BigE - if the transformer has a single center tapped winding and not two separate windings you cannot use one bridge per winding as suggested above. You can use two bridges with each producing positive and negative rails, one per channel. I like option 6 - the two bridges isolate the channels as early as possible. The resistance of the umbilical and it's bit of inductance will help reduce ripple. Not sure you'd gain much over a CRC in the amp box, though.
I think you should have at least some of your capacitance in the amp box. Film bypass at the output devices sometimes helps, too. Film bypass at the electrolytic bank is subject to some controversy. It's possible to create ringing with the film cap and the electro's inductance. I've done it, but haven't noticed a change. Film caps at the output seem to make an improvement in sound quality.
If you do have 2 separate windings, one bridge per rail is the way most go. In this case I'd use 4 bridges, one per winding per channel as johnhenryharris suggests taken a step further.
I think you should have at least some of your capacitance in the amp box. Film bypass at the output devices sometimes helps, too. Film bypass at the electrolytic bank is subject to some controversy. It's possible to create ringing with the film cap and the electro's inductance. I've done it, but haven't noticed a change. Film caps at the output seem to make an improvement in sound quality.
If you do have 2 separate windings, one bridge per rail is the way most go. In this case I'd use 4 bridges, one per winding per channel as johnhenryharris suggests taken a step further.
I have to agree. 3-box holds no advantages other than having your transformer physically separated from the audio amp.
But anyway, have the transformer, dual bridges, and set of high ripple rated caps in the first box. Example capacitor DC on the umbilical. Then to the CRC filters in the PSU boards in each channel.
Most of the ripple will be contained in that box.
What is the exact transformer you are using?
To get full isolation between the two channels (in separate boxes), you will need a 4 secondary transformer in the 3rd box.
That is the ONLY way to get complete signal ground isolation between the channels.
You CANNOT get isolation between the channels sharing a transformer with a centre tapped secondary nor with one having a dual secondary.
The Problem of the non isolation comes when all exposed conductive parts and the three Safety Earths have to interconnected.
That is the ONLY way to get complete signal ground isolation between the channels.
You CANNOT get isolation between the channels sharing a transformer with a centre tapped secondary nor with one having a dual secondary.
The Problem of the non isolation comes when all exposed conductive parts and the three Safety Earths have to interconnected.
The three box amp is because of space restrictions. Currently, I have a stereo amp that I need to reach over to operate the TT. I wanted dual mono, but I have this big transformer that is doing nothing.
It is a Plitron, that has 5 secondary CT windings -- probably a five channel HT transformer. I had intended to use it as a power conditioner to provide balanced power to the line level gear, but did not like the results.
A three box unit would enable the transformer to go off to one side, and the amps behind each speaker, opening a path to the TT. A one box unit would be 20" deep and 19" wide, making access even worse. I'd like to fit it in the rack, but doing so causes the TT to pick up transformer vibration.
Maybe the best idea is to build it first, put the transformer on the rack and see if I can get away with one box...... It would then take two people to move it -- another disadvantage.
To deal with ground loops, I had envisioned connecting the chassis with the shield of the umbilical cord, the cord would have +/-/Audio Gnd... Safety earth connects to the transformer box, as does the shield and MAG is connected to the same point, with a ground loop breaker.
It is a Plitron, that has 5 secondary CT windings -- probably a five channel HT transformer. I had intended to use it as a power conditioner to provide balanced power to the line level gear, but did not like the results.
A three box unit would enable the transformer to go off to one side, and the amps behind each speaker, opening a path to the TT. A one box unit would be 20" deep and 19" wide, making access even worse. I'd like to fit it in the rack, but doing so causes the TT to pick up transformer vibration.
Maybe the best idea is to build it first, put the transformer on the rack and see if I can get away with one box...... It would then take two people to move it -- another disadvantage.
To deal with ground loops, I had envisioned connecting the chassis with the shield of the umbilical cord, the cord would have +/-/Audio Gnd... Safety earth connects to the transformer box, as does the shield and MAG is connected to the same point, with a ground loop breaker.
5 centre tapped windings opens the door to 5 isolated amplifiers spread around the room.
alternatively you could parallel two identical centre tapped windings for one remote isolated amplifier and parallel two other identical centre tapped windings for another remote isolated amplifier.
That leaves on winding for other uses.
alternatively you could parallel two identical centre tapped windings for one remote isolated amplifier and parallel two other identical centre tapped windings for another remote isolated amplifier.
That leaves on winding for other uses.
Washing Mosfets?
Hi All
I just got my heatsinks drilled and tapped.
Before fixing the mosfets with Keratherm, I would like to know how to clean the mosfets' tabs and legs, that are somewhat oxidized. Is it ok to wash them with steel wool, rinse with distilled water and finally dry them?
I've already done this with bipolars, but I'm worried with ESD when it comes to Fets.
Thank you
Daniel
Hi All
I just got my heatsinks drilled and tapped.
Before fixing the mosfets with Keratherm, I would like to know how to clean the mosfets' tabs and legs, that are somewhat oxidized. Is it ok to wash them with steel wool, rinse with distilled water and finally dry them?
I've already done this with bipolars, but I'm worried with ESD when it comes to Fets.
Thank you
Daniel
Hi All
I just got my heatsinks drilled and tapped.
Before fixing the mosfets with Keratherm, I would like to know how to clean the mosfets' tabs and legs, that are somewhat oxidized. Is it ok to wash them with steel wool, rinse with distilled water and finally dry them?
I've already done this with bipolars, but I'm worried with ESD when it comes to Fets.
Thank you
Daniel
Short the gate to the source, or all 3 terminals together, by soldering or conductive foam, before such handling.
I have always "cleaned" the attachment surface (drain) of MOSFETs using 400 grit or finer emery paper. Put a sheet of emery paper grit up on a very flat surface and rub the MOSFET drain around on it to clean and remove any surface roughness. The MOSFET legs can be cleaned with most anything that is non-corrosive.
A MOS gate can easily be destroyed by casual handling or improper packaging, especially in low humidity conditions. During assembly, if you don't have a static mat and wrist strap, you can use a piece of sheet metal, metallic cookie sheet, aluminum foil, etc. as a work surface. Also, try to keep touching the metal with one hand while working.
Dishwashing liquid and water (warm or cold) is very good for cleaning devices, PCBs etc.
The leads should all be pre-tinned.
If there is any discolouration, either due to contamination, or corrosion, then a quick swipe with flux and a tinned hot soldering iron will clean off everything and leave you with newly tinned leads. The new tinning will also have reduced the levels of ROHS products that get used in modern production.
That makes for better joints when you use your eutectic 63/37 solder.
The leads should all be pre-tinned.
If there is any discolouration, either due to contamination, or corrosion, then a quick swipe with flux and a tinned hot soldering iron will clean off everything and leave you with newly tinned leads. The new tinning will also have reduced the levels of ROHS products that get used in modern production.
That makes for better joints when you use your eutectic 63/37 solder.
Hi All,
I have completed the first channel of the F5t v3 (with +/- 48v rails).
Problem is I get 0mA bias across the negative rail (for ease of measurement I have some 1% 5w 0.1r resistors or current sensing resistors just before the voltage on the connection on the board so I measure voltage drop to determine current draw.)
P1 pot on positive rail increases and decreases bias. P2 does nothing.
Any hint on how to determine where the fault is? Could it be a cold solder point or maybe an unwanted connection somewhere?
I have an idea that the bias pot could be faulty. If there was a problem with the pot would it result in 0 bias?
Thank you very much for any help you are willing to give me.
ClassZ
I have completed the first channel of the F5t v3 (with +/- 48v rails).
Problem is I get 0mA bias across the negative rail (for ease of measurement I have some 1% 5w 0.1r resistors or current sensing resistors just before the voltage on the connection on the board so I measure voltage drop to determine current draw.)
P1 pot on positive rail increases and decreases bias. P2 does nothing.
Any hint on how to determine where the fault is? Could it be a cold solder point or maybe an unwanted connection somewhere?
I have an idea that the bias pot could be faulty. If there was a problem with the pot would it result in 0 bias?
Thank you very much for any help you are willing to give me.
ClassZ
Measure the resistance across the pot as it is installed.
You can attach your probes to any of the other resistors that parallel the pot.
Check with the pot at one end of the track. Check with the pot at roughly middle of the track. Check with pot at the other end of the track.
If all of these measure zero ohms, then either the pot is stuck on zero ohms, or the output FET is blown and now reads zero ohms.
You can attach your probes to any of the other resistors that parallel the pot.
Check with the pot at one end of the track. Check with the pot at roughly middle of the track. Check with pot at the other end of the track.
If all of these measure zero ohms, then either the pot is stuck on zero ohms, or the output FET is blown and now reads zero ohms.
Thank you very much Andrew,
Just two additional pieces of information.
I have used irfp240 and irfp 9240. I did not modify any other values in the schematic.
By output FET do you mean any any of the IRFP9240?
Would a fault with any other active device on the board, affect the bias of the negative part of the circuit?
Would the thermistor have anything to do with the bias?
Thank very much.
Just two additional pieces of information.
I have used irfp240 and irfp 9240. I did not modify any other values in the schematic.
An externally hosted image should be here but it was not working when we last tested it.
By output FET do you mean any any of the IRFP9240?
Would a fault with any other active device on the board, affect the bias of the negative part of the circuit?
Would the thermistor have anything to do with the bias?
Thank very much.