Replacement transistors in Leach Superamp. Help needed!

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#22
tiefbassuebertr said:
Please note the nessesary of relatively large heatsinks for the MJE340/350 in the predriver - 168V by usual idle current between 10 and 15 mA means 1,7 until 2,5 watts loss power !!!
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In the S-Leach they only have 1/4 of the 168V rail on each one. That puts them at less than a watt. Still, a little heat sink will improve stability of the q-point.
TO-126 beats TO-5/TO-39 in free air and on infinite heat sink.
 
#25
wg_ski said:
In the S-Leach they only have 1/4 of the 168V rail on each one. That puts them at less than a watt. Still, a little heat sink will improve stability of the q-point.
TO-126 beats TO-5/TO-39 in free air and on infinite heat sink.
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Exactly. Therefore I also prefer the TO-126
Nevertheless I would try to get such large of the heathsink, that the temperature on it not more than 30 degrees above ambient temperature (please note: internal ambient temperature inside of the amplifier). Here an interest URL with youtube video about diy of this amp and schematic:

Leach SuperAmp Plans
http://users.ece.gatech.edu/mleach/superamp/circuit.pdf

And another amp site with advices regarded the MJE340/350
A HiFi Power Amp


Concerning the not easy to find SANYO Types 2SA1407/2SC3601 (200V/400MHz ft) or 2SA1479/2SC3789 (300V 70MHz ft) I think you find also a supplier in your country: Here two weblinks for ask
1) http://semicon.eu.sanyo.com/distribution/SemiconductorsMay09.pdf
or 2) this address also responsible for your country:
Name of Distributor : Yleiselektroniikka Oyj
Contact person: Mr. Sauli Nilsson
Address : Luomannotko 6, PL73
02201 Espoo
Finland
Phone : 00358-9 452 621
Fax : 00358-9 4526 2202
e-Mail : ilpo.Hamunen@yeoy.fi
Web site : YEInternational - ETUSIVU
Sales region : Finland, Baltic countries
Product area : Semiconductor, Laser diodes

Please note, not all suppliers of hard to find parts have a website.
 
#27
AudioAmpFanat said:
The power supply rails in my amplifier will be about -84 0 +84 DC!
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requires you to use >=180Vce0 transistors wherever they can see the full voltage during operational conditions. If the transistors are cascoded to never see more than half the full rail voltage then >=100V devices can be used

You also need to look at the current rating at the elevated voltages these transistors will operate at and you must de-rate that current to suit the worst case operational temperature you believe will apply to your situation.

This de-rated SOAR design is absolutely crucial to reliability.
 
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#34
So now i have soldered almost all resistors and diodes to the PCB's.
Next im ging to solder are capacitors, but i have few questions about those "mica" capaciors used in leach original design :

Are they some special "high-end" tipe mica condensers, can i use regular mica condensers?
And what to do if i don't have exact nominal?
for example i have:

51pF instead of 47pf
200pF instead of 180pF

Can i use them in my leach superamp PCB's?
 
#35
Will work fine. He recommends mica because they are stable. There are also high stability ceramics but people will still complain about those. There is also polystyrene or polypropylene.

The key element here is that they must be stable with temperature/voltage changes as they are used for either compensation or filtering, so their values must not change much. They should also be tight tolerance.
 
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