I was searching Google (TH search engine doesn't work well for me...) for info on my BX-1 (recently got one going) and I think it sounds great! But today I ran across this thread, and several statements seem just wrong: examples: - Nakamichi frequency response is processed such that tapes recorded on a Nak don't sound good on other brand decks? They will sound "dull"? -BX-1 Dolby B reduces high frequency recording to 16k through some kind of MPX filter? which can be deleted on BX-2? This thread is from 2008, so very old, and I read through to see what people said about the deck (one person used to work at Pacific Stereo! Several said they had sound companies/music stores and sold Nak's...) https://forums.stevehoffman.tv/thre...-a-nakamichi-bx-1-serviced-for-us-100.159055/ Those of you with lots of NAK experience, what is truth and what is BS? There are so many self-prescribed "experts"... Thanks in advance
p.s. my BX-1 doesn't have a MPX button for blocking that FM radio carrier frequency (19khz?) out... which i understand that will mess up Dolby B processing, but I never record from radio...
I always thought that was a given but I'm not an expert, I've always heard that since the early 80's. It's like a two cars, a fast one and a faster one, they both use the same gas but the faster one uses it better. Nakamichi being the pinnicle of tape decks would record an excellent tape, playing that tape on a lesser deck won't sound as nice. I think a better question would be does a tape recorded on a lesser deck sound better played back on a Nak? My last Nak Belt broke last year so I don't have a running machine, none of mine are spectacular except for the RX-202. I bet Elite-ist could explain it better, he has most of the cool top-end decks.
I did look at the service manual, and there is a MPX board in the BX-1, so something must turn it on... wonder if you could put in a switch to disable it?
I did find on BX-2 (sister deck) diagram in Sce Manual: seems simple, if I could see clearly where to insert switch... BX2 doesn't have a separate MPX board, appears to be integrated on main board. Now my question, would this make BX-1 a better sounding deck if MPX was deleted when using Dolby?
What you are talking about here is the IEC and IEC II standard, look it up. Nakamichi did use a different standard to other at one time. If you use the MPX Filter, it just strips out the 19kHz carrier signal from the FM signal so not to interfere with Dolby. MPX disappeared as newer FM tuners strips the 19kHz signal out after has used it and before it puts it through to the rest of the Hi-Fi chain.
Since you are not going to record from the radio (I also never did this in my younger days, and have no plans on starting now), just take MPX filters for L and R channels out, substitute for a nice piece of copper wire. Physically they are located on the separate "MPX P.C.B. Ass'y" board: and their location on BX-1 schematics: When restoring my RX-550 I had to take these filters out because MPX filter for the L channel got busted. See two pieces of Yellow wire instead of the filters: I do not expect to hear any difference, this is a boombox after all... But most of the folks at Naim and Linn chatrooms believe that in hi-end audio "Less is More" BX-1 is definitely a hi-end deck, so there is a chance you will hear the difference P.S. To clarify: since your MPX filters work as intended, you do not have to desolder them, just take them out of equation by shorting IN and OUT by copper wire
@Jorge : excellent! I was hoping there could be a way to "jump out" the MPX filter... I don't want to damage the deck, and your idea seems pretty straight forward. since the filters are located on the separate board, could I just jump with copper wire? I can't see all the traces on the SM diagram, but I do see "IN" and "OUT" marked beside each filter: can it be as easy as just connecting IN to OUT? Maybe I am making this too easy... I haven't opened the deck today to look at the board layout... p.s. nice looking boombox! @Jorge : Excellent!! That makes it easy!! (I didn't know you could edit like this!!)
I blew up the MPX card diagram to be easier to see... I've been trying to see where the switching takes place, must be on the main board.. I would think jumping here should work... just want to make sure I put in the right place.... Thanks for the help mike in SC
@Dfcruiser - you got me confused - what do you mean? Hopefully some of the pros here notice this thread but to me it looks like MPX filter is always in the signal path. If BX-2 has MPX defeat switch, you may want to compare BX-1 and BX-2 schematics and layout. Otherwise try copper jumpers. also - if you want to play extra-safe then wait for comments from @Valentin or @Longman I haven't burned anything during restoration (yet!) but I never mess with stuff I am afraid to ruin. My own Nak LX-5 was serviced by Willy Hermann
I downloaded the Bx1 schematic the filter in question on the diagram and in the green and red square I will only follow the signal on one channel which from the input enters the volume control and a preamplifier of the Chip ua7300pc.. on the output of this (pin 11) it enters the filter through a resistor... and re-enters the cip from pin 12... after the input resistance you can take the signal and connect it to pin 12 in order to exclude the filter circuit as @Jorge says
@Jorge : sorry for any confusion: I had read somewhere(Audiokarma link in the initial post) that with the BX-1 : No Dolby = no MPX filter; Dolby ON = MPX filter, so was trying to understand how MPX filter was switched on. Second part was could I take that filter out of the circuit, as the FM carrier is not an issue anymore (plus I don't record from FM). You are right, it does look like MPX is in all the time! @Silver965 : thank you for looking at the BX-1 circuit in such detail: I wish I had these diagrams plotted out, so much easier to trace! Helps me see what I'm looking for. It would seem the BX-1 would be improved if this MPX filter was out of the signal path... besides being a simpler circuit. I won't do anything to risk if I'm not comfortable, it's still a Nak BX-1!! thanks, mike
the filter on Nak Bx1 is always active... instead on Nak Bx2 it can be excluded with the switch But the circuit is even more complex and managed in another way
Dfcruiser if I were you, I would leave the deck as is. Unless you have a very revealing system, you will not notice the difference between MPX on and MPX off. Be happy with what you have, or risk wrecking the deck.
OK, I admit defeat... I had seen the switch in BX2 diagram (post 6) and had hoped BX1 would be simply finding where something like this would fit on the BX1... MR. Nakamichi is much smarter than me! I will take the advice and leave it alone! I still have the head switch to replace, then can enjoy the deck! Most important thing, this confirms the MPX filter in the BX1 is engaged full-time. Thanks @Silver965 , @TooCooL4 , @Jorge for looking at this in detail! Mike in SC
