Re: Re: Specs ???
Not only current! Ever taken apart and analysed a CD-931? I nearly had a fit analysing the PDB. There is an old post from me in the digital section.
Bruno Putzeys said:
The specs are not just those of the amplifier. They include the rest of the on-board signal processing circuitry as well. I find most consumer goods designers have serious problems making small signal electronics that produces less distortion and noise than the power amplifier. One would normally expect the power amplifier to dominate the THD figure but the current breed of consumer boxes have made me readjust to a different reality
Not only current! Ever taken apart and analysed a CD-931? I nearly had a fit analysing the PDB. There is an old post from me in the digital section.
capslock said:
The TDA8938 and the TDA8939 were designed alongside eachother. Both are functionally two-channel comparator+power stages. The TDA8938 has bipolar inputs with very low noise but is unable to sense signals near the negative supply. The TDA8939 has CMOS inputs which are far noisier but it will sense near the negative supply. The reason for this is that the TDA8939 is intended for open-loop use, where the comparator is only used with one input biased half-way the logic signal swing, so that it can interface with any thinkable logic level. The TDA8938 on the other hand was targeted explicitly at UcD control. The term UcD only pertains to a particular way of building a self-oscillating control loop.
Either chip is agnostic as far as the control system is concerned. The TDA8939 and TDA8938 "aren't UcD" and "aren't open-loop" either. Just depends on what you do with them.
Re: Volume control
The TDA8939 is not a UcD. It does not have a control loop on board.
You are referring to the application schematic in the data sheet. This schematic shows the chip used in a digital-PWM amplifier. All parts together form a digital-PWM amplifier, which can be volume-controlled using the power supply. The application schematic does not show a UcD.
A UcD built around a TDA8939 uses the same chip, inductors and filter capacitors. The rest is different. This schematic is not in the data sheet.
The TDA8939 is not a digital-PWM amplifier. It does not have I2S inputs or noise shapers on board.sx881663 said:
The TDA8939 is not a UcD. It does not have a control loop on board.
You are referring to the application schematic in the data sheet. This schematic shows the chip used in a digital-PWM amplifier. All parts together form a digital-PWM amplifier, which can be volume-controlled using the power supply. The application schematic does not show a UcD.
A UcD built around a TDA8939 uses the same chip, inductors and filter capacitors. The rest is different. This schematic is not in the data sheet.
Bruno,
With all due respect, there seesm to be a lack of universal definition for digital amp as some people considers UCD as analog Class D. Mind explaining more to the crowd?
Also, out of curiosity, saw a CS42418 chip on DFR. Judging its 2-ch ADC and the lack of a "Direct" mode on DFR, would one be better off feeding 2-ch stuff to SL/SR or C/SUB inputs (config as multi-ch input) and use the corresponding terminals to drive his/her speakers to bypass the unnecessary ADA conversion?
AK
With all due respect, there seesm to be a lack of universal definition for digital amp as some people considers UCD as analog Class D. Mind explaining more to the crowd?
Also, out of curiosity, saw a CS42418 chip on DFR. Judging its 2-ch ADC and the lack of a "Direct" mode on DFR, would one be better off feeding 2-ch stuff to SL/SR or C/SUB inputs (config as multi-ch input) and use the corresponding terminals to drive his/her speakers to bypass the unnecessary ADA conversion?
AK
AK47 said:
Technically, there is no such thing as a "digital amp". Current, voltage and time are analogue quantities, only numbers are digital. It's clear that all amplifiers, class D or otherwise have to get down to the nitty gritty of volts and amps at some stage in their operation.
The phrase "digital amplifier" having been coined now, I would give some leeway to its usage to denote something that derives a switch control signal from a digital signal, and that uses this control signal to drive power switches without further processing, i.e. an "open loop digitally controlled class D amplifier". All the rest is plainly analogue.
It appears difficult to settle the terminology thing, for what I see as two reasons.
1) Some may not fully understand the abstract notion of "digital", and think square waves are digital (a square wave is analogue, although it may be used to encode data - conversely, the waveform from a modem is not a square wave but nevertheless encodes data).
2) Some may think it sexier to call their amplifier design "digital", fearing the bland "class D" label or worse, "analogue" would detract from the perceived quality of their work.
Both of these reasons are subjective. This accounts for the invariably heated tone of any debate concerning d-terminology.
Have a look at
http://www.diyaudio.com/forums/showthread.php?s=&threadid=56709
Good question. I don't have the schematics of the dfr9000 so your guess is as good as mine.AK47 said:
Bruno Putzeys said:
You can buy the servicemanual at:
http://www.doknet.nl/
Cost: € 20 on CDR in PDF-format.
Hello i'am new in this great Forum.... Excuse me Mr Bruno Putzeys for my little experience(newbie) on the hf and the Class D but the TACT/texas instrument Equibit System is not a real digital amplifier??? My M2150 TACT haven't a DA converter and he have a spidf cinch in. No dac in the schematic. thank you for your response. I have two hypex 160 in my subwoofers very great amplifiers !!!!
