# Frost Drive Mods: The Ice Scream Sammich



## Chuck D. Bones (Oct 7, 2019)

I posted pix and a description of my Frost Drive build here in the Build Reports forum. This post provides the details of the modifications I performed. A schematic is attached at the end of this post.

The Frost Drive is a clone of the VFE Ice Scream, which is derived from the Ibanez TS-9 Tube Screamer.  I started out with the Frost Drive _Mint Flavor_ parts values.  Let me be clear: except for the MID control, the Frost Drive works great as-designed.  These mods are me putting my own spin on it and expanding the tonal palette.
My mods fall into three categories.  You can do some of these in any combination, or all of them like I did.
1) Changes I made based purely on personal preference or parts availability
2) Adding features to the diode clipping network
3) Correcting the MID control

*Changes based on personal preference*
I won't bore you with the details.  I substituted some parts based on personal preference or availability.  None of this impacts performance.
TL072 instead of JRC4558
FDH400 instead of 1N4148
2N5210 instead of MPSA18
A1M instead of D1M for the DRIVE pot
C100K dual instead of C10K dual for the MID pot

D taper pots are hard to come by, so I used the readily available A1M.  I asked Peter Rutter about this and he told me he chose the D taper because it makes it a little easier to dial in low gain settings.  The comparison of A & D taper is discussed in this thread.

I could not find a C10K dual pot, but I did find a C100K dual at Pedal Parts Plus.  The MID pot sub and mods are described here and in detail in the last section of this post.

*Diode Clipping Network*
This is mod is the most complicated, but the payoff is a dramatic increase in tonal palette and control. The diode clipping network gives the various Tube Screamer derivatives their personalities.  When Peter Rutter designed the Ice Scream, he included a DIP switch for selecting symmetric clipping, two levels of asymmetric clipping,  or no clipping diodes.  Other OD designs of his have pots in the feedback loop that dial in different diode or MOSFET clippers (see the VFE Alpha Dog, Scream and Pale Horse).  This mod was inspired by those pedals.  I moved the diode CLIP switch to the front panel, rewired it slightly, replaced two of the diodes with green LEDs and added an HCC (Harmonic Content &  Compression) pot in series with the silicon diodes.  The CLIP switch selects between symmetric LEDs, symmetric silicon diodes or an asymmetric LED / silicon diode combination.  When the silicon diodes are selected, the HCC pot controls how hard they limit the signal.  At full CW, the silicon diodes provide the maximum harmonics and compression.  At full CCW, the diodes barely affect the signal at all.  In Asymmetric mode, the HCC pot adjusts the degree of asymmetry and compression.  In LED mode, the HCC pot is out of the circuit.

Parts added:
Two green LEDs
DPDT ON-ON-ON toggle switch
C250K pot
Parts deleted:
Two 1N4148 diodes
DIP switch

To accomplish this mod, leave out D2, D4 and the DIP switch (SW1).  Install an LED in the lower pair of holes where SW1 used to be, with the cathode to the left.  Looking at the terminal side of the CLIP switch, wire the pair of terminals at the top end of the switch to pin 2 of the HCC pot. Wire the center terminal on the left side to the D2-A pad on the board.  Wire the center terminal of the right side to the D4-K pad (we use "K" for cathode so we don't confuse it with a capacitor).  Connect an LED between the lower left terminal and pin 3 of the HCC pot, with the anode connected to the switch. Connect a wire from pin 3 of the HCC pot to the top left pad where SW1 used to be.  Connect the lower right switch terminal to the D2-K pad on the board.  I mounted the second LED on the front panel for a "seeing eye" effect, but sadly, it barely glows.

*Mid Control*
The Frost Drive's Mid Control circuit comes right out of the Ibanez ST-9, with some component rescaling.  Somewhere along the way, the design got corrupted and the MID control isn't working as originally intended.  The circuit is simple: a bridged-T network in the feedback loop creates a midrange hump.  Changing the resistors in unison changes the center frequency of the hump, keeping the gain and bandwidth constant.  The ratio of the two capacitors sets the gain and bandwidth.  The stock capacitor values produce a gain just over 7dB at the peak and a 2 octave bandwidth.  The tuning range is 190Hz to 2.1KHz (3.5 octaves). 

The fixes for the taper and/or rotation direction are described here.  I tweaked the values of C3, C5, R4 & R5 to make the tuning range a little wider.  You can use these values to get the same tuning range as the Frost:
MID pot = C100K dual
C3 = 4.7nF
C4 = 12nF
R4 & R5 = 10K
Or use the values I used for a slightly broader tuning range:
C3 = 6.8nF
C4 = 18nF
R4 & R5 = 6.8K


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## Barry (Apr 19, 2020)

Using an A10K Pot I then use the values in Red to get the broader sweep?
MID pot = C100K dual
C3 = 4.7nF
C4 = 12nF
R4 & R5 = 10K
Or use the values I used for a slightly broader tuning range:
C3 = 6.8nF                68nF
C4 = 18nF                180nF
R4 & R5 = 6.8K         680R


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## Chuck D. Bones (Apr 19, 2020)

Correct.  Caps go up by 10x, resistors go down by 10x.


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## cooder (Apr 20, 2020)

This is great, thanks for the super indepth explanation! I also was a bit befuddled by the weak difference that the mid pot makes in my build.
Will inplement the suggested changes, thanks!

Also, I'm still interested if you could have your eyes go over the SoftII as asked in an earlier thread, I find it too bass heavy after playing it for awhile. If you could give me/us your take on that would be greatly appreciated too. Cheers!


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## Chuck D. Bones (Apr 20, 2020)

There is another tweak you can do to make the mid peak more or less pronounced.  The ratio of the caps sets the peak midband gain. The values I used give a 7dB peak.  Not huge, but noticeable.  If you want a stronger mid peak, bump C3 down and C4 up.  As long as you change each one by the same percentage (just in opposite directions) then the tuning range is the same.  Don't get too carried away.  Example: Change C3 to 4.7nF, C4 to 27nF.  Tuning range is about the same, but now the mid peak is almost 12dB.

When I get a chance, I'll take another look at the SOFTii thread.


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## cooder (Apr 20, 2020)

Awesome, thanks again for sharing your knowledge and insights!


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## HamishR (Apr 28, 2020)

When (if!) my board arrives I will reread this before even getting the iron hot. I have got a dual C10 pot but it's the type with the PCB lugs which stick straight out, with no 90 degree bend.  I can add some wires to make it work.


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## ErickPulido (Jul 6, 2020)

Hi, please correct me if I am wrong, I want to build this one for so long, my questions are:
I am using the A100K dual pot so the values are
used for a slightly broader tuning range:
C3 = 6.8nF
C4 = 18nF
R4 & R5 = 6K8
but to obtain the 12db boost Change C3 to 4.7nF, C4 to 27nF , am I right?

Can I use this pedal without charge pump?

What version do you recommend Mint or Sherbet?


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## Chuck D. Bones (Jul 7, 2020)

ErickPulido said:


> Hi, please correct me if I am wrong, I want to build this one for so long, my questions are:
> I am using the A100K dual pot so the values are
> used for a slightly broader tuning range:
> C3 = 6.8nF
> ...



Correct.

While it is possible to run this pedal without the charge pump, it would require a lot of modifications to get it to work.  Not recommended.

I went for middle-of-the-road and built Mint flavor.  Sherbet has a little more gain.  If you want the most gain, build Sherbet.


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## ErickPulido (Jul 7, 2020)

Chuck D. Bones said:


> Correct.
> 
> While it is possible to run this pedal without the charge pump, it would require a lot of modifications to get it to work.  Not recommended.
> 
> I went for middle-of-the-road and built Mint flavor.  Sherbet has a little more gain.  If you want the most gain, build Sherbet.


thank you so much I'll build mint too, and with charge pump


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