Headphone stage & preamp output

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JR.
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Re: Headphone stage & preamp output

Post by JR. » Tue Jul 01, 2014 10:28 am

Yup, that's the concept... The bootstrap with those values will be down -3dB at 9Hz which should be OK...

JR

Edit- I do not have first hand experience with either opamp,, for that application it may be worth looking at data sheet for how close to the rails it will swing.

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carlmart
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Re: Headphone stage & preamp output

Post by carlmart » Wed Jul 02, 2014 2:56 am

-3dB @ 9Hz isn't a bit too low? No can can get there.

This is the MC33078 datasheet. Voltage swing looks quite good, close or better than 4556.

http://www.ti.com/lit/ds/symlink/mc33078.pdf

It's a pity that comparison didn't include this chip.

One thing I found peculiar in this schematic was the level setting.

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Re: Headphone stage & preamp output

Post by JR. » Wed Jul 02, 2014 9:27 am

Loses 1V from each rail so +/-5V from 12V rail with the bootstrap, less from simpler buffers.

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ricardo
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Re: Headphone stage & preamp output

Post by ricardo » Sat Jul 12, 2014 9:05 pm

carlmart wrote:Version 1, if I remember well, is the one I build more than 20 years ago. I believe mine was powered with 9v or 12v supply.

Gain arrange was fixed back then, with a pot a the input. This version would be closer to the one I need now.

Version 2 is based on what a reputed mixer did use, but you can consider it a generic boosted version, as I could google a lot of them all alike.
If you use NJM4556, you can do without the extra transistors & complexity.

Version 1 will have xover distortion into certain loads.

MC33078 is a pnp i/p topology based on Raytheon RC4136 and used in practically all NJM OPAs. It's a slightly poorer (pnp) 5532 despite what the specs say. I've got a handwritten note on my copy of the datasheet which says "avoid" but no explanation.

Might simply be I don't see any PROS vs cheapo 553x :) I like many of the NJM OPAs which use the same topology.
Last edited by ricardo on Mon Jul 14, 2014 2:25 am, edited 1 time in total.

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mediatechnology
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Re: Headphone stage & preamp output

Post by mediatechnology » Sat Jul 12, 2014 9:19 pm

MC33078 is a pnp i/p topology based on Raytheon RC4136 and used in practically all NJM OPAs. It's a slightly poorer (pnp) 5532 despite what the specs say. I've got a handwritten note on my copy of the datasheet which says "avoid" but no explanation.
I use the MC33078/79 sometimes.
Having a quad version (the '79) is useful.
It's not a bad part - but not outstanding either.
My recent application is in a processor side chain.

One thing this series has going for it that the 5532/34 and LM4562/LME49710/LME49720 don't is that the MC33078 does not have differential input clamp diodes.
Thus, you can make a comparator from one (from a leftover unused section), peak detector, clamp, clip indicator etc.
It's ideal when the inputs need to move >600 mV from each other.

The MC33078 doesn't have enough output current for 'phones compared to a 4556.

The low power MC33178 that you show in version 2 doesn't have the output current of the 33078, it has a lower slew rate, and is no longer available in through-hole.
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Re: Headphone stage & preamp output

Post by carlmart » Sun Jul 13, 2014 4:23 am

ricardo wrote:If you use NJM4556, you can do without the extra transistors & complexity.
Would it move 50-75 ohm phones to good levels without the drivers? One bad thing about all video cameras is that headphone levels is rather low, that's why I thought of boosting.

I'm using the 33178 in all the preamp stages that are not THAT chips because that's the one they use on all ANs. No problem in switching all of them to 4556 if sound will be better. I might even build a prototype with DIP sockets and compare them.
I use the MC33078/79 sometimes.
Having a quad version (the '79) is useful.
It's not a bad part - but not outstanding either.
Which one is outstanding?
The low power MC33178 that you show in version 2 doesn't have the output current of the 33078, it has a lower slew rate, and is no longer available in through-hole.
I'm not sure if any of them will have enough current to move any pro casket from Sony, Beyer or Sennheiser, which are the usual pro standards. That's why I thought of adding the output boost, the one of the with the boostraps. I won't be using any TH chip anywhere. But I would like to make a prototype version with sockets just to listen to the last chip before the THAT 1606 and the headphone. I would use some SMD adapters on those that are not TH for that test, even if the final version will be SMD altogether.

Now I'm researching on interstage SMD electrolytic caps, that seems to be another can of worms. Lower loss caps should be the ones to look for. The tan ? data, which should be as low as possible, but is only shown for 120Hz. Higher voltage types seem to be better there, so 100v might sound better.

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mediatechnology
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Re: Headphone stage & preamp output

Post by mediatechnology » Sun Jul 13, 2014 6:31 am

The MC33078 and MC33079 are the same op amp; one dual, one quad.

The 5532, LM4562, LME497X0 AD797 et al are all better parts but not necessarily in your application.
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Re: Headphone stage & preamp output

Post by carlmart » Sun Jul 13, 2014 7:03 am

I meant other chips, not the MCs.

The application here is quite similar on both cases: a preamp x10 amplifying stage, and a headphone stage.

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Re: Headphone stage & preamp output

Post by carlmart » Sun Jul 13, 2014 3:00 pm

Now this looks like a very nice headphone chip that was suggested to me:

http://www.cn.njr.com/PDF/NJM2113_E.pdf

I think I might get rid of the boosters with it.

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Re: Headphone stage & preamp output

Post by ricardo » Mon Jul 14, 2014 2:06 am

mediatechnology wrote:One thing this series has going for it that the 5532/34 and LM4562/LME49710/LME49720 don't is that the MC33078 does NOT have differential input clamp diodes.
:o Evil! Truly EVIL !!?!

Carl, you can't use NJM2113 with headphones cos balanced output. It's meant for cheapo single speakers.

NJM4556 is almost certainly a dedicated high quality headphone amp and will give more current, better THD bla bla. Read the NWAVguy pages for details of the headphones a single won't drive to ear bleeding levels. There's not a lot. Two, used like he does, will drive everything. In fact, YOUR limitation is your single 12V supply.

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