Ibanez Howard Roberts 70s HELP!

[Jessek3672]

Hey all,


I was wondering if there's any possibility that anyone might own an Ibanez Howard Roberts and/or could give some insight into the wiring of the second/treble roll off sound control. Guitar currently works and sounds excellent but only the one tone control works. Push pull component functions 100% on the control, just not the potentiometer.




Any help would be greatly appreciated!

[starjasmine]

Sorry, I see no images.

[Cunamara]

There are a master volume, treble cut and mid cut control. I haven't seen any mention of a push-pull pot on the websites I have seen for this instrument. Is that original or has the guitar been modified (e.g., replacement pickup)? I have heard of people disconnecting the mid cut on Epiphone and Gibson HRs. I haven't found a schematic either, but I would think that the mid cut would have a resistor-capacitor combination to focus its action to lower frequencies than the treble tone pot.

Here is a Gibson HR schematic, which I don't have the skills to make sense of:

https://www.utstat.utoronto.ca/mikev...GibHRschem.jpg

Is there an inductor in the control circuit, similar to the Bill Lawrence Q filter? Instead of a resistor-capacitor circuit? Hmmm. Bill Lawrence reportedly designed the circuit.

The parent web page:

https://www.utstat.utoronto.ca/mikev...s/guitars.html

[Jessek3672]

Hi Robert,

Thankyou so much for all this information! I'm unsure whether or not the pot is the original or a modification. Thankyou so much for the schematic, I'll run it by a tech and see if they can make more sense of it than me.

[Marty Grass]

My Gibson HR had a non-functional midrange cut pot. Being OCD, I wanted to restore it to the original condition. It just needed the pot replaced.

If it were more complicated than that, I'd have replaced the harness with Gibson's specs.

I don't know anything about a push-pull. Neither Gibson nor Epiphone had that AFAIK, and I've owned both models.

[Jessek3672]

Thanks MG, this is something that I'm likely capable of doing myself. I'll try this fix this week, Thankyou so much!

[Cunamara]

if I am actually seeing what I think I am seeing on the Gibson schematic, there appears to be an inductor, which probably serves as the mid cut. The effect would be essentially like removing windings from the pickup coil, which would thin the sound a bit or maybe even a lot. That would depend on the values of the various components.

The block to the left on the schematic with the six dots is probably the pick up. Block to the right would be the circuit; I don't know what the circles represent, however. There are two 250K potentiometers in the diagram .03 mfd capacitors being specified; one would be the tone and the other would be the inductor/mid cut. The third pot at 300K looks likely to be the volume pot. However, I have no idea whether Ibanez used that circuit or cooked up something else to approximate it. David a.k.a. jimmybluenote on the forum might have an idea about this, given that he worked for Ibanez.

In the photos above, there are capacitors on all three pots; The two green chiclet ones are poly film capacitors, and the disc shaped one is ceramic. It seems a little unlikely that those would have been mixed coming from the factory, but who knows? It is a little odd to have capacitors on all three pots; usually when one sees them on the volume pot, it is of a very tiny value and there is usually also a resistor in parallel serving as a treble bleed. I'm not seeing that here.The push-pull switch in the up position seems to be shunting signal to ground (the black plastic coated wire) and in the down position, shunting the signal to another pot. Which one of these was the volume pot?

[Jessek3672]

Hi all,

I believe I've fixed it, swapped out the push pull (which I hadn't used anyways) for a standard 500k pot, rewired the cables to the push/pull and its functioning as intended. Thankyou all so much for your help!

[va3ux]

That is not original. Or at least not original to the Gibson schematic for that pot, assuming Ibanez copied everything from the Gibson original. That pot originally was not push-pull - it was a regular pot with an inductor and capacitor combination to make a bass/mid cut control. Apparently the inductor eventually fails and rather than replace it, guitar techs just remove it and re-wire it as a standard tone pot with the capacitor. So in this guitar that would be 2 regular tone pots in parallel. In your case with the push-pull pot, my guess is that that extra switch contacts are used to bypass this control altogether. So you have the option of 2 tone controls, or the usual single tone control with the pot pulled out (or pushed in depending on how it's wired). Just a guess, but that's the only thing that makes sense.

Inductors are not all that common in guitar tone control circuits but there were a few other guitars besides the Howard Roberts that used them : I believe the Gibson LS6 used one, the Les Paul recording, 1 or 2 bass guitars, and any Gibson guitar with a Varitone switch uses a single inductor with different values of caps switched in series with the inductor.

I have a Mann Howard Roberts with 2 tone and 1 volume but I've never bothered to take everything out to see what's there (or what's left). I think it's time I had a look.

[Marty Grass]

Howard Roberts was a versatile player. He must have found value in the second tone control. I'll bet few used it besides him. It does cut some of the mids out, which is interesting.

Not many of the earlier Epiphone and the later Gibson versions sold compared to the ES-175 and maybe even the L-4. But it's a great guitar. The later Epiphones and the Asian clones of the HR were much more affordable.

[Cunamara]

Inductors are not all that common in guitar tone control circuits but there were a few other guitars besides the Howard Roberts that used them : I believe the Gibson LS6 used one, the Les Paul recording, 1 or 2 bass guitars, and any Gibson guitar with a Varitone switch uses a single inductor with different values of caps switched in series with the inductor.

Bill Lawrence designed the electronics for possibly the HR and certainly the L6S. I think the Varitone was Gibson's cheaper approximation of Bill's design. Wilde Pickups (operated by Bill's widow and daughter) still sell a Bill-designed inductor, the Q Filter. One might be able to approximate the original HR wiring with one of those.

There is also an examination of a D'Aquisto by Ken Parker on YouTube. When looking at the electronics, Jimmy D had installed an inductor under the pick guard. Sadly we never get to hear the guitar be played in Ken's videos.

[entresz]

I agree re the Q Filter, it would work as an effective mid control.

I installed one in a L6S reissue I owned previously. It sounds very much like the effect of removing winds of the pickup. They're very useful especially on guitars with darker sounding pickups.