Kir_For_Pleasure
Well-known member
thanks !
TASCAM M-3500 ajusting voltage rails....with pics and schematics
- Thread starter pacemaker
- Start date
Help Support GroupDIY Audio Forum:
Hi Guys ,
first, Wkrbee, thanks for all those tips,
but it's a bit hard for me to understand the impact of all these changes,
increasing C114,C104 and C105 coupling caps is understandable for me,
but the rest of your mods seems related to the opamps upgrade rigth ?
Anyway thanks for sharing these J.W. mods,
I will keep this precious intel and study it later when i will be less a noob ;-)
I'm still struggling with my tascam PSU current handling capacity,
i used some PSU calculator,read threads and studied the PSU section in electronic for dummies,
( i authorize you to laugh ;-) )
As the 10d4b41 diodes bridges, 2SD845 and 2SB755 regulators seems strong enough to handle a lot of current
i also noticed that the transformer has 3X18V secondaries wich powers the +15,-15 and +12v
the fuses after transformer secondaries are 6.3A ,
i guess the secondaries migth be able to deliver at least 5A ?
If i'm right, it seems that the only "weak point in this PSU might be the caps ?
they are 22000uF,i know they help "filter" the DC coming form the diode bridges
How about changing them for a higher value like 47000uF ?
i also might have understood that changing resistor to ground might help too ?
any help,teach or knowledge would be greatly appreciated
here's the PSU schematics
http://img267.imageshack.us/img267/4968/psu1r.jpg
regards,
francois
first, Wkrbee, thanks for all those tips,
but it's a bit hard for me to understand the impact of all these changes,
increasing C114,C104 and C105 coupling caps is understandable for me,
but the rest of your mods seems related to the opamps upgrade rigth ?
Anyway thanks for sharing these J.W. mods,
I will keep this precious intel and study it later when i will be less a noob ;-)
I'm still struggling with my tascam PSU current handling capacity,
i used some PSU calculator,read threads and studied the PSU section in electronic for dummies,
( i authorize you to laugh ;-) )
As the 10d4b41 diodes bridges, 2SD845 and 2SB755 regulators seems strong enough to handle a lot of current
i also noticed that the transformer has 3X18V secondaries wich powers the +15,-15 and +12v
the fuses after transformer secondaries are 6.3A ,
i guess the secondaries migth be able to deliver at least 5A ?
If i'm right, it seems that the only "weak point in this PSU might be the caps ?
they are 22000uF,i know they help "filter" the DC coming form the diode bridges
How about changing them for a higher value like 47000uF ?
i also might have understood that changing resistor to ground might help too ?
any help,teach or knowledge would be greatly appreciated
here's the PSU schematics
http://img267.imageshack.us/img267/4968/psu1r.jpg
regards,
francois
The power supply will ultimately be limited by the transformer, since it takes more copper and iron to pass more power, but you can get marginally more output by other means.
The reservoir capacitors will top off 2x per cycle of the mains frequency, and then decay at a linear rate based on current draw, and amount of capacitance. The bottom of this ripple trough will set when regulators drop out of regulation.
If you increase the current drawn from your power supply there will be two apparent changes. First the slope of the capacitor discharge will be steeper, since you have more current being drawn from the same size capacitors. This means the bottom of the ripple waveform will go lower and possibly below the margin regulators can ignore. The second change is since the average current drawn is higher there will be a slight extra I x R loss in the transformer windings so the top of the ripple waveform will also be slightly lower.
Increasing the reservoir capacitance 2x will decrease the rate of decay by 1/2, so the Vp-p of the ripple will be roughly cut in half. So in a marginal power supply this could be enough.
Also check the heatsink temperature on any pass regulators that may be running hotter due to increased current draw. If you can't hold a finger on the heatsink it may be too hot.
JR
The reservoir capacitors will top off 2x per cycle of the mains frequency, and then decay at a linear rate based on current draw, and amount of capacitance. The bottom of this ripple trough will set when regulators drop out of regulation.
If you increase the current drawn from your power supply there will be two apparent changes. First the slope of the capacitor discharge will be steeper, since you have more current being drawn from the same size capacitors. This means the bottom of the ripple waveform will go lower and possibly below the margin regulators can ignore. The second change is since the average current drawn is higher there will be a slight extra I x R loss in the transformer windings so the top of the ripple waveform will also be slightly lower.
Increasing the reservoir capacitance 2x will decrease the rate of decay by 1/2, so the Vp-p of the ripple will be roughly cut in half. So in a marginal power supply this could be enough.
Also check the heatsink temperature on any pass regulators that may be running hotter due to increased current draw. If you can't hold a finger on the heatsink it may be too hot.
JR
ethervalve
Well-known member
Hey folks,
Some friends of mine just bought a 24 channel M-3500. Does anyone, perchance, know if its power supply is the same as the 32 channel version?
Some friends of mine just bought a 24 channel M-3500. Does anyone, perchance, know if its power supply is the same as the 32 channel version?
Hi John,
thanks for the info,
i just got an answer from tascam about the power transformer :
"The only info we have is what's in the OM/SM,(which you probably have)."
great answer ! ;-)
John, please can you tell me, regarding the 6.3A fuses,
wich are between the diode bridges and each Tx 18VAC secondaries
Am i right to presume that fuse value have to be a few more than the needed current for the console
and a little less than the available current of the transformer ?
If i'm right,
This TEAC 5320058500 transformer might have 3X18V output at 8 or 10A ?
Right ?
thanks for the info,
i just got an answer from tascam about the power transformer :
"The only info we have is what's in the OM/SM,(which you probably have)."
great answer ! ;-)
John, please can you tell me, regarding the 6.3A fuses,
wich are between the diode bridges and each Tx 18VAC secondaries
Am i right to presume that fuse value have to be a few more than the needed current for the console
and a little less than the available current of the transformer ?
If i'm right,
This TEAC 5320058500 transformer might have 3X18V output at 8 or 10A ?
Right ?
pacemaker said:
Probably.
The fuse is placed at that circuit node to protect against driving an AC short circuit should a diode fail. Diodes typically fail as a dead short, so the AC winding output directly driving a capacitor to ground would draw beaucoup current. It is possible the fuse value was determined by some safety agency to prevent the circuit board from catching fire in the event of a fault, while the fuse is surely sized large enough to not open in normal use. Depending upon the transformer design, it can probably put out a lot more power short term, than it can handle long term. It will take time to heat up all that copper and iron, but at some point it will exceed safe operating temperature for winding insulation, etc.
FWIW you can experiment by loading down the power supply with additional power resistors, but you will need enough wattage in the resistors to prevent burning them up, since they will get very hot. Don't place the resistors near the transformer so you can assess the transformer heat rise separately.
JR
Ok Thanks for your reply john,
so without power transformer rating , the only way to calculate
PSU loading capacity is with loading resistor ?
As i don't have 20W resistor on my bench, i guess i will have to let down... :-(
Or if i'm lucky, maybe someone here know the PS3500 power rating ?
I will change the 22000uF caps with some 30000uF or 47000uF
i still would like to fine tune the +/-15v voltage rails,
the schematics are here
http://img267.imageshack.us/img267/4968/psu1r.jpg
http://img153.imageshack.us/img153/6541/psufinal.jpg
I'm not sure if the correct resistors to adjust are R003 and R004 560ohms or R005 and R006 15kohms
any thoughts ?
Thanks for the allready given help
Regards,
Francois
so without power transformer rating , the only way to calculate
PSU loading capacity is with loading resistor ?
As i don't have 20W resistor on my bench, i guess i will have to let down... :-(
Or if i'm lucky, maybe someone here know the PS3500 power rating ?
I will change the 22000uF caps with some 30000uF or 47000uF
i still would like to fine tune the +/-15v voltage rails,
the schematics are here
http://img267.imageshack.us/img267/4968/psu1r.jpg
http://img153.imageshack.us/img153/6541/psufinal.jpg
I'm not sure if the correct resistors to adjust are R003 and R004 560ohms or R005 and R006 15kohms
any thoughts ?
Thanks for the allready given help
Regards,
Francois
That certainly looks like more than enough heat sink.
Why do you need to fine tune the 15V rails?
JR
Why do you need to fine tune the 15V rails?
JR
the +15v is 15,80v
and the -15 is -14,90v
I would like to adjust them for the perfect voltage,
and would like to learn too,
the different PSU i built, Mnats, peterC and others available here,
had resistor to ground adjusting the voltagen
On the 3500 schematics, i wasn't sure wich ones settle the voltage,
I'm hesitating between two,
With the answer, i will be able to learn and understand this circuit ,
Regards,
Francois
and the -15 is -14,90v
I would like to adjust them for the perfect voltage,
and would like to learn too,
the different PSU i built, Mnats, peterC and others available here,
had resistor to ground adjusting the voltagen
On the 3500 schematics, i wasn't sure wich ones settle the voltage,
I'm hesitating between two,
With the answer, i will be able to learn and understand this circuit ,
Regards,
Francois
pacemaker said:
OK, I'm guessing some here but it looks like the +V is established by ratio of R007+R008 vs. R025.. to make +15V rail voltage smaller, either make R007 or R008 smaller, or R025 larger. -15V rail is probably mirror image of +15v times -R005/R006. I suspect if you tweak the +15V rail to be closer to 15V. the -15V rail will follow automatically.
This should not make any difference in the sound.
JR
maybe i'm too anal with the details !
i thought it was best to set the voltage to the precise level,
and i also thought power transformer and opamps
works best when +/- rails are matched ,
My project was to match tensions and build a star scheme power distribution with bigger cables,
like i've done for the ground,
I might have read this on a console modification thread
Do you think it's overkill ?
Regards,
Francois
i thought it was best to set the voltage to the precise level,
and i also thought power transformer and opamps
works best when +/- rails are matched ,
My project was to match tensions and build a star scheme power distribution with bigger cables,
like i've done for the ground,
I might have read this on a console modification thread
Do you think it's overkill ?
Regards,
Francois
If it makes you feel better do it.. It should be harmless...
JR
JR
Kir_For_Pleasure
Well-known member
How does it sound with the 2ACA ??
Kir_For_Pleasure
Well-known member
about starground, are you connecting the grounding coming from psu to the starground point ?
Kir_For_Pleasure
Well-known member
Stargrounding done..miss the radioprograms that i use to hear before ;D
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