About the same but cheaper.
I shorted my 3 pair mt-200 amp right out - can't kill it.
Member Jwilhelm blew a 50A mosfet relay with just one pair - to test it !! (the MT's also
exploded)
OS
It's me again!
So... I tossed out everything in my Output/Driver/VBE section, and installed the new parts except for the outputs. I forgot to order a new R27, so it's still 68ohms. I then attached a 1k resistor, as instructed, from the emitter of each driver (Q14 & 15) to the output rail (the one L1 attaches to at the top).
I installed the fuses (no "sacrificial resistors. Was I correct not to use them?), attached the bulb, attached my multimeter across R36, and let it rip.
The bulb didn't light. The LED's did. No snap crackle pop.
After adjusting R30, I have 1.100 volts across R36 (it took many turns). I checked R32, and have .37 volts across it. I checked R14, and I have 8.25 volts across it. When I measure across the fuse, I get .6mV.
All this was done with the bulb attached. No 10R resistors.
So am I clear to install the outputs? Yes, right? Anything else I should check first to be sure all is in working order?
Sorry for all the questions. I'm probably (definitely) in a bit over my head.
So... I tossed out everything in my Output/Driver/VBE section, and installed the new parts except for the outputs. I forgot to order a new R27, so it's still 68ohms. I then attached a 1k resistor, as instructed, from the emitter of each driver (Q14 & 15) to the output rail (the one L1 attaches to at the top).
I installed the fuses (no "sacrificial resistors. Was I correct not to use them?), attached the bulb, attached my multimeter across R36, and let it rip.
The bulb didn't light. The LED's did. No snap crackle pop.
After adjusting R30, I have 1.100 volts across R36 (it took many turns). I checked R32, and have .37 volts across it. I checked R14, and I have 8.25 volts across it. When I measure across the fuse, I get .6mV.
All this was done with the bulb attached. No 10R resistors.
So am I clear to install the outputs? Yes, right? Anything else I should check first to be sure all is in working order?
Sorry for all the questions. I'm probably (definitely) in a bit over my head.
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Hi,
So I'll just scrap that idea, then. Since building this amp, with all the bells and whistles (PSU's, soft start, speaker protection, setting it up properly, etc.) will most likely present a challenge as it is, I should just leave it at that and not try to improve on it, when I'm clearly in over my head already
- And I haven't even heard the amp yet, in the first place.I just hope it will prove to be an improvement over the built-in power-amp section of my Rotel RSX-1067 - and that the difference is audible, not just measurable.
PS: How does one decide which components to use, one output device versus another? What's important for sound quality and stability? Max collector current, current gain, power dissipation, transistion frequency, something else?
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I boosted R30 to 500Ohms, installed the outputs, removed the 1k resistors, put the bulb in line, and powered it up with one multimeter across one of the fuses, another on TP1 and TP2, and another set to measure DC Offset (positive on output, negative on ground).
The fuse read 33.5mV.
TP1 and TP2 read 118mV.
My DC offset is 400mV.
Edit:
R14 is still at 8.25/8.25v.... R32 is still at 0.36v-0.39v.
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MPSA18= Hfe min 500 and max 1500.
Too bad that they do not have gain groups - no way to tell if you have 500 or 1500+
KSC1845(f) = Hfe 300/600
I plugged in a Zetex 1048a (below-) , the highest gain model I had (Hfe 1200+).
Yes , the phase margin was "on the edge" (possible instability).
If you have Hfe 1200 (or even 1500) MPSA18 , increase R14-R15 to 220R.
This brings the phase margin back to 78deg - stable , (see below.. 180-102deg.=78).
Also shown below is the high gain zetex models with the resistor changes.
I ran this with the global feedback resistor (R6/R3 - gain) at 22k/27K/and 33K - good.
I tried to get my amp to oscillate when I first built it. Lowered the Q10 miller cap to 47p (nope-all was good). When I lowered R14/15 to 10R (misread the resistors) , I really oscillated and could not set the bias.
Totally SMOKED the zoble resistor !! This was with standard KSC1845(F-Hfe300-600).
PS - you might want to consider using the ksc1845(f) or BC546 BC547(a-b) as LTP.
Also , if the current mirror (Q5-Q6) has uber high gain ... this will have the same effect - something to consider.
OS
Hello Ostripper!
Sorry to bring this old post up, but what transistors for Q1 and Q2 other than KSC1845(F) have you used since then?
Thank you.
If it's of any help I have used ss9014. If I remember correctly Hfe was about 550 at Ic=2mA. I think it was D (400-1000) rather than C (300-600). LTP emimtter resistors are 121ohms Dale low noise and the pot (R17 I think) to regulate offset is 2k. Q3-4 are 2n5551 while q5-6 are 2sa1015, Q8 is 2sc1815, fo Q7 I think I used 2sc2240 but I'm not sure.
R2=121ohm Dale to minimise noise and R6=27k.
Offset is close to zero, bias about 65mA (possibly I should increase it to 75mA), R27=68 ohm, clipping protection diode is Bas45a. I works very well and only warm in my active system.
cheers,
R2=121ohm Dale to minimise noise and R6=27k.
Offset is close to zero, bias about 65mA (possibly I should increase it to 75mA), R27=68 ohm, clipping protection diode is Bas45a. I works very well and only warm in my active system.
cheers,
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ksc1815/ksa1015
for ltp/CM , and the ss9014/ ksa1015.On my wolverines ... (badger-like).
I've just moved to the BCxxx low vce groups. These could be used on the badger ,
you would have to swap C-B leads.
BCxxx has just a tad lower noise than the ksa/c's.
Both type input stage devices , I have to stick my ear right to my 91db/1W
tweeters to just barely hear it (noise).
OS
I respect your point. But I hope you do realise that just this thread alone has a LOT to read, and only a small percentage of the entire contents may be applicable to question(s) asked.
I can't speak for others, but I am doing the proper research first, rather than diving in head first. For those of us who are less in the know (like myself), a lot of what's in this thread may not make much sense, let alone that knowing where to start looking may be just as unclear. So a straight, to the point answer is of a lot more help than trying to make sense out of all the posts, that in some cases, look more like Chinese than anything else.
James.
If you see a 100n cap directly parallel with an electrolytic, without significant trace length, without significant resistance, there is no ballast for matching the far different parts, therefore assume that the small cap is ceramic X7R or disc.
However, if you see a little ballast and a value closer to 10n, then polyester may be used.
However, if you see a little ballast and a value closer to 10n, then polyester may be used.
I'm running 44Kuf X 2 with 470u + .33u poly's now. I've scoped similar
supplies. Just a small sawtooth ripple. No massive ringing and no degradation
of SQ.
After reading I concur that the X7R's might be a better choice , especially
for fast recovery rectifiers. New OEM sub amps put SMD X7R's right
under the main supply caps - stripped 2 for parts recently.
But , this is not critical (nothing will explode).
Choice of caps is quite the topic on an audiophile forum ....
OS
supplies. Just a small sawtooth ripple. No massive ringing and no degradation
of SQ.
After reading I concur that the X7R's might be a better choice , especially
for fast recovery rectifiers.
New OEM sub amps put SMD X7R's rightunder the main supply caps - stripped 2 for parts recently.
But , this is not critical (nothing will explode).
Choice of caps is quite the topic on an audiophile forum
....OS
True, I have it and read it, multiple times.
There are a few set-up and component options. Choosing a power rail voltage over another may (will?) have it's effects on the amp circuitry and/or ultimate sound quality, depending on the intended speakers you're going to use. The same goes, undoubtedly, for choosing components (output devices, drivers, etc).
I may be making this more complex than it really is, or I maybe I'm just "difficult". But I prefer to really know what I'm about to do, before I dive in head first and painfully discover that I jumped in at the wrong end of the pool. And besides that, it's an interesting topic to study, learn more as I go and browse the forum.
When I'm going to do this, I'd rather do it right the first time.
No .... In fact this is the one type of design that is most immune to rail voltage
choices.
My similar design holds the same operating currents from the full 73V rail all
the way down <20V ( CCS based designs do this best).
If the ultimate dynamics while playing loud are what is meant by SQ , then
>60V rails might be the preferred choice.
OS
I'll post a summary of what I intend to do, soon, for you guys to comment on. I have a bunch of questions about this project, but I get the feeling some of you think they're irrelevant, since it seems I can't go wrong with this project. That feels reassuring, although though asking questions and getting relevant answers, I can only learn.
Anyway, let's see what you guys think of my plans, in a while.
Anyway, let's see what you guys think of my plans, in a while.