Intersound IVP layout

[jimladladlooklike]

Hi mates,

I originally posted this in the Schematics/Layouts section of this forum but thought it may get more attention here.

I have a habit of sporadically searching this forum for a vero layout for the Intersound IVP. If any of you have tried the same then you'll know that there's nothing of that kind, just schematics left over from abandoned projects.

Finally had some spare time and I decided to start designing a layout myself. I've split it up into sections and so far have made a layout for the PS, preamp stages (inc decoupling supply) and the bass + treble controls.

If anyone would like to help/check what I've done so far or give any advice then please feel free to do so. I've attached what I've got plus the schematic I'm working from below.

[Rob Strand]

FWIW, the 43 ohm resistor on the emitter of the tube-sound current source is actually 430 ohm.

https://www.diystompboxes.com/smfforum/index.php?topic=119132.msg

In another thread, I found a clear picture showing the 430 ohm on the PCB.

https://www.diystompboxes.com/smfforum/index.php?topic=121884.msg


There was also this stuff on the transformer,

https://www.diystompboxes.com/smfforum/index.php?topic=119131.msg

[jimladladlooklike]

Thanks v much! I imagine i will factor in the transformer to be honest. Do you think there would be any benefit apart from saving space in doing it the way suggested on that thread?

[iainpunk]

transformer ''abuse'' gives a completely unique response, both in saturation, saturation dependent bass cut, hysteresis loss, and a host of other good sounding effects. you can also saturate a transformer asymmetrically by having a small DC run through the transformer. i have a transformer based fuzz somewhere, (broken after a beer spill during a gig), its a shame that transformers are heavy, bulky and expensive, otherwise i'd use them a lot more.

cheers, Iain

[jimladladlooklike]

Great to know. I will definitely go ahead and use a t-former in that case.

[iainpunk]

trying out different transformers can be a good idea if you have multiple. if you know what you are doing, you can even mod a transformer to sound the way you desire. when i build the transformer fuzz, i cut a big slot in the core to make it saturate faster, but you have to know what you are doing when changing the transformer, because if you over do it or do it wrong, you might need to get a new one.

cheers, Iain

[teemuk]

Most important is that differential voltage amp circuit and extracting its output differentially, whether with transformer or another diff. amp. I doubt there will be significant transformer saturation with associated low signal voltages and guitar's limited bandwidth. (Especially if you don't want a "farting" overdrive tone).
You could always A/B both arrangements, transformer vs. differential and find out yourself. I have a hunch the transformer merely acts as LC filter, if even that.

[teemuk]

Differential provides symmetric soft clip (enough to convert triangle to sine) when no negative feedback is applied and input is constrained to low amplitudes.

Any transformer's effects on this topology are negligible enough to be ignored by likes of Vox (i.e. Valvereactors, VBM1), Hughes&Kettner (i.e. QT600), dozens of signal generator manufacturers and so on.

[jimladladlooklike]

Hi Teemuk

Thanks for the info. Think I will attempt to find an appropriate transformer as I would like to make as faithful a clone as is possible on a perfboard!

[digi2t]

Where does one find the C2M pots for the EQ section?

I thought about tossing this Phil's way for a PCB, but the pots stonewalled that thought.

[daverdave]

I recently built the tube sound section of the IVP with two of the 4 band parametric eq sections as a standalone pedal, to get around the need for the 2MC pots I used dual gang 1MA pots wired with both pot elements in series and wired 'backwards', so that CCW is wired to the op-amp non-inverting input and the CW and centre pins are wired together.

This gives the correct frequency sweep but the downside is that the pot works in reverse, so that the upper frequency is CCW and the lower is CW. That doesn't really bother me though.

[MikeA]

Where does one find the C2M pots for the EQ section?

I thought about tossing this Phil's way for a PCB, but the pots stonewalled that thought.

There's a different schematic (Electrovoice/Tapco version) at https://projectivp.wordpress.com/ that calls for A2M pots.  I've been looking at that one in LTSpice and tried B2M pots, which are readily available, and the frequency spread doesn't look too bad, but I haven't built it yet, so that's a guess.  PCB's are available for the input, 2-band and Tube Voice sections, if you just add the 4-band EQ you've got all the important stuff.  2nd input and clean channel could be omitted, along with the send/receive jacks and balanced output.
 

[Mark Hammer]

It is often the case that such semi-parametric  EQ sections overlap substantially in their tunable resonant frequencies, and rarely the case that there is NO overlap.  I assume this is to allow for maximum flexibility.

But how much flexibility and overlap in resonant frequency between adjacent bands does a musician need?  I'm merely asking the question, not concluding they don't need any.  For example, the PAiA 4-band semi-parametric EQ, with a very similar design, sweeps its centre frequencies from 35-680hz, 150-3000hz, 450-8500hz, and 750-15000hz.  If one were to chop those ranges by half, you'd still have a fair amount of overlap.  Maybe not enough to "tune a room" with several distinct resonances, but a more-than-reasonable capacity to re-voice many instruments.  The IVP's resonant  EQ bands are stated as tunable between 30-240hz, 100-800hz, 450-3600hz, and 1200-9600hz, with bass and treble shelving controls attending to the rest.  As in the PAiA instance, a 50% reduction in range for each section still leaves a fair and usable amount of overlap, though I suppose that depends on the weirdness or quirks of the signal source or user's timbral end-goals.

In that spirit, I suggest trying out C1M pots, and seeing if it's something you can easily live with, whether permanently or until a source for C2M pots is found.

[MikeA]

In that spirit, I suggest trying out C1M pots, and seeing if it's something you can easily live with, whether permanently or until a source for C2M pots is found.

+1, I gave this a try in LTSpice and the difference with C2M is minimal.  All it does is raise the low-end cutoff on each band a bit, and there's still more than sufficient overlap.  Hi-end of each band is not affected.   2MC vs 1MC low end cutoff:  Frequency band 1, 30Hz becomes 40 Hz.  F2, 100Hz >> 130 Hz.  F3, 450Hz >> 620Hz.  F4, 1.2kHz >> 1.6k Hz.  For reference, the high-end of each band in sequence remained at 240, 800, 3.6k and 9.6k.  I'm sold on C1M for this design.

[Rob Strand]

If you really want it, it's possible to maintain the exact same behavior of the 2MC pots using 1MC pots.
All you have to do is halve *all* the resistances in the EQ section and double the caps.   The idea is called scaling.
Technically you should change the boost/cut pots to 25k as well.

[jimladladlooklike]

So I've gotten to the point where the mixer amp and EQ section are laid out and I have some questions:

Could this be run off of a 9v pedal power supply by incorporating a 9v to 16v converter?

The post EQ section based around U8 - what is it's purpose? Is it needed if I decide to leave out the effects loops?

Could I leave out the clean voice section and just include the tube voice section? And what exactly should I eliminate if I choose to do so?

[iainpunk]

The post EQ section based around U8

there is no U8 on the schematic,

if i understand correctly, you want the input mixer, the elaborate EQ and the tube voice, without effects loops?


cheers, Iain

[jimladladlooklike]

Apologies, I was looking at the Tapco version. This is the part I'm confused about:



And yes that's right

Cheers

[iainpunk]

that's an audio indicator LED, i believe.
it triggers when the level reaches a certain threshold, and lights an LED. the diode with the arrow pointing away, its datasheet tells me its an red diffused led.

cheers

[jimladladlooklike]

Okay, well I don't think I need that, so will leave out.

Regarding the amended schematic you uploaded (thank you by the way), will I need to incorporate the output amplifier stage or will the 4558, 2n4401 and 2n4403 form what is effectively the same thing? If the latter is the case I presume I just use the "effects send" as the output for the circuit?

Thanks again