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PostPosted: Sat Mar 28, 2020 11:23 am 
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Finished my Brown Face trem build, works fine, trem is great... nice and trippy. However, the guitar tone gets substantially brighter when the pedal is engaged. So much so as to render the pedal useless unless amp or guitar tone settings are set to compensate. If amp or guitar are set to darken the tone for use with trem on, when the pedal is switched off the tone is too dark. As I said, this difference is substantial and makes it unusable as an on/off switchable effect. Is there a fix for this?


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PostPosted: Sat Mar 28, 2020 11:38 am 
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That does not happen with mine at all. My bet would be on a component misplacement. If you post photos of your build, we can help you take a look. Make them clear, well-lit, and large enough that we can easily see the color bands on the resistors.

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PostPosted: Sat Mar 28, 2020 12:40 pm 
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Hey Scott! Thanks for your help. Here's a pic...


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IMG_1104.jpeg
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PostPosted: Sat Mar 28, 2020 12:41 pm 
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Subscribed. Mine is like this too (though I wouldn’t call it unusable). I just figured is was frequency cancellation.


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PostPosted: Sat Mar 28, 2020 1:53 pm 
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Since the Depth Symmetry trimpot mixes the low and high signals, maybe try adjusting that. I notice that the slot on the trimmer on yours is straight up and down, i.e 12:00/6:00. I have mine set at about 45 degrees CW, ~1:30/7:30. Not sure that would do the trick for you, but it's something to try.

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PostPosted: Sat Mar 28, 2020 1:55 pm 
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Morgan wrote:
Mine is like this too.

Well, this makes it seem less likely that it's a component misplacement (no offense to OP!). :mrgreen:

And as it turns out, all the resistors look correct to me. Harder to tell the other components, but judging from your soldering quality and the quality of your photo, your attention to detail seems pretty high. Might be worth checking the components with markings on the side, just to be sure.

My knowledge of how this circuit works is quite limited, and certainly less than Morgan's. Perhaps Keith will have some advice to offer.

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PostPosted: Sat Mar 28, 2020 2:07 pm 
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duhvoodooman wrote:
Since the Depth Symmetry trimpot mixes the low and high signals, maybe try adjusting that. I notice that the slot on the trimmer on yours is straight up and down, i.e 12:00/6:00. I have mine set at about 45 degrees CW, ~1:30/7:30. Not sure that would do the trick for you, but it's something to try.


Thanks for the advice. I have tried adjusting the trimpots many different ways, the brightness issue does not change.


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PostPosted: Sat Mar 28, 2020 2:20 pm 
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DVM - I assume your build is not overly bright when engaged either?

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PostPosted: Sat Mar 28, 2020 3:56 pm 
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The signal is split into a high pass filter and a low pass filter and then the two signals are mixed back together. A lot of mid range should be missing. This is normal because the low pass filter has a roll off frequency of about 75Hz @ 6dB per octave. I'm not sure what exactly the high pass filter roll off frequency is because it's not an RC filter that can be calculated....it's just really small decoupling cap that only lets in high frequencies, but I would probably guess it to be around 7k5Hz. 6dB per octave isn't very sharp, so all the midrange between 75Hz and 7k5Hz isn't completely missing, but it's going to definitely sound a lot thinner than your bypass signal. In order to get the overall volume level back up to about unity gain with bypass, the remaining frequencies need to be boosted. So the higher frequencies are going to be very prominent.

These were the frequencies selected by Fender. The intention of this pedal is to sound like the vibrato channel on a brown face Fender. It's not meant to sound "transparent". You can modify it to be more transparent, but this may have an effect on the actual harmonic tremolo.

You can let more low frequencies into the high pass by replacing C4 with a larger value cap.

You can let more high frequencies into the low pass filter by reducing R4. This might actually be the way to go even though allowing more highs to pass when your complaint is that it's too bright may sound counterintuitive. You'll actually be letting more low mid range in. But you'll also be increasing the volume/output of the low pass filter, so you'd be increasing the amount of low signal that is ultimately mixed back in with the high pass filter. This will allow you to turn down the level trimmer, thus reducing the highs.

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PostPosted: Sat Mar 28, 2020 7:23 pm 
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Morgan wrote:
DVM - I assume your build is not overly bright when engaged either?

It's definitely brighter than my dry signal, as would be expected based on how the circuit works, but not excessively so. I think it emulates the Fender tremolo sound quite convincingly. And there's always the treble control on the guitar (most of 'em, anyway) and the amp (ditto) to dial it down if needed. But I was just playing a bright guitar (Squier CV Tele Custom, bridge pickup) through the pedal into a bright amp (Allen Sweet Spot, a modified BF Fender Princeton Reverb circuit) and the treble is strong but not overpowering.

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PostPosted: Fri Jul 31, 2020 7:43 pm 
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Spent the day taking this pedal apart and adding sockets to R4 as Keith suggested. Tried a bunch of lower values I had in my spare parts bin and found 100K worked the best.

The bright peak is now gone and it sounds much closer to my original signal when engaged. I wasn't sure I could live with the brightness of the sound, but now I really like it. 100% worth the time and effort to disassemble the pedal for this mod.

I didn't have any resistors higher than 100k that wasn't over 220k, so not sure if it would improve things. I can only say I liked 100k better than lower values I tried. YMMV.

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PostPosted: Thu Aug 13, 2020 10:43 pm 
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I'm experiencing this same brightness issue. I need to have my guitar set very dark in order for the sound from the Brown Face to be useable. I does sound awesome once I dial in that tone though.

It's possible tweaking the trim pots more would fix it, but I'm finding them very very sensitive. I don't have any spare resistors, but I will post back when I get a chance to experiment.


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PostPosted: Mon Aug 17, 2020 10:35 am 
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doomtronic wrote:
I'm experiencing this same brightness issue. I need to have my guitar set very dark in order for the sound from the Brown Face to be useable. I does sound awesome once I dial in that tone though.

It's possible tweaking the trim pots more would fix it, but I'm finding them very very sensitive. I don't have any spare resistors, but I will post back when I get a chance to experiment.


The trimpots won't have any effect on the brightness.

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PostPosted: Mon Sep 07, 2020 1:37 pm 
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kimonostereo wrote:
Spent the day taking this pedal apart and adding sockets to R4 as Keith suggested. Tried a bunch of lower values I had in my spare parts bin and found 100K worked the best.

The bright peak is now gone and it sounds much closer to my original signal when engaged. I wasn't sure I could live with the brightness of the sound, but now I really like it. 100% worth the time and effort to disassemble the pedal for this mod.

I didn't have any resistors higher than 100k that wasn't over 220k, so not sure if it would improve things. I can only say I liked 100k better than lower values I tried. YMMV.
byoc wrote:
The signal is split into a high pass filter and a low pass filter and then the two signals are mixed back together. A lot of mid range should be missing. This is normal because the low pass filter has a roll off frequency of about 75Hz @ 6dB per octave. I'm not sure what exactly the high pass filter roll off frequency is because it's not an RC filter that can be calculated....it's just really small decoupling cap that only lets in high frequencies, but I would probably guess it to be around 7k5Hz. 6dB per octave isn't very sharp, so all the midrange between 75Hz and 7k5Hz isn't completely missing, but it's going to definitely sound a lot thinner than your bypass signal. In order to get the overall volume level back up to about unity gain with bypass, the remaining frequencies need to be boosted. So the higher frequencies are going to be very prominent.

These were the frequencies selected by Fender. The intention of this pedal is to sound like the vibrato channel on a brown face Fender. It's not meant to sound "transparent". You can modify it to be more transparent, but this may have an effect on the actual harmonic tremolo.

You can let more low frequencies into the high pass by replacing C4 with a larger value cap.

You can let more high frequencies into the low pass filter by reducing R4. This might actually be the way to go even though allowing more highs to pass when your complaint is that it's too bright may sound counterintuitive. You'll actually be letting more low mid range in. But you'll also be increasing the volume/output of the low pass filter, so you'd be increasing the amount of low signal that is ultimately mixed back in with the high pass filter. This will allow you to turn down the level trimmer, thus reducing the highs.
I have one of these in the mail coming my way right now!

I definitely want to do this mod. Where on the board are R4 and C4? I noticed in the images theyre labeled by the value of the cap / resistor, rather than the sequence in the circuit

Also, is there a way to decrease the minimum speed?


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PostPosted: Mon Sep 07, 2020 2:02 pm 
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zizyphus wrote:
I definitely want to do this mod. Where on the board are R4 and C4? I noticed in the images theyre labeled by the value of the cap / resistor, rather than the sequence in the circuit

See marked up PCB image below.

Attachment:
harm_trem_C4_R4.jpg
harm_trem_C4_R4.jpg [ 53.5 KiB | Viewed 457 times ]

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PostPosted: Tue Sep 08, 2020 8:28 am 
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duhvoodooman wrote:
zizyphus wrote:
I definitely want to do this mod. Where on the board are R4 and C4? I noticed in the images theyre labeled by the value of the cap / resistor, rather than the sequence in the circuit

See marked up PCB image below.

Attachment:
harm_trem_C4_R4.jpg
Thank you!


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