Hammond L100 AO-43 amp project help?

For those building and repairing amps on their own. Learna and share ideas.

Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Sat Mar 07, 2015 7:34 pm

Picked up the faceplate from the printer's this morning. It was printed on 11x17 80lb stock and laminated with a non-reflective layer and actually looks very nice. This is a Beta version and is now fitted so I'll finalize all the knob lettering positions relative the mounted pots. I see I managed to have the Overdrive On/Off backwards and the Treble and Bass cut switch lettering needs to exchange places. The final colors I couldn't judge until now that I have one back from the printer. I make the final adjustment to the color match up with the boards that will become the cabinet.

Visio Faceplate printed at the UPS Store nearby
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For $4 and change I am real happy with the results with this service from UPS (http://www.upsstoreprint.com). You upload the press ready file from your computer, they print it and email you when it is ready for pickup. Turnaround was 24 hours.

:thumbsup:
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Re: Hammond L100 AO-43 amp project help?

Postby Unit_1 on Sat Mar 07, 2015 9:39 pm

FOUR BUCKS for a faceplate, wow! you just can't beat that

so how did you make the holes in it? drill? exacto?
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Wed Mar 11, 2015 4:02 pm

Unit_1 wrote:FOUR BUCKS for a faceplate, wow! you just can't beat that so how did you make the holes in it? drill? exacto?

Yes I cut them out with an xacto knife. I had them put on 80lb stock so they are stiff but not thick like card board. Too thin to drill. They cut out clean and the pot holes being less than perfect circle cuts is concealed by the retaining washer and nut so it worked out well.

I got a wild hair after getting the amp to its current state and decided I still wanted to try getting the original Hammond Vibrato chassis working as another control on the amp. This chassis came with the separate Vibrato AO-41 and Preamp/Percussion AO-42 chassis so it was right here. The unit is really neat in that it uses phase shifting to vary the frequency of the tones. Its components are 3 phase shifting stages, a saturable reactor coil for each phase, a voltage amp, an oscillator and the driver.

After looking at the schematic and component placement for a while (quite a long while) I figured out what to try in order to tie this into the amp chassis since it was designed to integrate with the preamp/percussion unit which I am not using. So here is what I tried and it seems to work well. However I welcome alternative suggestions for how I cut & pasted this unit into the amp circuitry.

Vibrato Connections?
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1. With a DPST switch I cut into the signal path right after the tone controls but before the volume control. So the switch either passes the signal through to the amp's volume control as normal or it is diverted to the Vibrato unit and back and then into the amp volume control.
2. Made a cable to carry the filament and B+ voltages to the remote Vibrato chassis. For those I used the existing and now unused amp-to-vibrato unit cable headers from where the salvager had cut the cables.
3. I placed a 5M pot in place of the external Vibrato control tabs so the Vibrato effect can be dialed. It is seen dangling from a short cable.
4. Supplemented the amp chassis circuitry with the Vibrato return and chorus path termination needs.

Testing the Vibrato Control Pots
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Still have to mount the rca connectors to the back of the amp chassis, add 2 more control pots for the Vibrato rate and width and another switch for turning the Vibrato Chorus loop On and Off and then decide how/where to expose the vibrato controls since the amp chassis is full and there is no room for more control pots. Have to decide if I add a separate panel or make the current amp chassis faceplate artificially bigger in order to accommodate more controls.

The last thing still going through my head for a change is a footswitch...
Last edited by housekustoms on Tue Dec 15, 2015 11:49 pm, edited 3 times in total.
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Fri Mar 13, 2015 8:52 pm

Integrating the Hammond AO-41 Vibrato unit worked out well and sounds great. True phase shifted frequency vibrato..cool. My first thought when I heard a chord through it was Tommy James' Crimson and Clover. Really wavey.

Vibrato is Working
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Now to add some control pots to key points that control the speed and the "width" or "depth" of the effect. Then one more I read about that sounds like a nice feature is a balance control to mix unaltered and vibrato signal to your liking. So I'll be trying these in this round of changes as noted in the schematic.

Updated Schematic
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I will add some sound clips soon too.
Last edited by housekustoms on Tue Dec 15, 2015 11:45 pm, edited 3 times in total.
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Sun Mar 15, 2015 12:01 am

After spending time again last night I was able to get holes drilled in the original vibrato chassis for the new control pots. I couldn't get the blend of dry and wet vibrato signal to work right so I abandoned that for now.

So I went with three controls. One I'll call level and it replaces the original control tabs that were used to select vibrato or not and then also small vs. normal vibrato. So I think of this one as the level for lack of better term (suggest better please). The other two are static resistors on the factory schematic that state they are as listed or adjusted for the vibrato rate and another for the width. I replaced each with a pot of slightly greater value than the resistor it replaces and use them as variable resistors. They each admittedly affect the sound but not with the predictability I would have expected by the factory terms width and rate. They all three seem to be able to affect the rate of the pulse and in different ways each can change the sound of the vibrato tone from a spanky snappy sound to a watery bubble to an echo chamber sound. The pulsing can be made quite strong or quite subtle.

I think I'll go with this for a face plate for the Vibrato unit itself. It will be tucked up against the inside left side of the cabinet (when viewed from the front) and so it's controls will about in the middle of the left side of the cabinet and available from the outside of the cabinet through a cut out window. Just a side mounted mini-control panel since there isn't any room in the main control panel.
Visio created, UPS printed faceplate - $4.00
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And here's a couple of picture of the units.

Vibrato Working now
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Cable Connections
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Still thinking about how to add a footswitch for the reverb and vibrato. If anyone has done this I'd appreciate hearing about what and how you did so.

Thanks!
Last edited by housekustoms on Tue Dec 15, 2015 11:43 pm, edited 1 time in total.
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Mon Mar 16, 2015 11:39 pm

I liked the darker color arrangement on the faceplates so I'll go with that. Here are the components with the darker faceplate mockups. I'll have them put on card stock now and then that will be that!

Also a name was decided on for this amp...the Organ Donor. Seems appropriate :Doh:

Organ Donor...born an Organ, evolved into a Guitar Amp
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:highfive:
Last edited by housekustoms on Tue Dec 15, 2015 11:39 pm, edited 1 time in total.
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Re: Hammond L100 AO-43 amp project help?

Postby PeterS on Tue Mar 17, 2015 7:20 pm

That vibrato circuit is fascinating, isn't it? You can find the original patent online, I remember reading it a few years ago.
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Thu Mar 26, 2015 12:44 am

PeterS wrote:That vibrato circuit is fascinating, isn't it? You can find the original patent online, I remember reading it a few years ago.

It is and most impressive in the variety of sounds available from the oscillator. Anything from gentle swaying breezes to thumping snappy sounding rhythm is available via the three attributes that have now been exposed as pots for user control; level, width and rate. I especially like being able to dial in a level of motor boating that I happen to like. It reminds me of 70's Crimson & Clover from Tommy James.

I also ended up revisiting the mix control and it is better placed and working better so now if you activate both the vibrato and the chorus (via their on/off toggle switches) you can then control the mix of wet and dry signals. Just one more neat effect available within the amp controls. It still isn't working as well defined as I'd like so I may not keep it. I'll tinker some more.

That new control manifested itself as a 4th pot on the vibrato control panel so I've updated both the schematics and the faceplate layout to reflect the changes. Still waiting on a 10m linear pot for the Vibrato Level and will swap it in as soon as it arrives. That will better emulate the original values the organ applied via its switches.

Other than review it for the possibility of adding footswitch on/off control of the reverb, overdrive and vibrato and chorus controls, I think I've beat this up pretty good and gotten about as much as I'm going to get out of the hardware. I'm open to suggestions however!!

Pretty much done with the circuitry now
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Last edited by housekustoms on Tue Dec 15, 2015 11:38 pm, edited 1 time in total.
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Tue Apr 07, 2015 1:20 am

I think adding a footswitch to this is beyond my reach right now. I'll have to study this more.

So in the meantime, I went ahead and began building a combo cabinet for this. It will house 2 10" speakers, the amp chassis, the 2-spring reverb tank and the vibrato amp chassis.

Cabinet is figured African Mahogany
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Last edited by housekustoms on Tue Dec 15, 2015 11:36 pm, edited 1 time in total.
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Re: Hammond L100 AO-43 amp project help?

Postby Unit_1 on Tue Apr 07, 2015 3:29 am

Wow! that's some sweet looking wood there Steve!
:thumbsup:
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Wed Apr 15, 2015 1:40 pm

Got the speakers in now so about all that is left is to wrap up mounting the Magic Eye tubes into the cabinet and finalizing the faceplates so the chassis can be mounted. Most of the controls will be on the top facing up "Fender" style except the Vibrato controls which are on the right side of the cab.

Organ Donor in 2X10 cab with JBL speakers
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On the home stretch now...have the Vibrato faceplate attached and the chassis installed. Just the amp chassis left to install now.
Last edited by housekustoms on Tue Dec 15, 2015 9:23 pm, edited 5 times in total.
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Sat Apr 18, 2015 1:20 am

Well I couldn't ignore the need for footswitch control of the vibrato, reverb and overdrive. I've laid out to the best of my knowledge how I can perhaps do this. Is it possible someone can take a few minutes and see if I am way off base here. Just saying :-)

2 issues...completely different.

1. Do these make sense functionally? I am pretty comfortable they will work but always benefit from folks with more knowledge than me.
2. This one concerns me...I'm concerned that the vibrato jack is exposing high DC voltage between pin 2 of V4 in the Vibrato unit and ground. I get a varying reading when I monitor it and it varies from 0 up to b+ (255). It cycles so quickly there is no stable reading. The AC is nearly zero (it is very low mv AC) but not the DC. I suspect this is a function of the oscillation circuit but not being expert, it is just a slightly educated guess. Not sure why the voltage to the control grid would be cyclical this way. I know I have much more to learn. I am a sponge if anyone has any answers.

Updated schematic:
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Thanks either way in advance if anyone can offer opinions, advice or criticism!!!
Last edited by housekustoms on Tue Dec 15, 2015 9:22 pm, edited 1 time in total.
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Re: Hammond L100 AO-43 amp project help?

Postby PeterS on Sat Apr 18, 2015 1:31 pm

Your circuit looks fine - you might get some popping noises on switching if the switching causes a shift in a DC level somewhere --- it looks ok but those things can be hard to predict --- I would build it and see, and solve the popping if it happens.

I don't know why the grid of V4 should be able to go up to high voltages --- it should not be able to go to any higher voltage than the cathode. if the grid becomes more positive than the cathode it starts to draw current (i.e. electrons from the cathode get sucked into the grid), which usually prevents it going any more positive... check your connections and check the measurement...
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Tue Apr 21, 2015 2:11 am

PeterS wrote:I don't know why the grid of V4 should be able to go up to high voltages --- it should not be able to go to any higher voltage than the cathode. if the grid becomes more positive than the cathode it starts to draw current (i.e. electrons from the cathode get sucked into the grid), which usually prevents it going any more positive... check your connections and check the measurement...


I opened up the Vibrato unit and saw that in assembling the cover to the unit last time, I nudged R124's grounded side into the + side of C116. :Doh:

Adding the 4 pots and the slide switch into the AO-41 chassis was an exercise in stuffing 25 lbs into a 10 lb sack. I replaced the electrolytic caps with much smaller diameter equivalents when I changed them out. This made room for the pots without their housings touching the existing components but I was careless when reassembling the 1st time it is clear. One of the leads of the chorus pot was pulling on R124 and had drawn it into C116's lead. I reoriented them and reassembled the unit and indeed the footswitch now functions and no B+ voltage is showing when I meter it.

Image

The reverb and overdrive footswitch controls worked well too. I am trolling ebay for a 3 button footswitch that can be modified to my needs. Really don't want three separates footswitches. A saw an unlabeled 3-button switch that seems like a good fit.

I am glad it didn't end up causing permanent damage or give me a new hairdo. :nutjob:
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Re: Hammond L100 AO-43 amp project help?

Postby housekustoms on Fri Jun 05, 2015 7:00 pm

Updated schematic with footswitches removed (technically they worked but were too noisy)
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Updated faceplates
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Chassis Layout using original Hammond circuit board
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Last edited by housekustoms on Tue Dec 15, 2015 9:21 pm, edited 4 times in total.
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