freestompboxes.org

death by audio dba reverberation machine gut shots and demo:

thought these might be of interest. thanks to MEC at ilf who posted the first three there originally.















https://i31.photobucket.com/albums/c364 ... g~original

very thirteenth floor elevators stuck down a well. i like this one a lot.

Awesome!

Any chance of the capacitor values.?

You are a god among men.
Since it appears as if some traces go underneath the brick, do you thing you could try Metering it to confirm connections? Also, do you know the values for the electrolytic caps?
Again, thank you.

jrfox92 wrote:
You are a god among men.
Since it appears as if some traces go underneath the brick, do you thing you could try Metering it to confirm connections? Also, do you know the values for the electrolytic caps?
Again, thank you.

hey jr, good to see you in this thread.

alas you overestimate me. not a god, just an anarchist with a passion for noise. gut shots not of any pedal i own (i wish, sounds great) just a handful of detailed-enough shots i gathered from various places that might allow us to make a start at a trace.
as mentioned in the original post, the nice detailed shots are from MEC at ilf. you may be able to find the original thread via google or google image. nothing more than pics though. they're quite a tame lot re tracing.

had meant to do a bit of photoshopping before now, composite front back and a clean pcb to start. will bump it up the list now you've reminded me.

Ah, no problem.
I'll get around to working up the pcb layout on diylc within the week, then a schematic and vero (if I can figure out all the connections).
Hopefully I'll manage to do all the things I had planned to this week, but it seems as though work is going to be filling up most of my time for the next couple of days.

If I can't find all the connections, and can't coax out some of the layout from Glass Hero, I might just end up buying one myself once my paycheck comes around so I can finish the trace.

notnews32 wrote:This is one of my all-time favorite reverb circuits. It's very particular.. I've had to send mine into DBA because one of the ICs blew out.
I will be stalking this thread!

hey notnews, i recognise the name from gfx. good to see you here.

would be good to see some decent gut shots and values if you are up for posting some when you get it back. i cadged a bunch from here and there but better when they are all one source and the owner can fill in value gaps quickly to resolve uncertainties.

am in agreement with you about the particular tone, which is why i posted what i could find. like a morose cousin of the recent eqd levitation reverb (if you know that one). perhaps they have a lot in common at the circuit level. but dba darker and wetter i think.
'new and improved with 50% desolation and existential angst'.

jrfox92 wrote: If I can't find all the connections, and can't coax out some of the layout from Glass Hero, I might just end up buying one myself once my paycheck comes around so I can finish the trace.

the schem i made is on an external hard drive.. i have been looking but have not found it yet.. I opened up my reverberation machine last night and will make a new trace over the weekend..

sorry about losing the schem, i may have named it something obscure and cant remember it, or it may have been on a hard drive i cleared off.. I have over 20TB of external storage, things tend to get lost..

Glass_Hero wrote:

jrfox92 wrote: If I can't find all the connections, and can't coax out some of the layout from Glass Hero, I might just end up buying one myself once my paycheck comes around so I can finish the trace.

the schem i made is on an external hard drive.. i have been looking but have not found it yet.. I opened up my reverberation machine last night and will make a new trace over the weekend..

sorry about losing the schem, i may have named it something obscure and cant remember it, or it may have been on a hard drive i cleared off.. I have over 20TB of external storage, things tend to get lost..

Oh, cool, that's no problem. I just remembered you mentioned you had a layout and figured you'd get around to sharing it eventually.

Yeah, I've learned that I'm filling up my memory incredibly fast solely from the few schematics and PCB/Vero/Perf layouts of cool pedals I've found on the Internet.

Reverberation Machine..

Thanks Glass, I've been curious about this pedal for awhile. Never played one but the sounds I've heard are pretty wild. It's amazing how simple the circuit is, I would have guessed they were pushing the input of the brick to get some of those overdriven sounds. Looks like it's mostly just mostly post-op amp distortion.

many thanks for the schematic glass hero.

i'm not familiar with the TLC27M4A. have read through the datasheet trying to make what sense of it i can, including the application information (fig.49 single rail ac amplifier seems to be used as is in u1 here). http://pdf.datasheetcatalog.com/datashe ... lc27m4.pdf

is there any audible reason why dba might have chosen this chip over more commonplace equivalents? for example, are any aspects of its spec particularly suited to the demands/requirements of a belton brick reverb? it's not something i've seen applied to a belton reverb build yet and i've looked at quite a few.

The TLC27 doesn't seem like it was used with any particular intent. It seems to be a BiCMOS opamp so high input impedance, low bias current, low input offset voltage, low power consumption. Nothing really critical for this design, I could be wrong. My guess is DBA liked the way it distorted and it was cheap. These guys aren't necessarily known to design around theory or anything.

tabbycat wrote:many thanks for the schematic glass hero.

i'm not familiar with the TLC27M4A. have read through the datasheet trying to make what sense of it i can, including the application information (fig.49 single rail ac amplifier seems to be used as is in u1 here). http://pdf.datasheetcatalog.com/datashe ... lc27m4.pdf

is there any audible reason why dba might have chosen this chip over more commonplace equivalents? for example, are any aspects of its spec particularly suited to the demands/requirements of a belton brick reverb? it's not something i've seen applied to a belton reverb build yet and i've looked at quite a few.

disorder wrote:The TLC27 doesn't seem like it was used with any particular intent. It seems to be a BiCMOS opamp so high input impedance, low bias current, low input offset voltage, low power consumption. Nothing really critical for this design, I could be wrong. My guess is DBA liked the way it distorted and it was cheap. These guys aren't necessarily known to design around theory or anything.

this opamp is used in the Space Ring and probably the DBA-7M4 dynamic mic preamp found on the dba customs page.. look at things like slew rate and gain product bandwidth when comparing to other opamps..

example tl07x series:
http://www.ti.com/lit/ds/symlink/tl072.pdf

then consider this statement from the tlc27m4a datasheet..

"full-power response
Full-power response, the frequency above which the operational amplifier slew rate limits the output voltage
swing, is often specified two ways: full-linear response and full-peak response. The full-linear response is
generally measured by monitoring the distortion level of the output, while increasing the frequency of a
sinusoidal input signal until the maximum frequency is found above which the output contains significant
distortion. The full-peak response is defined as the maximum output frequency, without regard to distortion,
above which full peak-to-peak output swing cannot be maintained.
Because there is no industry-wide accepted value for significant distortion, the full-peak response is specified
in this data sheet and is measured using the circuit of Figure 1. The initial setup involves the use of a sinusoidal
input to determine the maximum peak-to-peak output of the device (the amplitude of the sinusoidal wave is
increased until clipping occurs). The sinusoidal wave is then replaced with a square wave of the same
amplitude. The frequency is then increased until the maximum peak-to-peak output can no longer be maintained
(Figure 5). A square wave is used to allow a more accurate determination of the point at which the maximum
peak-to-peak output is reached"


the reverb brick and ring mod circuits produce signals with frequencies above what the opamp can provide without significant distortion..

Interesting. As far as I understand GBP is simply the constant BW at whatever gain you currently have your opamp configured in? Higher gain means less BW? So in this case I guess more high frequency from each opamp stage and possibly the brick itself?

And as far as slew rate goes in the pedal circuit world... better slew rate = larger output swing/higher frequency before clipping?

Is it just me are DBA kinda bad at circuit design? Why not make a buffered, less noisy reference voltage with the spare opamp instead of individual voltage dividers for each opamp? It would even require less components. This looks like a Also whats up with the volume pot?

knutolai wrote:Is it just me are DBA kinda bad at circuit design? Why not make a buffered, less noisy reference voltage with the spare opamp instead of individual voltage dividers for each opamp? It would even require less components. This looks like a Also whats up with the volume pot?

I wouldn't say that DBA circuits seem like circuits made by people who have a shitload of history with proper circuit design or electronics engineering or anything.
They're just some guys that are making circuits based on a general understanding of what they're doing.

But, I think that's what makes DBA pedals so unique, because everything is a little unnecessary and there's all sorts of weird stuff going on in their pedals that don't need to be happening but probably help shape the sound of the pedal.
At least the prices are getting generally cheaper for the noted quality. They really need to fire whoever does their soldering and hire me and let me move to New York and live in their building and steal their custom pedals.

yes. Taking their design-finesse into account, DBA pedals are way overpriced. On the other hand they come with a lifetime warranty, which is very admirably.
Biasing the way they do in this pedal would only add internal noise to the audio. Won't shape the (desired) sound in any way I can see

knutolai wrote:Is it just me are DBA kinda bad at circuit design? Why not make a buffered, less noisy reference voltage with the spare opamp instead of individual voltage dividers for each opamp? It would even require less components. This looks like a Also whats up with the volume pot?

knutolai wrote:Biasing the way they do in this pedal would only add internal noise to the audio. Won't shape the (desired) sound in any way I can see

hey knutolai, if you have any specific refinements or ideas for improvements for the pedal i would definitely be interested in reading about them and trying them. i like the dba stuff but am not 'reverential' or 'purist' about their designs. to me they are just a starting point for ideas, the same as every other design, be it cheap or boutique.

if they can be tweaked to functioning in a way that i can think of as sounding or functioning 'better' (always subjective) i am all for it. am waiting for that ic to arrive before i can start playing, but do post your ideas and mods if you think they will make it more interesting, or at least less compromised by its design shortcomings.

thanks for the input.

disorder wrote:Interesting. As far as I understand GBP is simply the constant BW at whatever gain you currently have your opamp configured in? Higher gain means less BW? So in this case I guess more high frequency from each opamp stage and possibly the brick itself?

And as far as slew rate goes in the pedal circuit world... better slew rate = larger output swing/higher frequency before clipping?

Slew rate is the response of the opamp or speed at which it can reproduce a clean signal.. so yes the tl072 has a slew rate of 13V/us and the TLC27m4 has 0.8V/us.. the Tl072 can produce non-distorted signals faster than the tlc7m4..

The GBP is based on unity gain of a non-distorted signal.. you can still have signals pass thru the amp that are above this but they are distorted.. and yes as you increase gain you decrease the clean BW.. The tl072 has a unity BW of 3MHz, whereas the tlc27m4 is around 650~900kHz..

So this is a slower amp with a smaller BW.. All signals that are faster or outside of the bandwidth produces the distortion you hear in the pedal.. and since the dry signal in the amp has a gain of 22k/10k and the wet signal is 100k/10k.. and then the mixer stage has a gain(amplitude) control which allows both the wet and dry signals to distort.. i would say they intended to use this opamp, noise was part of the design.. when i built a test circuit for the space ring i used a tl072 and i wasnt getting the right sound.. i swapped it out for a tlc274m (very similar to the tlc27m4) and got the right tones out of the circuit.. check your datasheet for whatever opamp you want to use, but be careful because they are sometime written to market a substandard part as if it was the greatest opamp ever.. use a socket and put in different opamps til you find the one you like best.. Also when picking your opamps look into the datasheets of the dual and signal packages amps as they some times have better information (equivalent circuits, specs, etc..) in the signal package amplifier datasheet than the quad package amplifier datasheet..

if you have any specific refinements or ideas for improvements for the pedal i would definitely be interested in reading about them

You could do the biasing similar to this:


Read about using a common reference voltage here:
http://www.muzique.com/lab/buffers.htm

I don't have time to redraw the schematic, but hopefully you get the idea.