Conrad Johnson Premier Four pics.
Here are some more pictures of the Prem-4 having removed the covers.
http://www.saabphotos.com/gallery/al...0/DSCN0993.jpg
Power supply transformer, btw all the blue caps are for power supply smoothing and filtering, each is 1300uF 350V. They are wired in series pairs with 100K/2W resisters in parallel with each one. The plate voltage is 500V.
http://www.saabphotos.com/gallery/al...0/DSCN0996.jpg
Output transformer, these are supposed to be special, don't know the details.
http://www.saabphotos.com/gallery/al...0/DSCN0997.jpg
Labels are peeling off due to age.
http://www.saabphotos.com/gallery/al...0/DSCN0999.jpg
Right, I have 30 years experience in electronics related fields, have a circuit diagram and I am still crapping myself at taking the covers of this thing. What I am about to do could kill.
Underneath now.
The PCB is double sided but not plated. No solder resist so hand soldered. No silkscreen. Not impressed, especially as I notice what might be a wiring error (white/red wires go to a green wire and not what appears to be the pin intended for connection).
Most of the wiring on the right is from the output transformers. The amplifiers is ultralinear so 5 wires per transformer.
the potentiomters are for setting the bias for each output tube. I think Kudos for using decent size pots for this and not presets.
First thing check the power supplies.
The iron items on the right are 320mH, 600mA DC chokes, these are wired between the 500V smoothing caps (2) and a seperate pair of filter caps for each channel. The "regulated" or rather "isolated" supplies come from the latter with each input tube having its own "isolated" output.
The isolated voltages are 20V higher than they should be. will need to look into this.
The heater supply is top left near the orange cap, This was not working correctly, half the rectifier has blown up (seems a common problem for me), replaced it on this side of the PCB. Now the input tubs glow nicely.
http://www.saabphotos.com/gallery/al...0/DSCN1000.jpg
here is the dead rectifier
http://www.saabphotos.com/gallery/al...0/DSCN1009.jpg
One of the channels had blown its plate fuse, most likely culprit is a cathode resistor which is 20R wirewound. By measuring the cathode to ground resistance with the tubes removed should find it, and sure enough we do. But to replace it means getting at the other side of the board and that means de-soldering some wires. I desoldered the left hand side ones after making lots of photos. This is quite scary. Before messing with this always check the big caps are discharged before approaching. Fortunately the resistors across the caps discharge them fast and the resistors are in good condition.
http://www.saabphotos.com/gallery/al...0/DSCN1004.jpg
Crikey, theres a lot of expensive caps in here.
http://www.saabphotos.com/gallery/al...0/DSCN1006.jpg
I am using an I-pod for source, it works well. It works fabulously well with my friends I-phone, but I don't want to blow that up.
http://www.saabphotos.com/gallery/al...0/DSCN1007.jpg
Hopefully you can see the blown cathode resistor. near to it you can see why it went bang. Things have a habit of falling through the holes onto circuit boards in my house. This is one bad thing about circuit boards without a solder resist. Going to examine the rest of the board for FOD.
http://www.saabphotos.com/gallery/al...0/DSCN1008.jpg
These presets are to match the gain in the phase splitter. No need to touch them yet.
http://www.saabphotos.com/gallery/al...0/DSCN1010.jpg
Near the bottom is the circuit that allows for the bias setting. There is 1M between the cathode and the LF353 input and a 6V2 Zener to ground. I confess I don't really understand how this is supposed to work. Presumably the zener is there to prevent a big excursion taking out the op-amp.
http://www.saabphotos.com/gallery/al...0/DSCN1012.jpg
Power supply isolator previously discussed. The high value brown resistors tend to drift, and these 560K resistors actually measure close to 700K. I will remove them and place them on the other side of the board for easy replacement later, maybe when this warms up the will be correct. The other resisters measure OK. This might explain the elevated voltages I read on the isolated supplies.
http://www.saabphotos.com/gallery/al...0/DSCN1013.jpg
I think the 50uF caps are there to keep the input tube heaters alive when the power goes off long enough for the HT supply to discharge.
http://www.saabphotos.com/gallery/al...0/DSCN1014.jpg
20R W/W resistors are also used to connect the screen grids to the ultralinear tappings.
http://www.saabphotos.com/gallery/al...0/DSCN1015.jpg
Input valves go here
http://www.saabphotos.com/gallery/al...0/DSCN1016.jpg
I have removed the Shakeproof washer and the blown resistor at this stage
http://www.saabphotos.com/gallery/al...0/DSCN1017.jpg
Ok after re-assembly, I am using only 4 of the 8 output tubes. Each transformer tapping is driven by two tubes in parallel. We should be ok with just one tube so we have 50W instead of 100W, at least to check the amplifier is working.
At this stage I have not replaced the plate fuse (they are Very Expensive, only have 3 spare). The amp will actually work with a very small current (there is an LED across the fuse that tells you it is blown, the current through the LED is sufficient for the amplifier to give a very low output when it works. Of course the bias is then wrong so the LEDs are lit.
http://www.saabphotos.com/gallery/al...0/DSCN1019.jpg
Plate fuse is in now, amp is running.
http://www.saabphotos.com/gallery/al...0/DSCN1022.jpg
Lights out
http://www.saabphotos.com/gallery/al...0/DSCN1023.jpg
Start to put some covers back on and audition, while thinking about getting new parts. Those W/W resisitors are outside spec and maybe should be replaced. The high value Allen Bradleys are easy enough to find.
http://www.saabphotos.com/gallery/al...0/DSCN1025.jpg
It sounds very good, not sure replacing the Vishay W/W for KOA Film type is worth the risk, open to suggestions.
Alternative uses for a Quad 306
More pictures of Oxford in bits...
Doing a clearout and found some more pictures of the Oxford that my be of interest to turntable fans.
Sorry about the timewarp, but this is where we were last time with the bearing section removed. Just noticed that the thing is still plugged into the mains and on!
http://www.saabphotos.com/gallery/al...0/DSCN0827.jpg
Underneath the plinth - it is fixed with four bolts (damped by cobwebs)
http://www.saabphotos.com/gallery/al...0/DSCN0828.jpg
Near armboard. We will remove the little screws near the edge in a bit.
http://www.saabphotos.com/gallery/al...0/DSCN0829.jpg
The plinth is connected via some ribbon and DIN plugs. IMO this is bad but it is at least cheap and would have helped keep the price of the table reasonable. We enter the realm of questionable engineering here - (IMO) emulate with caution.
http://www.saabphotos.com/gallery/al...0/DSCN0830.jpg
The plinth has been unbolted.
This is the sorbothane isolation for the table. It is critical to the design. It is not thermally stable though and it sags under the enourmous weight of the platter and the heat from the PSU beneath.
http://www.saabphotos.com/gallery/al...0/DSCN0831.jpg
It should look something like this but the turrets (next picture) would actually fall through if any weight were placed upon them. The spikes of the bearing assembly rest somewhere in the bolt heads.
http://www.saabphotos.com/gallery/al...0/DSCN0832.jpg
http://www.saabphotos.com/gallery/al...0/DSCN0833.jpg
Maybe we will fare better with the plinth. Need to inspect it just in case there are organisms inside.
Lets take the screws out
http://www.saabphotos.com/gallery/al...0/DSCN0835.jpg
0 bio-entities detected, but hmm.
http://www.saabphotos.com/gallery/al...0/DSCN0836.jpg
Switch PCB, V1.1 already.
http://www.saabphotos.com/gallery/al...0/DSCN0837.jpg
Motor, the optocoupler is looking for a short length of black tape.
http://www.saabphotos.com/gallery/al...0/DSCN0839.jpg
Note to DIYers Don't ever let a wire bend at a solder joint (ie use sleeves) this is for mechanical integrity as well as to to keep things from shorting out. Please also say no to IDC for this.
http://www.saabphotos.com/gallery/al...0/DSCN0840.jpg
See that tape on the motor more clearly here. Not sure what happens if it falls off. seems to be well stuck, good.
http://www.saabphotos.com/gallery/al...0/DSCN0841.jpg
The other side is prepared to accept the motorised Air-Tangent arm lift wiring.
http://www.saabphotos.com/gallery/al...0/DSCN0842.jpg
The brass mountings are where the plinth is bolted to the base below
http://www.saabphotos.com/gallery/al...0/DSCN0843.jpg
The white screw mount is cheap simple and effective as far as I can tell. Going to look under the PCB for amusement..
http://www.saabphotos.com/gallery/al...0/DSCN0844.jpg
No connector for the ribbon, sigh. The FR4 should be cleaned up also, can get nasty splinters with this stuff.
http://www.saabphotos.com/gallery/al...0/DSCN0845.jpg
Corner cabinet fixing is discrete. I know nothing about woodworkery mindyou.
http://www.saabphotos.com/gallery/al...0/DSCN0846.jpg
This is a little disappointing, probably why I "lost" these photos.
Due the fragility of the ribbons/DIN fix them securely with gaffer tape before attempt at cleaning.
http://www.saabphotos.com/gallery/al...0/DSCN0847.jpg
Gonna use this. It works well on my flatscreen.
http://www.saabphotos.com/gallery/al...0/DSCN0856.jpg
Filled the holes with kitchen paper.
http://www.saabphotos.com/gallery/al...0/DSCN0857.jpg
Better.
http://www.saabphotos.com/gallery/al...0/DSCN0859.jpg
Not cobwebs but clingfilm for temporary storage.
http://www.saabphotos.com/gallery/al...0/DSCN0864.jpg
Continued...
IMPROVED - Quad 306 Chicken Warmer Mk2
So, no way can I afford the PS Audio Power Plant, but for grins put this together:
It is a sinewave generator feeding a Quad 306 which then drives a backwards transformer to power an illuminator.
http://www.saabphotos.com/gallery/al...0/DSCN1724.jpg
Can probably improve this arrangement with a more suitable transformer and using both channels of the 306.
http://www.saabphotos.com/gallery/al...0/DSCN1725.jpg
Close up of transformer.
http://www.saabphotos.com/gallery/al...0/DSCN1726.jpg
After the chicken was warmed up, I tried connecting it to a pair of Acoustat Interfaces. The older type interfaces have lots of mechanical hum (caused by the 5kV energising transformer). By adjusting the frequency the Hum can be completely removed. They are near silent at 60Hz, which is where I suppose they were designed to operate. Makes me wonder what the importers of this stuff actually do to earn those fat commi$$ions.
There should be plenty of power remaining to run the turntable and phono stage in the system which uses a passive preamp and another Quad 306 which will just have to run from real mains.
Still testing to see if there is definate audible improvement using this clean supply, but IMO just getting rid of the mechanical hum is a big plus.
Peter.
PS: I think I should mention that this might be dangerous and may harm you or your 306.