For a fast, simple and low cost test setup I have used a regulated Vce supply (5V or 10V) and a resistor to generate a base current from (Vce-Vbe). [Or at least the typical Vbe.] If I want to test at 1A I select the resistor to give Ibase=1A/(Typical Datasheet Current Gain).
Then I measured Ice and Vbe during the test with two meters. The current gain calculation is simple. It will not be at exactly 1A but it is close enough for good relative matching of one batch of transistors.
The transistor should be on a heatsink.
Then I measured Ice and Vbe during the test with two meters. The current gain calculation is simple. It will not be at exactly 1A but it is close enough for good relative matching of one batch of transistors.
The transistor should be on a heatsink.
well, everything is alive! after replacing all the 80v/120uf caps with 100v/150uf, the 50v/10uf with 63v/10uf, and the 16v/470uf was already a nice nichicon, so i let that alone. replaced the 0.05ohm 1w's with 2ws
then got genuine pairs of 5171/1930s and 5200/1943s, measured VBEs (they were all really consistent), matched VBE average of all 4 on each rail to within .25mV (for the 5200/1943s), and fired it up with 28v's off two bench supplies, and it's playing again!!
now it's time to finalize my power supply. i tried the cheapo aliexpress route and blew $100 after getting 2 in case one died (one died when my amp modules fried, other was DOA), so now i'm going to get the SMPS500R from connex (sold by hifimediy as they have US based stock for quicker/cheaper shipping), likely headed to the +/-54v, not the 60v. not sure pushing it that hard for an additional 30w is worth it. plus, powering tarkus speaker which tops out around 75w, so bringing 150w to the table sounds good
q1) anyone else have any decent power supplies worth checking out to run with this? connex seems to be well regarded here vs rolling the dice on ebay/aliexpress?
q2) this is going to sound pretty naive, but this design isnt considered a BTL design correct (pretty sure it's not)? reason i ask is i picked up AC 85~265V Speaker Protection Board 30A Relay High power for Max 900W Amplifier Board for speaker protection which claims it's BTL compliant, but if i'm not BTL, then i wont have to wonder. i will say it's nice having it run off mains voltage and not a winding/separate power source as even the connex only has DC aux, not AC like a lot of the speaker protection boards want
then got genuine pairs of 5171/1930s and 5200/1943s, measured VBEs (they were all really consistent), matched VBE average of all 4 on each rail to within .25mV (for the 5200/1943s), and fired it up with 28v's off two bench supplies, and it's playing again!!
now it's time to finalize my power supply. i tried the cheapo aliexpress route and blew $100 after getting 2 in case one died (one died when my amp modules fried, other was DOA), so now i'm going to get the SMPS500R from connex (sold by hifimediy as they have US based stock for quicker/cheaper shipping), likely headed to the +/-54v, not the 60v. not sure pushing it that hard for an additional 30w is worth it. plus, powering tarkus speaker which tops out around 75w, so bringing 150w to the table sounds good
q1) anyone else have any decent power supplies worth checking out to run with this? connex seems to be well regarded here vs rolling the dice on ebay/aliexpress?
q2) this is going to sound pretty naive, but this design isnt considered a BTL design correct (pretty sure it's not)? reason i ask is i picked up AC 85~265V Speaker Protection Board 30A Relay High power for Max 900W Amplifier Board for speaker protection which claims it's BTL compliant, but if i'm not BTL, then i wont have to wonder. i will say it's nice having it run off mains voltage and not a winding/separate power source as even the connex only has DC aux, not AC like a lot of the speaker protection boards want
I think you wasted a lot of money. But if it makes me happy.
This is also worth it.
I don't know how it works now. What have you learned.
I think perhaps the context was lost over this long forum posts
ljm, I originally ordered a pair of the l20.5 from ebay, and they lasted about 3minutes before dying, assuming the components were pretty junk from the distributor
so in my attempt to 'beef' them up I replaced a number of components
did the caps need to be replaced? no, but it kept me from having to wonder if they were next to go
did the resistors need to be replaced? no, but I think I damaged one or two just trying to identity their resistance, so I replaced them all (they were mounted upsidedown)
did the transistors need replacement? yes!
they died very, very quicklyall in all, wasn't a huge cost other than the transistors, only because I didn't know the quality of the other board components and didn't want to have to replace anything else
what did I learn? honestly more than I've ever learned about amplifiers! learned how to test transistors, learned about VBE, learned I know nothing about this stuff and I was excited to learn more. great experience overall. glad they died so I could (minus the whole money part)
HelloI think perhaps the context was lost over this long forum posts
ljm, I originally ordered a pair of the l20.5 from ebay, and they lasted about 3minutes before dying, assuming the components were pretty junk from the distributor
so in my attempt to 'beef' them up I replaced a number of components
did the caps need to be replaced? no, but it kept me from having to wonder if they were next to go
did the resistors need to be replaced? no, but I think I damaged one or two just trying to identity their resistance, so I replaced them all (they were mounted upsidedown)
did the transistors need replacement? yes!
all in all, wasn't a huge cost other than the transistors, only because I didn't know the quality of the other board components and didn't want to have to replace anything else
what did I learn? honestly more than I've ever learned about amplifiers! learned how to test transistors, learned about VBE, learned I know nothing about this stuff and I was excited to learn more. great experience overall. glad they died so I could (minus the whole money part)
Beware of sellers on eBay because some provide fake transistors to increase their margin on sale. As a general rule, it is the final power transistors that are fake, small signal transistors being in principle less interesting to adulterate in terms of price!
The simplest being when you have doubts, to replace the power transistors with transistors purchased from Farnell or other radiospares. If the seller is really a crook (if the purchase price of the modules is really low) you can also replace the driver transistors.
Personally, I do this with a preliminary test of the modules with current-limited lab power supply, BF generator and resistive power load. To test at full power. It greatly limits collateral damage when it goes into a spin.
Relatively speaking, l20.5 has a higher probability of damage than l20v10I think perhaps the context was lost over this long forum posts
ljm, I originally ordered a pair of the l20.5 from ebay, and they lasted about 3minutes before dying, assuming the components were pretty junk from the distributor
so in my attempt to 'beef' them up I replaced a number of components
did the caps need to be replaced? no, but it kept me from having to wonder if they were next to go
did the resistors need to be replaced? no, but I think I damaged one or two just trying to identity their resistance, so I replaced them all (they were mounted upsidedown)
did the transistors need replacement? yes!
all in all, wasn't a huge cost other than the transistors, only because I didn't know the quality of the other board components and didn't want to have to replace anything else
what did I learn? honestly more than I've ever learned about amplifiers! learned how to test transistors, learned about VBE, learned I know nothing about this stuff and I was excited to learn more. great experience overall. glad they died so I could (minus the whole money part)
It is not because of the quality of the power tube.
But heat conduction.
L20v10 has L-shaped aluminum. And is fixed very tightly. It is not easily damaged.
L20.5 is relatively difficult to install. If one transistor is not fixed tightly. It is easily damaged.
I don't think there is a reference that escapes counterfeiting. There are so many dishonest sellers on these platforms, that it is almost impossible to escape them! That being said when the price is really undervalued the risk of buying rotten components increases drastically. What I do in principle when I have a doubt I systematically replace the transistors with models purchased from reliable sources such as farnell or radiospare. And so far I haven't had any problems.
I know what you mean.
There are really many fake goods in China. Including L10 and L20 designed by me
L15 is fake. They use dummy elements.
However, l20.5 is not fake at present.
At present, I am the only one selling l20.5.
No one else can produce it. So it's not fake.
But this does not mean that l20.5 will not be damaged.
Any transistor. I can easily break it.
i purchased toshiba1943/5200s from digikey, a reputable site here in the US, so i'm confident they are legit. can't speak for any design off ebay containing 1943/5200s being legit however. i'm sure there are many fakes out there
i'm curious who you'd recommend buying from to ensure we are getting your quality boards here in the US, can you provide a link?
https://www.ebay.com/itm/363060959180 this was the listing of the item i purchased in 2020
LJM shop at Taobao
L20.5 雙聲道 HIEND 超低失真 0.0015% AP 實際測量 原裝進口管
https://world.taobao.com/item/521617686292.htm
Many times I have problem to access from Spain. With a VPN, solved.
KTB817 KTD1047
https://world.taobao.com/item/1753208058.htm
L20.5 雙聲道 HIEND 超低失真 0.0015% AP 實際測量 原裝進口管
https://world.taobao.com/item/521617686292.htm
Many times I have problem to access from Spain. With a VPN, solved.
KTB817 KTD1047
https://world.taobao.com/item/1753208058.htm
L20.5 is also available with NJW 0302g 0281g transistor.edition
The parameters of njw0302g 0281g are the same as those of 2sa1943 2sc5200.
However, l20.5 installation is more complicated. I prefer l20v10.
L20v10 also uses 817 1047 X4 each circuit board. It has a thermally conductive aluminum.
Installation is easy. Not easily damaged.
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Hey,
my L20.5 Monobridge-Amps. PSU are each Hypex SMPS3K400 SMPS
Greetings, have a nice Day
Michael
my L20.5 Monobridge-Amps. PSU are each Hypex SMPS3K400 SMPS
Greetings, have a nice Day
Michael
Attachments
I suggest using a lower voltage as much as possible.
Because it's safer. Reduce fever. And the voltage is independent of performance. It only needs to be greater than the actual output voltage. I recommend using+-33VD C
