Small, 30W amp, triple (pre-drivers, drivers, outputs), with TIP3055/2955 outputs.
25V - 30V rails, op-amp input (TL-071 and LT-1056 tested).
Darlington VAS, 2-pole compensation.
50mA idle current per output pair.
The sim (attached) matches the real world very well; no problems with building it 'as is'.
Just adjust idle current, and it works.
Negligible output DC offset (0.2 mV).
The output devices were matched for Vbe.
I really like the sound, slightly on the bass-heavy side for some reason, but very meaty and rich.
Sounds like a big amp.
25V - 30V rails, op-amp input (TL-071 and LT-1056 tested).
Darlington VAS, 2-pole compensation.
50mA idle current per output pair.
The sim (attached) matches the real world very well; no problems with building it 'as is'.
Just adjust idle current, and it works.
Negligible output DC offset (0.2 mV).
The output devices were matched for Vbe.
I really like the sound, slightly on the bass-heavy side for some reason, but very meaty and rich.
Sounds like a big amp.
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How much supply capacitance is on the rails? You need 22,000uF per rail minimum.
The schematic has the unity gain capacitor shorted out.
The schematic has the unity gain capacitor shorted out.
In actual build C10 it's not shorted...
It was shorted in the sim, to sim square waves... I corrected the image..
My PSU does have 22mF on each rail.
On the board, I have 470uF per rail.
Correction: I checked - my PSU has 40mF per rail.
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Nice. The circuit is that of a bigger amplifier (with higher voltage transistors). Was there a reason for using TIP3055/2955?
Ed
Ed
1) Mostly nostalgic. These transistors are being criticized as not really suitable for audio in 21st century, but I remember these
amps from the 80s, and wanted to check if it's my memory failing, or perhaps a decent amp still can be built with them.
According to the sim, and my listening tests, these devices are still good 🙂
This is the 2nd amp with these devices I built recently. 1st one is described here.
2) I designed this PCB for 'eventual' bigger amp (higher rails, different transistors), but they did not sim as well as 3055s; which is strange...
Since I already have plenty of bigger amps I guess will stick to smaller ones for now.
I used 2N3055/MJ2955 in the 1980s. They certainly were good for audio (within their voltage ratings).
Ed
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TIP3055/2955 certainly have price and availability on their side but there are other similar size and rated, cheap transistors out there which happen to have good linearity and higher Ft too - well worth trying out. Considering their low cost too, KEC's versions of D1047/B817 make a fine sounding amp - on par with several Rotel products which used the Sanyo originals exclusively for what seems like decades. https://www.datasheetcatalog.com/datasheets_pdf/2/S/D/1/2SD1047.shtml
https://pdf.datasheetcatalog.com/datasheet/kec/KTD1047.pdf
https://pdf.datasheetcatalog.com/datasheet/kec/KTD1047.pdf
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I made a mistake when soldering electrolytic caps on 15V rails for the op-amp, and the ones the +15V rails had reversed polarity.
These 2 caps survived 30 hours of playing music, and finally one of them exploded, and scared the hell out of me 🙂
No damage to the amp, it still works. But these caps are not bad - survived so long with reversed polarity!
I replaced them with new ones, and we're back in business...
I remember similar cases/mistakes in the past, and caps were exploding just after several minutes....
These 2 caps survived 30 hours of playing music, and finally one of them exploded, and scared the hell out of me 🙂
No damage to the amp, it still works. But these caps are not bad - survived so long with reversed polarity!
I replaced them with new ones, and we're back in business...
I remember similar cases/mistakes in the past, and caps were exploding just after several minutes....
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Even at 15V that is still impressive to last that long! My experience has been BANG!! within seconds to 1 minute 😆
audio fun 👍 the VAS is biased by the feedback loop, although R14 is capping that offset swing, thanks for sharing
@minek123 I think i m going to build this, After i Finish the Circlophone. I do not know why but I fancied a Opamp input stage amp... and TIP's make it more Economical and more over easy sourcing.
Could BD139 and 140 be used intead TTC and TTA's.
Also could you let me if we could use the Buson V6 opamp (I have 2) , I know its stereo, I will create a small board that will connect to Mono opamp...
Could BD139 and 140 be used intead TTC and TTA's.
Also could you let me if we could use the Buson V6 opamp (I have 2) , I know its stereo, I will create a small board that will connect to Mono opamp...
Theoretically YES, you can do all of this, BUT:
a) Sim would have to be re-done, and I'm sure changes (e.g. in compensation) will be needed.
Triple output is likely to be sensitive to this kind of changes, and VAS stage is sensitive to op-amp changes.
b) From my experience with BD139/140 - when you but them you never know what it really is. There is plenty of no-name (unknown brand) BDs,
so the model you have in LT Spice may not match the actual devices you are using. So real build will behave differently than the sim.
It's much easier to get TT devices from reputable seller and with correct Spice models, rather than wasting hours fighting with oscillations later on.
If you buy known brand BDs from reputable seller, with correct models, most likely they will cost the same as TTs.
c) Burson v6 opamp, given its high price, seems like a overkill for this application. In my personal opinion you will not hear, nor measure,
any difference from 50 cent TL071
Conclusion - try the sim with different devices, and if everything looks good (Thd, fft, stability) give it a try.