Folks,

I have been struggling with this project since last April. And I received good advice and suggestions back then.
But it got to the point where I felt that I no longer believed that the LM386 was the right IC for this project. (It was pointed out to me that it was ancient.)
So I've redesigned things a bit and will be using two MC33171N ICs.

The schematic was redone but was largely unchanged. That is, I substituted the new ICs and added, changed or removed connections accordingly.
So, for example, there's no longer the bias cap from the LM386 pin 7. And there's no longer a pin 1/8 gain adjustment.
But as the overall design is from an LM386-based schematic that I found on the net (and failed to store the link) certain components are still in place.
For example, the product info on the MC33171N shows me a freq. vs. impedance graph which suggests to me that the IC's output, unlike the LM386, is not 8 ohms.
Can anyone tell me what the likely impedance would be based on my circuit?
Also, there are a few holdovers as I mentioned. What purposes are served by the 220μF and 470nF caps on the output stage? For that matter I never understood the purpose of the two 470nF caps leading into the "Summing" 2-gang balance pot.
So I welcome your answers and suggestions.

Thank you,
Roy

 

Please post the old and new schematics so we have some clue as to the actual circuits. With no link to the previous thread, title, date, or anything else, we are blind. Many parts have multiple datasheet versions on the web, often with significant changes. Please post links to the datasheets you are using.

The 33171 is a good replacement for and upgrade to an LM358 dual opamp. It is *not* a single-channel audio power amplifier.

If you are running on a single 9 V battery, you can't get more than 1.26 W out of a theoretically perfect output amplifier - and the LM386 definitely is not that. Expect less than 1 W best case. At that power level, the LM386 is fine.

But - the LM386 is not just a normal opamp with an extra-beefy output stage. Its internal topology is significantly different, especially in the input stage. You will get better audio if you do the differential cancelling in a true opamp and follow that with the 386 as only an output stage.

ak

 

If you’re driving an 8-ohm speaker, consider adding a dedicated power amplifier after the MC33171N. TDA2030 or PAM8403 will work.
https://www.st.com/resource/en/datasheet/tda2030.pdf
https://www.mouser.com/datasheet/2/...SrpuUK7JJioqjktdGUKVEMRu2-75mYE-kry_CizxTMXjV

 

The MC33171 is too noisy for audio. Instead use a low noise opamp designed for audio like an OPA134 single opamp or OPA2134 dual opamp. Then it feeds a power amplifier IC that is low noise and is designed for audio (you do not say how much output power you want).

 

The LM386 is only marginally more powerful than common op-amps; Radio Shack sold boards that used it to drive headphones. It would be woefully inadequate to drive small insensitive mid-woofers or full-ranges. There's loads of op-amps that would be better suited to a virtual-ground mixer. Things that have been popular in the past include TL072, AD712, NE5532. I'd highly recommend Walt Jung's Audio Ic Op-Amp Applications, but it seems to be out of print. Archive.org has the second edition to borrow (doesn't include cutting-edge applications like DAC output stages). but it's useful enough, or you can find it at pirate e-book download sites, I've heard. Douglas Self's "Small Signal Audio Design" may be helpful, too.

 

My observation is that at least for home theater systems the center channel amplifier delivers quite a few watts of output. So any amplifier will need to be much more capable than any small IC amplifier.
If the amplifier is just supposed to be a small signal summing amp, that is quite different yet.
Of course, it seems that we are starting this discussion at page 25 of the original, so the context is missing.

 

Please post the old and new schematics so we have some clue as to the actual circuits. With no link to the previous thread, title, date, or anything else, we are blind. Many parts have multiple datasheet versions on the web, often with significant changes. Please post links to the datasheets you are using.

The 33171 is a good replacement for and upgrade to an LM358 dual opamp. It is *not* a single-channel audio power amplifier.

If you are running on a single 9 V battery, you can't get more than 1.26 W out of a theoretically perfect output amplifier - and the LM386 definitely is not that. Expect less than 1 W best case. At that power level, the LM386 is fine.

But - the LM386 is not just a normal opamp with an extra-beefy output stage. Its internal topology is significantly different, especially in the input stage. You will get better audio if you do the differential cancelling in a true opamp and follow that with the 386 as only an output stage.

ak

thank you for your reply.
i've yet to put it all toggether but the 33171 output (along with the center channel [now passive] circuit) will become input to a PAM8403, powered by an LM7805.
the main power is a regulated 15 VDC module from Avion Studios.

 

If you’re driving an 8-ohm speaker, consider adding a dedicated power amplifier after the MC33171N. TDA2030 or PAM8403 will work.
https://www.st.com/resource/en/datasheet/tda2030.pdf
https://www.mouser.com/datasheet/2/...SrpuUK7JJioqjktdGUKVEMRu2-75mYE-kry_CizxTMXjV

thank you for your reply.
i'll be using a PAM8403 for amplification.

 

The LM386 is only marginally more powerful than common op-amps; Radio Shack sold boards that used it to drive headphones. It would be woefully inadequate to drive small insensitive mid-woofers or full-ranges. There's loads of op-amps that would be better suited to a virtual-ground mixer. Things that have been popular in the past include TL072, AD712, NE5532. I'd highly recommend Walt Jung's Audio Ic Op-Amp Applications, but it seems to be out of print. Archive.org has the second edition to borrow (doesn't include cutting-edge applications like DAC output stages). but it's useful enough, or you can find it at pirate e-book download sites, I've heard. Douglas Self's "Small Signal Audio Design" may be helpful, too.

thank you for your reply.

 

My observation is that at least for home theater systems the center channel amplifier delivers quite a few watts of output. So any amplifier will need to be much more capable than any small IC amplifier.
If the amplifier is just supposed to be a small signal summing amp, that is quite different yet.
Of course, it seems that we are starting this discussion at page 25 of the original, so the context is missing.

thank you for your reply.