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Hi, I’ve just finished a dual build cramming the EA Tremelo and the Add-Verb circuits into a 1590B enclosure. As it will mount beneath my pedalboard with only 30mm of clearance and switched remotely via a mini-looper, I have used internal Bourns trimpots and a 9mm dual-gang pot for the reverb in place of large external pots (all matching the values of the original design). Also, 3PDT switches have been replaced by micro 2PDT switches to be mounted on the side to enable either effect independently. I first tested without LEDs at all as I don’t require them (resulting in no effect signal), so they are now soldered in which is fine and remain on. I have bridged S4 and S5 on both circuits as the effects were not working without LED or SW bridging. S6 are left empty.
At this point the entire circuit is working perfectly and sounds great, with both effects being independently switchable; however, with two different guitars I get bad clipping using humbuckers unless the volume is rolled back to below about 50%. When I coil-split and roll-back to about 80% volume it sounds fine. One guitar has EMG (81/85) and the other has BKP Silos. I have trimmed the internal volume pots on the circuits right back to unity gain but it seems the input is what is clipping them. The entire circuit sounds perfect with no clipping when both effects are disabled (via the DPDT switches) despite using max guitar volume.
I have a bit of experience in pedal repairs and building, but this was my first dual-circuit build. I have double-checked all the solder joints and there are no shorts between the stacked PCBs. All components were double-checked for correct values and I have tested for unwanted bridges using a multimeter.
My question is: Is this simply a case of the circuit designs being incompatible with high-output pickups? Or have I made an error in the build, somehow effecting both circuits? If it is a circuit design issue, what mods can I make to alleviate the clipping and accept higher output pickups? I don’t want to have to roll back my volume when enabling trem/reverb.
Aside from this, I found the build guide and PCB great to work with! Thankyou for taking a look, appreciate any advice.
It does sound like your pickups are too hot
If you know which circuit / part of the circuit the clipping starts at try lowering op amp feedback resistors like the 200K R3 in the add verb I’d try 100K
+1 Billy! Lowering R3 will reduce the gain of that input stage.
I also note that the EA has no input resistor in the schematic. Adding one might tame that circuit. However reducing the signal level for these circuits may not work for other guitar signal levels.
But, I really think that a better solution might be to move these two circuits further down the chain in the pedal board. Modulation and reverb circuits are usually placed near the end of the signal chain. This gives them a more complex signal that makes their effect more pronounced and pleasing. It also will allow preceeding circuits to adjust the signal level which can prevent overloading these two.
This is all about proper gain mapping through the pedal board. I hope this helps.
Thanks a lot for the advice Billy. I have no idea regarding the circuit design side of things but I’ll try a 100Kin R3 for the Add-verb and see if that helps.
Wilkie, thanks for the advice also – much appreciated. The pedal will feature last (12th) in the signal chain of pedals; however, I absolutely intend to use it clean without preceding effects at times, hence the concern about usability.
How would I add an input resistor to the EA Tremelo circuit to tame the input level? Are there any recommended values and where should it be placed in the circuit? All of my guitars have similar pickups so I will likely face the same problem with nasty input clipping without a fix for this. Currently, the volume trim pots for both circuits are turned all the way down so there is room to turn them back up if needed.
Also, the volume pot for the Add-verb behaves very strangely – when the guitar volume is rolled up, it decreases the overall volume (still with horrible clipping in my case as described) but when I roll it down below 50%, it seems to automatically lift the volume floor up – I can’t work it out.. I have them both at the lowest value for now.
I have to say I am quite disappointed, having spent $80 AUD per kit on these circuits – plus all the hours planning out the build, to find they are largely unusable. I wish the description would have included a warning about the clipping issue. I don’t think my pickups are extraordinary options and would have expected these effects to work with them like any other DIY kit I have built.
I am still keen to try some mods to make this usable though. I would like to seek some support from anybody who has had involvement in the design of these circuits before I start pulling them apart again – hopefully this is the right forum for that advice?
Thanks both for your kind input so far.
Before we dive into modifying both circuits, I want to highlight that these designs have been available for over 10 years and are widely used by other DIY communities using the exact same values. If it were a design issue, there would be an extraordinary amount of posts discussing them. I have only found one post concerning volume issues, which I suspect was also related to high-output pickups.
Wilkie’s suggestion of adding an input resistor is a gain-mapping modification and not indicative of any missing component in the actual circuit design. He frequently builds combo pedals and owns guitars with both high-output and low output pickups, so this is routine for him particularly since pickups change the gain of everything from the guitar through to the amp. (hence his reference to gain mapping)
I suggest simply replacing the 27k resistor at R2 on the Add-verb with a 100k resistor. This might be tricky if the brick is in the way, so please be careful when lifting the brick to desolder—be mindful of its solder joints. You may need to reflow the brick joints when finished.
This change can likely rectify the entire issue, although your description of the guitar volume pot and its interaction with the Add-verb circuit may indicate an entirely separate issue. However, let’s take it one step at a time.
The EA Tremolo is another widely popular circuit among the community, known for its excellent buffer, which naturally boosts the signal. High-output pickups will accentuate this effect. The simplest solution is to lower the Volume control, effectively adjusting the gain mapping, but only after fixing the Add-verb problem.
It’s recommended to build and test each circuit individually before combining them when creating combos. There are several good combo building guides on the Guides Page.
I hope this helps!
I think Barry’s suggestion of increasing R2 would definitely reduce the signal level driving the 1st stage I’d try a 100K pot or trimmer wired as a variable resistor there or simply socket it and try different value resistors to see which value works best with your pickups
Thankyou very much for the detailed advice guys.
Barry, based on your description of these circuits having no/limited known issues over time I am now convinced the problem lies elsewhere – I just can’t work it out and I am hesitant to modify reliable circuits. I’ve been trying everything I can think of to troubleshoot this as I’m convinced I’m missing something obvious. Tested with different power supplies, batteries, cables, ran it after various other pedals, tried a few other guitars with medium output pickups (less clipping but still there), reflowed everything carefully, tested all resistors again – can’t work it out which is frustrating. No clipping with other DIY builds or similar pedals.
Before I replace R2 I need to understand why both circuits have input clipping, as they are wired with independent switches – i.e. I can run neither, both together or one at a time via the independent 2PDT switches. The only things I can think that would affect both in any configuration are something to do with grounding, jacks, power or common signal wires – but I feel as though I have checked everything so far.
I’ll revisit this next week after more testing – if I come up with nothing I’ll lift up the Belton brick and try some different resistance values – it still wouldn’t explain the EA Tremelo clipping when the reverb is bypassed through..
I appreciate all the help so far, thanks.
I recommend replacing the 27k resistor at R2 on the Add-verb with a 100k resistor. Based on what you’ve mentioned, it seems like your pickups are hitting the first stage too hard, and R2 functions like a Preamp control. Adjusting it is similar to tweaking a gain knob on a mixing desk to better manage the input level.
This procedure should take about 5 to 10 minutes if you have a desoldering pump or desoldering braid.
Thanks, I was out of 100k resistors so am currently awaiting another order. Will report back once R2 is swapped out. Even if this addresses the issue for the reverb, my concerns remain about the utility of the tremolo circuit. Are there other specific components I should be ordering for the input circuit for that?
I suggest buying a resistor assortment kit of common values on eBay.
Very handy if you do not have stock.
As for values required for your Tremolo I do not know yet since this is something new and I do not have a guitar with active pickups to test with myself. I will have some suggestions, but would like to get the Reverb sorted first.
Thanks, I do have a whole lot of resistors around but was out of 100K which I received tonight.
So I’ve replaced R2 with 100k. This does three things: 1. no more input clipping which is great, 2. significant volume drop – although with the pedal gain all the way up I almost get the level back up to unity, 3. significant tone loss – I’ve lost fidelity and high-end and it sounds boxy now which will affect my entire signal chain whenever reverb is on.
Also to reiterate for clarity, the original clipping issue did not only occur with active pickups, just anything relatively high output.
Any other ideas? I’m all for trying different R2 values but if it also sucks tone as a byproduct I am worried that I would never enjoy using this.
Ah whoops – quick update, I thought the input clipping was gone but I just tried with another guitar and it is definitely still there – just not as bad and only sounds nasty on hard pick attack. I guess this doesn’t help with troubleshooting.
“I guess this doesn’t help with troubleshooting.”
Not giving up yet, but the lack of headroom is clearly an issue based on your report.
The only change we made was to the Input Buffer Stage Gain: The original stock setting was R3 200k/R2 27k, giving a gain of 7.4. We modified it to R3 200k/R2 100k, resulting in a Gain of 2.
While a Gain of 2 should be fine with hot pickups, you’ve indicated that you’re out of available volume headroom and still experiencing clipping with one guitar. That’s a challenge.
As a result of your findings I suggest replacing R2 with a 33k resistor. Then, as Billy suggested, reduce R3 to 100k as an alternate way to lower the gain, giving you a Gain of 3. This should help bring back some Volume headroom as well as bass and treble that may have been lost by reducing the overall gain.
I suspect you will still experience clipping with hotter pickups.My thought is to get a little more Gain in the Input Buffer Stage for better Volume and less apparent Bass and Treble reduction first. If you are still getting clipping then I would try replacing R7 with a 10k.
An audio probe would be helpful if you have one to verify exactly where in the circuit the clipping is occurring.
Thanks again Barry. I replaced R2 and R3 as above with very similar results to the first method of reducing input buffer gain – much less clipping, a lot of gain drop and the same tone loss when brought back up to unity.
Given that both circuits indeed sound very nice with their default resistor values with single coils (I played through this for about an hour last night to dial the settings), I have decided to leave them as is and build a separate 1590B box with reverb/trem for humbuckers. I’ll swap the boxes out as required as the board will have a modular system on the underside anyway with various late-chain options.
When I setup an audio probe next time I might prod around for curiosity sake. I’ll let you know if I find anything of note.
I really appreciate you all enduring my hot pickups saga and for your time & advice.
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