G.A.S Goliath

[Cambe]

Hello,

I have a G.A.S Goliath pre preamplifier i would like to use with a low output mc and a preamp that does not have mc output. What is the power requirements for the Goliath? My Theobe is not working.

 

[llwhtt]

I just answered your AK post. +/- 28VDC. What's wrong with your Thoebe? I can repair it if you need. I'm a GAS/SUMO addict and have almost all of the common units EXCEPT a Thoebe. I rebuilt a Thoebe a few years ago but never got to run a Goliath with it. Can you remove the cover and tell where the wires to the external Goliath connector go. I don't remember if there are some decoupling RC networks between the power supply and the connector, I don't think there is. Both Thaedras have an RC decoupling network between the PS and the head amplifier, that could be why you see +/- 22VDC on the head schematic, instead of +/- 28VDC.

Craig

 

[Cambe]

Thanks for replying llwhtt.
The Theobe is humming very loudly. Take off the the back cover off the Theobe right?

 

[llwhtt]

The top cover, should be some wires, black, gray and white going to the connector on the rear if IIRC. Your Thoebe probably has a bad PS/regulator card. Can you post a picture looking straight down into the unit?

Craig

 

[Cambe]

Okay, I will and get back to you in a few minutes.

 

[Cambe]

llwhtt,

Here is a few shots of the inside.

 

[llwhtt]

Did you find the wires? Can you post apicture where they connect to the main board? From those pics I would say those are all original capacitors, probably long gone, notice how the heatshrink covering has shrunk down the sides of the capacitors. These preamps, Thaedra and Thoebe, run a tad on the warm side.

Craig

 

[Cambe]

The wires to the power input jack are red and violet brownish. Yes, this was originally bought new so, I guess the heat over time has caused this.
Here is more pictures, I can take more with better lighting if needed.

 

[llwhtt]

It's just too crowded in there to see what's going on. I'll have to look for the mother board schematic when I get home. I can measure my Thaedra to see what the head amp voltage should be 22 or 28.

Craig

 

[Cambe]

Yep!
Thanks.

 

[llwhtt]

I found the answer in an email from Mike Bettinger, there's no decoupling circuit, the rear connector is straight off of the regulators. The wires in the one I rebuilt were white and gray, I guess they used whatever color they had at the time. Soooooooooooooo there's your answer +/- 28VDC, don't know what the current is though. I'll figure that out when I get home.

Craig

 

[Cambe]

Thanks for confirming the voltage. Yes, the current would be helpful.

Cambe

 

[llwhtt]

My Thaedra I has 91 Ohm resistors in the RC decoupling network. Voltage drop is 4.3-4.4VDC so current draw is approx. 50ma. So your power supply will need to supply +/- 24-28VDC @ a min. 50ma.

Craig

 

[Cambe]

Thank you llwhtt.
Do you have any recommendations for a suitable power supply design layout that fits the requirements?

 

[llwhtt]

Since this seems to be a temporary fix, you ARE going to get Thoebe fixed aren't you, I would just get a bench top regulated dual power supply. Probably cheaper than making one. MCM Electronics has #72-8690A for $159 but is backordered at the moment.

Craig

 

[Cambe]

Hi llwhtt,
I plan to order Salas BIB or SSLV1.1 PCBs from Tea-Bag. Yes, I do plan to get the Theobe
fixed. I will contact you soon about it.

 

[llwhtt]

I was studying the Thoebe layout on the Japanese Amp8 site and it looks as tho the headamp is fed from two big resistors so I would shoot for the +/-24VDC. Do your connector wires connect at the end of two diagonally positioned resistors?

Craig

 

[Cambe]

llwhtt,
From what I can see the resistors are marked 10 ohms.

 

[llwhtt]

10 Ohms won't drop much voltage at 50 ma. I guess the power supply voltage don't matter all that much. The Head Amp schematic says +/- 22VDC, my Thaedra I, which uses the same PCB has +/- 24VDC and your Thoebe will probably have close to +/- 28VDC. I've never seen a Goliath in person is there any thing in it besides the Head Amp PCB?

Craig

 

[Cambe]

I will take off the covers and take some photos of what is inside.