Hi Valery,
Problem here in the U.S. is you can find KSC3503 only in the "D" grade and KSA1381 only in "E" grade. That's what Mouser here stocks.
I brought this issue up in one of Apex's threads and there were mixed opinions on using 2 different Hfe parts. Some saying mixed grades will work okay together and others saying they wouldn't use them.
What's your opinion on using these 2 different grade devices together?
Also, a quick search for KSA1380 returns nothing. Are you sure this is the correct number?
Thanks...
More 4700uF caps finally came in so I made up a second CRCLC PSU. Now running dual PSU's true dual monoblock operation but single 300VA transformer with 45v rails. Bass on each channel now has even more headroom and ease of play.
Nice! You can normally notice more accurate imaging in such configuration because of the lower cross-talk. This is the right config for really good amp
Hi Ammel,
No worries. Because of the specifics of current drive topology, some reasonable hfe mismatch will not affect the front-end operation (common base cascades). Driver stage - ok, the matched pair is always better, however mismatch up to 30-50% - in a worst case you will have some 2-nd harmonic increase - nothing critical.
I have checked - 1380 is normally marked as 2sa1380.
The ones I buy locally are made in China but they work fine. I often use 2 different ratings - same issue, D and E - but I buy then bulk and group by hfe. If 3503D is showing 90 and 1381E is showing, say, 120 - you are fine, no problem.
Cheers,
Valery
Are you using a dual secondary with dual bridge rectifiers?More 4700uF caps finally came in so I made up a second CRCLC PSU. Now running dual PSU's true dual monoblock operation but single 300VA transformer with 45v rails. Bass on each channel now has even more headroom and ease of play.
or centre tapped secondary with paralleled bridge rectifiers?
Nice! You can normally notice more accurate imaging in such configuration because of the lower cross-talk. This is the right config for really good amp
I noticed a huge improvement in the sound-stage with mine when I went to the dual supplies.
That means that the Power Ground of the two channels and the Centre Tap are all at the same voltage (+- a bit of noise).
Be careful you don't build in a loop using that commoned Zero Volts and all the other items that reference to this Zero Volts.
Have you added in D.Joffe's HBRL & HBRR? This additional resistance attenuates the noise current that flows around the input loop.
Not familiar with HBRR/HBRL?
This is a pretty standard ground connection topology I am using with a star ground tied to earth ground. Power supply 0v referenced to power ground/earth ground for both PSU's. I see that perhaps having an 70v dual secondary trafo with each on its own full wave bridge would have isolated each PSU but then I still would have referenced 0v on each PSU to earth ground.
The amps themselves have the usual 10R ground lift resistor. Signal input ground is referenced to this ground.
I should add that this amp and this power supply setup is the quietest I have had to date. Absolutely no hum or hiss with source connected but no music playing. I can put my ear almost touching tweeter or woofer and it is dead silent.
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Maybe the HBRL & HBRR are already incorporated in your PCB/sch?
Read D.Joffe and why a stereo amplifier ends up having a loop around the input circuit and why the noise current around that loop increases the noise voltage at the input to the amplifier. He explains the noise mechanism and gives us the solution.
Read D.Joffe and why a stereo amplifier ends up having a loop around the input circuit and why the noise current around that loop increases the noise voltage at the input to the amplifier. He explains the noise mechanism and gives us the solution.
but the common PSU Zero Volts prevents isolation of the channels.
A stereo amplifier with 4 secondaries can achieve complete isolation, 2 secondaries cannot.
A mono block achieves complete isolation with it's 2 secondaries.
Separate transformers definitely isolate each channel better, but this amplifier was designed to be a less expensive option to an all out no holds barred ultimate build. Dual transformers would substantially raise the cost, and quad secondary transformers are harder to find in this continent with a large increase in cost as well. I personally don't feel the improvement achieved with the extra cost of completely separate supplies is really cost effective. If one is going to spend the extra money for completely separate supplies, it would likely be more sensible to move up to an amplifier design such as the Vertical NS-OPS at the same time.
This is a very impressive sounding amplifier for the build cost. It's the first 90W amp to stay connected to my home system for more than a couple days. I can't hear any hint of noise on my Klipchs. That's not easy to do with such a sensitive speaker.
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It's currently my best sounding amp to date. I am working on making a real case for it - which says a lot.
I can confirm this. It was a very audible improvement immediately. You don't realize how much this can improve until you hear it. Quite dramatic - I'm very surprised at the change for the better.
This is like one of the cheapest high bang for the buck mods anyone can do for their sound system. Most folks on SS forum have monoblock amps - but how many use a separate rectifier/caps filter. Making the PSU point to point kept things compact and easy to make.
I prefer monoblock designs in mine normally. AndrewT is correct. You can have ground loop issues with a single transformer. Dual transformers eliminates the possibility.
Hello
greetings i would like to try schematic in post#339 is there any single sided PCB
for this amp as i have all parts
warm regards
Andrew
greetings i would like to try schematic in post#339 is there any single sided PCB
for this amp as i have all parts
warm regards
Andrew
Hello vzaichenko
greetings THANK YOU for replying i love your designs now that i have
KSA1381E and KSC3503E will try this amp
warm regards
Andrew
greetings THANK YOU for replying i love your designs now that i have
KSA1381E and KSC3503E will try this amp
warm regards
Andrew