Double Bass Manual for Walter Woods MI 100-8

[Ric Vice]

Thanks for the welcome, FF!!! Kinda figured I'm not alone in the search..but gotta try!

Walter's amps are wonderful, I own two of them a Electroacoustic Ultra, and the MI-400-8 (the big brother to the MI-100-8). Having one repaired now costs $600.00 flat rate, return shipping is included.
There are no available schematics for any of his amps, with the exception of the ones he put inside next to the power supply of the early MI-100-8's. Walter's the only person who has access to
schematic's for his builds, and he removes the serial no's from his key components, to protect his designs. He's often out on vacation, because the summers in Palm Desert CA can get very hot.
That said, he's always been very good to me, and repaired my amps in a timely manner.

Ric

 

[Povl Carstensen]

I have an MI 200-8 "Sweeper" with three band parametric equalizer. Reading about the respect for Walters amps here has certainly only elevated my appreciation of it.

 

[shwashwa]

Here are a couple of pics of my WW.

As you can see, I still have the name tag from Walter on it.

just out of curiosity, does anyone know the frequency of the mid knob on this model?

 

[shwashwa]

Here are a couple of pics of my WW.

As you can see, I still have the name tag from Walter on it.

Just adding to the collective wisdom of this thread for future generations.... so, i have this head and one of the more "modern" electracoustic ones from the mid 90s. i've heard people say that this head behaves much like a tube head, but i had never played through a tube head so i had no way of knowing. so, for the last month i have been using a fender bassman 100T, which work great for upright by the way but its huge and heavy. now that the bassman is in the shop getting some tube issues fixed im practicing with this amp again, and i can say that yes, it does feel like a tube amp, in a very good way. its warm and musical. probably the best sound i get with my upright (i have an AI and an swr Baby Blue, and another WW also). with the 2 gain controls you can get into some mild tube like overdrive (not distortion really) which adds a nice warmth to the sound and makes the strings somehow feel fuller under my fingers. i actually took the fender to a few gigs lately , it sounded really good on the 25 watt setting, but its huge. ill be taking this amp to the gig this weekend but i have to say it sounds and feels more like the fender tube amp than it does the new walter woods model.

 

[robgrow]

The early Walter Woods amps have preamps with class A, discrete FET-based circuits, which can add a significant amount of harmonic distortion. Walter did a good job of getting a tube-like sound with a solid-state amp, which was one of his original design goals. This was at a time when solid-state amps did not have the best reputation for the way they sounded. The WW Electracoustic amps use IC opamp-based preamps, which have a lot of headroom and much less harmonic distortion. They sound great in their own way, but it is a different sound than the early MI amps. I like both the early and the recent amps.

 

[Ric Vice]

The early Walter Woods amps have preamps with class A, discrete FET-based circuits, which can add a significant amount of harmonic distortion. Walter did a good job of getting a tube-like sound with a solid-state amp, which was one of his original design goals. This was at a time when solid-state amps did not have the best reputation for the way they sounded. The WW Electracoustic amps use IC opamp-based preamps, which have a lot of headroom and much less harmonic distortion. They sound great in their own way, but it is a different sound than the early MI amps. I like both the early and the recent amps.

+1 When Walter built the MI series amps he pretty much nailed the sound of a tube amp, with a head that weighed only 7 1/2 lbs. and produced 100 watts RMS. At the time there was nothing else like them on
the market. It's a very unique amplifier. My MI-400-8 produces 400 Watts RMS into an 8 ohm load, it has a wonderful EQ section.

Ric

 

[Freddels]

When I bought mine back in '84, I was coming from a Sunn 2000S amp. The WW had THAT sound that I was used to so I never missed the tubes. I've been playing with it and it still sounds great. I may have to pull it out for some upcoming gigs. I've been rotating the knobs back and forth b/c of some scratchy pots and it seems to help.

 

[Ric Vice]

When I bought mine back in '84, I was coming from a Sunn 2000S amp. The WW had THAT sound that I was used to so I never missed the tubes. I've been playing with it and it still sounds great. I may have to pull it out for some upcoming gigs. I've been rotating the knobs back and forth b/c of some scratchy pots and it seems to help.

+1 I was coming from my Ampeg B-15N(C) when I purchased my first MI-100-8 in 1980, it sounded like a tube head with 4 times the power at a fraction of the weight. A little CAGI Deoxit should help with your scratchy pots.

Ric

 

[Roger Mouton]

Sales brochure? I've never seen one . . . ever. The only one that I ever saw was on the back of my Rufus Reid book (and that's how I purchased mine).

I have a sales brochure and it should be complete with the Walter Woods envelope it came in, thus maybe a date reference. I had sent a request for information and received a fairly prompt reply. It's what I would call a small, multipage pamphlet that would fit into a No. 10 envelope. I'll have to hunt it down, copy it as a jpg and post it. From reading the various Walter Woods posts throughout the years this sales brochure may have been the only sales brochure Walter Woods ever had. Anyone?

 

[Roger Mouton]

OK, here are the pages from my WW Sales Brochure. The envelope was postmarked August 13, 1999, San Bernardino, CA. The envelope has some faint "watermark" graphics with the old P.O. Box address in Van Nuys and 213 telephone Area Code. The left end of the envelope has the current Sterling Lane, Palm Desert address on it and some attempt to cover over or blacken out a previous address in Indio. If you're not familiar with Southern California, Indio is near Palm Desert, which is near Palm Springs etc.

I clicked on one of the WW links provided previously in this thread (it may have emanated from the EB side) and read a few interesting pages, then realized that there are over 30 pages in the thread. Oops, that much reading is not for me and besides I recall reading most of it before anyway. The WW devotees are many and there are some great posts to follow. Maybe even one of mine, inquiring whether Walter Woods ever worked for Tommy Gumina at Polytone before going out on his own. I know somewhere on the forum I might be able to look it up and as I recall, it was rumor anyway. The rumor being that Walter suggested Polytone needed more powerful amps and Tommy was against it. As of a few years ago he still was against it but that's another story.

The brochure was constructed using 2 sheets of 8 and 1/2 inch X 8 inch paper, folded over, thus making 8 pages and what I think is generally called a hand-held brochure. Somewhere it was posted that Walter Woods is making only the Ultra High Power (blue light) amp.

 

[shwashwa]

OK, here are the pages from my WW Sales Brochure. The envelope was postmarked August 13, 1999, San Bernardino, CA. The envelope has some faint "watermark" graphics with the old P.O. Box address in Van Nuys and 213 telephone Area Code. The left end of the envelope has the current Sterling Lane, Palm Desert address on it and some attempt to cover over or blacken out a previous address in Indio. If you're not familiar with Southern California, Indio is near Palm Desert, which is near Palm Springs etc.

I clicked on one of the WW links provided previously in this thread (it may have emanated from the EB side) and read a few interesting pages, then realized that there are over 30 pages in the thread. Oops, that much reading is not for me and besides I recall reading most of it before anyway. The WW devotees are many and there are some great posts to follow. Maybe even one of mine, inquiring whether Walter Woods ever worked for Tommy Gumina at Polytone before going out on his own. I know somewhere on the forum I might be able to look it up and as I recall, it was rumor anyway. The rumor being that Walter suggested Polytone needed more powerful amps and Tommy was against it. As of a few years ago he still was against it but that's another story.

The brochure was constructed using 2 sheets of 8 and 1/2 inch X 8 inch paper, folded over, thus making 8 pages and what I think is generally called a hand-held brochure. Somewhere it was posted that Walter Woods is making only the Ultra High Power (blue light) amp.

View attachment 544327 View attachment 544328 View attachment 544329 View attachment 544330

that's the amp he's currently making today. i have that one as well as the older one. i was never really clear on what the balance knob did

 

[Ric Vice]

As far as I know, Walter never worked for anyone else as builder, but it's entirely possible that he may have done that. I believe that he worked for Boeing Aircraft, before going out on his own. Thus, his familiarity with SMPS power supplies. I have one of his earlier "flyers" from the
MI series amplifiers. It's just a two sided sheet with pictures of amplifiers. It was printed on the back of the early runs of Rufus Reid's "Evolving Bassist.

Ric

 

[robgrow]

Roger Mouton, thanks for posting.

re: "Balance" control on the Electracoustic amps. When boosting or cutting with the bass and treble controls, the balance control either boosts the lows and cuts the highs or boosts the highs and cuts the lows depending on which way it is turned. It has a seesaw-like effect and effectively expands the range of the bass and treble controls, with it is very interactive. The effect of this control can range from very subtle to pretty dramatic. When bass and treble controls are at 12 o'clock, the balance control is effectively out of the circuit and does nothing.

 

[Freddels]

Does anyone know what the EQ frequencies are on the MI-100?

This is still one of the best sounding amps.

 

[MrSidecar]

Does anyone know what the EQ frequencies are on the MI-100?

This is still one of the best sounding amps.

Freddels,

all I have is simulation data (from hacking the schematic into CircuitLab), but that told me that the bass and treble are +/- 20dB shelving at outer extremes (don't remember the exact frequencies, but it was designed so the two bands did leave the middle of the freq band untouched, pretty normal for a two-band shelving tone control circuit), and the midrange control was the special one: +28/-33dB (!) at 500Hz, with a rather broad Q, so that cranking the mids all the way up or down resulted in +/-10dB at 100Hz and 2500Hz.

That does not say all that much about how the amp "sounds", as there are factors like THD and maybe intermod distortion that play a big role in that as well. But that were the freqs I found.

That caveat is important, both because I have never really heard any Walter Woods amplifier, and, more importantly, it is most likely these different kinds and amounts of distortion that contain much of the character of the amp (and any amplifier, especially those with discrete preamp circuits).

Best
Sidecar

 

[robgrow]

MrSidecar, your simulation may not show you a few things: The EQ on the MI-100 (and all early WW amps) is extremely interactive, and the preamp is designed to add harmonic distortion, much like a vacuum-tube preamp. This gives the characteristic "warmth" that you really have to hear for yourself to appreciate. Also the mid-frequency band of the EQ is centered either at 500 or 800Hz depending on which channel of a dual-channel model or how a single-channel model was ordered. The EQ filters are also very broad, especially the mid band.

 

[Ric Vice]

MrSidecar, your simulation may not show you a few things: The EQ on the MI-100 (and all early WW amps) is extremely interactive, and the preamp is designed to add harmonic distortion, much like a vacuum-tube preamp. This gives the characteristic "warmth" that you really have to hear for yourself to appreciate. Also the mid-frequency band of the EQ is centered either at 500 or 800Hz depending on which channel of a dual-channel model or how a single-channel model was ordered. The EQ filters are also very broad, especially the mid band.

+1 the MI-100's were, and probably still are the closest thing you'll get to a all tube amplifier. When most manufactures were struggling with solid state bass amplifiers. Walter nailed it.

Ric

 

[MrSidecar]

MrSidecar, your simulation may not show you a few things: (...), and the preamp is designed to add harmonic distortion, much like a vacuum-tube preamp. This gives the characteristic "warmth" that you really have to hear for yourself to appreciate.

Err,.. yes, that's what I meant. Like I said, I have never heard a WW, and EQ frequencies alone don't reveal much. Thus, the caveat.

Also the mid-frequency band of the EQ is centered either at 500 or 800Hz depending on which channel of a dual-channel model or how a single-channel model was ordered.

That's interesting- I didn't know about the variations, although I remember having read something about the two channels being voiced differently (one more geared towards electric, one more towards upright, was what I read). I only had a single-channel schematic at hand, and that one was obviously designed with the 500Hz center frequency.

The EQ filters are also very broad, especially the mid band.

Yes, I saw that and mentioned it...

Best
Sidecar

 

[Chris Fitzgerald]

OK, here are the pages from my WW Sales Brochure....

Man, gotta love that "partial" list of buyers. Talk about an endorsement!

 

[MrSidecar]

Hey all,

it just so happens that I, despite my undisputed love for my Lehre hand built amp, bought an old (at least it looks old, definitely first generation) MI100-8, partly to see how my beloved amp compares to the legend, and also because I have always wanted one and now the opportunity came along. It should be on its way by now. I'll post findings and probably measurements.

best
sidecar