All-Star Reverb

Stompboxes circuits published in magazines, books or on DIY electronics websites.

All-Star Reverb

Postby induction » 23 May 2013, 21:39

After breadboarding several BTDR-based reverbs (the BYOC 2-knob, the GGG D-Verb, and the Box of Hall), I combined all the bits that I liked from each of these circuits and made a few tweaks to fit my taste. A few people have asked me about it, so I figured there's enough interest in this variation to post it here. In honor of the circuits I blatantly ripped off, I call it the All-Star Reverb.

All_Star_Reverb.png


All_Star_vero.png


The dwell circuit is modified version of the BYOC dwell circuit, but it takes the output directly from the brick instead of from the reverb pot. This decouples the reverb control from the dwell control, allowing you to crank the dwell at low reverb levels, adding some versatility. The gain of the dwell op-amp is also modified: it goes as high as possible without oscillating. Finally, the dwell path gets its own output from the brick, instead of being split off of the output path. Unlike some of the other dwell controls (Ghost Echo, Tenebrion) the dwell path diverts before the differential amplifier stage that combines the wet and dry signals. Thus the dwell path has no dry signal in it. I find that purely wet dwell paths have a very different character than combined wet/dry dwell paths. Wet-only dwell sounds more ambient and effect-like, and extends the decay time considerably without increasing the perceived size of the room. Mixed dwell paths seem to mostly make the reverb louder. They increase the perceived size of the room, and I find they sound more jumbled and less focused, but more realistic. Both sounds are valid, but I prefer the wet-only dwell because it gives a useful sound that isn't available from the mixed-dwell circuits. The sound is more artificial, but if you want realistic spring reverb you just turn the dwell control to zero.

The damp control is modified ever-so-slightly from the box of hall. It affects the output path only, not the dwell path, so it is fed by only one of the brick outputs instead of both of them. The result is nearly identical at minimum damping, but gives around twice the treble roll-off at maximum damping. When I breadboarded the box of hall, I wasn't sure I needed a damp control. The more I used it, the more obvious it became that the damp control was essential. Reducing treble from the reverb signal is a brilliant way of adding depth and space without calling attention to the reverb. Like a good compressor, you might not even realize it's turned on, but you definitely notice if you turn it off. Brighter sounds are also useful, but are more noticeable as an effect.

The gains of the last op-amp stage were chosen by trial-and-error. I initially chose gains that gave unity to both the wet and dry signal, and found that the dry signal was above unity. So I aimed at a slight gain reduction for the dry signal and got unity. I don't understand why the gains came out wrong, but I accept it. I suggest you breadboard it first, just to be sure.

I built mine with buffered bypass and tails. The layout will accomodate true bypass if you prefer, or you can add a true bypass/tails switch if you want both.

tails_switch.png


In the vero layout, the brick (BTDR-2H) is mounted directly to the board, and sits underneath it. This reduces the number of brick connection wires from six to two and prevents you from having a free-floating brick flopping around in your pedal, but it also means that the brick should only be soldered in when you're sure the rest of the components are correctly in place. You may want to use temporary wires to test the circuit before you mount the brick permanently to the board.

The only down-side I've found is that the circuit doesn't behave well after my amp. I run a Vox AC4TV through a resistive dummy load/line out box, into a LM386-based power amp with an input buffer (like a ruby, but without the bass attenuation), and into a 12" cabinet. I like to set the Vox to edge-of-breakup or higher, and would prefer to put the reverb between the Vox and the power amp, but when I do this the reverb has a strange ascending pitch as it decays. (Maybe I should try buffering Vref?) It behaves normally in front of the amp, but I'd prefer to put it after.

I used a medium brick in my build.

Anyway, I hope someone finds it useful. Sorry about the blurry photos. Comments and suggestions are welcome.

Northwest Harris-20130331-00565.jpg


Northwest Harris-20130403-00570.jpg


All-Star-exterior.jpg
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Re: All-Star Reverb

Postby joe_pineapple » 24 May 2013, 08:11

thanks for sharing yr (re)design with us induction. i especially liked the explanations that you gave for the reasoning behind yr adjustments.
"..the finished product is just the garbage left over from the work." R.G. Keen
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Re: All-Star Reverb

Postby sinner » 24 May 2013, 20:39

More treads like this :thumbsup
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Re: All-Star Reverb

Postby ch1naski » 26 May 2013, 19:33

Thanks for posting this, would love to hear it. :D
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Re: All-Star Reverb

Postby kaycee » 01 Jun 2013, 08:33

Nicely documented Sir :thumbsup
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Re: All-Star Reverb

Postby induction » 03 Jun 2013, 19:45

ch1naski wrote:Thanks for posting this, would love to hear it. :D


okey dokey.


Link


Signal chain: telecaster -> 'circuit comparable to a Timmy' -> reverb -> Vox AC4TV -> dummy load/lineout -> LM386 power amp -> 12" open back speaker (from my Behringer modeling amp) -> SM58 -> Tascam US-122 interface -> Cubase.

No post processing at all.

I twist the knobs around (very unsystematically) a lot to sample as much of the parameter space as possible. I recorded it late at night at a fairly low volume (sleeping 6-week-old in the house), but it should give you the general idea.

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Re: All-Star Reverb

Postby Fredenando » 03 Jun 2013, 20:48

Me gusta!! :applause:

Sorry, votes don't work...

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Re: All-Star Reverb

Postby LaceSensor » 09 Jun 2013, 14:28

Built this up and no joy. Will have to debug when the weather isnt so warm making me hot and bothered.
grumble etc.
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Re: All-Star Reverb

Postby induction » 10 Jun 2013, 15:16

Did you build it on vero or breadboard? Let me know if I can help, or if anything in the layout is unclear.

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Re: All-Star Reverb

Postby LaceSensor » 11 Jun 2013, 19:28

induction wrote:Did you build it on vero or breadboard? Let me know if I can help, or if anything in the layout is unclear.


Vero. Pretty sure I did it right.
I just get my clean sound through.

Should all the grounds be tied together, or separate ground and audio ground?
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Re: All-Star Reverb

Postby induction » 11 Jun 2013, 21:33

I have the power ground and the signal ground separate.

Did you do true bypass or buffered?

Someone else has told me that his build didn't work until he replaced the 100R with a jumper. I don't understand why that made a difference, and I used the 100R with no problem, but it's something to try.

Feel free to post some pictures and I'll take a look.
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Re: All-Star Reverb

Postby destro » 13 Jun 2013, 03:45

Yep, that was me. Been dragging my feet on getting a modified layout with predelay control a la ghost echo. Still messing with blend option of wet and dry signal. Anyway, when I had the 100ohm in there everything was good (regulator was giving m 5v, tl074 was getting 9v, etc...)and then the voltages would drop as soon as I would connect powwer to the brick. I thought I had fried the brick. Got another one, same problem. On a whim bridged the 100ohm and everyhting fired up. I am using the big regulators as opposed to the small ones. Work and kids eating up free time at the moment, gonna get it posted this weekend though.
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Re: All-Star Reverb

Postby Beedoola » 18 Aug 2013, 01:29

I built this and I'm getting a really low reverb level - even with everything dimed. Initially, I thought it might be the 100R because I was getting below 5v for the regulator and the TL074 was only getting 5 volts on the VCC. After bypassing the 100R, I got 5v for the regulator and 9V for the TL VCC.

There controls all seem to work and I can hear the reverb but its very low..
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Re: All-Star Reverb

Postby Beedoola » 19 Aug 2013, 00:58

Is there a reason you can't edit a post after a while?

DISREGARD my last post.

I had R2 at 100k instead of 10k :slap: I still have the 100R bypassed, however.

Circuit works wonderfully!! :horsey: Consider it verified :applause: :hug:

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Re: All-Star Reverb

Postby induction » 19 Aug 2013, 16:23

At Beedoola's request, I've modified the circuit to double the amount of wet signal available. It's a simple mod (3 resistors), and it doesn't change the dry level. I haven't tried it myself, but I'm told it works well.

All_Star_even_wetter_vero.png


Explanation for those who are interested: I modified the gain structure of the final op-amp stage (differential amplifier) which sets the gain of the wet and dry signals. This seemed like a better idea than increasing the gain of the inverting amplifier feeding the brick because it won't overdrive the brick and won't cause self-oscillation at high dwell settings.

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Re: All-Star Reverb

Postby induction » 26 Aug 2013, 16:29

Yesterday my All-Star turned into a wind machine: no dry signal, no wet signal, just white noise. Since Destro told me that his circuit wouldn't work until he removed R14, I tried jumpering around R14, and that solved the problem instantly. R14 was included to reduce power supply noise because I was not using true bypass, but it seems to make the circuit unstable. I have no idea why the problem took so long to show up on my build, but I have removed it now, and find no increased hiss in bypass or effected signal. If you have built the circuit or plan to, I recommend you remove this resistor. I have taken down the old schematic and layouts, please use these instead.

All_Star_Reverb_Rev1.png


All_Star_Rev1_vero.png


All_Star_even_wetter_Rev1_vero.png


I apologize for any inconvenience.
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Re: All-Star Reverb

Postby Motter » 27 Aug 2013, 16:57

Do you have a schematic for the resistive load you use in your AC4?
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Re: All-Star Reverb

Postby induction » 27 Aug 2013, 17:47

Here you go.

load_line_schematic.PNG


load_line_vero.png


I used a 25 watt power resistor for the dummy load.
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Re: All-Star Reverb

Postby induction » 14 Sep 2013, 19:55

Freppo rightly pointed out that when I removed the power filter resistor, I forgot to remove the cut from the track side of the layout. Here are the corrected veros.

All_Star_Rev1_vero.png


All_Star_even_wetter_Rev1_vero.png
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Re: All-Star Reverb

Postby induction » 16 Sep 2013, 16:37

Accidentally deleted the schematic instead of the layout. Here it is again.

All_Star_Reverb_Rev1.png
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