Newbie looking to build a multi channel amp

[AnimeAi]

I'm a complete newbie when it comes to building my own audio equipment but I have a good idea of what I want. I realise that I could probably spend another £500+ on a second AV receiver but would prefer to have a go at this project myself.

What I Have now:

• Sony STR-DN1050 AV Receiver upmixing (if necessary) stereo to 7.1 sound.
• 7.1 Sound in a single room
  • 1 x Tannoy Fx Sub
  • 2 x Celestion Ditton 15 XR (Front)
  • 2 x Celestion SP15 (Side)
  • 2 x Celestion 3 MKII (Rear)
  • 1 x Ruark Epilogue (Centre)
  • 2 x Celestion Ditton 15 (Currently disassembled and waiting on parts to rebuild the crossover)
• Inputs from:
  • PC
  • XBox One
  • WiiU
  • Virgin Media Box
  • HiFi (CD Player)

The AV Receiver has analogue stereo outputs for "Zone 2".


What I want to do:

• Use the "Zone 2" Output on the Sony STR-DN1050 to connect to a home made 8 channel amp.
• The amp will have a single stereo input.
• The amp will have 8 channel (4 stereo pairs) of outputs
• The amp needs to be able to drive none, one, two, three or all four of the stereo outputs at a time. This needs to be controlled by a switch (rocker switch or volume control switch - like that on an old fashioned radio is fine).
• Each output requires its volume to be adjustable from the amp (manual dial is fine).
• 15-30W RMS per channel is more than sufficient, I don't need my ears to bleed!
• The outputs will connect to paired speakers in different rooms of the house (bathroom, kitchen, bedroom etc).

From what I understand I will need to build/aquire:

• Input signal splitter - Split the 2 channel input into 8 channels without reducing the signal quality. At this stage if I simply connected the two input channels to all 8 output channels the output would automatically be at least quartered and require much higher amplification leading to potential distortion. Building a pre-amp circuit into the splitter may prevent this. Likewise if I simply wired multiple speakers into a single output I'd be quartering the speaker impedence (or worse!) and potentially blowing the amp out.
• 4 or 8 chimpamp type circuits (depending on whether they are mono or stereo circuits)
• Some form of PSU to power everything.

Budget: ~£200



I would like to use prebuilt amplifier circuits such as:

(EDIT: Examples removed and actual links added - looking to spend £50 or under if possible total for the amps)

• Mono Amps
  • 8 X £3.70 (£29.60) TDA7293 100W per channel
  • 8 x £2.49 (£19.92) TDA2030A 15W per channel (Also dual at £5.99)
• Stereo Amps
  • 4 x £8.87 (£35.48) TP2050 50W per channel
  • 4 x £8.99 (£35.96) TDA4198 100W per channel
  • 4 x £8.99 (£35.96) STA508 80W per channel
  • 4 x £11.29 (£45.16) TK2050 50W per channel
  • 4 x £4.99 (£19.96) PAM8610 10W per channel
  • 4 x £8.47 (£33.88) TPA3116D2 50W per channel
  • 4 x £1.83 (£7.32) TDA2797 15W per channel
  • 4 x £4.99 (£19.98) YDA138-E 10W per channel
  • 4 x £8.59 (£34.36) TS-50WGF-A 50W per channel
  • 4 x £9.89 (£39.56) TDA7492 25W per channel
• Needs a heatsink (Additional Cost)
• 4 x £9.40 (£37.60) LM1975 20W per channel

What I'm after are suggestions on how to build the audio splitter and how best to conenct that to the chimpamp type circuits. How best to power the amp - would a laptop power supply with the correct voltage be sufficient etc?



Despite searching for the past 6 hours online I'm struggling to get these answers and have had to swallow my pride as a man and ask for help! Many thanks for reading this and many, many thanks in advance for any constructive answers and/or advice you may have for me!

 

[AndrewT]

Build a mono amp first.
Learn what needs to be done to get good performance.
once you have the mono amp perfected, you can try a two channel amplifier and using the knowledge gained with the mono you can try to get the two channel to perform as well as the mono.

I suggest that only after you have successfully achieved a hum and buzz free (noise + hum <0.1mVac) for both builds that you design the layout of your multi-channel amplifier.

 

[sreten]

At this stage if I simply connected the two input channels to all 8 output
channels the output would automatically be at least quartered and
require much higher amplification leading to potential distortion.

Hi,

No. What will quarter is the input impedance, not any voltage level.
Using 4x dual 47K pots for volume will give 10K input impedance.

rgds, sreten.

 

[AnimeAi]

Build a mono amp first.
Learn what needs to be done to get good performance.
once you have the mono amp perfected, you can try a two channel amplifier and using the knowledge gained with the mono you can try to get the two channel to perform as well as the mono.

I suggest that only after you have successfully achieved a hum and buzz free (noise + hum <0.1mVac) for both builds that you design the layout of your multi-channel amplifier.

Point taken, I'm looking to run before I can walk - I do understand that. Sadly I've got a few single stereo amps (manufactured, not home built) dotted around from past projects and would really prefer not to constantly plug them in and out.

While I've never worked with amplifiers, I've done several speaker refurbs and rebuilt the crossovers. The theory is similar - use quality components to get a quality finish. Don't cut corners. Use things like silver solder for better audio transfer. Shorter wires are better. Etc?

As the aim of this is in the long run to save money while having a bit of fun during the long rainy weekends (since I simply could buy another commercial AV reciever and save myself a hell of a lot of hassle!)

Hi,

No. What will quarter is the input impedance, not any voltage level.
Using 4x dual 47K pots for volume will give 10K input impedance.

rgds, sreten.

Surely with all four amps sharing an input signal it would reduce the amount of signal available to each amp? One signal to two amps would halve it, one signal to four amps would quarter it? (Assuming all four amps are powered on). I understand that the impedance would be quartered - just the same as connecting four speakers to a single amp (bringing a single 8 ohm speaker down to 2 ohms and probably blowing the amp becuase there isn't enough resistance) but is this an issue for an unamplified signal? What is the standard impedance for an amp or set of active speakers/headphones which this type of signal would normally drive? I presume you're suggesting to place the pots before each of the amps?

Please excuse my ignorance, this is an area of science/physics/electronics I've not had a huge amount of experience in!

If this isn't the case and four amps can happily share a single signal without degredation (using the four 47k pots for volume as you suggested), this project might not be as difficult as I have predicted...

 

[sreten]

Hi,

There is no signal loss as long as the output can drive the input impedances.
Standard line input impedance is > 10K, up to about 50K.
If you connect 4 bulbs across a battery the voltage does not quarter so
the power drawn is the same, the battery will supply near 4 times the
current at near the same level into the quartered load impedance. *
Same case here, the current drawn quadruples, but as long as
the load is 10K or more the output voltage will not drop at all.

Yes, it is easier than you envisaged.

rgds, sreten.

* why connecting 4 8 ohm speakers tends to blow amplifiers
up, signal level is the same, but the current is quadrupled.
It will only work if the amplifier is 2 ohm load capable.

 

[AnimeAi]

Hi,

There is no signal loss as long as the output can drive the input impedances.
Standard line input impedance is > 10K.
If you connect 4 bulbs across a battery the voltage does not quarter so
the power drawn is the same, the battery will supply near 4 times the
current at near the same level into the quartered load impedance.
Same case here, the current drawn quadruples, but as long as
the load is 10K or more the output voltage will not drop at all.

Yes, it is much easier than you envisaged.

rgds, sreten.

Ah, so the AV receiver I have will likley boost its own output to match the impedance of the "amp" plugged into it? Failing that it would simple have a lower level of signal going to each amp if it was unable to boost the output to match? If I have each of the pots turned down to a low resistance, (aka high volume) am I not likely to have too little resistance on the circuits as a whole or am I overthinking this one?

On another note, while searching I've come across this pre-amp module and was wondering if there was any benefit in running the audio signal through the pre-amp before splitting the input off to each amp, or indeed through four pre-amps after splitting the input but before each amp. I like the design of that module as the opamp can be replaced with any 8 pin 5-18V chip letting me try a few of the OPA* series...

Since I now know I don't need to build some form of complex signal splitter/booster/magic box to drive the multiple amps from the single source I can probably mock up a few plans and work out enclosure sizes based on the variations I might make.

I have a feeling that working out how best to power this amp and potentially pre-amp(s) is going to be the hard part now!

 

[Bigun]

I honestly don't know if this is a good idea for a project - buy buying modules and wiring them up you won't really get to have the fun and learning of amplifier design - it's going to be all about wires and drilling holes in metal.

I'd suggest modify an existing AV receiver, this is just what I did for fun: http://www.diyaudio.com/forums/solid-state/230403-tgm6-modified-pioneer-ht-amplifier.html

There also some deals on eBay (you can still modify it too), e.g.
Pyle 19in Rack Mount 8000W 8 CH Stereo Mono Amplifier AMP 8 Channel 068888899031 | eBay

 

[AnimeAi]

I've mocked up a (highly simplified) circuit diagram for this project. Each of the five pots will be a dial on the front of the enclosure. The OpAmp bypass and OpAmp are something I'm toying with the idea of having found this preamp circuit (linking again since the previous link broke lol). It might make it into the final design, it might not.

Questions:

1. Is a 10k pot sufficient for the preamp or should that be 47k too?
2. Is a preamp likely to improve or degrade the audio quality overall?
3. For the switches on each of the 4 amps, is it enough to switch just the power to them, or should I isolate the audio signal source too?
4. I've decided that to keep costs down I'm going to use a 500W PC PSU. I've added a smoothing capacitor in parallel across the two bus bars the black/yellow leads from the PSU will be connected to. Should I do anything more to dimish ripple? Is there anything else I can do here?
5. As I'm now limited to 11-13V DC (the 12V rails are never exactly 12V!) I'm now restricted to these modules: TDA2030A, PAM8610, TDA7297, or YAMAHA YDA138-E. Does anybody have any suggestions or advice? Would I be better off posting this question in the "Class D" section?
6. I'm concerned that the Yamaha chip has no heat sink or easy way to mount a heat sink - is this likely to be an issue?

@Bigun: I understand where you're coming from but building an entire amp circuit is going to be beyond my skill and budget level for now - in the future it's somewhere I'm likely to go to 😉 I'm going to work my way up to building a DAC - probably a PupDAC or similar for now.

 

[sreten]

Hi,

This hasn't been thought through at all. You have Zone 2 outputs
at line and speaker level. Using Zone 2 reduces AV to 5.1 from 7.1.

As ever RTFM and really understand your options. If you drop the
need to drive multiple pairs of zone 2 speakers at the same time
you don't need any other amplifiers, just a speaker selector box.

Also look at line systems for distributed audio installations.

rgds, sreten.