Use a switched
1/4" jack (like the Neutrik NMJ4HC-S or NYS2122). The DI should be
wired between the input transformer and the input to the board. When
there is no jack inserted, the circuit flows normally through the switched
jack (like its not there at all). When a 1/4" jack is inserted, then
the switch "cuts off" the input transformer and the circuit flows from the
1/4" plug, through the jack and into the board. Here is a
of one I
What are bypass caps?
In theory, electrolytic caps are slower and
therefore don't handle high frequencies as well as other caps. By
placing a high quality Polypropylene cap of very small value (~0.01uF) in
parallel (in parallel, capacitance values are added together...) across the
electrolytic cap, we can help it handle the higher frequencies. In
theory this might add more "air" to the sound or allow for better (faster)
response of transients. Here is a
of one I did.
soldering them on the backside of the board is a whole lot easier.
the bypass caps really make a big difference?
ears will have to answer that for you. It adds a little expense in
parts and labor to the project and if there is any difference its probably
very subtle. You have to decide if its worth the additional time and
Hey, can you rack some modules for me?
This is a great project when you can do it yourself. You save money
and you can say "look what I did!". If I were to charge a decent rate
for time (labor) and parts, the overall costs starts to get pretty close to
some of the modern boutique preamps that sound really good too. So
only if you can do it yourself, do I encourage trying it.
Can you update that Bill of Materials? I can't find part xyz
Admittedly that BOM is a few years old now, but you should be able to find a
similar part fairly easily if you check the Mouser or Digi-Key websites.
Parts and inventories can change frequently and I just don't have time to
keep up with it. This BOM is really meant to just help you get
Where can I get schematics for the PM1000?
Yamaha PM1000 Schematic Part 1
Yamaha PM1000 Schematic Part 2
I need a knowledge of electronics to do this project?
should understand basic circuits and it helps to understand the components
used in these circuits. You also need decent soldering skills and
unsoldering skills (if you intend to recap).
Speaking of re-capping, should I do that?
PM1000 line was manufactured in the mid to late 1970's. My math says
that's well over 30 years going on 40 now. Electrolytic capacitors
tend to have a lifespan that is less than that. The dielectric will
dry up and they either a) create an open or b) short out. If they
open, then they stop doing their intended job. If they are filter
caps, then you get noise. If they are in the audio path, you get no
audio! If they short out they might blow a fuse, or blow off the
board... or if they are in the audio path, they stop serving their
purpose (which might be to block DC). So at a minimum, replace the
What about swapping the other caps?
As noted on
other pages, it's recommended to replace the tantalum caps with
polypropylene to improve the sound. Also increase the size of the
input cap (3.3uF is a good value) and also of the output cap (an
electrolytic -- 220uF works nice). Optionally you can replace the EQ
caps if you want to change the EQ center points. If you don't then
leave those as is.
What input and output transformers should I use?
If you can get
the original input and output transformers, then those are a great match for
the boards. If not, then you can experiment. The original input
transformer is spec'ed at 600:600 ohm and the output transformer the same.
If you can't get the original type, then use a high quality transformer
(Jensen, Cinemag, Altran, etc.) of similar specs, you will probably be
What does the PM1000 sound like? Is it really as good as a Neve 1073?
or an API 312?
Really - that
question again? OK, here's the deal... if money was not a
concern would you be trying to rack some old channel strip hoping it sounded
like the one you really want or would you just buy the real thing?
Yeah, I thought so... So the answer is no. They do not
sound just like a Neve 1073. They don't sound just like an API 312
either. They sound like a... Yamaha PM1000. Yes, that's a
pretty accurate description. Yamaha was definitely trying to
compete with some of the other popular brands at the time and I'm sure
design considerations were made based on that... Now I happen to think
the PM1000 sounds pretty good and it's definitely in that "thick" or colored
sound arena. They work well on drums and I like the DI on bass
guitars. Frankly I've used them on all kinds of stuff (vocals,
guitars, percussion) and never had any complaints. But face it, if you
have unlimited cash, I'm sure there is better sounding stuff out there
(modern and vintage). Go get it. I just can't see paying
over $1000 (a 1073 is more like $3K and up today...) for one channel of
preamp when there are so many great options (including the PM1000) far below
that. That's why my personal studio has other preamps too.