Tiptop VCA User Manual

VCA

Voltage Controlled Amplifier

www.tiptopaudio.com

Tiptop Audio
VCA User Manual

The Tiptop Audio VCA is a single-channel variable-slope voltage-controlled amplifier in
Eurorack format. It has the following controls (top to bottom):

1. LEVEL - sets the output volume

2. SHAPE - varies the response curve of incoming CV from Logarithmic, Linear,

Exponential

3. OFFSET - opens and closes the VCA by adding CV oset

4. CV IN - attenuator for signals coming through the CV IN jack

5. CV IN jack

6. Audio IN jack

7. Audio OUT jack

Let's learn the VCA functions in details:

(LEVEL) Master Volume:

The simplest function of the amplifier is to use the level knob to increase the volume of an
incoming audio signal and send the amplified signal out through the audio output. The master
volume control knob sets the VCA signal output level. It is a post-VCA gain stage which lets you
match the VCA out level with other sounds in your system. It is also useful to help compensate
for volume dierences between the dierent VCA response shapes.

Variable Response Curve Control:

At its heart, this VCA uses a novel design of control circuitry a function that lets you sweep
continuously through three dierent response curves: Logarithmic, Linear, Exponential giving
you all three shapes in a single module. This special control circuitry was invented by
Mr.Osamu Hoshuyama, a long time synthesizer circuit designer from Japan. The design was
adopted into the VCA module to make it a great sounding synthesizer VCA for all duties:
Gating audio, Amplitude Modulation eects, CV Modulation and Audio Level controls. These
are important features in a VCA. For example, when processing CV signals, linear response is
preferred, on the other hand processing audio signals exponential response curve is prefered
(this is our ear's natural response curve). Having the possibility to morph between the two is
important as quite often an ''in-between'' response curve is required. Being able to fine tune
the response curve is also important when mixing and matching modules from dierent
manufacturers. The third shape, Logarithmic response, is an unorthodox response curve that
opens up yet more room for shaping the incoming CV.

With this design, dierent shapes will have dierent gain and the CV IN and LEVEL knobs are
used to re-adjust the volume after adjusting the shape. When incoming CV is a tad below CV
clipping point (Clip light LED), that is where the gain of all 3 shapes becomes fairly even. This
is the factory default setting (using the BIAS ADJ trimmer at the back you can adjust this point
to your liking. More on that later).

To hear how the Response Curve Control (SHAPE) knob works patch the following:

1. Patch a slow 10Vp.p Triangle wave from your VCO or LFO into the CV in on the VCA

2. Turn the OFFSET knob o

3. Turn the CV IN knob all the way up till the CV Clip LED flashes. Now slowly turn it back
to the point where it stops flashing.

4. Connect a sound wave from another VCO playing a constant audio tone into the VCA
Audio IN. Set the SHAPE knob to the center.

You should hear a linear response of the VCA, it follows the CV in triangle wave shape,
slowly turn the knob counter clockwise, you will hear how the shape turns logarithmic, turn
the knob fully right and you will hear how the shape turns exponential. Is there a significant
gain dierence between the exponential and the other shapes? There most likely is.
Re-adjust the CV IN knob while playing the shape knob to find a CV setting that provides
even gain for all shapes. Observing the VCA output signal using an oscilloscope is very
handy to help understand this patch.

In normal use we won’t spend much time to set the even-gain point for all shapes, instead
we set a shape and adjust the CV IN and LEVEL knobs to the gain we want. This takes a bit
of knob twiddling but is sure worth for having all those shapes available to us in a single
module.

Logarithmic Linear Exponential

LFO

SOUND SYSTEM

Oset Control:

Oset generates CV that gets mixed internally with CV from the CV IN jack. This addresses
three primary functions. First, manually open up the VCA; second, when you don't want
complete silence between the notes and would rather have a constant signal present,
allowing you to increase or decrease signal when CV is applied. The third is when the VCA
is used with a bipolar signal like a LFO. With no oset control, a bipolar signal will open the
VCA only during its positive swing. By setting the oset in the middle, correct bipolar
modulation can be achieved.

CV Attenuator:
Manual control for adjusting the level of signals applied to the CV input. When the CV LED
flashes it means the incoming signal peak is clipped. This is useful to prevent envelopes
from getting their peak signal clipped which aggressively cuts o the dynamic response of
the VCA. This is another unique feature of this VCA.

Signal Input:

Connect audio or CV signals that you want to process with the VCA here. When the RED
LED flashes the audio is clipped, this can be good if distortion is what you are looking for.
For some sounds like nicely rounded bass drums or bass lines, clipping will have negative
eect on their original qualities.

CV Input:

The CV input is a dual-purpose input and lets you use the module as either a Voltage
Controlled Amplifier (VCA) or as a Amplitude Modulator synthesis eect (AM). As a VCA, the
CV input will take in CV signals from Envelopes, LFO’s, Step Sequencers, Random CV
Generators etc. When used as Amplitude Modulator, the CV input takes audio in from a
VCO or any other sound source.

Signal Output:

The output of the VCA.