I have a JVC QL 5 turntable and have updated all capacitors with great results in sound quality. I would like to replace the (2) NJM4558D op amps due to their high frequency limitations. I'm afraid in a quartz locked system with a reference to an oscillator this op amp may be creating noise that will have negative effect. What could replace it in this kind of circuit. I know what to replace it with in audio outputs in CD players, etc, but not sure in this situation. Anyone upgraded op amps in this turntable or others?
Garnet
Garnet
Why would a high frequency limitation of the opamps be a disadvantage ? It could work to the circuits advantage and even be a consideration for stability.
I heard from a couple of people that it tends to oscillate at high frequency - sounded like a negative thing to me. I do want to update them.
Do that people have some proof for such claims because that part is classic and even used often as unity gain buffer which means that it is extremely stable.
Both opamps see only very low frequency signals in this circuit and I still stand by what I say that the 4558 is perfectly suited to this application, however I can understand wanting to experiment... I used to be like that.
Have you looked with an oscilloscope to see if any spurious HF is generated at the output of these opamps, which would then back up the clams made by others?
If you are determined to experiment then an oscilloscope is a must as you will need to prove that any changes made don't introduce other issues.
You could try the NJM2068 opamp.
Have you looked with an oscilloscope to see if any spurious HF is generated at the output of these opamps, which would then back up the clams made by others?
If you are determined to experiment then an oscilloscope is a must as you will need to prove that any changes made don't introduce other issues.
You could try the NJM2068 opamp.
I know the 4558D is super popular - its the output device in my Denon CD player that was made in 2007. The JVC QL 5 was made in 1978.
Thanks for the suggestions and advice I will look at the NJM2068.
Thanks for the suggestions and advice I will look at the NJM2068.
wanting to change op amps
The cliche comes to mind... "if it ain't broke, don't fix it". First, find out if the device is causing an issue. If it's not, leave it alone. If it is, fix the problem.
The cliche comes to mind... "if it ain't broke, don't fix it". First, find out if the device is causing an issue. If it's not, leave it alone. If it is, fix the problem.
What's the purpose of this 4558 in that TT? Is it in an audio circuitry at all? If not, why bother with a replacement?
Best regards!
Best regards!
The two opamps are in the motor drive amplifier and the turntable rotational feedback network. All LF stuff in an application that the 4558 excels at.
IIRC, it is a 100Hz buzz signal tracking RPM. The '4558 is about 1000X better than needed.
Don't use airplane thinking to design a house foundation.
Don't use airplane thinking to design a house foundation.
For a low frequency or DC application one would consider parameters such as 1/f noise, offset voltage, offset drift, and input bias current. Subbing a high grade audio op amp may or may not make improvements in these parameters. You can buy op amps with these in mind, and they are different from what you would choose for audio. If the level of low frequency noise (offset and drift are just very low frequency noise) of A typical general purpose op amp is good enough there’s no reason to upgrade.
Thanks Mooly for the suggestion (NJM2068). Its exactly what I was looking for, lower noise and high slew rate. All I'm doing is trying to make a really special example of the QL 5 even better - the bearing has been modified, transformer put in remote box etc. I use this table to evaluate changes I make to an arm I'm designing. It is a simple machine to change arms on compared to me others, Lenco, Oracle, etc.
I just want everything in the circuit to be efficient, no excess heat or vibration, and obviously I don't know much about op amps - just change old 70s ones for AD or BB latest offerings.
I just want everything in the circuit to be efficient, no excess heat or vibration, and obviously I don't know much about op amps - just change old 70s ones for AD or BB latest offerings.
Swapping opamps always needs care and can sometimes throw unexpected issues in your path. Swapping out devices for really high speed high performance alternatives doesn't always work although I doubt the NJM2068 will give any problems here.
Have a read at this old thread:
Swapping Op-Amps... you have checked to see it's stable haven't you ?
Have a read at this old thread:
Swapping Op-Amps... you have checked to see it's stable haven't you ?
I second that, especially in mechanical drive systems like here. Mechanical lag and overshoot can easily introduce opamp overshoot if it is 'to fast for it's own good'. Even with a scope you really need a schematic and understanding what you are doing to avoid going backwards.
Of course, any change will greatly improve the sound, so maybe this is all too pessimistic 😎
Jan
I have the schematic, and a tech who will check it before and after. Just wanted to find a replacement from people who did this before. The NJM JVC used was certainly up to the task - the turntable worked perfectly with all original parts for 40 years.
- Status
- Not open for further replies.