Tone Bender Mki builds rehash and musing

As of today, if you google up stuff like:

Mki tonebender transistors hfe and leakage

There’s just no way to get all the info on one page. People in the know are keeping their mouth shut as to what the best leakage and hfe combinations should be, to get an up an running mki.

I’d just save Electric Warrior from the bunch, an extremely knowledgeable guy who is not afraid of sharing his views. He’s active on fsb and on the dam forum.

Now this pedal.. There’s no easy way to pull it off. 

You think you’ll go the easy route and buy a tested, measured set of mki trannies online? Ok, no. Dont do it. The build will sound shit. They dont even come close to the ideal values-heres my experience with tested transistor kits:

Measured set 1: “compatible subs”

Q1: 2N404 (how original) hfe 81 lkge 0.04 (yeah, right)

Q2: 2N404 hfe 136 lkge 0.12

Q3: 2N404 hfe 93 lkge 0.00

I even spent more money on a set of mki matched OC75s, I made a couple of clones some time ago, just to review them again the other day to find the bitter truth: no sustain on notes up the fretboard. Fail.

Ok so i broke one of the clones open, socketed all the transistor points with alligator clips and i plunged into my collection of germaniums.

This idea on my mind:

John Barry’s guitar player asked Gary Hurst to increase the sustain of his Maestro FZ1 pedal. He changed the transistors, power supply and resistor values to go with the mods, and the first (Mark One as we call it today) Tone Bender was born. 

How is it supposed to sound?

-the Maestro FZ1’s tone is “brassy”, and it can be also very velcro like, turning the guitar into a ratty device (the green acres tune) so it’s got a varied range of sounds on tap

-the Maestro FZ1a sports less dynamic range as units were mass produced, so bias can often be unfocussed, lets say it’s buzzy but also voiced very differently from the FZ1

-(not on topic but since it was used a lot back in the 60es i’m gonna throw this in too) the (germanium) Mosrite Fuzzrite has a “synth”-like sound, the guitar’s articulation and dynamics are greatly reduced, almost squashed.

We have very little evidence of original, still working mki pedals, and we are all accustomed to the youtube links to listen to those. Pedals age, and they do not sound as they used to, when they were new.

But keep it in mind: like a Maestro FZ1 with more sustain.

Put these people, the players, on the map. British freakbeat as we now call it-before it was just called r&b. Ok most of them used british pedals. Tone Benders. Some just diyed the Maestro, or whatever they could copy, even guys like Syd Barrett (early Pink Floyd) would tinker with building their own pedals.. These “minor” bands never toured the States, the money they had, went on clothes, and maybe a better rig, for sure not on a US made pedal-ok maybe some of them had bought a Maestro in the wake of Satisfaction. They made the european summer circuit, scaring the continent’s patrons shitless with their fuzzy sound-lol.

Also, they sound way more obnoxious than american garage bands, save maybe the texans-the cowboys i assume, switched to the more aggressive, silicon fuzzes earlier than anybody else, because of the temperature boiling their fuzzes at gigs.

American bands were looking up to Great Britain up to a certain point. But not the other way round unless you were a top player that visited the other side of the pond enough to be influenced by the vibe-or until the summer of love, but thats 2 long years later than what we’re on about here.

Americans were into the Yard-Birds big time.. The Litter sported the open tones of oc75 induced harmonics of the Tone Bender on their signature regional classic Action Woman-complete with Yardbirds style rave on (that the Yard Birds in turned had copied from people like Lonnie Mack’s) and thats 1968, a few months shy from the Zeppelin’s telecaster-and-possibly-a-Bender-into-a-modded-HiWatt debut.

Back to 1965 now.. Would you like to  listen to some Mki? Get the British Freakbeat compilations and dig.. there may be some.

Tone Bender Mki: high treble content, dark british amps, loud and with lots of sustain to cut through the mix. Think Baby I Go For You by the Blue Rondos, or Ronno. Like an half cocked wah. No velcro like the Maestro, but still based on the Maestro. Resistors to open up the sound.

I’m delving into the idea of the possible Maestro modification: putting an OC75 on q1 as a driver, and leaving 2N270 on q2, q3, on a mki build. After all, the original q2 and q3 in the mki are two 2G381, a random torrid germanium transistor never to be heard of again. Same as the 2N270.. probably the cheapest parts they could find.

Im going back to my Maestro builds, and an old geofex article.

-q1 must leak to activate q2, q3 leakage means sustain. If i remember correctly..

Here is my build:

Q1: oc75 hfe 78, lkge .32

Q2: 2N270 hfe 108, lkge .21

Q3: 2N270 hfe 401 (!!?!)*, lkge .66

*now a value like that should give you an idea of how shitty a transistor that is.

Don’t hunt for 2N270s. It’s not worth it. You’ll end up with a hole in your pocket and no satisfaction. Their specs are all over the place. And they dont sound like they measure. I went through a large batch of Fairchild 2N270, at an excellent price, and sorting them out has been hell. Thank God i have only about 20 RCAs, i keep them locked, they look nice and fat in their new old stock boxes and i will never use those. But they are the same. No quality control, folks. Or rather.. those were the times.

You can achieve the same results using other leaky transistors. Dont worry about the tone, the layout provides the tone on this one.

Dont change the layout values: leave the 470k resistor there. 

Keep q1 hfe at round 70-80, leaky, q2 hfe in the 90-120 region, with leakage, and q3 not over 100 but it should leak loads.

πŸ˜‰ good luck.

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Hohner Basset

When i bought it it looked like this


I opened it up to clean it and realised this wasnt its original colour.


It really was taupe gray before, but the years had the plastic chassis yellowing

I decided to restore it to its original colour (or as close as i could…)

After 5 months of great fun, I had to open it up because the output went silent.

Gutshots of the Hohner Basset!

Lets start with the DIN jack that connects it to the bass amp..


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Keyboard:

Circuit board and caps jungle:

Inside the white enclosure there’s a lamp and a ldr.. this assembly is the actual “percussion” section.

You press a note on the keyboard, the light goes off slowly (sustain) according to the knob position, when not in auto mode.

Video below..

Pcb: 3.1967!!

Ahem this means the caps have been doing their job for 50 long years! Only one of the capacitors has failed, please note- the blue valvo 100uF cap now measures 1uF!

Output DIN and 3 pronged jack, fuse

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Video showing the lamp going off when a note is keyed.

Hohner Cembalet repair

My beloved Hohner Cembalet I has gone silent, all of a sudden.

Here we go with a few pics i took for reference of the main board.

They may help someone else whos trying to fix his Cembalet.. I hope.

Schem and user manual (in kraut):

Hohner Cembalet User Manual with schematic

Update: the Cembalet healed itself and now it works great. I did not have to do anything to it, it just works again, magic, bang.

A friend who’s an electronic repairer said that the most important part to watch out for is the inductor (Spule in german), as it’s custom wound to specs for this instrument.

Yamaha RS7000 keyboard soft touch button repair

I bought some soft touch button replacements for my RS7000, because the keyboard had to be banged on to operate.. 

Here’s how i carried out the button repair.

Disclaimer: please carry out this repair only if you have electronic skills such as soldering, desoldering, handling pcbs and know how to handle electronics. Remove the mains plug on the RS7000 and use care. Do not touch the power supply components. I shall not be held responsible if you hurt yourself or other people or the machine in the process.

First of all, check the new buttons. There are a few tutorials on how to check switches’ functionality using a digital multimeter on the net, google that up. 

Remove all the knobs from the front panel.

Wash them with soapy water using an old toothbrush!

Turn the unit face down, using some soft padding to relieve the knobs from the weight.

Keep this pic as a reference: the position of the midi sockets.

There are 3 types of screws..Put them somewhere safe (i used three fruit jam lids) and remember where each type goes. An additional set of two very thin screws belong to the scsi port. 

As a rule of thumb:

short ones-> they hinge the metal sheet that separates the top from the bottom pcbs. The top left and middle left ones secure the bottom to the metal cover of the power supply as you will realise opening the unit.

Remove the bottom lid. 

Unscrew the midi assembly and the buttons holding the input/ output panel in place and take it off.

Take pictures of the pcbs. 

Pay extra attention to the cables, what goes where. How they are turned, and move them the least you can. They are the right lenght to be assembled, very neatly laid out, Yamaha styleπŸ˜‰πŸ‘ŒπŸ».

The bottom cables are all tied together and they originate from under the shielding metal sheet..right where we want to get! Carefully, gently rock them to pull them out of their sockets.

You will have to remove the card reader assembly, the flat wire (just pull it) and all the screws that link the metal sheet to the case will have to go (pay no mind to my pics cos mistakenly i unscrewed also some of the pcb’s).. 

Below, this is the central layout, the wiring harness pops out from underneath the metal sheet shielding. 

The plastic motherboard shield will have to go. Please note how its left side kind of sits on top of those surface mounted chips. 

Gently lift the shielding metal sheet, get your girlfriend or boyfriend or your best caring and patient relative to hold it up for you.


Remove the cables that hold the keys assembly in place, and carefully slide it out from one side.

Here is the ugly mother.. Turn it around and take a look at how the key covers are snapped in their places. It takes a little inward motion using two fingers from the bottom side, push and they will spring out.

Put them in a sink and wash them with shower soap and water. Brush them with that old beaten toothbrush. Carefully, but with authority. 

Please note that generally there are soft touch and clicking buttons, maybe you want to dust the encoders too, i took a rag and dusted the pcb too, TAKING EXTRA CARE.
If you are feeling tired and the stress of the procedure so far has got you on your knees, put the board in a padded cover and go to sleep.

When you are in the right mood and focused, you may proceed.

Take a look at how the soft buttons are put, their position from all angles. Your new ones will have to be laid out just like that. Maybe even better, if they all look twisted like mine!

Turn the board over, using a hot soldering iron heat up one of the two soldered poles of the switch and using a desoldering pump suck the solder off. Do the same for the other. 

The nice folks at Yamaha have bent the two poles in opposite directions, one upwards – the other downwards, so that to remove the button you must heat up a bit the two points (solder side) while gently applying a circular motion to the button, taking it with two finers, component side..

πŸ‘ Like in this video:

RS7000 removing soft touch switches

Using the same procedure, you could also replace a few LEDs if you feel inclined, just be careful with the LEDs height.

Once you are done replacing the faulty keys, put the button masks back on. 

The tap button does not have an LED, but its mask is like all the others (check pic)-it’s all right.


Putting everything back in its place, take special care with the central wire harness: the cables have to reconnect to their original sockets, so beware if they get stuck somewhere they should not-you might not be able to plug them in. Reassemble everything with care in respect to the wires.

It is quite a long procedure, also given how many screws you will have to work with-panic may take over you once you realise there are two pcb levels in this machine, but fear not. It CAN de done!

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Ram’s Head Battersea Power Station Big Muff β‚½i

    

When i was a Londoner, id often catch the 24 bus on sunday mornings from Hampsted Heath to its final destination, Pimlico. There was a pub there, next to the bus station where we would go have brunch and shoot pool. In the afternoon we would visit the Tate, usually.

And we would enjoy the beautiful, post modern view of the Battersea Power Station from Pimlico.

Gilmour used a rams head Big Muff on Animals.

Built for a friend on a pcb by OP ELECTRONICS, IT. Transistors BC239C from ebay seller, Whazzgroover. Sprague caps, etc

First time i mess with a hot glue gun, and i guess you can tell! 🐣

Musical Devices