PM-1000 project FAQ

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I have gotten so many questions over the years that I finally decided to put together this Frequently Asked Questions (FAQ) page.   Enjoy...

  1. 1.  How do I wire the DI jack?

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 picture of one I did.

2.  What are bypass caps?

n 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 picture of one I did. 

Tip:  soldering them on the backside of the board is a whole lot easier.

3.  Do the bypass caps really make a big difference?

Your golden 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 money.

4.  Hey, can you rack some modules for me?

No, sorry.   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. 

5.  Can you update that Bill of Materials?  I can't find part xyz anymore.

No, sorry.  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 started.

6.  Where can I get schematics for the PM1000?

Yamaha PM1000 Schematic Part 1
Yamaha PM1000 Schematic Part 2

7.  Do I need a knowledge of electronics to do this project?

Yes.  You 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).

8.  Speaking of re-capping, should I do that?

Yes.  The 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 electrolytic caps.

9.  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.

10.  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 happy.

11.  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.

More PM-1000 Resources

The Viewing Room Five Fish another schematic
Tape-Op Gearslutz Group DIY
Mouser Yamaha

My other DIY projects:

Sub-kick Project

Bass Traps Project

Other Mic Pres

Mic Mod Projects


Last updated 07/16/2013