Mark185
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Motivation for this project came from the large amount of DIY boom box projects I see online that are based on cheap car speakers and low cost TPA3116 chip amps. Rather than buy some cheap car speakers, I thought why not use some of these old Insignia home theater speakers as the starting point? I am also doing this to further my knowledge of how to use Sigma Studio to implement digital signal processing using commonly available DIY boards. I know most of the commercial market has moved on from Analog devices ADAU DSP chips but they are still available at relatively low cost for the DIY market.
This speaker was the subject of many DIY mod discussions years ago because it was so inexpensive and relatively easy to modify for DIYers. I think it has faded from the scene over time but you can still find them on ebay for less than $100 a pair. John Krutke at Zaph wrote about them and did some detailed measurements that can still be found:
Danny at GR Research also wrote about them and used to sell a crossover kit upgrade that was actually pretty decent.
I bought 2 pairs of these speakers on sale for at total of $50 years ago and they have been sitting in storage for a long time. I decided to pull them out and see what could be done with the current crop of inexpensive DSP boards and amplifiers. I used Google Gemini to suggest how to biamp them with active crossover based on the work of Zaph and Danny and use DSP to replicate what they did. My starting point is a TinySine TSA8802 board with a 2 channel amplifier, ADAU1701 DSP chip, and 2 channel analog outputs that will go to a ZK-3002 amplifier for the woofers. I am starting to become somewhat proficient with Sigma Studio and it was fun for me to figure out how to do this.
My schematic started with the TinySine supplied firmware and I modified it extensively. I kept the input part of the diagram that accepts Bluetooth or analog inputs and auto selects Bluetooth if present. I scrapped most of the rest of their diagram. My implementation adds the following:
This speaker was the subject of many DIY mod discussions years ago because it was so inexpensive and relatively easy to modify for DIYers. I think it has faded from the scene over time but you can still find them on ebay for less than $100 a pair. John Krutke at Zaph wrote about them and did some detailed measurements that can still be found:
Zaph|Audio
Zaph|Audio archive: Zaph|Audio. DIY speaker designs and measurements by John Krutke. Preserved and hosted by Madisound Speaker Components.
zaphaudio.com
Danny at GR Research also wrote about them and used to sell a crossover kit upgrade that was actually pretty decent.
I bought 2 pairs of these speakers on sale for at total of $50 years ago and they have been sitting in storage for a long time. I decided to pull them out and see what could be done with the current crop of inexpensive DSP boards and amplifiers. I used Google Gemini to suggest how to biamp them with active crossover based on the work of Zaph and Danny and use DSP to replicate what they did. My starting point is a TinySine TSA8802 board with a 2 channel amplifier, ADAU1701 DSP chip, and 2 channel analog outputs that will go to a ZK-3002 amplifier for the woofers. I am starting to become somewhat proficient with Sigma Studio and it was fun for me to figure out how to do this.
My schematic started with the TinySine supplied firmware and I modified it extensively. I kept the input part of the diagram that accepts Bluetooth or analog inputs and auto selects Bluetooth if present. I scrapped most of the rest of their diagram. My implementation adds the following:
- Bass, midrange and treble controls linked to external potentiometers. My implementation has true tone controls with index selectable bass shelf curves, midrange peaking curves, and treble shelf curves. The TinySine firmware split the signal with a 3 way active filter and used simple gain controls for each band before mixing them back together. This can introduce phase distortion and I do not believe it is as good as the approach I implemented.
- Following the tone controls, I have a parametric filter to correct the 800 Hz region where the Insignia woofer has known response problems.
- A 2 way crossover follows the 800 Hz filter and is set at 3000 Hz 24 dB Linkwitz Riley.
- The Hi Pass branch then has a 3000 Hz parametric filter to correct for the horn loaded response irregularity of the coax tweeter that was documented by Zaph.
- The PEQ tweeter signal then goes to a volume control with external potentiometer before being passed to the DACs 1 and 0 that go directly to the onboard amplifier chip.
- The Lo Pass signals for the woofers are passed to a 24 dB/octave Butterworth hipass filter to protect the woofers because they are in a poorly designed ported enclosure.
- Then the lo pass goes into a 5 band PEQ which is there just in case I need to tune the woofer response further. For now, the filters are all set flat.
- Outputs from the PEQ go to DAC 2 and 3 on the 1701 chip which are analog outputs and I will connect them to the ZK-3002 amplifier board.
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