Hi,
I have a Burmester 785 preamp that uses the lf356 op amp , as nobody seems interested in buying it I thought I’ll keep it and if possible upgrade the op amps but is that possible? I mean is there an improved newer op amp that I can simply install then use without having to make other modifications.
I have a Burmester 785 preamp that uses the lf356 op amp , as nobody seems interested in buying it I thought I’ll keep it and if possible upgrade the op amps but is that possible? I mean is there an improved newer op amp that I can simply install then use without having to make other modifications.
It's hard to make anything but a wild guess without a schematic. What aspect of performance do you want to improve?
The LF356 is very good opamp so you are changing it without specific goals in mind.
Measure the supply voltage as it might possibly be higher than you expect seeing as some versions of the LF365 are specified to -/+22 volt operation. Fitting anything other than FET device might give higher offset voltages within the circuit.
Measure the supply voltage as it might possibly be higher than you expect seeing as some versions of the LF365 are specified to -/+22 volt operation. Fitting anything other than FET device might give higher offset voltages within the circuit.
The 356 is not only a good opamp, but it also has peculiarities not shared by the likes of TLO71, for example it can drive directly large capacitive loads without any protection.
If it drives a shielded cable directly, a replacement could get in trouble
If it drives a shielded cable directly, a replacement could get in trouble
Up to a point but you need to be aware of what can happen. As well as supply voltage you have to consider supply current as well, A difference of a few ma may not seem much but multiply that by the number of opamps and the difference between one opamp drawing say 3ma vs one drawing 12ma becomes significant if the PSU is designed for the lower value (such as Zener regulated shunt supplies).
Have a look here as well:
https://www.diyaudio.com/community/...-checked-to-see-its-stable-havent-you.191389/
@Elvee makes a good point on load driving abilities.
Also check if any offset null pins are in use (unusual but it happens) as different opamps can have different nulling requirements.
Check the supplies first as that could either be a total non issue or severely limit your choice depending...
Different opamps have different decoupling requirements for stability, have different compensation needs and randomly swapping them can lead to RF oscillation - often manifesting as a reduction in audio performance and increase in noise. So its best done with an oscilloscope to hand to ensure nothing funny is going on.
Circuits may also be assuming properties of the opamp (such as low offset, low bias current, high output drive capability, etc) - understanding the requirements of the circuit is really useful to avoid some of these pitfalls. For instance replacing a FET opamp with a bipolar opamp may lead to massive DC offsets or very scratchy potentiometer operation due to the higher bias currents.
Thanks guys , I appreciate you all sharing your knowledge.
As it’s far more complicated than I initially thought I reckon I’ll leave it alone. 😁
As it’s far more complicated than I initially thought I reckon I’ll leave it alone. 😁
It looks quite a job too without socketed chips - better to start by measuring existing performance first in case there is some issue, and to provide a baseline.
Well I nearly asked if it was worth you asking. I take the answer was a no 😀
One thing I wondered about were those ceramic caps that have the appearance (going off the physical layout of them) that may be across pins 1 and 8 of the opamps. Pin 8 has no connection on an LF356... so it would be interesting to know if the cap did go to pin 8 or not.
For some reason the final opamp doesn't seem to have these. Could that be an LF356 and the others something else?
Conspiracy theories 🙂
For some reason the final opamp doesn't seem to have these. Could that be an LF356 and the others something else?
Conspiracy theories 🙂