Hi All!!
I am trying to have some fun with op amp swapping with an old bose 901 equalizer series IV. I also have a series III which is fully discrete. The series IV euqualizer came with LF353, pretty bad. I mounted machined socket so I could swap them. I then installed RC4558, bad highs, super harsh. I moved to TL072, improved things, smoother, but loss of volume. Changed to NE5532, getting better. Do you have any other suggestion to mount a "better" opamp? I included schematics of one channel.
Thank you!!
I am trying to have some fun with op amp swapping with an old bose 901 equalizer series IV. I also have a series III which is fully discrete. The series IV euqualizer came with LF353, pretty bad. I mounted machined socket so I could swap them. I then installed RC4558, bad highs, super harsh. I moved to TL072, improved things, smoother, but loss of volume. Changed to NE5532, getting better. Do you have any other suggestion to mount a "better" opamp? I included schematics of one channel.
Thank you!!
To stay in the lower price range, you could try OPA2134 or OPA2604 and see, what you think.
Way back, I heard some were satisfied with LM833 😉
Way back, I heard some were satisfied with LM833 😉
Thank you, I will try to get some of them and try. What would you recommend for something not in the lower price range? Thank you!!😀
Brown Dog board to make dual opamp out of 2 x LT1028 or 2 x LT1097 or 2 x LT1122 😉
I'd go for OPA1642 (JFET, because R values are quite high) but you'll need an adapter as its only SMD. If you want to go for the max, then ADA4625-2.
Mmm..I feel like I will stay with simple 8 pin opamp variety😉.
Thank you to everyone for the inputs!
Thank you to everyone for the inputs!
If you have a 'scope you should really look at the output that there's no oscillations.
Most modern opamps are much faster then the older types and may oscillate in a circuit not meant for them.
It will often work, but there are no hard and fast rules.
The harsness you mention could well be oscillation.
If you don't have a 'scope, try an RF detector build from a diode and a cap, lots on Google.
Jan
Most modern opamps are much faster then the older types and may oscillate in a circuit not meant for them.
It will often work, but there are no hard and fast rules.
The harsness you mention could well be oscillation.
If you don't have a 'scope, try an RF detector build from a diode and a cap, lots on Google.
Jan
Attachments
You also need to look at the power supply. It is unusual and limited in current delivery with neither rail regulated with respect to ground although each is stable with respect to the other. Note #2 on that diagram recommends TL072 and tbh I would take those over the 4558 (which is imo not good). That supply will not support four NE5532's or similar power hungry opamps.
If you noticed a difference in volume with TL072's then something is wrong. There should be no change in level with any suitable opamp fitted.
If you noticed a difference in volume with TL072's then something is wrong. There should be no change in level with any suitable opamp fitted.
The load on that U302 at the output is heavy, about 850 ohms the most. Not good.
I would at least double R327 through R330.
Jan
I would at least double R327 through R330.
Jan
An OPA 1642 would draw only slightly more power supply current (~1mA per IC) than a 4558 and would be a massive improvement in performance and is still relatively inexpensive (~$2 a pop).
I would also change all the polarized electrolytic capacitors for Nichicon ES MUSE bipolar caps.
I would also change all the polarized electrolytic capacitors for Nichicon ES MUSE bipolar caps.