Want To Know What Voltage To Apply.

[roytech9]

Hey Guys, I've Been Viewing This Site For Quite A While And Saw You Guys A Pretty Much Helpful.

My Problem Is That . I Have a "Gemini P-600" Amplifier And I Want To Modify It To Meet The "Gemini P-800"

The P-600 Has (1) each Of 2SC3281 & 2SA1302 Per Channel. But On The Circuit Board Has room To Add in Another pair. Making It (2) Pairs Per Channel . To Meet The P-800 Series. What I really want To Know Is What Voltage Change I gotta Make And Do I need To Change Any Components In The Circuit . The P-600 Has A -\+40 Volts Powersupply. Any Help Will Be Very Much Appreciated.

Here Are The Schematic , Sorry Schematic To Large To Upload
Location Gemini P-600 | Owners Manual, Service Manual, Schematics, Free Download | HiFi Engine

[AndrewT]

For each output device there are 3 resistors. Q109 has R118 Base stopper, R122 Emitter resistor, R126, protection trigger.

Extra stopper and the emitter resistors must be in place for every output device that you add.

The protection trigger resistor can remain, only monitoring one device in each half, or it too can be multiplied up, to monitor all the output device currents. If you do add extra protection trigger resistors then the total parallel resistance of the resistors must equal the existing 330r shown, i.e two 660r for a 2pr stage or three 990r for a 3pr stage. In both cases go down to the nearest E24 value (620r and 910r).

I can see the schematic and enlarge it, without going to the remote server.

[sreten]

Hi,

Leaving the supply as is you will extend the current capability if the supply is up
to it by adding the extra output pair. To get more power into higher impedance
loads you would need to up the rail voltages, to say +/- 50V.
What rail voltages does the P-800 have ?

rgds, sreten.

[roytech9]

@ AndrewT

Thanks Very Much . I Know I Gotta Put In Those Parts. I'll Be Using
For Base Stopper 10 Ohm 1/2Watt
For Protection Resistor 330 Ohm 1/2 Watt Cuz The Electronics Shop Close To Me Never have 1/4 Watt

@ sreten Thanks. But Too bad I have No Idea What's The Rail Voltages On The P-800

Also I'm Very Curious If I Raise That Voltage to -\+50 Volts If The Bias Voltage Is Gonna Get Too High.
As Of Now The Bias Voltages Are -\+ .482 Millivolts

[roytech9]

@ AndrewT
Sorry I have'nt edited My Last Reply .
I doubt very much that I'm gonna get more Wattage By Just adding In The Other Parts To The Circuit Board, Somehow I Know I MUST Raise The Voltage From -\+40 Volts To (Whatever) As Sreten Sugessted To Support Those Extra Outputs. If I Add The Extra Outputs and Have No Voltage Gain On That Circuit > well It's Like I'm Playing In Mud With no water To wash my feet... As I have Noticed For The P-600 and The P-800 there are No Parts In The predriver/Driver stage Modified , I just want to make Sure That If I add More Volts That I Don't get Biasover voltage and It blow Out all Outputs,

This Is How The AMP Operates. When U Turn On The Power.. Both POWER AND PROTECTION Led's Are Lit Till Abot 5 Secs. Then Priotection Led Switches Off and Speaker Relay Clicks.. As I have Noticed that When The Amp Is Switched On .. Bias Volts on Both Base Pins On The PNP and NPN Transistors Rise From (1.3) Volts then back Down To stable .482 Millivolts then The Speaker Relay Switches On.. What I'm Trying To avoid Is Raising the Rail volts and Having the bias Volts Go haywire at the same Time.. Will defo Blow My Outputs, That;s What I'm trying to refrain from.. If You Guys Can Simply Guide Me In The Way to Do this without Disaster will much help me.. again thanks Giuys For Taking Your Time To assist Me

[AndrewT]

to change the PSU voltage you will need to replace the PSU, Transformer and probably smoothing caps. That's an expensive job.
The amplifier then needs to be adjusted and checked for correct operation at the higher voltage. All the ancilliaries need to be checked that they are unaffected by the higher voltage.
Finally with a higher voltage and doubled output devices the heatsink will need to dissipate ~two and a half times more power. Throw away the heatsink as well and try to find room to fit a very much larger heatsink.
Are you ready for all that expense and amp redesign?

If you double up or triple the output devices but keep the same PSU and voltage then you don't get a significant power increase unless the amp was current limited in the first design.
Sometimes you might get a 5% increase in maximum output power by doubling up the output stage. In a poor amp that has saved cost by deliberately installing too few output devices you may find you get a 30% increae in maximum power. This although looks big on paper makes only 1dB more noise than standard. However it may very significantly improve the performance of the amplifier and this could result in improved sound quality coming from the speakers.

There are only two ways to find out. Ask someone who has done it before you, or do it yourself.

[sreten]

Hi,

HiFi engine has the P-800 service manual just as it has the the P-600.

No doubt the P-800 manual will show all the changes you need to make.

However the only point without updating the power supply of updating
the output section would be for low impedance loads and an increase
in the thermal efficiency, double output devices run cooler than singles,
as they have half the thermal resistance of a single pair, a single pair
is usually more than the heatsink, two pairs ~ the same, that's good.

Consequently SOA protection for doubled devices can be less restrictive.
Depending on your design philosophy this is great or utterly pointless.
IMHO it is worth doing, doubling output devices is more load tolerant.

It is worthwhile, but you won't get any higher power into 8+ ohms.
You will get a more load tolerant amplifier, for real reactive loads.

rgds, sreten.

This assumes of course, not only the board, but also the heatsink
has provision for doubled output devices, if it doesn't you are
wasting your time, sell what you have and buy the uprated.