Building Audio System, Have Questions About ICs?

So as the title states I want to design an audio system, I purchased an old shortwave radio someone gutted, but the case is in great shape and looks really cool, would make a killer looking amp.  So a little background, I want to make a stereo amp I can hook up several inputs to and my speakers; likely a turntable, iPod, radio, and whatever else I feel like.  The radio came with a nice little 5 position rotary switch for that.  The main problem I am facing is what ICs I want to use, and what order.  I have not dealt much with audio and at first I thought of buying a radio and just putting the guts into this unit, but I thought this would be a good project to dive into audio work.  You can't learn if you don't push your bounds a bit, am I right?

The first IC question is about chips like the PT2322.  There are several I have looked at that use a microcontroller for control, and I am not against using an Arduino Micro in this unit, but I am unsure of how the acknowledgment bit works.  The data input seems to just be a shift register, data gets clocked in, then latched.  Data is fed in in 8 bit strings, but then it mentions an acknowledgement bit as a 9th bit.  Is this bit for the latch, or is there a 9th bit fed in before everything is latched?  Should it be hi or lo?  As well I was looking at the commands, several commands have 7 of their 8 bits written as a *, does this mean that those bits can be set hi or lo?  I am sure these aren't difficult questions and I glossed over something important in one of the many data sheets, and that I do not use these chips with any regularity, if ever, doesn't help either!  But I like that these ICs all seem to have a 3 band tone control and volume control built into them.

If I were not to use an IC controlled by a microcontroller, I am looking at using a BA3812 for the tone controls, 5 band is a little more then I need, I really only wanted 3, not 2 but not more then 3.  Bass, treble and mid range.  But I could not find a 3 band IC without microcontroller inputs required for operation, and it was not for the lack of trying.  I can handle 5 bands though, however I am wondering, should I go preamp to equalizer to the main amp, or where would I wire in the BA3812?  This seems like a stupid question to me, I feel like an audiophile is going to come along and say, "You never put the equalizer after the preamp, it always goes here or there!" or something along those lines.  As well, regardless of where its going to get wired in, since I am doing stereo not mono, I assume I will need 2 BA3812's, but the datasheet supplies a circuit for 3 Chips as well.  Which would be suggested, 2 or 3?  I am wanting to control both left and right tone controls together, so using 5 pots instead of 10, and would also like to be able to have a balance control.  I didn't see anything about balance control in the BA3812 datasheet, would there be a good way of accomplishing that with these ICs or the use of a couple op amps maybe?  I didn't really look into balance, I should have before asking questions.

For the preamp the LM1036 seemed like a good choice.  I was reading into preamps, and they seem more important for the turntable then anything else.  The way the grooves on a record are cut they boost the high frequencies so they don't fade awayat lower volumes or something like that.  Because of that a preamp that boosts bass and cuts treble is useful and improves sound quality when using turntables.  Should I use a preamp only for the turntable input or for all inputs?  If I adjust the equalizer for records is a preamp necessary or should I use the preamp and set it with trim pots to boost bass and cut treble a little, or should it be fully adjustable as well?

As far as what to use for the final amplification I am at a bit of a loss.  A home theater system I have is 1500W and is adequately loud, but the system I have for my turntable right now think is only 250W I believe and it seems louder.  Never really understood wattages for "loudness"  or output on sound system.  I saw an IC (can't remember number, its a TDA though) dual 50W amplifier.  Not sure if 50W for each channel would be enough.  Advice would be helpful.

As a side note, if I do go the route of a microcontroller, I found this NJW1186 with stereo input and 5.1 surround output which I thought would be cool.

I really appreciate any help.

Thank you

iceng2 years ago

But have you soldering experience and DC power supply noise reduction knowledge.

What are your electronic wiring skills ?

KlockWork (author)  iceng2 years ago

4th year electrical engineering student. Steady hands, soldering is easy enough. I know for anything audio the power supply is important as to not add noise. A decoupled power supply would be ideal would it not? I have OCD, I can wire anything almost perfectly the first time. A friend had me rewire a motorcycle without the diagram or original harness, bought only black wire because he got a good deal on it and had me install a gauge cluster that should never have worked on that bike, but I rewired everything, modified the gauges and it all worked first time, even got the fuel injection firing the right cylinders first try which might have slightly been luck since I didn't actually know the firing order. In every lab I have ever had I have also used the least number of breadboards and finished faster then most other groups because I keep my boards very tidy so mistakes are few and far between and easily remedied if they pop up. My problem is I need to be very sure of what I am doing; if I am a little unsure I have a tendency to hesitate and make mistakes because I second guess everything from that hesitation forward. So far I have looked through dozens upon dozens of ICs for this project and I am going to make mistakes if I don't get some help.

iceng KlockWork2 years ago

Impressive, I have an OCD cousin who is an ME and urban_explorer.

Lets talk turntable :

A lot depends on the type of pickup 1)laser. 2)magnetic. 3)piezoelectric.

A Laser pickup does not slowly erode the physical record tracks and has the pre-amplification built in.... A Magnetic pickup is the most sensitive and delicate needle pick up and Does need the per-amplifier to work with very low signals it issues.... A Piezoelectric pickup is the low cost phonograph needle though a larger signal still needs a preamp.

Look into RIAA the equalization technique adopted by the recording industry.

Power Output depends a great deal on how much power your speakers can absorb. After that, how big is your room, how strong are the windows and what is your aural pain threshold ?

BTW I once had enough sound pressure that the delicate phono needle stared to jump tracks :-)

1500 Watts is sufficient for a good theater. Mine was 200W per speaker.

As far as the details of the circuitry you will find integrating the available elements may dictate and constrain your design.

I don't see the advantage of a micro to control your system only a further complication, and the Arduino is way to slow for streaming sound.

Good building.

KlockWork (author)  iceng2 years ago

Its not laser, its quite old, it is my parents originally actually. Can't go wrong with vintage. Fairly certain its magnetic, it was not cheap when they bought it either. I have a friend that has enjoyed a very good life thus far and has a $50000 turntable, I don't believe it was laser either though, but it looks amazing, crystal clear acrylic adjustable lighting and it floats on mineral oil, but I wonder if audiophiles prefer the needle over laser? They must, I imagine laser would be digital not analog like they want. I like the sound of laser though, no contact therefore no wear on the recording. I might have to look into that, but that's a tangent. As for speakers I wasn't sure if I would buy some for this or use the existing ones which are some Bose ones, again vintage. I would have to look into that as well for final power output.

Thinking about it a bit more today I think my plan will be to use an LM1036 or similar for the preamp, use some trim pots on the tone controls it has and set those based on the turntable input, then have it switch to a different set of resistors for all other inputs. Then I will run the signals through the BA3812's for 5 band tone control, and will set them up in a single chip configuration, one for each side, but each band from both sides controlled by one pot as to cut the number of pots down from 10 to 5. From there an op amp based balance control and then on to whatever I will decide on for final amplification. I will have to figure the power supply out after I get the rest figured out, as well I have 2 identical old neon 7 segment displays that look really vintage I was planning on using one for a clock and the other for displaying what station the radio was on as I was thinking I will put a radio in so there will be 4 inputs and a radio. I already have the clock working, but I am not sure about the radio. I don't listen to radio too much so I think I might buy a radio from the store that has a display that shows the station and use its internals and hack it to run the other neon display for the station.

I feel confident enough that I can probably dive in at this point. I think I just needed some reassurance that I wasn't going to totally botch this immediately! Thank you for the help.