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Leach Amp pcb group buy interest

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#602
evette,
Like I said if I can get enough interest for the pcb's I will have them made up. The last group buy did not show a large interested audience. This is a very large amplifier and the cost of construction might make some shy away.
I will post a new thread on the subject in August. That way if things go well most will be soldering around Christmas time.
I also would like to get my Leach clone 12 up and running before putting the boards out there. Good news travels faster. It will also give Jens some time to think about any adjustments he might like to include in another board run.

We might even get the super Leach project up and running this fall. In any case I figure we should have enough interest in at least a small group buy before September. I would like another pair of boards myself. I sold the extra set I was keeping to another member so he could build his amp. I plan on a trial run of one of my boards this weekend. I hope the smoke stays away.
I still have to assemble the two regulator boards and dial them in to 86 volts.

Tad
 
#603
tryonziess said:
evette,
Like I said if I can get enough interest for the pcb's I will have them made up. The last group buy did not show a large interested audience. This is a very large amplifier and the cost of construction might make some shy away.
I will post a new thread on the subject in August. That way if things go well most will be soldering around Christmas time.
I also would like to get my Leach clone 12 up and running before putting the boards out there. Good news travels faster. It will also give Jens some time to think about any adjustments he might like to include in another board run.

We might even get the super Leach project up and running this fall. In any case I figure we should have enough interest in at least a small group buy before September. I would like another pair of boards myself. I sold the extra set I was keeping to another member so he could build his amp. I plan on a trial run of one of my boards this weekend. I hope the smoke stays away.
I still have to assemble the two regulator boards and dial them in to 86 volts.

Tad
Click to expand...

Tad, dont you have some 6 or 10 transistor boards, perhaps Evette may interested in those.
Your doing well if you get your boards ready to go this weekend, let us know how it goes. Its cold here and my basement is freezing so my stuff is on hold.
 
#604
Luke, evette

I do have some boards left from the first group buy. These are the Leach clone 10 transistor amplifier. I have one of these up and running in my shop and it is a good bullet proof amplifier. If you would like some of these boards let me know by email. I only have 6 left.

Luke, what do you think is the practical frontend voltage limit for the Leach 12 per the BOM. I have used the BCxx devices throughout and was contemplating replacing 5 of them in to MPSA92/42 for safety. T14,16,1,29,15 which do not form the differentials or VAS. The use of 86 volts on the frontend has made me kind of skeptical.
I had originally planned on using the Sanyo, Toshiba devices but I did not want to reengineer the lag compenstion aspects. Any input.

Tad
 
#605
😛Hello mr Tad, running 86 volts across bc546 transistors is or could be kind of smoky. I would use mpsa42,92. These wouild seem to be safer. ( don,t worry about smoking the amps I do it all the time) 😀 If my hands weren,t so shaking i wouldn,t destroy so many. Anyway count me in for at least 8 boards.😉 Evette
 
#606
Hi Tad,

the front end is tied to 40V by the Zeners D3 and D5. The bias is 3.5 mA or so, so the current drops approx 40V across r27, r28 and r58 and then the Zeners at the tail drop another 40 V wrt ground.
With 86V rails a bc546 is approx seeing 52V, probably nearing the high side for a 65V part. Dont know, should work fine but not sure about longevity?
For the sake of a couple if bucks it may be worth thinking about the msa42/92.
 
#607
tryonziess said:
I had originally planned on using the Sanyo, Toshiba devices but I did not want to reengineer the lag compenstion aspects. Any input.

Tad
Click to expand...

You don't have to reengineer the lag if you put the Toshibas in the differential first stage. It's the VAS second stage transistors that might require different lag compensation caps.

I use high beta Toshibas in the differential and really like them. Different pin-out, though. Watch that!
 
#611
Any chance of getting another run of these 12 transistor version? And has anyone built a working amp with these boards yet? Guessing there were no errors? If no one will do another run then how about the gerber files to get them made my self? I didn't see them posted anywhere here. I don't see the 12 transistor version on Delta Audio's website either just the 10 and 6.

Also about PSU PCB's, I don't see an info page anymore but how about the ones from chipamp.com for the Aleph? It's a CRC based PSU board and is pretty nice and only 7 bucks.
http://chipamp.com/orders.shtml

Can see the parts list if you click on the link. I'm not sure if this would be adequate for the Leach 12 but seems like with the right value's it'd be really good.

Here is a link to the picture, they are pretty large I had bought a set of them a while back.

An externally hosted image should be here but it was not working when we last tested it.
 
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#612
Doug,
Why don't you make a new thread and start a wiki and gauge interest in a group buy for the 12 transistor Leach clone. As I stated earlier this is not a particularly cheap amp to build and the pool of potential builders dwindles with cost of parts.
I would be glad to run another buy if the quantity of boards reaches 100. Any amount less than that makes the cost per board about 25.00.
I hope to have my first board powered up very soon. I have been soldering the frontend regulators all week.

Tad
 
#614
I don't have time or money to run a group buy my self so it would have to be someone else. But I'd definitely purchase some.

Be very interested in seeing your results though! I've been wanting to build an amp with huge power so the cost doesn't bother me lol...should still be less money the the alternative amps I was going to buy which was the Emotiva XPA-1's.

I haven't seen any pics yet of the stuffed PCB's either, very interested in seeing them stuffed or bare they sound gorgeous with 12 devices 🙂
 
#619
There a number of ways to use this 12device PCB.

1.) as the standard Leach using a big 40+40Vac transformer that ends up able to drive down to 3ohms of severe reactance speaker. ~400W into 3r0

2.) almost Leach, but on higher voltage 45+45Vac, for severe reactance 4ohms speaker and above ~400W into 4r0. 50+50Vac for 6ohms and above, ~350W into 6r0.

3.) A high optimum bias on 40+40Vac or possibly a lower voltage that delivers a lot of ClassA before transitioning over to ClassAB for the big transients. This one will run pretty warm.
Try Re=0r1 and Vre~19mV for a ClassA output of ~2.25Apk giving ~20W into 8r0. ~175W ClassAB into 8r0 or 335W into 4r0.
 
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