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.
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.
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
Craig
Thanks for replying llwhtt.
The Theobe is humming very loudly. Take off the the back cover off the Theobe right?
The Theobe is humming very loudly. Take off the the back cover off the Theobe right?
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
Craig
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
Craig
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
Craig
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
Craig
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
Craig
Thank you llwhtt.
Do you have any recommendations for a suitable power supply design layout that fits the requirements?
Do you have any recommendations for a suitable power supply design layout that fits the requirements?
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
Craig
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.
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.
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
Craig
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
Craig