Problem minidsp/sure + powersoft digimod

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   You could make some opamp circuits that give you the required gain quite easily. Here is the basic diagram for a non-inverting opamp gain stage:
To get the gain you need, use 10k for R1 and 39k for R2. This gives an output (Vs) of about 1.24v RMS (+4dBu) for an input (Ve) of 0.32v RMS (-10dBv). It makes a 3.9x voltage multiplier.

You will also need a couple of extra components to make the real circuit:
- A 100k resistor from +IN to GND, this stops the input floating and potentially producing a high DC output if disconnected. 
- A 100r resistor in series with the output, this helps the opamp cope with driving subsequent cabling. 
- And, a 100nF cap from power + to - on the board near the chip, this stops oscillations. 

If you already have or can easily make a +/- 15v supply in the project, just use that to power the opamp. Otherwise, if you only have a single-ended supply, you will also need to use one opamp to generate a virtual ground at 1/2 V+, use that as your ground node inside the opamp circuit, and add 1uF non polar capacitors at the input and output to couple the AC signal. 

Note that this circuit will raise the voltage of the whole signal, including noise. I don't think the ADAU1701 has a very good signal-to-noise ratio, so you might still have a problem in the form of excessive hiss when no signal is present - the only solution to that is a better DSP board. 

Edited by studio45 - 07 August 2024 at 2:04pm

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studio45 Members Profile Send Private Message Find Members Posts Add to Buddy List Old Croc Joined: 16 October 2007 Location: United Kingdom Status: Offline Points: 3881	Post Options Post Reply Quote studio45 Report Post Thanks(0) Quote Reply Posted: 07 August 2024 at 2:00pm
	You could make some opamp circuits that give you the required gain quite easily. Here is the basic diagram for a non-inverting opamp gain stage: To get the gain you need, use 10k for R1 and 39k for R2. This gives an output (Vs) of about 1.24v RMS (+4dBu) for an input (Ve) of 0.32v RMS (-10dBv). It makes a 3.9x voltage multiplier. You will also need a couple of extra components to make the real circuit: - A 100k resistor from +IN to GND, this stops the input floating and potentially producing a high DC output if disconnected. - A 100r resistor in series with the output, this helps the opamp cope with driving subsequent cabling. - And, a 100nF cap from power + to - on the board near the chip, this stops oscillations. If you already have or can easily make a +/- 15v supply in the project, just use that to power the opamp. Otherwise, if you only have a single-ended supply, you will also need to use one opamp to generate a virtual ground at 1/2 V+, use that as your ground node inside the opamp circuit, and add 1uF non polar capacitors at the input and output to couple the AC signal. Note that this circuit will raise the voltage of the whole signal, including noise. I don't think the ADAU1701 has a very good signal-to-noise ratio, so you might still have a problem in the form of excessive hiss when no signal is present - the only solution to that is a better DSP board. Edited by studio45 - 07 August 2024 at 2:04pm
	Studio45 - Repairs & Building Commotion Soundsystem -Mobile PA

erick77 Members Profile Send Private Message Find Members Posts Add to Buddy List Registered User Joined: 23 February 2015 Status: Offline Points: 11	Post Options Post Reply Quote erick77 Report Post Thanks(0) Quote Reply Posted: 06 September 2024 at 12:39am
	You did not mention if you tried to source the Powersoft DSP cards/boards that were designed to plug in and play in those amps. A 30 second look at the data sheet shows the amps were designed for optional dsp cards. Crown use to do that with PIP cards/input panel for their macro-tech and com-tech amps. Parts-express.com has a number of different dsp cards for integration into a project. Rod Elliot has a number of board designs with available PCB if you want to go analog and make your own crossovers.. https://sound-au.com/index.html Mini DSP have some modular boards that plug and play with each other. Optimize your inputs and outputs the way you want. You do not mention what you are trying to use that is minidsp. does it have headers for different inputs and outputs ? probably does. For example they have "balanced input boards", and probably balanced output boards also... I think you can get that MiniDSP kit stuff at parts express also and ebay of course. ( minidsp started out with build your own kit IIRC ) Oh yeah and rod elliot's ESP (elliot sound products) site has input and output buffer/preamp boards . There is a forum with a community and much more detailed information on the design once you buy a PCB from him. Powersoft still makes the DSP cards for "digi-mod" amps : https://www.powersoft.com/en/products/dsp/dsp-lite-e Given that the Powersoft have dsp card slots in those amps; there are going to be low voltage provisions for said cards or a custom mod... Edited by erick77 - 06 September 2024 at 1:00am