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PostPosted: Fri Jun 14, 2013 11:48 am 
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Well...yeah you can. I've got my own ideas - just wanted to thank you for the inspiration. Never thought of switching the trem circuit before and I think it'll be a useful trick.

If you look around, you'll see that most of the tube oscillator circuits Fender used are basically the same. Turning off the trem is just typically accomplished by grounding part of the oscillator circuit. And bias vary trem (or opto trem for that matter) is insanely easy to implement once you already have the oscillator circuit there; it's kind of just a matter of what you do with that oscillating voltage (and you can apply it to the power tube bias like in a brown deluxe or blackface princeton, or you can actually just apply it to a 12AX7 gain stage like in a vibro champ - I actually think the 12AX7 method sounds really, really good and it's less hassle than wiggling the power tubes). So, if you have a harmonic trem circuit in the amp already, all you really have to do is come up with a switch that takes the voltage oscillation out of the harmonic trem portion of the circuit and applies it to whatever else you want to wiggle in the circuit, in the correct manner of course. It'll take some experimenting and probably a 3 or 4 pole rotary switch, but it should be able to be done in one motion (nice thing about amps - there is usually room for giant things like multi-pole rotary switches in there). Alternatively, I might just try grounding half of the cycle and switching some filtering, sort of like you've done in the cardinal, and see how that sounds. I don't know yet, I'll see when I get there. I'm just excited about the possibility! :D

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PostPosted: Fri Jun 14, 2013 12:03 pm 
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So you were using brownface trem = harmonic tremolo? Sorry, I got confused. In that case, yes, it's trivial to switch to a regular tremolo. There were like three or four different types of tremolo on brownface amps, and the harmonic is on several larger blonde models during the brownface era. It's an incredibly convoluted term. :(

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PostPosted: Fri Jun 14, 2013 12:16 pm 
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midwayfair wrote:
It's an incredibly convoluted term. :(

+1! :lol: Right; I'm planning an amp build with harmonic trem. Your Cardinal Trem circuit has given me the idea to install a switch so I can switch out the harmonic trem for a regular trem when I want to and I think that rocks. Thanks! :D

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PostPosted: Tue Jun 18, 2013 6:53 am 
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Ordered on Friday and received them yesterday. Fastest turn around time I've had yet :shock:

oddly enough, my vactrols from Allied were ordered and came at the same time too...


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PostPosted: Fri Jul 26, 2013 4:15 pm 
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anyone have any pictures of a finished product/gutshots? I'm populating my first board now for a friend


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PostPosted: Fri Jul 26, 2013 4:20 pm 
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kwame wrote:
anyone have any pictures of a finished product/gutshots? I'm populating my first board now for a friend


aballen's build.
Image

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PostPosted: Mon Nov 25, 2013 2:20 pm 
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This is the Univibe mod! Very exciting.

THEORETICAL

So, Dane Kinser (eldanko) over on Madbean accidentally discovered that you can make the Cardinal sound like a vibe by replacing C6 with a much bigger cap, in his case 33nF. This got me thinking whether we could use a single toggle to replace the center mode with the vibe mode.

It requires a DPDT on/on/on.

It's wired thusly:
DPDT on/on/on
1 4
2 5
3 6

-Jumper 1 and 5.

-Replace R6 on the PCB with a much larger value, e.g. 33nF.

2: This is the ground connection (pad 2).

3: This connects to the pad on the PCB that goes to C6 (pad 1)

4: This connects to the pad on the PCB that connects to the gate of Q3 (pad 3)

-Solder a smaller value cap across lugs 3 and 6. (See below for values and cutoff frequencies.) We will call this the "switched" cap.

The modes will now be:

Up/right - Normal tremolo
Center - Harmonic
Down/left - Vibe

How this works:

In the center, C6 + switched cap create series capacitance.

When the switch is up/right, the emiter of Q3 is connected to lug 5, which is jumpered (internally) to lug 1, which is now connected to the ground connection.

When the switch is down/left, C6 is connected to ground, and the cap across lugs 3&6 are disconnected.

Switched + C6 cap values and calculations:

-2.7nF + 33nF will equal ~2.5 nanofarads. Cutoff frequency will be 6366. This isn't that close to the original 7234, but remember that we're dealing with harmonics and it's better to go a little lower rather than higher with the cutoff.
-3.9nF + 33nF will equal ~3.5 nanofarrads. Cutoff frequency will be 4547 (not too far from Dane's 4822 with a 3.3nF)

R5 could be (VERY) mildly adjusted as well if you want to hit a particular cutoff frequency. For instance, if you want to get even closer to the cutoff frequency of the stock values, you can use a 9.1K with 33nF and 2.7nF caps to get a cutoff of 6995. Or to get really really close to Dane's original cutoff, you can use an 8.2 with 33nF and 4.7nF caps.

It would be best to experiment with the larger value cap in C6 first to get the vibe sound you want and then calculate the switched cap based on that.

I will give this a go in one of my builds, maybe in the tap tempo version since I need to open it up to add Josh's optical bypass to it.

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PostPosted: Mon Nov 25, 2013 5:59 pm 
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Wow - a great circuit potentially gets even better! :shock:

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PostPosted: Thu Apr 03, 2014 1:02 pm 
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Folks, I'm going to say that the Macron photocell clones can't he used in this with the values shown. I have a friend who is going to help fix the issue, since he has two built with both sets of vactrols (and he says that the Macron photocells sound completely different and have much less depth). If we discover a solution, I'll be sure to post it here.

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