Good advice , Tad!
Luckily I have all the parts for my boards, with the exception of the power transistors(I'm currently on disability, and, after picking up the 200C chassis, my budget is strained ).
Anyone find an inexpensive source for these? (preferably the MJL4281/MJL4302* for my 75v rails).
Thanks again,
-chas
*if anyone is willing to trade, I have some caps, diodes and 2 large heat sinks suitable for building a pair of these amps.
They are significantly less expensive, but their safe operating area is a bit smaller than MJL4281 and MJL1302. Probably fine for loads that are not very reactive and stay close to 8 ohms (or mains in most home situations), but I'd be concerned if you were trying to drive fairly continuous high power into 4 ohms or less, like subwoofer duty.
I hope to find enough time to get an IRFP240/9240 amp running in the next few weeks. I don't have much in the way of test equipment, but if all goes well, that's a lower cost rugged alternative.
Mouser has the Fairchild replacement for the IRFP240 is FQA19N20C @ $1.74 and the IRFP9240 is FQA12P20 @ $1.44. The FQA12P20 seems to handle reactive loads better than the NJWs.
I hope to find enough time to get an IRFP240/9240 amp running in the next few weeks. I don't have much in the way of test equipment, but if all goes well, that's a lower cost rugged alternative.
Mouser has the Fairchild replacement for the IRFP240 is FQA19N20C @ $1.74 and the IRFP9240 is FQA12P20 @ $1.44. The FQA12P20 seems to handle reactive loads better than the NJWs.
Bob, Are you going to use mosfets in the Leach?
If you do not mind using IR components Future electronics sells IRFP output devices REAL cheap. I bought about 400 for the A-75 and, of course, other projects.
Can you purchase direct from On Semi. There stated budgetary price is 1.85.
Tad
If you do not mind using IR components Future electronics sells IRFP output devices REAL cheap. I bought about 400 for the A-75 and, of course, other projects.
Can you purchase direct from On Semi. There stated budgetary price is 1.85.
Tad
I offered to pay and ONsemi told me to carry on using the samples arrangement.tryonziess said:
I had a similar response from TI. They will sell direct if you are going to buy a large quantity every month, otherwise use samples or a distributor.
IIRC OnSemi's budgetary number is for 1,000 pcs/month.
Thanks for the lead Tad. I figured I'd build a mosfet output version just to see how it works, since I already have plenty of Fairchild mosfets.
FWIW, I changed the Vbe multiplier to a Vgs multiplier with a ZVN3310 and changed the resistors in the new Vgs multilier to values like the A75, keeping the diodes for thermal compensation. The predriver and drivers went away. I may have to increase the VAS bias (and heat sink it), or add a Mosfet driver. Maybe I'll kludge in an IRF610/9610 VAS stage to handle 20 mA or so. We'll see which way I go.
IIRC OnSemi's budgetary number is for 1,000 pcs/month.
Thanks for the lead Tad. I figured I'd build a mosfet output version just to see how it works, since I already have plenty of Fairchild mosfets.
FWIW, I changed the Vbe multiplier to a Vgs multiplier with a ZVN3310 and changed the resistors in the new Vgs multilier to values like the A75, keeping the diodes for thermal compensation. The predriver and drivers went away. I may have to increase the VAS bias (and heat sink it), or add a Mosfet driver. Maybe I'll kludge in an IRF610/9610 VAS stage to handle 20 mA or so. We'll see which way I go.
Bob,
How many times will they let you take samples? I thought once was fair both ways.
It is looking like I will have a few boards leftover. You need some to "Frankenboard". I wonder if a Loveltech in a cascode would work as a driver for this amp? I do not know if you could get the voltage down enough.
The same offer extends to anyone else out there. I need to dispense with 12 units if my math is right. I will be shipping the majority out this Monday and Tuesday. The boards are up for grabs on Friday if the original folks do not respond.
I would like to thank everyone who has responded to this group buy on how well things are working. I wish I could get this kind of cooperation from people I deal with daily. Heck some of you live all the way on the other side of the planet or more politically correct to say I live on the other side from you. Go figure.
Tad
How many times will they let you take samples? I thought once was fair both ways.
It is looking like I will have a few boards leftover. You need some to "Frankenboard". I wonder if a Loveltech in a cascode would work as a driver for this amp? I do not know if you could get the voltage down enough.
The same offer extends to anyone else out there. I need to dispense with 12 units if my math is right. I will be shipping the majority out this Monday and Tuesday. The boards are up for grabs on Friday if the original folks do not respond.
I would like to thank everyone who has responded to this group buy on how well things are working. I wish I could get this kind of cooperation from people I deal with daily. Heck some of you live all the way on the other side of the planet or more politically correct to say I live on the other side from you. Go figure.
Tad
I agree with you Tad, no more than once for samples. The sample program is really for business, they hope that occasionally they will get an order as a result.
Too bad the Loveltechs are all gone. I bought some 2sJ74 and 2SK170 to try a jfet front end for this amp.
The whole project is sliding to the right because I was drilling and tapping heat sinks today and broke two drill bits and two taps. Anyone have suggestions for removal or should I just redrill the whole pattern shifted a few mm?
Too bad the Loveltechs are all gone. I bought some 2sJ74 and 2SK170 to try a jfet front end for this amp.
The whole project is sliding to the right because I was drilling and tapping heat sinks today and broke two drill bits and two taps. Anyone have suggestions for removal or should I just redrill the whole pattern shifted a few mm?
Hi Bob,
Sorry about your luck. I've had the same experience. I've broken my share of them too.
I suggest you grind the drill or tap flush and relocate the hole.
I have found that using an adjustable clutch cordless drill provides the control I need to avoid breakage. Lubricant and frequent cleaning of the drill and tap is necessary. This is an acquired skill.
I've tried tap removal tools. They are expensive considering the nature of the project with no guarantee of success.
Sorry about your luck. I've had the same experience. I've broken my share of them too.
I suggest you grind the drill or tap flush and relocate the hole.
I have found that using an adjustable clutch cordless drill provides the control I need to avoid breakage. Lubricant and frequent cleaning of the drill and tap is necessary. This is an acquired skill.
I've tried tap removal tools. They are expensive considering the nature of the project with no guarantee of success.
Boards
Tad,
ygm
Thanks for the recommendations. I will download datasheets and check the "Best hi-volt BJT's" thread for details.
-chas
Tad,
ygm
Thanks for the recommendations. I will download datasheets and check the "Best hi-volt BJT's" thread for details.
-chas
Bob,
I have had some luck using a diamond burr in the Dremel tool and grinding the little suckers out. With the small amount of torque we general use the hole can be salvaged or drill larger,tap, insert bolt grind off and retap. Lately I have had good luck using dish soap instead of oil for these jobs. Anytime you drill and tap 4-40 holes it is tedious. They make a nice drill press unit for use with Dremel tools. Makes things alot easier.
By the way has anyone tried Small Parts for stainless bolts and stuff. They have good prices and great service and incredible inventory.
I happen to have a dozen Loveltechs. I will gladly let you have some to experiment on something we both might benefit from. I really do not know what I bought them for. Guess because they were scarce.
I need to build a current source amp for .5 ohm duty to use with my ribbons. So I do not think I will build an F 3. I think Nelson designed the F 1 for this purpose. Unless a small tube amp will push .5 ohm duty. Must do some research.
To all who are buying the Leach boards. Please build this amp. If you do not do anything else just build this one. It sounds real nice. Jens has made it almost foolproof with his layout. TRIPLE check everything the first time as you build.
Enough rambling
Tad
I have had some luck using a diamond burr in the Dremel tool and grinding the little suckers out. With the small amount of torque we general use the hole can be salvaged or drill larger,tap, insert bolt grind off and retap. Lately I have had good luck using dish soap instead of oil for these jobs. Anytime you drill and tap 4-40 holes it is tedious. They make a nice drill press unit for use with Dremel tools. Makes things alot easier.
By the way has anyone tried Small Parts for stainless bolts and stuff. They have good prices and great service and incredible inventory.
I happen to have a dozen Loveltechs. I will gladly let you have some to experiment on something we both might benefit from. I really do not know what I bought them for. Guess because they were scarce.
I need to build a current source amp for .5 ohm duty to use with my ribbons. So I do not think I will build an F 3. I think Nelson designed the F 1 for this purpose. Unless a small tube amp will push .5 ohm duty. Must do some research.
To all who are buying the Leach boards. Please build this amp. If you do not do anything else just build this one. It sounds real nice. Jens has made it almost foolproof with his layout. TRIPLE check everything the first time as you build.
Enough rambling
Tad
I usually use a drill press, but was doing it at the alternate shop. the clutch on my drill was set too high when tapping and I was pushing to get the 4 heat sinks done and drilled too fast.
I'll probably just grind flat and move the mount for the output device slightly. Unfortunately, one of the holes I busted a tap in is the front end mount. I'm thinking that's a drill out and fill with epoxy.
For those of you with enough heat sink width, Mouser sells spring clips for mounting TO-247, etc. It takes a #6 screw so you're less likely to break a tap. It also presses down on the body of the device right over the die, so is likely to give better thermal contact. I bought them last time I broke a #4 tap, but forgot I had them...
Tubes and low impedance go together like cats and dogs. You're better off with a Pass design running at low rail voltages and lots of bias.
Chas - the matching between N and P on the NJW devices is better than MJLs - they should sound better.
I'll probably just grind flat and move the mount for the output device slightly. Unfortunately, one of the holes I busted a tap in is the front end mount. I'm thinking that's a drill out and fill with epoxy.
For those of you with enough heat sink width, Mouser sells spring clips for mounting TO-247, etc. It takes a #6 screw so you're less likely to break a tap. It also presses down on the body of the device right over the die, so is likely to give better thermal contact. I bought them last time I broke a #4 tap, but forgot I had them...
Tubes and low impedance go together like cats and dogs. You're better off with a Pass design running at low rail voltages and lots of bias.
Chas - the matching between N and P on the NJW devices is better than MJLs - they should sound better.
😕
Now(considering my chassis/traf runs +/-75v rails, and my speakers are 4ohms),
I'm reading that:
even though MJL4281A/4302A have higher voltage ratings(Vceo/Vcbo=350 vs 250v) the lower voltage NJW3281G/1302G's should sound better than the MJL4281A/4302A's, due to the better matching between N and P on NJW devices? So d'ya think 5 pairs will do it?
While I DO want better sound (my Leach will replace a small "Class-A" amp(which only runs pure Class-A to 7-8W with a 4ohm load), I'm just checking to make sure I'll be within SOA...
-chas
clm, Somewhere on Rod Elliot's website is a fantastic article referring to the 4281 devices. They were designed for us just to be used in Audio. Though I am by no means an expert on this I can say that I have read nothing but good stuff about the 4281.
However there are some here who prefer the older devices saying we do not use the increased frequency characteristics so why pay for it. Leach himself chose slower devices for his initial amp. You can not go wrong with either and could save some money. That is always good.
Tad
However there are some here who prefer the older devices saying we do not use the increased frequency characteristics so why pay for it. Leach himself chose slower devices for his initial amp. You can not go wrong with either and could save some money. That is always good.
Tad
Try to avoid analysis paralysis. For the levels most of us listen, a single pair of almost any transistor is probably enough for mains use.
The NJW are probably safe for home mains use at 75V if you use a good size heat sink and your speakers are not particularly reactice or low impedance. If you're used to 7-8W they ought to be fine unless you are looking to get really loud with your newfound power.
If you want to be absolutely sure you have the most robust output section, spring for the MJL4281 and 1302. If you want to save a few bucks and see if the NJWs are better sounding, go that way. The price difference is about $35 per channel.
The NJW are probably safe for home mains use at 75V if you use a good size heat sink and your speakers are not particularly reactice or low impedance. If you're used to 7-8W they ought to be fine unless you are looking to get really loud with your newfound power.
If you want to be absolutely sure you have the most robust output section, spring for the MJL4281 and 1302. If you want to save a few bucks and see if the NJWs are better sounding, go that way. The price difference is about $35 per channel.
The mounting clips I mentioned earlier are http://www.mouser.com/Search/ProductDetail.aspx?qs=IQR8xM2KsGgn8sWnGiROuQ== not cheap but tapping for #6 screws is easier than #4
Might as well start a new builder's thread...
My OT question:
If I run an 800+VA 50-0-50 Transformer, (70VDc rails right?), can I also run a PSU 2.2 65V regulator off the same trans secondaries for the amp's front end?
My OT question:
If I run an 800+VA 50-0-50 Transformer, (70VDc rails right?), can I also run a PSU 2.2 65V regulator off the same trans secondaries for the amp's front end?
yes you could, but you would waste about 5V in your outputs. A small 2 x 5V or so transformer or additional windings in series with the main windings would give you enough extra voltage to burn in the regulator and still use your main transformer's capabilities.
With the "65V" kit you can just dial in 70V on the front end with the pots. You can also use fixed resistors to set the voltage.
With the "65V" kit you can just dial in 70V on the front end with the pots. You can also use fixed resistors to set the voltage.
If your power supply does not drop significantly what other benefit is a separate regulated frontend. I mean two 1kva trannies with 70 volt rails should not drop enough to notice. Should it? That's almost 10 amps per mono block in class AB.
When purchasing the transformers it only costs about 20.00 to go from 625 to 1000 VA. Where else can you get that kind of juice for 20.00 bucks.
Bob, you once commented about separate supplies for the differential and vas. Would that be worth the trouble if the psu is stout to begin with?
My current amp project has regulated frontends all separate grounds and such and it is a pain to get all that wire looking nice and neat and pretty. The things we are so proud of. Building a small plane could be easier. At least there are no number 4 screws. How about a few thousand rivets. I am beginning to see why people my age play golf.
Shipped out all the domestic stuff today. International will go out later this week.😎 😎
Tad
When purchasing the transformers it only costs about 20.00 to go from 625 to 1000 VA. Where else can you get that kind of juice for 20.00 bucks.
Bob, you once commented about separate supplies for the differential and vas. Would that be worth the trouble if the psu is stout to begin with?
My current amp project has regulated frontends all separate grounds and such and it is a pain to get all that wire looking nice and neat and pretty. The things we are so proud of. Building a small plane could be easier. At least there are no number 4 screws. How about a few thousand rivets. I am beginning to see why people my age play golf.
Shipped out all the domestic stuff today. International will go out later this week.😎 😎
Tad