1176 Rev D Slow attack knob mod

[Diamondj421]

I have a Hairball Rev D FET/Rack but it’s PCB has gotten pretty messed up from tinkering over the years. I just got a new PCB so I’m about to rebuild it and would like to mod it to be like the UAD 1176 Anniversary Edition. I’ve already found schematics on how to adjust the ratios to 2:1, 4:1, 8:1 and 20:1. I’ve seen schematics on how to implement the “Slo” attack mode but can’t figure out how to have it active when the attack knob is switched to what would be the “Off” position on a standard 1176 (fully CCW). Most people seem to have it as an option that can be turned on by an alternate switch. Could anyone help me figure this out? I’ve spent a good amount of time trying to find more info on it but am coming up short. I’ll attach the schematic below. Thanks in advance!

 

[TwentyTrees]

To make sure I understand, you're looking to switch in the "slow" mode with a switch at the CCW end of the attack pot's rotation? Pots with rotary end-stop switches are less common than push/pull, but they're out there. I did the same with my MS76 (PCB Grinder dual 1176) - works great. Your exact switching solution will depend on whether the pot on your switch is normally open or closed, SPST / SPDT - as the schematic shows, you're looking to short a series resistor when the switch is not engaged, so SPST normally closed is ideal.

Alternatively, just using a 250k log pot rather than 22k gives a max attack time of around 10ms-ish, based on how the original times are calculated. The feel is pretty similar to the original values in the faster half of the rotation, being log. Depends how slow you want things. I used a 250k pot that then switches in a further 500k for around 30ms or so.

 

[Diamondj421]

To make sure I understand, you're looking to switch in the "slow" mode with a switch at the CCW end of the attack pot's rotation?

Precisely! It’s like the attack knob on a UREI/UAD 1176. When the knob is turned all the way CW you get faster attack, CCW is slower and then if you turn it further still, it clicks it to “off”. Does that make sense? I’m not sure what that type of pot would be called.

 

[Diamondj421]

I’m assuming I can use my multimeter to figure out which legs are connected when it’s switched to the off position but I’m struggling to understand what to do from there. Would I use hookup wire to run it to a point in the circuit or is it as simple as just popping the 220k resistor between the legs?

 

[Bobby Baird]

I just added more capacitence to the switch position to hold the time longer.

 

[Diamondj421]

I just added more capacitence to the switch position to hold the time longer.

Ok. I think I just everything just clicked in my head. So when the knob is engaged, turning it increases/decreases the resistance. Therefore, when it’s switched off, there’s no resistance at all. So by putting a resistor (or capacitor in your case) across the legs for the off position, you’re applying resistance (220kOhms in this case) instead. Am I on the right track?

 

[Bobby Baird]

https://www.electronics-tutorials.ws/rc/rc_1.html
Basicly more resistace longer for the cap to charge. Bigger value cap longer to charge. Several ways to skin a cat.

 

[Bobby Baird]

https://www.mouser.com/ProductDetail/315-2415F-25KHeres the pot with the spdt switch I used.

 

[Bobby Baird]

Ok. I think I just everything just clicked in my head. So when the knob is engaged, turning it increases/decreases the resistance. Therefore, when it’s switched off, there’s no resistance at all. So by putting a resistor (or capacitor in your case) across the legs for the off position, you’re applying resistance (220kOhms in this case) instead. Am I on the right track?

Actually, the switch is in series, so by changing cap value effectively changes time constant, so c27 .022uf goes to wiper and "A" lager value like .22uf goes to wiper and "B" switch position. Common lug gets the full 25k resistance max position of the pot. Look at photo above. 470R is on my ratio board.

 

[Bobby Baird]

I believe its .022uf max .8ms .22uf max 8ms 2.2uf max 80ms
G-comp popular slow attack time values for 1176 aka slow mod. c27 .27uf for 10ms .82uf for 30ms.
Someone please correct me if I'm wrong.

 

[Bobby Baird]

Turns 1176 into Buss Comp attack time territory.

 

[TwentyTrees]

Yeah, I looked into changing the cap value when doing this mod on my MS76. I went with switching in series resistance as changing the cap also changes the release time constants by the same factor, which wasn't what I was looking for in my build.

 

[Diamondj421]

I appreciate the input but I’m still struggling to wrap my head around this. What exactly do I need to do so that when the attack knob is set to “bypass”, it still applies compression but with a slower attack? I don’t want to change out the knob that I currently have since I still want to attack knob to act like a standard 1176 attack knob when not in slow mode. I guess part of my problem is that I’m not understanding how the knobs circuit works. I have the data sheet for it but things just still aren’t clicking for me. I’ll attach it and the Attack/Release PCB below.

 

[Bobby Baird]

Since you are trying to mod the 500 series version created by Mnats and Mike at hairball. I would ask them directly to see if this is possible on this platform. Not as easy to mod as a 19" rack cause the pcb is designed for through-hole pots I assume. Never built one of these.

 

[Diamondj421]

Since you are trying to mod the 500 series version created by Mnats and Mike at hairball. I would ask them directly to see if this is possible on this platform. Not as easy to mod as a 19" rack cause the pcb is designed for through-hole pots I assume. Never built one of these.

This version is a rack unit but it’s the newer version which has a PCB for the attack/release. I was about to give up but after looking at the build guide for the older Hairball FET/Rack I have a better idea of what you’re referring to in your picture. The attack knob on the new version is through hole. It also has 6 pins so if I can figure out which are 1, 2, 3 and A, B, C like the Alpha you used, I should be able to use the same wiring you used.

Prior to being able to switch to slow mode, was that switch position “bypass” like a standard 1176? If so, we’re golden.

The only part that’s throwing me for a loop is how to keep the compression circuit from being cut out when the knob is switched to that “slow (originally bypass)” position.

 

[Bobby Baird]

This version is a rack unit but it’s the newer version which has a PCB for the attack/release. I was about to give up but after looking at the build guide for the older Hairball FET/Rack I have a better idea of what you’re referring to in your picture. The attack knob on the new version is through hole. It also has 6 pins so if I can figure out which are 1, 2, 3 and A, B, C like the Alpha you used, I should be able to use the same wiring you used.

Prior to being able to switch to slow mode, was that switch position “bypass” like a standard 1176? If so, we’re golden.

The only part that’s throwing me for a loop is how to keep the compression circuit from being cut out when the knob is switched to that “slow (originally bypass)” position.

Yes the new ver. FET rack has the gain reduction off switch integrated into the attack pot. It's a dual gang pot with the second gang being a spdt switch. In this case you wont be able to sub the series resistor here because the pot will need to be used for the gain reduction off function. Alternatively you can add a spdt switch to the panel to control the slo-mod. This would most likely invole cutting a trace on the attack release board to insert the series resistor between the attack and release pot to a switch. Unfourtanly it looks like this design doesn't allow for easy modification. I don't understand why modern designers don't integrate new design features in old designs like this to allow the builder to choose if they want the mod to the original circuit are not. You simply add pads to do so with a bypass header if not desiered. Would make the platform more flexable IMHO. Some are just purist I guess.

 

[Bobby Baird]

You could do like Twenty Trees recommended and just put in a 250k dual gang pot instead if you can source one for that footprint. Like I said just contact Mike and inquire about the modification. He is really helpful. I'm sure he's already been asked this same question.

 

[jkurzweg]

Has anyone tried a 100k or 250k pot for a slower attack time instead of the standard 25k attack pot in a 500 series Hair Ball FET/500 ? Curious if it works by just replacing or if it's more involved---- I'm sure it increases the likelihood of more distortion creeping in with hot signals and therefore might not be wise in a rev A , but im thinking of trying it in a rev D or F. Guessing 100k would get me close to 4ms and 250k almost 10ms. I know people have talked about slow attack mods for the rack units, but i haven't seen any reports back yet if it works, or if there are any issues with doing it. - thanks

 

[TwentyTrees]

As long as your replacement is the same physical dimensions as the pot supplied in the kit, it should just be a matter of substituting the one with the other. It works with the 1176 circuit, as earlier posts in this thread attest. No issues that I've encountered.

 

[c1184701]

To make sure I understand, you're looking to switch in the "slow" mode with a switch at the CCW end of the attack pot's rotation? Pots with rotary end-stop switches are less common than push/pull, but they're out there. I did the same with my MS76 (PCB Grinder dual 1176) - works great. Your exact switching solution will depend on whether the pot on your switch is normally open or closed, SPST / SPDT - as the schematic shows, you're looking to short a series resistor when the switch is not engaged, so SPST normally closed is ideal.

Alternatively, just using a 250k log pot rather than 22k gives a max attack time of around 10ms-ish, based on how the original times are calculated. The feel is pretty similar to the original values in the faster half of the rotation, being log. Depends how slow you want things. I used a 250k pot that then switches in a further 500k for around 30ms or so.

Hi there, do you happen to recall what part you used for this, or have a link? I was just wondering if you found a 250k witches pot that fit the solder footprint of the original pot on the MS76.