if your CD player has s/pdif digital coaxial (RCA) output, you might consider an external DAC instead of a new I-V stage, plus the extra circuitry needed to implement the De-emphasis (DEEM) filter, output muting, etc...in addition to a separate power supply with +24V and -24V (split) rails.
the LHH200 output transformer isolates the signal ground from the player's internal ground for true (floating) balanced output. a quality 1:1 transformer (e.g. Lundahl can do this for SE signals, but also has both LF and HF bandwidth limitations). initial guess is that the upper of the two opamps tied to the transformer drives the transformer primary, and the lower opamp is used as part of an error correcting loop to compensate for the transformer's natural HF roll-off.
the LHH200 output transformer isolates the signal ground from the player's internal ground for true (floating) balanced output. a quality 1:1 transformer (e.g. Lundahl can do this for SE signals, but also has both LF and HF bandwidth limitations). initial guess is that the upper of the two opamps tied to the transformer drives the transformer primary, and the lower opamp is used as part of an error correcting loop to compensate for the transformer's natural HF roll-off.
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Would Nelson Pass's Zen iv plus B1 buffer suitable for the purpose?
Unfortunately, I have a hard time to get the Zen iv Board.
Unfortunately, I have a hard time to get the Zen iv Board.
if you are looking to replace op-amps in your LHH200, best way to do that is to start with a burson or similar discrete module to replace the existing NE5534/NE5532's following the DAC chips (this stage performs the I-V conversion as well as microprocessor selectable de-emphasis. The discrete op-amp modules should have sufficiently low output impedance and drive capability such that additional buffer stages are NOT needed. Easy enough to remove and replace with a fresh NE5534 (do not resolder in the old part that has been exposed to multiple soldering / de-soldering cycles) or another part such as OPA213x should the discrete opamp not provide an audible improvement.
Per earlier posts, a CD player needs to have switchable de-emphasis function under control of a microprocessor that reads each disc's TOC and embedded data flags to determine whether playback de-emphasis (-3dB at 3kHz increasing to -10dB at 10kHz) should or should not be applied. Muting is also important to prevent damaging glitches from reaching your headphones and speaker drivers present during power cycling, skipping tracks, etc... You will lose this functionality if replacing the entire output stage with another generic I-V solution such as nelson Pass's Zen I-V stage (besides being hard to source right now, and not a good drop-in replacement for the combination I-V and switchable de-emphasis stage, the small signal FETs need to be graded / hand-matched using a curve tracer or similar tool for best results and lowest distortion).
Might be some audible gains in replacing the FET's used for de-emphasis and muting switching with suitable relays, diode clamps, driver & level-shifter transistors. Many of the Philips / Magnavox / Marantz players use the same chipsets and similar topology on the analog stages, so other diyAudio threads may have tested & debugged circuits to replace the muting FET's with lower distortion relay-based solutions.
try a search for "Walt Jung" and POOGE CD player modifications
Per earlier posts, a CD player needs to have switchable de-emphasis function under control of a microprocessor that reads each disc's TOC and embedded data flags to determine whether playback de-emphasis (-3dB at 3kHz increasing to -10dB at 10kHz) should or should not be applied. Muting is also important to prevent damaging glitches from reaching your headphones and speaker drivers present during power cycling, skipping tracks, etc... You will lose this functionality if replacing the entire output stage with another generic I-V solution such as nelson Pass's Zen I-V stage (besides being hard to source right now, and not a good drop-in replacement for the combination I-V and switchable de-emphasis stage, the small signal FETs need to be graded / hand-matched using a curve tracer or similar tool for best results and lowest distortion).
Might be some audible gains in replacing the FET's used for de-emphasis and muting switching with suitable relays, diode clamps, driver & level-shifter transistors. Many of the Philips / Magnavox / Marantz players use the same chipsets and similar topology on the analog stages, so other diyAudio threads may have tested & debugged circuits to replace the muting FET's with lower distortion relay-based solutions.
try a search for "Walt Jung" and POOGE CD player modifications
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Is any mods post gonna end up with 80 dollars discrete op-amps suggestions that most probably have lower quality than the buffer that's already used?
Output transformers will always be the proffessional's way interconnect, but you need high quality ones which are usually in the range of 1..300 bucks for one piece.
I asked a question that remain unanswered: what do you need to buffer ? After the i/v stage there's usually an active or passive ultrasonic image filter.If you are going to use an active filter there's no need for another buffer.If you're not going to use any filter there's no need for a buffer at all.
If lhh2000 is having identical digital processing to your player then you should just copy it , use a modern op amp and find a good replacement for those output transformers.Studer A80 or 820 had simillar line output .Check their shematics as they had both transformer and transformerless options.Today you get really transparent op-amps and if you want to preserve Nelson Pass converter sound a neutral op-amp transformerless design is what you need.
Output transformers will always be the proffessional's way interconnect, but you need high quality ones which are usually in the range of 1..300 bucks for one piece.
I asked a question that remain unanswered: what do you need to buffer ? After the i/v stage there's usually an active or passive ultrasonic image filter.If you are going to use an active filter there's no need for another buffer.If you're not going to use any filter there's no need for a buffer at all.
If lhh2000 is having identical digital processing to your player then you should just copy it , use a modern op amp and find a good replacement for those output transformers.Studer A80 or 820 had simillar line output .Check their shematics as they had both transformer and transformerless options.Today you get really transparent op-amps and if you want to preserve Nelson Pass converter sound a neutral op-amp transformerless design is what you need.
I agree that more modern parts should provide better performance and faster recovery from DAC output glitches, especially the MSB transition that occurs near zero-crossing. IIRC the TDA1541 was offered in S1, S1 Crown, S2 double Crown grades, each having lower glitch energy / improved linearity. Not sure about TDA1540 as that was a long time ago.
perhaps the OP (original poster) would benefit from a list of modern op-amps to try out in the I-V stage immediately following the DAC chip. OPA134 for single opamps, and OPA2134 for dual opamps (both in 8-pin DIP package) come to mind. OPA132 & OPA2132 are identical to 134/2134 except lower guaranteed DC input offset, so are more expensive and therefore less desirable in this application. use of parts still available in 8-pin DIP is preferable for direct retrofitting, as 8-SOIC and smaller SMT packages would require an additional brown dog or similar adapter and familiarity with SMT soldering.
I am just confirmed with my friend, the opamp use for output stage of the LHH2000 are NE5534 is for SINGLE OPAMP, while the NE5532 is for DUAL OPAMP.
OPA2134 is hardly a good choice for iv stage, opa2132...faster settlement time but i need to check if it's unity gain stable.ada4898 and many others more suitable but he already has a fancy fet input i/v converter.He only needs a good op-amp for the image filter and possibly one more as a line output buffer if he can't afford good output transformers.Ihad once a phillips cd 304 mk1 with tda1540, but I wasn't impressed with its sound...too much effort to mod something like that in my opinion.I need to be impressed by the stock version of any equipment to think of modding it.Any modern dac will destroy tda1540 with very simple additional circuitry.
Few minutes ago, my friend told me the best IV is a resistor. And a quality resistor like bulk metal foil plus a nano core line output transformer should be better than any IV stage plus buffer.
But I concerned about the output impedance.
yes, ADA4898-1 and 4898-2 as I am not familiar with those parts, per datasheet description, these ADI parts are unity gain stable, with much faster settling time, so would be better than opa 2132/2134 for the I-V stage.
resistor has very linear I-V characteristic, but will bump into DAC's output voltage compliance limitation unless you keep the resistor value very low so that the output swing is ~100mV.
resistor has very linear I-V characteristic, but will bump into DAC's output voltage compliance limitation unless you keep the resistor value very low so that the output swing is ~100mV.
I used various op-amps in technics class AA configuration found in slp-999.Lm6172 at the output needed some base response enhancement that was fairly easy to do but sounded best.Input op-amp choice becomes way less critical in that iv converter arangement.Besides you might very well be interested in studying elliptical filters for ultrasonic image removal that you find in my thread.As there was no schematic with them i did a bit of reverse engineering for that nec810 cd player.
https://www.diyaudio.com/community/threads/nec-cd-810-revival-and-mods.338152/#post-5809151In my view technics slp 999 was the best and most advanced embodyment of a high end cd player of the 90's yet nec810 remembered us what elliptical filters are for.
https://www.diyaudio.com/community/threads/nec-cd-810-revival-and-mods.338152/#post-5809151In my view technics slp 999 was the best and most advanced embodyment of a high end cd player of the 90's yet nec810 remembered us what elliptical filters are for.
yes, as others have said, there is a very good chance you dont need a buffer. The borbely design is specified to drive low impedance headphones, so driving some cables and an amplifier input wont be a struggle (although I wonder if they realise how low they go these days)
regarding the borbely IV, its a rather esoteric, but well designed discrete circuit. His designs always use rare and hard to source parts; mostly the fets, but by now, probably a lot more than just the fets. Do you actually have a populated board for the IV, ready to run, with power supplies? (good chance it will require more current than what is available in the player). If not, how were you planning to source and match the required parts? can you buy all that from fetaudio? I guess it was spencer that took over Erno's kit business. Do you have the knowledge and equipment, as well as budget for that? If you have just been told the borbely IV is good and opamps are crap and are progressing thinking its going to be straight forward, you will be disappointed. You'll excuse me for saying it sounds to me like you dont have the required knowledge for dialling in the IV once you build it and adjusting to suit the TDA. Make sure you get spares for the fets while you are at it, they will not be available forever and the price keeps going up. I'm not sure your friend is helping matters ...
regarding the borbely IV, its a rather esoteric, but well designed discrete circuit. His designs always use rare and hard to source parts; mostly the fets, but by now, probably a lot more than just the fets. Do you actually have a populated board for the IV, ready to run, with power supplies? (good chance it will require more current than what is available in the player). If not, how were you planning to source and match the required parts? can you buy all that from fetaudio? I guess it was spencer that took over Erno's kit business. Do you have the knowledge and equipment, as well as budget for that? If you have just been told the borbely IV is good and opamps are crap and are progressing thinking its going to be straight forward, you will be disappointed. You'll excuse me for saying it sounds to me like you dont have the required knowledge for dialling in the IV once you build it and adjusting to suit the TDA. Make sure you get spares for the fets while you are at it, they will not be available forever and the price keeps going up. I'm not sure your friend is helping matters ...