How to bypass the Dolby board on a Sansui 9090db?
- Thread starter z-adamson
- Start date
sKiZo
Hates received: 92644 43.20°N 85.50°W
Luck with that ... most of the audio gets routed through that thing at one point or another as it also controls the entire ganged bank of pushbuttons to the right of the volume control. I suppose you COULD try just hard wiring the AUX input on the back directly to the preamp section, but I'm thinking that would leave you with basically a bare bones integrated amp. I believe tone and channel balance and such are also gone if you do that. Terrible waste of an excellent feature rich machine ...
Last edited:
sKiZo
Hates received: 92644 43.20°N 85.50°W
Ever SEEN the board of which we speak?
(shudder)
PS ... seems to me that relay is an integral part of the protection system as well. Lose that, and lose the amps as well. Be interesting to see a link you're referencing to show exactly what's being successfully bypassed - I'd suspect they're just talking the dolby section itself? That looks like it'd be doable, but that's usually not the reason anyone ever considers working on the board ...
And yes - I've pinned and refurbed a similar board on my QRX 9001 - not a job for the faint of heart!
(shudder)
PS ... seems to me that relay is an integral part of the protection system as well. Lose that, and lose the amps as well. Be interesting to see a link you're referencing to show exactly what's being successfully bypassed - I'd suspect they're just talking the dolby section itself? That looks like it'd be doable, but that's usually not the reason anyone ever considers working on the board ...
And yes - I've pinned and refurbed a similar board on my QRX 9001 - not a job for the faint of heart!
Here's a link to someone highlighting the pass through sections on the board.
http://audiokarma.org/forums/index.php?threads/sansui-9090db-dolby-board-pictures-f-2655.491375/
http://audiokarma.org/forums/index.php?threads/sansui-9090db-dolby-board-pictures-f-2655.491375/
kevzep
Its all about the Music
Why not just service it and have it running as intended by Sansui?
The board is integral to the amplifier, and bypassing, which will be more of a complete headache, more time consuming than servicing it, and a bigger PITA than you can imagine.
Bypassing it will severely reduce the resale value too, I for one would not want to buy a bastardised 9090DB...
Just fix it...
The board is integral to the amplifier, and bypassing, which will be more of a complete headache, more time consuming than servicing it, and a bigger PITA than you can imagine.
Bypassing it will severely reduce the resale value too, I for one would not want to buy a bastardised 9090DB...
Just fix it...
sKiZo
Hates received: 92644 43.20°N 85.50°W
I did find this, and apparently you can bypass just the dolby section, leaving the switching functions intact. No reference to exactly how it's done without losing a LOT of other features as well.
http://www.audiokarma.org/forums/in...in-sacramento-california.677925/#post-9052083
Not sure if QRXRestore is back up and running since Jim died, but be worth checking.
(RIP @Trnsfmr ... you ARE missed. )
There's also a note in the same thread that suggests leaving the tape loop alone (and disabled due to the dolby bypass) and rewiring one of the phono in sections? That opens yet another can of worms, and wouldn't give you a true loop for recording anyway. I also see some reference in the same thread about losing a lot of gain ... never a good thing in my world, as it probably puts you out of the receiver's "sweet spot".
And once again - it's not the dolby section that's the usual culprit, and that can be bypassed already with the twist of the wrist. Again, be interesting to know exactly what the "problem" is here ...
http://www.audiokarma.org/forums/in...in-sacramento-california.677925/#post-9052083
Not sure if QRXRestore is back up and running since Jim died, but be worth checking.
(RIP @Trnsfmr ... you ARE missed. )
There's also a note in the same thread that suggests leaving the tape loop alone (and disabled due to the dolby bypass) and rewiring one of the phono in sections? That opens yet another can of worms, and wouldn't give you a true loop for recording anyway. I also see some reference in the same thread about losing a lot of gain ... never a good thing in my world, as it probably puts you out of the receiver's "sweet spot".
And once again - it's not the dolby section that's the usual culprit, and that can be bypassed already with the twist of the wrist. Again, be interesting to know exactly what the "problem" is here ...
Last edited:
z-adamson
Addicted Member
You bring up an interesting idea.
Could you or anyone else in the know provide any insight as to how exactly to do this and what exactly will be lost?
I am not seriously considering this, but I may if there is a way to keep tone controls, loudness etc.
z-adamson
Addicted Member
I understand the advantage to keeping it working as intended. But, sometimes things need to be changed for a variety of reasons.
kevzep
Its all about the Music
Totally your call, but its unnecessary as the problem can be resolved a lot easier than what you are proposing, I have done a few Dolby boards on the QRX9001's and they are even worse than the 9090, and I don't find them to be an issue at all really....
z-adamson
Addicted Member
Interestingly, that shop is only a few hours from me.
They only charge $45 for this mod (bypassing the dolby).....so how big of a job can it be?
kevzep
Its all about the Music
They've done all the hard work already, the PITA part is figuring out the best way to do it. Once the formula is established its pretty easy.
sKiZo
Hates received: 92644 43.20°N 85.50°W
Yup - if you're within driving distance and they're up for business, that'd be the way to go. I know S&H can be a killer for a unit that size, and I wouldn't want to mail it without some seriously bulletproof packaging.
Fallwalking
New Member
You can bypass the dolby functions, but you will lose the tape functions if you do this. You will remove the input wires to the dolby board F-2655, inputs 29 (right) and 30 (left), and move them and their respective grounds to the inputs of the mono/stereo switches before the resistors R01/R02 on the F-2654 board. You can also do this by moving them to pins 35(right)/36(left) on the ribbon cables if you don't have a bad ribbon cable. Or just pin the board like everyone says.
... The 8080DB I am working on has some issue with the actual selector switch (many broken pins) so bypassing it is the only way to go in order to get some function back. Replacing the selector switch or entire board is also a possibility, but the time and part cost isn't quite there for an 8080DB.
If you'd like a synopsis of how the selector works, here it is: Input -> Selector -> Tape 1 -> Selector -> Tape 2 -> Selector -> (FM Muting) -> Selector -> Mono/Stereo -> Loudness -> | Balance -> Volume -> | Tone
By moving the input you're bypassing the Tape and FM muting sections, but FM muting will still remain since it only influences the input signal, not the signal that is carried. Good times.
... The 8080DB I am working on has some issue with the actual selector switch (many broken pins) so bypassing it is the only way to go in order to get some function back. Replacing the selector switch or entire board is also a possibility, but the time and part cost isn't quite there for an 8080DB.
If you'd like a synopsis of how the selector works, here it is: Input -> Selector -> Tape 1 -> Selector -> Tape 2 -> Selector -> (FM Muting) -> Selector -> Mono/Stereo -> Loudness -> | Balance -> Volume -> | Tone
By moving the input you're bypassing the Tape and FM muting sections, but FM muting will still remain since it only influences the input signal, not the signal that is carried. Good times.
very nice of you to post this.
