Попробую поставить в мастер и пару линеек LT1355. Посмотрим что изменится. Вот тут есть что посмотреть
http://www.gearslutz.com/board/so-much- ... -mods.html
Понимаю, что затягивает... буду переделывать.
Вот собственно и подтверждение моим ощущениям - один в дин:
Here's the results of the work I did last week on an original version, an 8 bucket model without the relays I saw at Namm.
First, the Audio Precision test results:
Frequency response; -1 db at 20 hz, -3 db at 55k hz, line input to master mix output.
Stereo crosstalk; - 58 db 20~20k hz, a straight line.
Noise = -85 db 500 to 20k hz. 60 hz psu noise = -71 db at 60 hz, -80 db at 183 hz.
Phase shift; + 38 degreees at 20 hz, -26 degrees at 20k hz. Low end phase shift is non-linear in nature.
THD+noise; .1% at 0 dbu, .02% at +20 dbu.
THD vs frequency; .2% at 20 hz, .01% at +15 dbu, .04% at 20k hz at +15 dbu.
CCIF IMD; .002% at +15 dbu.
The first thing I noticed was this mixer is noisy. It actually washes out the THD measurements until one sets the levels very high, +15 to + 20 dbu to get the signal out of the noise floor. The low end sounds thin and doesn't improve with low end boost EQ. The modified input channel doesn't have that problem as I used 220 uf caps to replace the small 22 uf caps. The noise floor is also very low on the modified channel but I didn't get enough bench time to measure it alone.
The EQ needed a few fixes to make it wide ranging. C7 and C8 were changed to Wima FKP-2's. C11 and C12, the hi mids I used Wima MKP-3 1500 pf 1k v. Those fit nicely. R96 and R98 are changed to 4.75 k to allow a 20k hz sweep range.
C44,45, the low mids were changed to Wima MKP-2 .033 uf. R96, 98 are changed to 3.32 k to allow a 1500~50 hz range.
Low EQ is too high into the mids, I used .22 uf Wima MKS-2 for C22,23 to move them down one octave. It now looks symetrical on the AP next to the hf curves.
There are no electrolytic power supply bypass caps in these modules. They need to be installed. I used 470 uf Panasonic thin case FM's in place of the ceramic caps C1 and C5. I installed .1 uf mono ceramics on the rear of the pcb. There are no psu buss fusing resistors installed either. Lot's of local .1 uf mono ceramics were installed at several locations on the power rails to ground.
One other flaw I found is on the 1510 mic preamp chip. There is a 220 pf cap across the 2 inputs. That was enough with older parts like SSM2017 and BB INA217. The that 1510 tends to be unstable with that so it requires a pair of 470 pf mono ceramics from pin's 2 and 3 to pin 5 = ground. That fix alone could solve some of the ghosting effects I found. The switches also cut out a bit so they should be watched and replaced if necessary with the original Shadow brands, not the EI switches that are stock.
There are 26 22 uf caps that need replacement. I used Panasonic 220 uf 25v FM's with Wima .01 uf MKP-2's on the rear for air. Several opamps needed phase compensation caps, 22 pf's were installed across the feedback resistors on IC6 and 4. That is a lot of coupling caps, further tests may remove some of them if low offset, low bias opamps are used.
The PCB was good quality, no flux, thick traces, easy to rework. the RHoS solder is very pasty, I needed to resolder several connections like the mic XLR.
When I get a chance to address the master section I can offer more insights.
Jim Williams
Audio Upgrades
Вход
Регистрация
FAQ
Поиск
