With regards to Dolby BC: to keep it achievable and simple, go for Dolby B first. Keep room for later to add Dolby C when needed. Like the DOL circuit, it can be made entirely of discrete components if it needs to be redesigned from scratch. Combined with the 6 transistors for the pre-amp: more readily available components that can be easily rearranged on the PCB. Even better, the DDII, D3 or DDIII donors, already feature Dolby B: even re-using an IC would not be a problem. DC2 units on the other hand are relatively rare, and I would not like to upgrade mine.
@Levia Chan : I recently received files that do allow us to compare the Aiwa DSL stage 1 with DD-100 DOL, thanks to @Valentin and Magneticblood. I am not biased as I don’t have any DSL or DOL devices, but since DOL uses discrete components only I suppose there is ample room for improvement for modern headphones. DOL sounds really bass heavy, while DSL only slight amplifies lower frequencies. DOL = MegaBass max, skipping the normal-mid if you ask me. Makes sense too when you check the studio headphones (DR-S3 rebadged) the DD-100 came with. Modern headphones are much better / different, so reusing the DOL circuit as-is is useless. Please send me a private message if you would like to know more.
Apologies about lack of update, I have been looking at components to use with the DOL circuit to enable a adjustable amount of bass, found a few trim cap that looks promising for prototyping with various values to determine which one would matter the most for bass response (because such trim cap is relatively expensive)
I believe it would be beneficial to have an adjustment option. The newer headphones don’t require the 80s output of devices like the D6C, D3 or DD100. This additional board or complete PCB will come at a cost; how expensive is a variable resistor or cap in a circuit? Perhaps the additional room required will be the constraint.
The trim cap is around £3 each, with a pair needed for the circuit (one for each channel), Their footprint are under 6mm so they can safely occupy the original footprint because of the externalising of the toggle switch
Acceptable costs looking at the overall goal. If the mod can be done under a 100 Euros, I am in. Dedicated daughterboards, different batteries, easily accessible charging port (or perhaps just a change to ensure 5V charging via the standard barrel jack?), adjustable sound enhancements through the battery cover? Therefor, don't put caps in their original spot since it is hard to reach. Relocate them to a separate small PCB that can be housed in the battery compartment. The battery covers I got via @Valentin (he can provide the source) are 3d printed and can easily be changed to accommodate adjustment through holes. When the PCB is small enough, using AAA (IKEA Lada high capacity or Panasonic Eneloop Pro) instead of AA cells might just leave enough space. Especially when a second daughterboard for the majority of the DOL components is put in the original DD-100 space, that the DDII and DDIII both have available. Marian put relatively large capacitors in the space, see the link in the PDF that I shared on page 1 of this thread.
5V charging via the barrel jack should be easier to do than my previous usb c idea, I am putting that in my list Using a single 14500 battery should do the trick of outputing 3V with one single AA sized battery, leaving enough space for some circuitry(although around half the capacity), that being said, I am not sure if putting the trim cap there is a good idea, it already need two switches in there to toggle DOL and line-out(and/or toggle Dolby B for DD)
Following up with the cx20218 situation, quite a few of them had responded with available stocks and prices, I don't know what currency but they are quoting in-between 1.23 to 20, which if it's USD it's acceptable, if it's CNY I am emptying their stocks On another news, I have translated a few part of DC2 and DD100's Schematic into Eagle, awaiting if CX20218 is available so I could settle down with a design While I wait I have ordered some parts to build prototyping circuit for the quartz lock part, we'll see how that goes
If for release 1 you focus on DD models that have Dolby B, only 2 switches will be needed? It would be amazing if the additional circuitry could fit in an AA cell housing, meaning the original compartment can stay as is with only some wires sticking out. Would you consider replacing the standard red LED with a RGB one? For instance: red (standard), orange (output DOL), green (line out port A on), and blue (line out port A and DOL)? That would be something. Can they do a certain test prior to purchase to validate part of the claimed functionality? Although if you opt for a discrete component redesign, more flexible component placement and sourcing costs would be a benefit.
The RGB led idea is a great idea, need to go back and check if there's parts that will fit the dimensions easily, if not there's still tricks that could make it work (i.e. making an cutout and put the smd rgb led on the other side) For the switches I would be using reversed mounted dip switches (smd dip switches mounted upsidedown with cutout in the PCB), they are tiny and great for these kind of application. I have been trying to get the discrete component dolby B going, but at the moment I can't find a proper schematic diagram specifying what diode(?) it's using so it's currently on hold updated: no need to change controller, just need a i2c rgb controller and it should do the job
