You guys!!! I barely have enough time to just put the things together. Now do not get me wrong we want the best setup we ca, but, we only have so much hobby time. If I can get it to work I will usually build a second unit and go the radical distance.
Chas, I will put a photo together this evening and either post it or email it to you. I usually run the dc from the wall wart to my regulators and create a ground with two caps. Plus and minus tied together in the middle for ground. Plus hot and minus hot on the outsides. I am not sure if this is correct, but it works. Just like a small scale psu for an amp. The regulators are variable Linear Technologies devices. I set the volts to as close to 15 as I can get. (Per Nelson and Norm's matching criteria). You can vary the voltage to whatever you need by adjusting the screw on each reg. You can use resistor variable regs also. They cost about a quarter. Using a 30 volt wart you get some room for the regs to work and more available voltages. Now where is my camera!!!
Another note. Harbor Freight has some nice little DVM for 1.99 this month. They are good for the times you need to read half a dozen voltages at the same time. Like when you are setting up your driver boards and bias. They have built in hfe and stuff.
I have a good Fluke but can not afford more than one of them. Tad
Chas, I will put a photo together this evening and either post it or email it to you. I usually run the dc from the wall wart to my regulators and create a ground with two caps. Plus and minus tied together in the middle for ground. Plus hot and minus hot on the outsides. I am not sure if this is correct, but it works. Just like a small scale psu for an amp. The regulators are variable Linear Technologies devices. I set the volts to as close to 15 as I can get. (Per Nelson and Norm's matching criteria). You can vary the voltage to whatever you need by adjusting the screw on each reg. You can use resistor variable regs also. They cost about a quarter. Using a 30 volt wart you get some room for the regs to work and more available voltages. Now where is my camera!!!
Another note. Harbor Freight has some nice little DVM for 1.99 this month. They are good for the times you need to read half a dozen voltages at the same time. Like when you are setting up your driver boards and bias. They have built in hfe and stuff.
I have a good Fluke but can not afford more than one of them. Tad
Transistor matching
Actually, I'd prefer NOT to pay(I'm cash-impaired now, but I've got so much stuff to trade)!!
My two local DIY buddies and I have pooled together dozens of output devices(no doubt from different production batches) and we'd like to try and group them into matched sets, or at least pretty close to avoid a mismatch. We may attempt to build the setup Tad is describing from available parts.
The Leach amp will be replacing an expensive commercial amp which I plan to sell (like Tad did with his McIntosh) to pay the bills. Luckily, my sweet wife tolerates all this up to the point where I tried using the dining room table for a work bench!
With all the effort/hassle involved in building these amps, it sure would be nice to know we've done everything we can to get the best performance from them (i.e. best sonics,lowest distortion, etc.). After all, the biggest expense in this hobby is our TIME.
Thanks and Cheers,
-Chas
Actually, I'd prefer NOT to pay(I'm cash-impaired now, but I've got so much stuff to trade)!!
My two local DIY buddies and I have pooled together dozens of output devices(no doubt from different production batches) and we'd like to try and group them into matched sets, or at least pretty close to avoid a mismatch. We may attempt to build the setup Tad is describing from available parts.The Leach amp will be replacing an expensive commercial amp which I plan to sell (like Tad did with his McIntosh) to pay the bills. Luckily, my sweet wife tolerates all this up to the point where I tried using the dining room table for a work bench!
With all the effort/hassle involved in building these amps, it sure would be nice to know we've done everything we can to get the best performance from them (i.e. best sonics,lowest distortion, etc.). After all, the biggest expense in this hobby is our TIME.
Thanks and Cheers,
-Chas
I actually sold off all of the Mcintosh stuff because the Leach is a much better amp. I constructed the chassis to be more robust than the Mac and used better parts. Being that most 25 year old Mac products are still being used I can expect my Leach to last till I expire. My grandkids can then have the pleasure of Dr. Leach and Jens protege. And of course all of this forums input.
If I can finally get ;my A-75 amp up and running I think I will try working with some pic-chip products. They can be so useful. They offer some fabulous training boards and software.
Tad
If I can finally get ;my A-75 amp up and running I think I will try working with some pic-chip products. They can be so useful. They offer some fabulous training boards and software.
Tad
Samoloko,
I used plastic housing mjl4281 output devices which do not require an isolation washer for mounting. I used sil-pad between transistor and heatsink and used no thermal compound. If you use mica insulators then you will need the thermal compound which Mouser sells under the Avid-Thermalloy brand. Some folks still use the compound even on silicone insulators. You can also go to ebay and buy the artic silver or use a more reputable source. The computer overclockers swear by the artic silver. I have both and can not tell any difference except in price. I hope this was some help.
Tad
I used plastic housing mjl4281 output devices which do not require an isolation washer for mounting. I used sil-pad between transistor and heatsink and used no thermal compound. If you use mica insulators then you will need the thermal compound which Mouser sells under the Avid-Thermalloy brand. Some folks still use the compound even on silicone insulators. You can also go to ebay and buy the artic silver or use a more reputable source. The computer overclockers swear by the artic silver. I have both and can not tell any difference except in price. I hope this was some help.
Tad
Another (dumb?) question
BTW, out of the several MJE340/350 transistors that we have in our group, some are made by Fairchilds and some by ON Semi.
I notice some fairly close matches were found(using a multimeter) between a few ON semi JE340(NPN) and Fairchild MJE350(PNP) devices.
So, my question is:
In this application (Leach clone at locations T8,T9,T13,T14), would it be better to have:
a) Complementary devices (PNP and NPN) with widely different hFE from the same manufacturer,
or
b)Complementary devices(PNP and NPN) with similar hFE, each from a different manufacturer?
Is it worth it to mix and match brands like that, is it a bad idea, or is all this a complete waste of time?
Thanks for tolerating such questions from us "noobs"
-Chas
BTW, out of the several MJE340/350 transistors that we have in our group, some are made by Fairchilds and some by ON Semi.
I notice some fairly close matches were found(using a multimeter) between a few ON semi JE340(NPN) and Fairchild MJE350(PNP) devices.
So, my question is:
In this application (Leach clone at locations T8,T9,T13,T14), would it be better to have:
a) Complementary devices (PNP and NPN) with widely different hFE from the same manufacturer,
or
b)Complementary devices(PNP and NPN) with similar hFE, each from a different manufacturer?
Is it worth it to mix and match brands like that, is it a bad idea, or is all this a complete waste of time?
Thanks for tolerating such questions from us "noobs"
-Chas
The idea behind thermal compound is to fill the gaps in the surfaces, however small to help insure a solid path for conduction rather than a bit of insulting air. Mica needs grease to fill its surface imperfections.
Sil-pads have some flexibility so they have gap filling ability - one of the reasons that they are used commercially (one less step).
The Aavid grease is fine - a single tube should last you a lifetime or close to it. You don't want a layer of grease between the parts, just fill the surface imperfections.
My take on things like Arctic Silver is that they are better than regular if you are going to over grease, but be careful since it is conductive - squeeze out on both sides of the isolator could cause a short.
Mica has slightly lower thermal resistance than sil-pad. that makes them "better" but in this application the difference is pretty insignificant. Aluminum Oxide works well, with lower thermal resistance than mica, despite its thickness.
I suggest using sil-pads w/o grease. Either way you go, be sure that there are no burrs or dirt on the mating surfaces.
Sil-pads have some flexibility so they have gap filling ability - one of the reasons that they are used commercially (one less step).
The Aavid grease is fine - a single tube should last you a lifetime or close to it. You don't want a layer of grease between the parts, just fill the surface imperfections.
My take on things like Arctic Silver is that they are better than regular if you are going to over grease, but be careful since it is conductive - squeeze out on both sides of the isolator could cause a short.
Mica has slightly lower thermal resistance than sil-pad. that makes them "better" but in this application the difference is pretty insignificant. Aluminum Oxide works well, with lower thermal resistance than mica, despite its thickness.
I suggest using sil-pads w/o grease. Either way you go, be sure that there are no burrs or dirt on the mating surfaces.
It seems like some real effort is going into the construction of this amp. May I make one VERY good suggestion. Get some high quality taps for your drilling and threading operations. One of the most aggravating things is to layout everything PERFECTLY and then have to move it because a tap broke. I have found that there is a very vast difference between run of the mill Home Depot taps and the ones that machinists have at their disposal. I bought some taps from the tool truck Matco at work and they were far superior to the Ace hardware, Lowes variety. Get some good tapping fluid. Personally I have had good results with Dawn detergent. But use what works for you. I do not think anyone on this forum has not broken at least one tap. NOT FUN.
Personally I would stick with like name transistors on this project.
The matching results may look good at the time but when in operation on the board they might change parameters.
I have dismantled several electronic devices for parts and noticed thermal grease being used on sil-pads. It is not supposed to be required in that application but I guess it does not hurt. I purchased a bunch of the Aluminum Oxide insulators for my next build. Going to see how they work. Bob put me on them.
How about some progress pictures folks.
Have fun. Tad
Personally I would stick with like name transistors on this project.
The matching results may look good at the time but when in operation on the board they might change parameters.
I have dismantled several electronic devices for parts and noticed thermal grease being used on sil-pads. It is not supposed to be required in that application but I guess it does not hurt. I purchased a bunch of the Aluminum Oxide insulators for my next build. Going to see how they work. Bob put me on them.
How about some progress pictures folks.
Have fun. Tad
tryonziess said:
This advise is GREATLY appreciated. I have not yet experienced the pitfalls...
I reallly hope to be one of the few, the proud.... aw heck, it broke anyways
Samoloko asks about what isolators are being used. For the life of me, I could not locate a TO-264 isolator other than the Aluminum Oxides. Not that I wanted to drive up costs, but these certainly won't have a negative impact. Anyone have experience in proper implementation of these?
You could, at the risk of increasing the low end corner. Realistically, at 15uF your corner frequency is <1 Hz, so you should be fine. I think Jens just chose that value to have fewer parts to order.
If you are sure that your preamp cannot send DC to your amp, you can eliminate them altogether (jumper) The original doesn't have caps on the input.
If you are sure that your preamp cannot send DC to your amp, you can eliminate them altogether (jumper) The original doesn't have caps on the input.