One more thing...ensure earthing continuity from TT to preamp to amp.
And you can use Li Ion cells in series for a rechargeable noise free DC supply.
And whatever you choose, see that the slew rate does not exceed 20 or so, or it can cause the main amp circuit to become unstable.
And you can use Li Ion cells in series for a rechargeable noise free DC supply.
And whatever you choose, see that the slew rate does not exceed 20 or so, or it can cause the main amp circuit to become unstable.
Pretty much every amplifier has an input HF filter. -6dB/oct. You limit the input bandwidth so you never pass signals close to the amplifier's roll-off frequency.
Now of course if anyone decides they know better than to follow good design practice ... well okay. Besides, very high frequency signals on records are noise. We used to use a pilot and needed response around 40 KHz for ancient quadraphonic records (remember those? I do). That is a special case. That and your RIAA curve cuts HF response, so your op amp, no matter how fast it is (as long as you designed it to be stable), it will not matter.
That being said, an extremely fast op amp is waste in this application. Go for low noise.
Now of course if anyone decides they know better than to follow good design practice ... well okay. Besides, very high frequency signals on records are noise. We used to use a pilot and needed response around 40 KHz for ancient quadraphonic records (remember those? I do). That is a special case. That and your RIAA curve cuts HF response, so your op amp, no matter how fast it is (as long as you designed it to be stable), it will not matter.
That being said, an extremely fast op amp is waste in this application. Go for low noise.
For a record player...the records were probaly mastered with a 4558, so that, 5532, and TL072 are good enough.
OPA series, check before selecting.
AD797 is a very low noise and adequate slew rate choice.
It is difficult to get here, so I built my unit with a TL072.
Later I found ready circuits with the parts soldered in are still sold, so I may have wasted my time building one.
A random net image from a Chinese seller, Indian sellers are offering theirs for only about $5.00:
View attachment 1380938
Exotic designs can land you in audio fool territory.
And the sound quality depends on your amplifier, speakers, and the room as well, I have plastered brick walls...a book lined room with sound absorbing roof tiles, and a carpet will make the same system sound very different.
Keep that in mind, please.
OPA series, check before selecting.
AD797 is a very low noise and adequate slew rate choice.
It is difficult to get here, so I built my unit with a TL072.
Later I found ready circuits with the parts soldered in are still sold, so I may have wasted my time building one.
A random net image from a Chinese seller, Indian sellers are offering theirs for only about $5.00:
View attachment 1380938
Exotic designs can land you in audio fool territory.
And the sound quality depends on your amplifier, speakers, and the room as well, I have plastered brick walls...a book lined room with sound absorbing roof tiles, and a carpet will make the same system sound very different.
Keep that in mind, please.
Hi NareshBrd,
If anything, they were mastered with NE5532 or NE5534, failing that a discrete circuit for earlier stuff. 4558 are too noisy and TL072 were not that popular in pro gear. They were really quiet compared to others of the day, but they don't sound very good. We saw those in "semi-pro" mixers and stuff, consumer amplifiers and preamps. The Japanese came out with some nice op amps also.
You have no idaea how many NE5532 or NE5534 op amps your signals run through! If not them, probably individual transistors, and before that it was tubes.
If anything, they were mastered with NE5532 or NE5534, failing that a discrete circuit for earlier stuff. 4558 are too noisy and TL072 were not that popular in pro gear. They were really quiet compared to others of the day, but they don't sound very good. We saw those in "semi-pro" mixers and stuff, consumer amplifiers and preamps. The Japanese came out with some nice op amps also.
You have no idaea how many NE5532 or NE5534 op amps your signals run through! If not them, probably individual transistors, and before that it was tubes.
My parameter was slew rate, the 4558 is slower than 5532, which is about 8, IIRC.
TL072 was about 13, slightly faster.
I had to change input and output resistors to get a clean sound, as the circuit I had copied from my Kenwood set was a AN6556 / M5218P circuit.
And used a socket, so just to check, I put a Kia 4558 (fuzzy), and a ST LM358 (terrible) during testing. Even a 741, that was ...don't even ask.
I think the picture above says 5532, quite adequate, can change the chip if you want a genuine one, or get a ready PCB, put capacitors etc. of your choice.
No point in designing and testing and spending hours when a $5 ready circuit is available..
TL072 was about 13, slightly faster.
I had to change input and output resistors to get a clean sound, as the circuit I had copied from my Kenwood set was a AN6556 / M5218P circuit.
And used a socket, so just to check, I put a Kia 4558 (fuzzy), and a ST LM358 (terrible) during testing. Even a 741, that was ...don't even ask.
I think the picture above says 5532, quite adequate, can change the chip if you want a genuine one, or get a ready PCB, put capacitors etc. of your choice.
No point in designing and testing and spending hours when a $5 ready circuit is available..
The amp used is a Philips India boom box, which had uPC1238 (NEC) in the output section, changed them to D2030/D1875, each channel has different chips as I was getting 4V DC on the ouputs, enough to possibly damage the 1970s Sony speakers in thier rose wood cabinets.
Tested on a Thorens table, 'Hotel California' as the test signal.
Clear enough at a decent volume, so experiment successful.
Clear compared to the MP3 played by my computer through a Kenwood set with Philips speakers. Particularly drum rolls and that famous guitar 'duel' on that track.
Second test with 'Stairway to Heaven' also satisfactory. Again that famous guitar bit was rendered properly.
Tested on a Thorens table, 'Hotel California' as the test signal.
Clear enough at a decent volume, so experiment successful.
Clear compared to the MP3 played by my computer through a Kenwood set with Philips speakers. Particularly drum rolls and that famous guitar 'duel' on that track.
Second test with 'Stairway to Heaven' also satisfactory. Again that famous guitar bit was rendered properly.
True in some respects. Going to a JFET input from Bipolar can have it's own issues. I try to stay with the original technology unless I have a good reason to change it. Non-inverting mode for a JFET isn't it's best from a distortion perspective.
The main problem is that second source (or third, or copies) may fail noise specs and other parameters. If the PCB is well laid out, I would rip anything questionable out and replace with known quantities.
The main problem is that second source (or third, or copies) may fail noise specs and other parameters. If the PCB is well laid out, I would rip anything questionable out and replace with known quantities.
You guys will not convince me of opamps, but that is not the topic of this thread 🙂
I have a pair of AD797 and I try it, just milling a pcb for it with a Hiraga. The Hiraga I will put together with BC560s first, so I have no big expectations, the AD797 may shine with that comparison, but I'm hunting for better transistors/arrays and designs with them.
Thanks,
JG
I have a pair of AD797 and I try it, just milling a pcb for it with a Hiraga. The Hiraga I will put together with BC560s first, so I have no big expectations, the AD797 may shine with that comparison, but I'm hunting for better transistors/arrays and designs with them.
Thanks,
JG
Firstly the AD797 was designed for ultrasound preamplifier use so yes it has an adequate slew-rate! In fact all audio opamps have plenty of slew rate, not usually an issue at all in audio design. For 20kHz on a +/-15V supply system you only need about 1.5V/µs for the fastest loudest signals, and at normal preamp signal levels 200mV/µs is enough.
1.5 to 20 seems a good band, higher rates can damage or distort the output sound.
That was what I meant, too high a slew rate means the output stage may not be able to cope with the rapid signal change.
Some of the audio fool sites have posts saying change to new chips in old amps, at times using SMD adapters in place of DIP chips, in the pre amp section, and result is wonderful improvement in sound.
I disagree.
A chip is much more consistent in quality compared to transistors, finding matched transistor sets (unless in SMD) will take a lot of effort as many producers have stopped or limited production of through hole components, not just transistors.
However, that is the spirit of DIY, the result must please the person who made the effort.
That was what I meant, too high a slew rate means the output stage may not be able to cope with the rapid signal change.
Some of the audio fool sites have posts saying change to new chips in old amps, at times using SMD adapters in place of DIP chips, in the pre amp section, and result is wonderful improvement in sound.
I disagree.
A chip is much more consistent in quality compared to transistors, finding matched transistor sets (unless in SMD) will take a lot of effort as many producers have stopped or limited production of through hole components, not just transistors.
However, that is the spirit of DIY, the result must please the person who made the effort.
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The OPA1612 dual opamp also makes a credible MC amp - 0.9nV/rt Hz so it’s at the same level as the AD797 and you can pack both channels into one opamp.
Hi NareshBrd,
If you don't re-compensate the amplifier for the new front end, of course it won't perform well. You can't blame the op amp on problems if the change wasn't done correctly. Also, you need to match the technology of the op amp, like JFET and Bipolar. They don't work equivalently well in every situation.
A faster op amp won't over drive the output stage unless control has already been lost. Feedback is next to instant for all intents and purposes, so it tracks.
If you don't re-compensate the amplifier for the new front end, of course it won't perform well. You can't blame the op amp on problems if the change wasn't done correctly. Also, you need to match the technology of the op amp, like JFET and Bipolar. They don't work equivalently well in every situation.
A faster op amp won't over drive the output stage unless control has already been lost. Feedback is next to instant for all intents and purposes, so it tracks.
Thank you! Now I'll have to go dig out my TAAs to see what Marshes preamp was all about🙂
1980... issues 3 and 4
The line stage used a MPQ6600A-2 but he had second thoughts later (in a letter) that perhaps the matching in the MPQ6100 package might have been more suitable.
With respect to the THATs, I'd be more interested in his later linestage even though the stacked PCBs I've laid out would have to be reworked. And the Leach MC preamp (which I'd also have to rework.
Thanks for pointing these out.
The line stage used a MPQ6600A-2 but he had second thoughts later (in a letter) that perhaps the matching in the MPQ6100 package might have been more suitable.
With respect to the THATs, I'd be more interested in his later linestage even though the stacked PCBs I've laid out would have to be reworked. And the Leach MC preamp (which I'd also have to rework.
Thanks for pointing these out.
I had to change the input and output resistors to compensate for using the TL072 in place of the original Japanese chips in the Kenwood amp circuit, after finding the sound was not at the right level.
And as for the technology and slew rates, the choices were TL072 and NJM (JRC) 5532, which is slightly slower.
In any case records have a dynamic range of about 60 dB, compared to 120 dB (IIRC) for CD, so this was a decent solution given my constraints, a one off using locally made parts on perforated board.
For a new unit, either I would get a batch of PCBs made (minimum is only about 20 for regular customers), or just buy a ready board, records are mostly gone, so are the players.
The music is now stored as data, on solid state drives with you or on the cloud.
As a data storage device, records are pretty poor, I want to listen to music, not rumble and scratches on worn records.
If someone wants to go deep and insist on making one, of course I will share my experience and try to help, till the limits of my knowledge and experience.
And as for the technology and slew rates, the choices were TL072 and NJM (JRC) 5532, which is slightly slower.
In any case records have a dynamic range of about 60 dB, compared to 120 dB (IIRC) for CD, so this was a decent solution given my constraints, a one off using locally made parts on perforated board.
For a new unit, either I would get a batch of PCBs made (minimum is only about 20 for regular customers), or just buy a ready board, records are mostly gone, so are the players.
The music is now stored as data, on solid state drives with you or on the cloud.
As a data storage device, records are pretty poor, I want to listen to music, not rumble and scratches on worn records.
If someone wants to go deep and insist on making one, of course I will share my experience and try to help, till the limits of my knowledge and experience.
Thanks!
Probably the input cap is not needed either, but I made a place for it at least. I know the output resistor I left in the circuit is way too high, will replace. I way thinking about a few hundred ohm, like 330.
I have a tiny milling machine and used to make simple, one sided PCBs, but I've broke my last milling tool yesterday :-(
I will just order PCBs from China once I finish with the Leach first design also.
Thanks,
JG