp did not give me.
I would follow the article as-is. As I said in my previous post it is ALMOST at the level of the Pearl 2 after the modifications.
If you are removing the circuit board to make any of the mods, you might as well do all the soldering at once.
I would follow the article as-is. As I said in my previous post it is ALMOST at the level of the Pearl 2 after the modifications.
If you are removing the circuit board to make any of the mods, you might as well do all the soldering at once.
Even if you only do the mod´s as described in the old HifiWorld article, I guarantee, you´ll be more than satisfied with the result. This is for sure one mod. that really works
If you replace ad744 with ad 743 or 745 you don't need the bipolar input anymore.
I'd suggest a very different and way cheaper mod:
Keep the bipolars, replace only the ad744 and the old ne5534 with NEW TI ne5534(yes, those cheap op-amps)-the newer ones are actually better than the old ones, rewire the bipolar frontend to the ne5534 and ground pin 2/3of ne5534 as it is wired here at page 38:
http://www-f9.ijs.si/~margan/Audio/Ironing_RIAA.pdf
remove r111, r112, c183, c184 as they are no more needed
r123 r124 might be usefull to be modified to 2k2 resistors as with the 1nf capacitor will cut all the useless highs preventing the next stage saturation.
rewire the power supply so that only the input transistors should be supplied from the capacitance multiplier, while the op amps should be run on unregulated but well filtered power supply (a pi filter would be good enough) and you should get the best you can get out of that circuit with a little bit of tweaking.Raise the power supply as much as your op-amps allow you to and just filter it with good quality capacitors just higher value2x100uf/25...35v , no regulator is needed.
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Thank you all of you for all this good informations, I had not even hoped for so much feedback!
Interesting suggestions you have dreamth. I am a bit scheptical to change to much since I like so much about the unit already. I have been tempted to skip voltage regulation before. There is a lot to think about and try out. Have you actually made these modifications to the Rotel unit?
I think some of the quaitys of the standard unit comes from the nice black gate capacitors it is filled with, so I am holding a bit back to change to much about powersupply.
Interesting suggestions you have dreamth. I am a bit scheptical to change to much since I like so much about the unit already. I have been tempted to skip voltage regulation before. There is a lot to think about and try out. Have you actually made these modifications to the Rotel unit?
I think some of the quaitys of the standard unit comes from the nice black gate capacitors it is filled with, so I am holding a bit back to change to much about powersupply.
If you're doubtful of trying anything on your Rotel then leave it like this.Anytime you made a modification just take care to be able to revert to the first design and it will all be ok, just don't be too religious about electronic components!Some of us destroyed a lot more expensive equipment than yours just to prove ourselves first that nothing is so special ...
I didn't do that mod, but it's simple to be done and it has the potential to prove a lot of interesting hypotheses .That mod on ne5534 was suggested first by the j-fet supertex semiconductor manufacturer and applied by some of the best engineers around here too.
I just made a quick assessment of what is worth doing given your schematic.Buying overly expensive components is not worth doing it with this design .There were a lot of companies who swore on transistor frontend for famously good op-amps, but they always ran into a big problem as they need that rc filter to compensate the phase linearity because of the higher gain with the op-amp combined .Well...that rc filter screwed allmost all these designs.The ne5534 allows though to replace the input stage with an external one(actually it allows the replacing of each of its 3 stages ) so you can get around the compensation problem and even make a better op-amp.The only downside of the ne5534 is the common mode distortion that can be improved with a better input and your front end transistor stage is actually better than what ne5534 has inside.
Actually i don't trust the previously suggested mod because of those solens...Nichicon bipolar electrolitics are way better than any non polar cap in the world in similar configurations.There are three reasons for that:
First: nonpolar capacitors are BIG and prone to pick-up or radiate noise.With this preamp it will pick-up the 100hz mains hum as it is next to the power filtering.
Second: The modders usually choose high voltage nonpolar capacitors used in valve equipment ,and they have bigger losses than their lower voltage equivalents in the semiconductor world.
Third: they are more prone to piezoelectric phenomenon than the electrolytic ones.
I didn't do that mod, but it's simple to be done and it has the potential to prove a lot of interesting hypotheses .That mod on ne5534 was suggested first by the j-fet supertex semiconductor manufacturer and applied by some of the best engineers around here too.
I just made a quick assessment of what is worth doing given your schematic.Buying overly expensive components is not worth doing it with this design .There were a lot of companies who swore on transistor frontend for famously good op-amps, but they always ran into a big problem as they need that rc filter to compensate the phase linearity because of the higher gain with the op-amp combined .Well...that rc filter screwed allmost all these designs.The ne5534 allows though to replace the input stage with an external one(actually it allows the replacing of each of its 3 stages ) so you can get around the compensation problem and even make a better op-amp.The only downside of the ne5534 is the common mode distortion that can be improved with a better input and your front end transistor stage is actually better than what ne5534 has inside.
Actually i don't trust the previously suggested mod because of those solens...Nichicon bipolar electrolitics are way better than any non polar cap in the world in similar configurations.There are three reasons for that:
First: nonpolar capacitors are BIG and prone to pick-up or radiate noise.With this preamp it will pick-up the 100hz mains hum as it is next to the power filtering.
Second: The modders usually choose high voltage nonpolar capacitors used in valve equipment ,and they have bigger losses than their lower voltage equivalents in the semiconductor world.
Third: they are more prone to piezoelectric phenomenon than the electrolytic ones.
Separating the op amp power supply from the capacitiance multiplier is to make the capacitance multiplier work better with only the transistor front end load.The op amps have enough PSRR to fight the noise of only a filtered supply line which also has a lower impedance than any regulator .The power supply of the op-amp being a bit higher than the transistor front end will also prevent input saturation.
Having read all your postings I feel somewhat tempted to clone this RQ970BX. Most peculiar problem appear to be the unobtainability of those frontend transistors. Their ratings and characterictis seem to be rather common, with the exception of this low Rbb' impedance, a parameter I don't know from other transistors. Are there any substitutes, though?
Best regards!
Best regards!
http://www.rchips.com/_upload/Product/pdf/Rohm%20Semiconductor-2SA1579-1514K-1038S.pdf
2sc4102 ROHM Semiconductor | Mouser United Kingdom
2SC3906 ROHM Semiconductor Bipolar Transistors - BJT | Mouser United Kingdom
http://www.mouser.com/ds/2/149/KSC1845-88467.pdf
zetex ztx 951, 1051, 1055 are good too just that the capacitances are a bit higher(better for mc carts or cascoded operation)
I have an old stock of 2sa1038 that i bought just by chance for pennies and they proved to be the best low noise transistors i ever saw. Looking for them i found two smd replacements as well as their complements.
I also have the ztx 1051 and ztx1055 from old stock and they actually behave very well in capacitance multipliers as they have very high hfe factors.
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Personally there are many other options out there you can build with available components. In my opinion, a lot of the "magic" of this phono stage is the fact that the entire power supply is Black Gate caps. Those are unobtanium and I am not sure you'd get the same quality building it with alternative parts. If you do give it a go, please post your impressions here as I would be very curious if it is "Black (Gate) Magic" or not.
I didn't say it was a bad design ... just not worth building trying to source obsolescent parts when there are plenty of known-good designs out there using available parts.
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