Build Your Own Clone Message Board

Just finished the build on the Reverb pedal. Love It!! I have read all of comments on the amount of reverb and will try some of the suggestions that have been mentioned as I am having difficulty finding the sweet spot.

One question. I am noticing a drop in guitar volume when the pedal is on. It's not a juge drop; just a noticable one. I have checked my build and everything is correct. I measured each resistor as I installed them. The pedal sounds great and will be a huge addition to my home build AX84 amp.

I built my reverb pedal last week and used it with my acoustic for the first time in church today. I'm really impressed with the pedal but I also noticed a distinct volume drop when I switch it in. I unfortuntaely don't have a signal generator and scope to test it accurately but I rigged up a simple chain - acoustic in to reverb pedal - and measured the output of the pedal with a digital multimeter when the guitar was strummed. With the pedal off, the meter recorded 35-40mV. With the pedal on, the equivalent reading was 25-30mV. So the overall pedal circuit gain is less than unity. I should perhaps mention that like other builders I substitued R14 with a pot (47k) and adjusted to give the amount of reverb I wanted. It ended up set at about 7k. I don't, however, think that this accounts for the less than unity gain overall.
To correct the gain back to unity, I guess that we need to increase the gain on either the input stage op amp (IC1a) or the output stage (IC2a) by changing the feedback resistor. The obvious choice is to change R25 (33k) on the output stage but this is locked in by "the brick". So before I start hacking my circuit board, I'm interested to hear if other builders apart from Lyle also have this problem.
It's been too many years since I studied op amp circuit design so I would appreciate advice from anyone more familiar with the subject on what to change to get unity gain on the overall pedal. Perhaps BYOC's designer could advise.

As an aside, I compared the pedal with the real Belton spring reverb in my Trace Elliot TA60CR acoustic amp and with all the reverb pedal controls set at 12 o'clock, I really couldn't tell the difference but of course, the pedal is more versatile. If I can just sort out the unity gain issue, I'll be absolutely thrilled with the pedal.

I just finished building the reverb pedal and I am totally in love with it. Awesome must-have pedal. I replaced the reverb linear pot with an analog pot as Stephen suggested, and I put a 7k5 resistor in R14 like others have. Yes, I have a small volume drop when the pedal is engaged....I've just been compensating either with my volume knob on my guitar or my volume pedal. I don't know enough about circuitry to know what parts to change to make the pedal a more unity gain circuit.

Sure do love it though, no complaints whatsoever.

I'd also like a "unity gain" mod, but if it's impossible I'd be fine without.
I think mine sounds great. When I use it, I just turn up the volume on my amp and drives - the reverb is either on all the way through the giving track, or completely off anyway, in my case.

I'm sure tonmann would know what to do, if it's possible to just change a resistor

Hi guys,

I just built one of these and unfortunately, I can't hear a volume drop. Can one of you audio probe the dry signal path to see where you're getting the volume drop? And turn the reverb level all the way down when you test it.


The dry path goes from lug 5 of the footswitch to C1, R2, pin 3 IC1, pin 1 IC1, C10, R16 (dry level), R23, pin 2 IC2, pin 1 IC2, R26, C17, footswitch lug 7.

In all likelihood, you'll want to reduce the value of R16 until you get unity gain. But it's best to probe it first to see if you can isolate an obvious drop somewhere.

mine has a slight noticeable volume drop as well.

Guys, I played with the value of R16 and lowering its value seems to do the trick. Good eye, Morgan. I put a 20k trim pot in its place (just what I had lying around) and dialed in what I could hear to be about unity gain. I heard it to be around 10k or just a little under if you want to put a set value in.

I would think increasing R25 would increase gain of the last op-amp. That could bump you up to unity.

Yep, I also made a mod at R16 today and it works great!
I was being lazy though, so I just added a 39K resistor in parallel to R16, and Bob's your uncle - unity gain.

Confirmed and approved

Changing the value of R16 will only affect the gain of the dry signal path and there seems to be an assumption that the less than unity gain problem is only on the dry signal. I do not believe that this is the case. Changing the value of R25 to a higher value will increase the gain on the op amp output stage and therefore increase the output level whether the signal is wet or dry.
I changed R25 from 33k to 47k and although I cannot measure accurately, the gain to my ear is now close enough to unity.

That's two votes for increasing R25!

... and two "votes" for R16. I didn't realize this was a competition... I suppose you have two choices here depending on what you want to do. If you want to increase the dry signal only, lower R16. If you want to increase the gain of the dry signal and the wet signal, increase R25.

+1 on the change to R25. Upped it to 47k (oddly enough w/ the 47K res. from the flanger regen mod <G>) and unity gain on both wet and dry is restored! Great!

Just finished the pedal and I have another vote for changing R25 to 47k.

I built a reverb and it sounds LUSH.
I am also having an issue with a volume drop. If i were to wire in a trim pot, how would i go about it?

Wanted to chime in on this.
I never really noticed the volume drop until a few days ago (have had the thing for a year, but rarely use it with the band). At rehearsal it got to be a real pain to up the amp volume every time I wanted to use the Reverb. So, I found this thread and made the modification to R25 ( from 33k up to 47K) Fixed the problem right there.
Something I want to add: Thank god BYOC uses the plated through holes. With a little heat, I was able to remove R25 from the top of the board, and solder in a new resistor without having to remove the Brick. Had this been a single sided board, I would have been so frustrated removing the brick. Thanks again BYOC for thinking of the little things.
-P

I'm about to build one of these reverbs. Should I just go ahead and modify r25 to 47k from 33k, or has the problem perhaps been fixed in the kits?

I don't think that there has been a deliberate change from 33k to 47k for R25. Looking back at the build, if I were to do the whole thing over again, I would just put a 47k in R25 and do the switchable R14 mod (makes for less wash), right off the bat. I added a switch for R14 after the fact, and it is a needed change in my mind. Then having to pull R25 a year later and change it was no big deal, but still not a simple task for a beginner.
-P

Just got this pedal in, and searched for volume drop in the forums. This mod took me all of 45 seconds to do, and it's perfect now. Score one for the BYOC members! Thanks guys!

Good to hear, beefyco! I love a happy ending.

Hi all,
I did the R25 mod because of volume drop. Swiched it from 33k to 47k and there was no change. I double checked my soldering and then tried a different 47k resistor. Still no luck. Any ideas?
Thanks

You could up it a little more (56K) but be careful, too much and you may get a volume bump or noise added in.
-P

Thanks, I'll try that.

I tried 56k and even up to 68k and nothing changed. I'm confused, frankly.
I wonder if there's a problem somewhere else,
the pedal sounds good on its own. maybe a little muddy, but nothing crazy. but when i engage it in a chain of pedals there's a significant db change. enough that i'd like to fix it.
any more ideas?
thanks.

With mine there was a change right away sO it may mean something is different elsewhere in the pedal? I'm no expert so I'll leave the diagnosing tO them but mine was an easy to distinguish difference right away