Wonder why Tascam didn't include higher end preamps and capacitors in the factory unit. Buying in the quantities they buy and having these installed at the factory wouldn't have added much to the production cost.
For one thing, most manufacturers aren't dealing with, or aren't concerned with, subjective sound quality. This is because only a small minority of their customers is interested in subjective sound quality. (Most consumers of portable recorders are interested in measurement more than in subjective sound quality).
Second, for a manufacturer to stay in business there must be some minimum ratio between production costs and MSRP. Let's assume here that this minimum ratio is 5 (often this is the actual ratio). That means that any additional $1 in production will be reflected as additional $5 in MSRP.
Now, considering the cost of only the OpAmp chips (we don't know what capacitors are replaced and their cost), the NJM4580 costs $0.225 for 2,000 pieces, the NE5532 costs $0.372 for 2,500 pieces and the LME49720 $1.23 for 2,500 pieces.
In the DR-70D there are 2 NJM4580 and 3 NE5532, which cost $1.566 for all 5 OpAmps. 5 x LME49720 cost $6.15. The difference is $4.584 in production costs, which need to be reflected as additional $22.92 at least in MSRP, or additional 7.66% of the present $300 MSRP. Replacing also capacitors will come up even higher, though we don't know by how much.
As long as there is no widespread demand from consumers, most manufacturers wouldn't increase to product's cost by 7.66% without a very good commercial reason.
For a DIY mod'er, LME49720 costs $3.16 (in small quantities), which is $15.8 for the 5 OpAmps. (A charge of $100 or $200 for such a mod by a pro mod'er looks to me reasonable, because of the time and the work involved, on top of the skill, expertize and know-how).
It looks like the majority of the people purchasing Tascam portable recorders are satisfied with the products as they are; only very small percentage of consumers are interested in subjective sound quality and hence are willing to pay extra for the mods. The Tascam DR-70D is being marketed as "Linear PCM recorder for DSLR" - a market of very little demand for subjective high sound quality. Those pros who are interested in subjective high sound quality would probably turn to products of Sound Devices, Nagra etc.
It looks like we (amateurs, or not full-fledged pros) are lucky to have products like the Tascam portable recorders, or mixers/recorders, at a very reasonable price and with adequate subjective sound quality of stock products.
As for Tascam coming with DR-60D MKII, assuming they did there what they did with the DR-70D, that is, replacing 3 of the NJM4580 OpAmps with NE5532 ones, here there is additional $0.441 in production cost, or additional $2.205 in MSRP, or an addition of 2.2%, which is really very little. When the sales of certain model start to decline, there is very good commercial reason to add very little to the production costs and come up with improved MKII.
(The above is derived from my experience working for electronics production company).
(Please excuse my English, it isn't my first language).
