Saved Copies
I hope Jens is doing alright, and that he will be able to keep up the website.
I've saved copies of everything, just in case... 😀
-Chas
I hope Jens is doing alright, and that he will be able to keep up the website.
I've saved copies of everything, just in case... 😀
-Chas
Setting the Output Bias
I have heard of doing this, but is it really necessary for best performance?
This is interesting, as I'd always assumed that more bias was better (witness the high-end amps that are biased over 10% of their AB ratings)...
Comments?
-Chas
I have heard of doing this, but is it really necessary for best performance?
This is interesting, as I'd always assumed that more bias was better (witness the high-end amps that are biased over 10% of their AB ratings)...
Comments?
-Chas
Chas, You can always go the route Dr. Leach recommends on his website. He settles for something on the low side. You will most definitely notice a difference in the quality of the music as you increase the bias up to a point. It is remarkable listening as you turn the small screw. The bass and midrange just come to life. Not many things we build show such remarkable improvements from just tweaking the bias adjustment.
Tad
Tad
So, you measure across each emitter resistor seperately, as opposed to measuring across + and - pairs simultaneously?
Hi,
yes, each one separately is one of the first things I do as soon as I've got it running.
I match the Re to better than 0.5% to ensure that the readings I take later actually mean something. The usual 5% is no good here.
This shows up how well I have matched the Vbe of the output devices.
Once I know the output stage is sharing the bias current fairly evenly across all devices, I usually attach a short pair of test leads to the closest to average for any future setting up.
yes, each one separately is one of the first things I do as soon as I've got it running.
I match the Re to better than 0.5% to ensure that the readings I take later actually mean something. The usual 5% is no good here.
This shows up how well I have matched the Vbe of the output devices.
Once I know the output stage is sharing the bias current fairly evenly across all devices, I usually attach a short pair of test leads to the closest to average for any future setting up.
Potted Power Transformer
Guys,
If anyone here is interested, there's one of the nice Pioneer 120W/channel Potted power transformer (Bando#ATT290) listed on eBay.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=260369312805&ssPageName=ADME:B:SS:US:1123
This really does make a nice amp with the Leach boards. I'm using two of them.
-Chas
Guys,
If anyone here is interested, there's one of the nice Pioneer 120W/channel Potted power transformer (Bando#ATT290) listed on eBay.
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=260369312805&ssPageName=ADME:B:SS:US:1123
This really does make a nice amp with the Leach boards. I'm using two of them.
-Chas
Attachments
Looks like someone snapped up that traf asap with buyitnow; however, another Pioneer (by Bando) 120W/ch potted trafo just came up (surprising, as these are pretty rare- esp. for $30):
e bay Item number: 260369512151
When using these, I calculate the resistor value for R3/R22 to be 2.7k ohms.
Any others have pics to share?
Cheers,
-Chas
e bay Item number: 260369512151
When using these, I calculate the resistor value for R3/R22 to be 2.7k ohms.
Any others have pics to share?
Cheers,
-Chas
hardware advise
Looking for some advise on mounting MJL15032/15033 to the heatsink.
I have mica insulator, it appears that I need some kind of isolation washer for the 4-40 screw.
If someone has a Mouser part number, or link to what they've used, that would be great
Thanks,
Rob
Looking for some advise on mounting MJL15032/15033 to the heatsink.
I have mica insulator, it appears that I need some kind of isolation washer for the 4-40 screw.
If someone has a Mouser part number, or link to what they've used, that would be great
Thanks,
Rob
Hi,
normally retailers of mica washers offer a To220 kit, including both the mica and the top hat washer for the screw fixing.
As an alternative, try bolting a strap across the To220 cases to clamp the devices to the mica washer/sink.
normally retailers of mica washers offer a To220 kit, including both the mica and the top hat washer for the screw fixing.
As an alternative, try bolting a strap across the To220 cases to clamp the devices to the mica washer/sink.
Rob, SmallParts.com has a pretty good assortment of these washers on it's website. If I have time today at work I will see if I can get a number.
The transistors that you are using do not have a plastic surround hole in them? Most of the units I have used have this built in plastic bushing already installed.
Tad
The transistors that you are using do not have a plastic surround hole in them? Most of the units I have used have this built in plastic bushing already installed.
Tad
Andrew, Tad
Thanks for the info. Transistors from Digi-Key, On-Semi, is a metal tab only.
I had considered spring clip mounting, but though there must be an easier way. The mica I have is actually for TO-3 that I got as an obsolete from work. I hadn't considered mounting of this part when building my original BOM (still not complete)
Heatsinks are yet to be tapped, so I still have time to pull in these little nuggets. smallparts.com is a new one to me...
Thanks for the info. Transistors from Digi-Key, On-Semi, is a metal tab only.
I had considered spring clip mounting, but though there must be an easier way. The mica I have is actually for TO-3 that I got as an obsolete from work. I hadn't considered mounting of this part when building my original BOM (still not complete)
Heatsinks are yet to be tapped, so I still have time to pull in these little nuggets. smallparts.com is a new one to me...
can you help
I would like to get best power transistors for this amp
my choice Is njw1302 3281 and mjl4281 4302
what do you prefer from these
I would like to get best power transistors for this amp
my choice Is njw1302 3281 and mjl4281 4302
what do you prefer from these
Mouser Part No.....
The Mouser Part Number INSULATING SHOULDER WASHER is 532-7721-8PPS.....has .040 inch shoulder for and hole for a #4-40 screw.
The Part No for the "THERMASIL III MOUNTING KIT" for one transistor is 532-4880SG. The kit has all the mounting hardware i.e. #4-40 screw, shoulder washer, flat washer, lockwasher, nut and and insulator. I have heard that the insulator may not be large enough for the MJL4302/4281's so if that is the case, buy the parts separately? Has anyone bought the kit??
The Mouser Part Number INSULATING SHOULDER WASHER is 532-7721-8PPS.....has .040 inch shoulder for and hole for a #4-40 screw.
The Part No for the "THERMASIL III MOUNTING KIT" for one transistor is 532-4880SG. The kit has all the mounting hardware i.e. #4-40 screw, shoulder washer, flat washer, lockwasher, nut and and insulator. I have heard that the insulator may not be large enough for the MJL4302/4281's so if that is the case, buy the parts separately? Has anyone bought the kit??
mouser #
Thanks Brute, that'll fit the bill for the washer.
The MJL4302/81's don't appear to need a shoulder washer. I'm going to use a flat, with the 4-40 going into a blind hole. There won't be any ft-lbs of torque going into this mounting scheme
I would like to know if anyone has found a TO-264 insulator. The Al-oxide pads (4180G) just fit the die area under these transistors
Samoloko, the MJL's were best for my application
Thanks Brute, that'll fit the bill for the washer.
The MJL4302/81's don't appear to need a shoulder washer. I'm going to use a flat, with the 4-40 going into a blind hole. There won't be any ft-lbs of torque going into this mounting scheme
I would like to know if anyone has found a TO-264 insulator. The Al-oxide pads (4180G) just fit the die area under these transistors
Samoloko, the MJL's were best for my application