• These commercial threads are for private transactions. diyAudio.com provides these forums for the convenience of our members, but makes no warranty nor assumes any responsibility. We do not vet any members, use of this facility is at your own risk. Customers can post any issues in those threads as long as it is done in a civil manner. All diyAudio rules about conduct apply and will be enforced.

Leach Amp pcb group buy interest

Status
Not open for further replies.
Jump to Latest
#402
Very nice Andrew!

You're the man! 😀

Delta T is critical here in Brazil, because average ambient temperature can be sometimes very high (in summer it can get as hot as 42ºC). Despite that, when it's hot we use air conditioner, so this is not a big issue - temparature is somewhat controlled and won't be higher than 25ºC in my listening room.

Here's the info provided by the manufacturer of the HS15560 heatsink. I put the 2 options that were considered:

An externally hosted image should be here but it was not working when we last tested it.


Thank you again for all the good info.
 
#405
I wonder if the ebay clone has the feedback loop installed. Copying others work seems to be something common these days. And we begin to wonder why more good amp layouts are not found for us diyers these days.
I would like to know how much Dr. Leach is getting for each of these sold. At 55.00 each they are clearing an easy 25. Not bad for an ebay add and mailing address.

Tad
 
#410
CIMG3250-1.jpg


this is waiting to get done, my extra large leach.....

CIMG3254.jpg


CIMG3251.jpg
 
#411
Tony,
Did you get a deal on those caps? 100 volt is not cheap.

Dub, I have a few Leach amp boards in the 10 trasistor version that you are welcome to buy. They have the output transitors on the pcb and you will not have to run wire all over the place like on Dr. Leach's board. Send me an email with your full name, email address, and mailing address. These are left over from the previous group buy.

Tad
 
#412
Hi Guys,

just been looking at the BOM again and have some questions.

1./ Why is the input cap 470uF, this seems really high for an imput cap, generally they are 2-5uF. If I have to go really high is 100uF bipolar high enough, I have some in stock?

2./ Would 100uF 16V work in the position of C15, its speced at 470uF 16V but would use what I have on hand if its alright?

3./ C4 and C22 have no value, any ideas?

4./ I recall Andrew telling me that I need 24mV across the emitter resistors for stability. I did some calcs and to get this thing idling at 240Watt Class A with 80V rails, I need 0.1 ohm resistors, these seem really low. Does any one think this is too low?
 
#413
Luke said:
4./ I recall Andrew telling me that I need 24mV across the emitter resistors for stability. I did some calcs and to get this thing idling at 240Watt Class A with 80V rails, I need 0.1 ohm resistors, these seem really low. Does any one think this is too low?
Click to expand...
use Cordell's stability formula to check that these devices can be used at this high voltage level with a low value Re.
I doubt you can go anywhere near as low as you have suggested on +-80Vdc.
 
#414
Sorry for offtopic:
I completed Leach amp 4.5 assembly for active subwoofer.
I have some doubts about small resistors are shown in attached picture.
These 10ohm metal film Vishy resistors according to the specification is 1/2w, but they are smaller than the standard 1/4w resistors. Are these little appropriate or should i replace them with bigger? Maybe someone has experience with them? Thank you.
 

Attachments

  • DSC05073.jpg
    DSC05073.jpg
    245.8 KB · Views: 273
#415
AndrewT said:
use Cordell's stability formula to check that these devices can be used at this high voltage level with a low value Re.
I doubt you can go anywhere near as low as you have suggested on +-80Vdc.
Click to expand...

Thanks Andrew, I take it I can find this formula on the forum? But it doesnt seem to make sense, if i follow the golden rule to keep the amp stable the resistor value goes low. If the resistor value is too low then the amp becomes unstable🙂

If I remember rightly, the aleph 2 uses 1 ohm and is stable, but this would not follow cordells rule would it? Am I missing something or does it not apply to fet amps?
 
#416
Cordell discusses it in detail in his interview thread.

BTW,
the internal emitter resistance also drops a bit of voltage.
As the external Re takes on lower values the Vre becomes lower as well.

Many have found that optimum Vre of 18mV to 20mV when Re=0r1.

Leach used 0r33, I suspect you will need to stay around this value for +-80Vdc. It depends very much on Rth j-C and Rth c-s and transistor gain. These are dependent on the device and insulator chosen as well as the chosen voltage.

Luke,
can you refer to the posts that have the latest schematic and the latest BOM?
 
Last edited:
#418
AndrewT said:
Cordell discusses it in detail in his interview thread.

BTW,
the internal emitter resistance also drops a bit of voltage.
As the external Re takes on lower values the Vre becomes lower as well.

Many have found that optimum Vre of 18mV to 20mV when Re=0r1.

Leach used 0r33, I suspect you will need to stay around this value for +-80Vdc. It depends very much on Rth j-C and Rth c-s and transistor gain. These are dependent on the device and insulator chosen as well as the chosen voltage.

Luke,
can you refer to the posts that have the latest schematic and the latest BOM?
Click to expand...

I need to do some reading on this topic.

The parts I have quoted are from the latest BOM and schematic.
 
Status
Not open for further replies.
Top Bottom