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unnecessary surgeries to an Akai S900
Old 30th January 2022
  #31
Gear Nut
 
🎧 5 years
Sampler fixed Nice and quiet now, working beautifully!!!
Old 30th January 2022 | Show parent
  #32
Gear Addict
 
SawneyBean's Avatar
 
Quote:
Originally Posted by ghaleon ➡️
Sampler fixed Nice and quiet now, working beautifully!!!
what was the final fix?
Old 30th January 2022 | Show parent
  #33
Gear Nut
 
🎧 5 years
Quote:
Originally Posted by SawneyBean ➡️
what was the final fix?
after the recap, I was testing it with my mixing board that had a channel die recently. Pulled the noisey channel and finally got to test the s900 properly.

The recapping seems to have fixed the noise problems!
Old 30th January 2022
  #34
Gear Addict
 
SawneyBean's Avatar
 
Thumbs up

Good to know, congrats on a successful fix!
Old 5th April 2022 | Show parent
  #35
Gear Head
Quote:
Originally Posted by ghaleon ➡️
after the recap, I was testing it with my mixing board that had a channel die recently. Pulled the noisey channel and finally got to test the s900 properly.

The recapping seems to have fixed the noise problems!
I have a working S900 that I really love and have been thinking of doing the full recap (all boards). Same intention as you and Hollowman, to keep it healthy for years to come.

How much time did it take you to complete the whole sampler?

Congratulations on fixing an amazing sampler
Old 5th April 2022 | Show parent
  #36
Gear Nut
 
🎧 5 years
Quote:
Originally Posted by Saulo Cisneros ➡️
I have a working S900 that I really love and have been thinking of doing the full recap (all boards). Same intention as you and Hollowman, to keep it healthy for years to come.

How much time did it take you to complete the whole sampler?

Congratulations on fixing an amazing sampler
start to finish it probably took a week using my free time! I bought a desoldering gun and I would say thats almost essential.
Old 26th September 2022 | Show parent
  #37
Here for the gear
 
Hi.

Can I use TL 072 or NE5532 to this audio output buffer?
Old 26th September 2022 | Show parent
  #38
Quote:
Originally Posted by zone12 ➡️
Hi.

Can I use TL 072 or NE5532 to this audio output buffer?
You can if it’s all you have but you don’t need a dual opamp. The NE5532 would perform better than the TL 072 as an output driver.
Old 26th September 2022 | Show parent
  #39
Here for the gear
 
Quote:
Originally Posted by Hollowman9 ➡️
You can if it’s all you have but you don’t need a dual opamp. The NE5532 would perform better than the TL 072 as an output driver.
Thanks for reply finally I want to use TL071. Two large capacitors in the your schematic power OPamp? Could you show me how they are supposed to be connected?
Old 27th September 2022 | Show parent
  #40
Quote:
Originally Posted by zone12 ➡️
Thanks for reply finally I want to use TL071. Two large capacitors in the your schematic power OPamp? Could you show me how they are supposed to be connected?
TL071 is not a good choice for this role. In general TL07X opamps have high common mode distortion with heavily loaded outputs.
The schematic shows how the capacitors are connected.
Old 27th September 2022 | Show parent
  #41
Here for the gear
 
Quote:
Originally Posted by Hollowman9 ➡️
TL071 is not a good choice for this role. In general TL07X opamps have high common mode distortion with heavily loaded outputs.
The schematic shows how the capacitors are connected.
Ok thanks. Do you recommend anything specyfic? I found 3 bipolar capacitors on your scheme. I don’t know where the 2 additional electrolytic capacitors are to be connected and what their capacity. Are electrolytes also bipolar? Could you help me? Your mod is fantastic!
Old 27th September 2022 | Show parent
  #42
Quote:
Originally Posted by zone12 ➡️
Ok thanks. Do you recommend anything specyfic? I found 3 bipolar capacitors on your scheme. I don’t know where the 2 additional electrolytic capacitors are to be connected and what their capacity. Are electrolytes also bipolar? Could you help me? Your mod is fantastic!
Thanks
There are two NP electrolytic caps which are the input and output blocking capacitors in the audio path. The value isn’t critical, I chose 47uf because I had them on hand. The higher the capacity here the lower the corner frequency of the high pass filter these caps create.

Inside the feedback loop around the opamp is a 100pf poly type cap for stabilization.
There’s also two 0.1uf monolithic ceramic capacitors between the supply pins of the opamp and ground for local bypass.
None of the values or types of these 3 are critical and can be substituted with the closest replacements on hand.
Old 27th September 2022 | Show parent
  #43
Here for the gear
 
Quote:
Originally Posted by Hollowman9 ➡️
Thanks
There are two NP electrolytic caps which are the input and output blocking capacitors in the audio path. The value isn’t critical, I chose 47uf because I had them on hand. The higher the capacity here the lower the corner frequency of the high pass filter these caps create.

Inside the feedback loop around the opamp is a 100pf poly type cap for stabilization.
There’s also two 0.1uf monolithic ceramic capacitors between the supply pins of the opamp and ground for local bypass.
None of the values or types of these 3 are critical and can be substituted with the closest replacements on hand.
Thanks! Do you recommend any specific opamp for this buffer? NE5534 ?
Old 27th September 2022 | Show parent
  #44
Quote:
Originally Posted by zone12 ➡️
Thanks! Do you recommend any specific opamp for this buffer? NE5534 ?
That one has worked great for me so far. Ones with high output drive current are good choices in general.
Old 28th September 2022 | Show parent
  #45
Gear Nut
 
🎧 5 years
Quote:
Originally Posted by Hollowman9 ➡️
That one has worked great for me so far. Ones with high output drive current are good choices in general.
I picked up an s950 last month, so my s900 is ripe for modding I figure!

Wondering if you ever made a step by step tutorial for your mod? Skill wise, I'm handy with a soldering iron, but can't read schematics that well
Old 28th September 2022 | Show parent
  #46
Quote:
Originally Posted by ghaleon ➡️
I picked up an s950 last month, so my s900 is ripe for modding I figure!

Wondering if you ever made a step by step tutorial for your mod? Skill wise, I'm handy with a soldering iron, but can't read schematics that well
The output buffer circuit was constructed with point to point wiring on a generic perfboard. A step by step tutorial would take longer to write than it took to make that board. I’m afraid this probably won’t happen.
Old 28th September 2022 | Show parent
  #47
Here for the gear
 
I made it today on stripboard. I’ll test buffor tomorrow 🤞 I think I will use the MIC input for this chrunchy output. Big thanks for your help 🫡
Attached Thumbnails
unnecessary surgeries to an Akai S900-b2fe337b-18e7-4626-aadb-6852d0133d16.jpeg  
Old 29th September 2022 | Show parent
  #48
Here for the gear
 
Buffor works fine I wonder if it is possible to make a switch that will redirect this dirty signal to record in this sampler?
Old 29th September 2022 | Show parent
  #49
Quote:
Originally Posted by zone12 ➡️
Buffor works fine I wonder if it is possible to make a switch that will redirect this dirty signal to record in this sampler?
That’s excellent! I’m happy to hear it worked out for you
Be sure to try various different sampling rates.
I looked into the possibility of adding a switch to bypass the filter in the sampling circuit but I had concerns about creating unwanted feedback loops. I don’t remember if I tried it using jumpers or not. Could be worth looking into.
Old 29th September 2022 | Show parent
  #50
Here for the gear
 
Quote:
Originally Posted by Hollowman9 ➡️
That’s excellent! I’m happy to hear it worked out for you
Be sure to try various different sampling rates.
I looked into the possibility of adding a switch to bypass the filter in the sampling circuit but I had concerns about creating unwanted feedback loops. I don’t remember if I tried it using jumpers or not. Could be worth looking into.
I noticed that with the change of bandwith there are peaks in the high band. I wonder if it is possible to use a simple RC filter in this circuit and filter out some high frequencies. Using a filter with the S900 would be ideal. What do you think about it? Let me know if you try to bypass this with a switch
Old 29th September 2022 | Show parent
  #51
Quote:
Originally Posted by zone12 ➡️
I noticed that with the change of bandwith there are peaks in the high band. I wonder if it is possible to use a simple RC filter in this circuit and filter out some high frequencies. Using a filter with the S900 would be ideal. What do you think about it? Let me know if you try to bypass this with a switch
If you have a synth with an external input for its VCF/VCA you can route the dirty output of the S900 into it and then trigger that synth for control over the dirty signal. This will allow you to filter the signal as much as you want as well as apply enveloped contouring if desired.

This winter sometime I’m planning to replace the LCD backlight on mine so I can tinker with other ideas then and take better pictures of it all too.
Old 29th September 2022 | Show parent
  #52
Here for the gear
 
Which chip is responsible for the anti-aliasing filter? Is that the MF6CN-50?
Attached Thumbnails
unnecessary surgeries to an Akai S900-9395f9d4-7729-4ea0-86e9-30e645ad4c28.jpeg  
Old 29th September 2022 | Show parent
  #53
Quote:
Originally Posted by zone12 ➡️
Which chip is responsible for the anti-aliasing filter? Is that the MF6CN-50?
Yes!
Old 29th September 2022 | Show parent
  #54
Here for the gear
 
Quote:
Originally Posted by Hollowman9 ➡️
Yes!
It is enough to bybass this filter to record the dirty signal?
Old 30th September 2022 | Show parent
  #55
Quote:
Originally Posted by zone12 ➡️
It is enough to bybass this filter to record the dirty signal?
Actually no.
Referring to the block diagrams in the service manual the filtering happens prior to the SAR. The MF6CN is a 36 db/oct with a corner frequency set by the CPU depending on the chosen sampling rate. After this is a fixed 12db/oct filter with a 18khz cutoff. Bypassing these filters won’t achieve the same effect. I modded a Yamaha R100 in this same manner, bypassing the filters in front of the SAR, and it’s a very different sounding result. As the input signal gets higher the high end becomes more distorted and trashy until eventually it becomes glitchy static. And that happens quickly and uncontrollably with peaky sources like drum loops. It isn’t musically useful glitches unless that’s what you’re aiming for.
Keep in mind this output we’re tapping in the S900 is technically the error correction feedback for the SAR. Looking at the schematics I don’t see a safe way to actually redirect this for recording because it’s being derived from the “recording process” itself.

Just sample it with another sampler.
Old 30th September 2022 | Show parent
  #56
Here for the gear
 
Quote:
Originally Posted by Hollowman9 ➡️
Actually no.
Referring to the block diagrams in the service manual the filtering happens prior to the SAR. The MF6CN is a 36 db/oct with a corner frequency set by the CPU depending on the chosen sampling rate. After this is a fixed 12db/oct filter with a 18khz cutoff. Bypassing these filters won’t achieve the same effect. I modded a Yamaha R100 in this same manner, bypassing the filters in front of the SAR, and it’s a very different sounding result. As the input signal gets higher the high end becomes more distorted and trashy until eventually it becomes glitchy static. And that happens quickly and uncontrollably with peaky sources like drum loops. It isn’t musically useful glitches unless that’s what you’re aiming for.
Keep in mind this output we’re tapping in the S900 is technically the error correction feedback for the SAR. Looking at the schematics I don’t see a safe way to actually redirect this for recording because it’s being derived from the “recording process” itself.

Just sample it with another sampler.
Thanks for answer. I wonder if making an lpf filter using a second NE5534 set at 18 or 20khz would help to reduce peaks in the high band. If so, put it before or after the OP buffer? I noticed that with the change of bandwith there are peaks in the high band. I also thought that you could make a switch on 8 voices bypassing the high-pass filters MF6CN on outputs. A similar mod is popular for the EMU SP 12/1200.
Old 4th October 2022 | Show parent
  #57
Quote:
Originally Posted by zone12 ➡️
Thanks for answer. I wonder if making an lpf filter using a second NE5534 set at 18 or 20khz would help to reduce peaks in the high band. If so, put it before or after the OP buffer? I noticed that with the change of bandwith there are peaks in the high band. I also thought that you could make a switch on 8 voices bypassing the high-pass filters MF6CN on outputs. A similar mod is popular for the EMU SP 12/1200.
Put filters before the buffer.
The complexity of modifying the voice channels is what deterred me from adding VCFs to the voices like I planned earlier in this thread.
That was more of a biting off more than I could chew type deal but if you want to give it a shot by all means.
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