Hi friends
I need your help regarding upgrading my opamps in my mark levinson 33H
All the modifications that I have made to those amps gives them a new life and the sound became more analog.
However my question is divided for 2 parts:
1. The first part since those 33H has few revisions the earliest version uses AD705 and later version uses OPA277P
I have contact Harman group and they say that instead of the AD705 they use LT1097
I have compere the specs of the OPA277P vs LT1097 and I see any reason why to use LT1097 since the OPA277P is better by all means.
Did I miss something???
2. The second question related to the oscillator board of this amp
Since this amp has an AC regenerator for the input stage.
The oscillator uses NE555N and this connected to a series 3 opamps AD712JN
I was thinking to upgrading those opamps
To an opamps that have better specs of noise rejection to have better cleaner AC
Instead of the AD712JN I saw 2 options
OPA2134
OPA1642
The 1642 has better specs and is much faster than the 2134 and I'm afraid of oscillating problems.
Since I'm not expert in electronics
Please help me to to decide what to do in this case
I'm looking for direct replacement
If you think of better opamps and more suitable please let me know
God bless you all
Thank you
I need your help regarding upgrading my opamps in my mark levinson 33H
All the modifications that I have made to those amps gives them a new life and the sound became more analog.
However my question is divided for 2 parts:
1. The first part since those 33H has few revisions the earliest version uses AD705 and later version uses OPA277P
I have contact Harman group and they say that instead of the AD705 they use LT1097
I have compere the specs of the OPA277P vs LT1097 and I see any reason why to use LT1097 since the OPA277P is better by all means.
Did I miss something???
2. The second question related to the oscillator board of this amp
Since this amp has an AC regenerator for the input stage.
The oscillator uses NE555N and this connected to a series 3 opamps AD712JN
I was thinking to upgrading those opamps
To an opamps that have better specs of noise rejection to have better cleaner AC
Instead of the AD712JN I saw 2 options
OPA2134
OPA1642
The 1642 has better specs and is much faster than the 2134 and I'm afraid of oscillating problems.
Since I'm not expert in electronics
Please help me to to decide what to do in this case
I'm looking for direct replacement
If you think of better opamps and more suitable please let me know
God bless you all
Thank you
Last edited:
Hmm, very complex circuit for an oscillator. Not sure the opamps have to be anything special at that frequency given they are parts of a low pass filter driving a transformer.
There is an argument for changing the Sallen-Key stages to multiple-feedback-path stages to reject more HF noise from the 555. By the same token there's a strong argument for replacing the 555 with a 7555 to put less switching noise on the 10V rail. The NE555 is a noisy beast.
There is an argument for changing the Sallen-Key stages to multiple-feedback-path stages to reject more HF noise from the 555. By the same token there's a strong argument for replacing the 555 with a 7555 to put less switching noise on the 10V rail. The NE555 is a noisy beast.
For building sinewave regenerators there are integrated classD modules available now for a very low price. For example this board : https://www.aliexpress.com/item/1005005509443098.html. However a classD regenerator in this instance may end up introducing more noise into the amp than it purports to eliminate.
Yes, seeing the schematic was what prompted me to post the regenerator module. If the opamps in the filter are in need of upgrading. wouldn't no opamps at all be an improvement? Also the classD regenerator module is capable of much higher power levels (with a suitable external set of MOSFETs) than your existing regenerator - it could potentially power the output stage of the amp not just the front-end.
Mark I have seen the 7555 it has so much better specs than the 555
However I don't understand if it's a direct replacement?
And secondly I saw that the 7555 has an output current of 100mA
Wile the 555 has an output current of 200mA
How can I tell if the 7555 can handle my circuit?
The version or implementation of 555 and maximum load current has nothing in common with this circuit.
This connection of 555 forms a very typical or even classical oscillator circuit.
And it is loaded on C601 R617 only.
There is only one moment of time when C601 R617 circuit could be [a kind of] critical in a sense of 555's load current - when amplifier is turned on and C601 is completely discharged (and is a short circuit). But the current is limited by 10K resistance of R617 anyway, so for the maximal 0.1A of a "new but weak 7555" output current its output voltage should be 1KV. There is no 1KV in this beautiful Mark Levinson, so it's not an issue at all.
My advice to you is very simple:
if it ain't broke, don't fix it.
There's no need to change anything about this great amp as long as it works and brings you joy.
This connection of 555 forms a very typical or even classical oscillator circuit.
And it is loaded on C601 R617 only.
There is only one moment of time when C601 R617 circuit could be [a kind of] critical in a sense of 555's load current - when amplifier is turned on and C601 is completely discharged (and is a short circuit). But the current is limited by 10K resistance of R617 anyway, so for the maximal 0.1A of a "new but weak 7555" output current its output voltage should be 1KV. There is no 1KV in this beautiful Mark Levinson, so it's not an issue at all.
My advice to you is very simple:
if it ain't broke, don't fix it.
There's no need to change anything about this great amp as long as it works and brings you joy.
The important thing is the 555 has a spike of 200mA or more of shoot-through current from supply to ground every time it switches. Horrible behaviour that was avoided in all the CMOS versions like the 7555.
Thank you for clearing me that
God bless you
Those levinsons was a dream of mine for more than 20 years.
So I am very familiar with their sound
However when I have made some upgrades and recapping the sound characters stays the same but more analog like.
I understand why some people claims if someone is working don't touch it.
But I'm not that kind of person and all the the people I'm talking with about this design says that the 555 is the noisest part of this amp so I do believe I will go for the LMC7555
However by your kindness since it's a nightmare to open and close this amp and the pcb is not so accessible I insist to modify the AD712JN opamps to much better specs and noise that are direct replacement
And mainly because it's a filter and the 60hz sinewave is passing through
Can you help me with that ?
Thank you mark
God bless you
I definitely go for the LMC7555
And as I have said and asked above
I still insist of upgrading the opamps AD712JN to
much better specs and noise that are direct replacement
And mainly because it's a filter and the 60hz sinewave is passing through
Can you help me with that ?
I'm intrigued. If I decipher correctly, the circuit produces a floating bipolar power supply, with DC outputs appearing on the right side of the schematic attached in post 3. Opto isolator U2 allows drive to be activated, again with isolation.
Have I missed something? Out of curiosity, what does the floating power supply drive?
Interesting.
Have I missed something? Out of curiosity, what does the floating power supply drive?
Interesting.
