What about C10 ? Gone? Or it should stay grounded?
Interesting, never seen this way of doing it, with C8 cap.
Interesting, never seen this way of doing it, with C8 cap.
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Gottcha
BD139 and 149 are branded CDIL part and CDIL is a good Indian company that exports a lot.
I have started loading the basket for TTC and TTB in farnell.
Understood what you were trying to say with the sim model issue with non standard part.
I am wondering what to do with burson v6 , initial plan was to use it as a buffer for PGA2311.
BTW, 10 Ohms causes the op-amp to current limit; not good. So I tried 100 Ohms thinking it would make THD worse, but it didn't? This will reduce gain by 1.5K/1.6K if you care. Anyway, thanx for something interesting to play with.
On could also insert a resistor (low kohm value) in the collector of the VAS's EF (Q1). It comes with some Miller effect but only at clipping, when collector swing of Q1 increases.
TTA's and TTC's have only half the BD's CB capacitance. This matters for VAS and its ccs. But they have slightly better SOA which matters for the drivers. MJE243/253 would be better in this position.
And I note that un-shorting C4 (the input coupling cap) degrades THD simulation??? So using 22uF instead of 2.2uF avoids that problem. I've seen this before and I'm not sure, but I think it's a sampling window issue.
I tried that initially, but for some reason decided not to use it. Don't remember now why....
Steve, I see you moved the probe 'before' R13 connection. Is this way of measurement more correct? This way feedback loop is 'less' open than before,..
The lower CB and input capacitance doesn’t matter as much in an EF3 as it does an EF2. You could put TIP41’s there. While it would not have this distortion performance it would work surprisingly well. Unlike the usual EF2 where you want to run screaming from the room when you hear it. Two little 6 cent TO-92’s make all the difference inthe world. MJE243 are NOT sustained-beta devices. Most BD139 are. This matters when you are chasing ppm-level distortion. The reason people don’t use them more is they’re only rated to 80 volts. Good ones are sustained beta AND have low quasi-saturation - low vceo is the price you pay to get it. That and nobody puts an fT rating but the regular sources make them at least 50 MHz, usually around 100. It’s simply decent by design. The MJE243 (and 171, 181) were designed for exceptionally low leakage. Presumably so they could be run right up to Vceo rating without issue - back in those days a 160V audio driver was hard to do (Motorola hadn’t figured out what Toshiba, Sanyo and others did yet). But the price paid is the usual mid-range beta hump reminiscent of the 2N3439.
Nothing wrong with TTA/C either in this design - it’s not like power dissipation is exceptionally high. Even with 2 ohms load. Vcc is low, which puts you in a favorable part of the SOA curve. Running three parallel outouts isn’t because 300+ watts of SOA is required - in this case it’s to get flat beta out to 15+ amps. That even out-strips a single MJL3281.
If you are chasing every degree of phase margin you don’t want ANY miller effect that you don’t need. Cob modulation also results. Trying to get distortion really low like this you have to beat down every contributor you can. Then it all comes down to layout…. and a new can of worms.
You noticed! 😁 I think so. After all, if it wasn't 2-pole, the miller cap "feedback" would not be included in the probed signal. Like normal compensation, it's another feedback loop. The voltage to R13 is normally the output voltage, not the stimulus voltage (created by the probe).
Yeah, but 1-pole miller cap is local feedback, this one here is global.
I'm not sure which way is more correct, but it makes a difference in PM/GM measurements..
With probe moved, good PM/GM is easier to achieve, which looks suspicious to me... I wish that was true 🙂
I'm not sure which way is more correct, but it makes a difference in PM/GM measurements..
With probe moved, good PM/GM is easier to achieve, which looks suspicious to me... I wish that was true 🙂
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This is the amp I built for car stereo use in a 3 transistor setup driving 530 9530 mosfets.
The op amp I used is an LF353.
Sound is fantastic as long as stability is maintained.
The op amp I used is an LF353.
Sound is fantastic as long as stability is maintained.
Hello Minek, why is this amp so conservatively rated (30 W) with no less than three output devices per half?
Is the fairly low supply of plus and minus 30 Volts the limiting factor? I would assume with a somewhat higher supply voltage ( +-35V) the output stage would be capable of delivering the 5 Amps required for 100W rms in 4 Ohms without any issues?
Is the fairly low supply of plus and minus 30 Volts the limiting factor? I would assume with a somewhat higher supply voltage ( +-35V) the output stage would be capable of delivering the 5 Amps required for 100W rms in 4 Ohms without any issues?
2N3055's are rated 60V, ie +/-30V, and there is the SOA problem. New BJT have better SOA and can handle 80V+, but not a great idea for ~40 year old parts. One pair could maybe survive 8 Ohms, but you need at least 2 pair for 4 Ohms (~100W) and 3 pair is insurance against recuring rebuilds. Today, if your amps are perishable, that's your choice, but professionals cannot afford a lot of returns. These transistors are cheap insurance. We do not push other parts to their limits so why power transistors?
You can use bigger output transistors, and make an amp with rails +/- 50V
Like this one: https://www.diyaudio.com/community/threads/unusual-amp-from-1987.357369/post-7095172
This one here was specifically made for 3055/2955 outputs.
Like this one: https://www.diyaudio.com/community/threads/unusual-amp-from-1987.357369/post-7095172
This one here was specifically made for 3055/2955 outputs.