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DIY Stompboxes => Building your own stompbox => Topic started by: jimladladlooklike on October 31, 2020, 01:22:32 PM

Title: Intersound IVP layout
Post by: jimladladlooklike on October 31, 2020, 01:22:32 PM
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.

(https://i.postimg.cc/5H985ms9/intersound-schematic.png) (https://postimg.cc/5H985ms9)

(https://i.postimg.cc/9RBJ3D6v/Intersound-IVP-power-supply-layout.png) (https://postimg.cc/9RBJ3D6v)

(https://i.postimg.cc/SX6G8XxJ/Intersound-IVP-input-preamp-stage.png) (https://postimg.cc/SX6G8XxJ)

(https://i.postimg.cc/pmN8Z278/Intersound-IVP-Treble-Bass.png) (https://postimg.cc/pmN8Z278)
Title: Re: Intersound IVP layout
Post by: Rob Strand on October 31, 2020, 06:15:41 PM
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
Title: Re: Intersound IVP layout
Post by: jimladladlooklike on November 05, 2020, 08:06:53 AM
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?
Title: Re: Intersound IVP layout
Post by: iainpunk on November 05, 2020, 11:02:20 AM
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
Title: Re: Intersound IVP layout
Post by: jimladladlooklike on November 05, 2020, 12:54:31 PM
Great to know. I will definitely go ahead and use a t-former in that case.
Title: Re: Intersound IVP layout
Post by: iainpunk on November 05, 2020, 02:55:10 PM
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
Title: Re: Intersound IVP layout
Post by: teemuk on November 05, 2020, 03:10:48 PM
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.
Title: Re: Intersound IVP layout
Post by: teemuk on November 06, 2020, 04:29:59 AM
(http://www.ecircuitcenter.com/Circuits/Function_Generator/Functi4.gif)
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.
Title: Re: Intersound IVP layout
Post by: jimladladlooklike on November 16, 2020, 08:11:21 AM
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!
Title: Re: Intersound IVP layout
Post by: digi2t on November 16, 2020, 10:13:12 AM
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. :icon_rolleyes:
Title: Re: Intersound IVP layout
Post by: daverdave on November 17, 2020, 02:26:41 AM
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.
Title: Re: Intersound IVP layout
Post by: MikeA on November 18, 2020, 01:28:53 AM
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. :icon_rolleyes:
  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.
 
Title: Re: Intersound IVP layout
Post by: Mark Hammer on November 18, 2020, 07:19:48 AM
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.
Title: Re: Intersound IVP layout
Post by: MikeA on November 23, 2020, 11:27:45 PM
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.
Title: Re: Intersound IVP layout
Post by: Rob Strand on November 24, 2020, 12:02:33 AM
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.
Title: Re: Intersound IVP layout
Post by: jimladladlooklike on February 14, 2021, 01:48:28 PM
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?
Title: Re: Intersound IVP layout
Post by: iainpunk on February 14, 2021, 02:47:48 PM
Quote
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?
(https://i.postimg.cc/PvGG3hnt/intersound-schematic.png) (https://postimg.cc/PvGG3hnt)

cheers, Iain
Title: Re: Intersound IVP layout
Post by: jimladladlooklike on February 14, 2021, 03:16:04 PM
Apologies, I was looking at the Tapco version. This is the part I'm confused about:

(https://i.postimg.cc/9DDp1qRy/20210214-201217.png) (https://postimg.cc/9DDp1qRy)

And yes that's right

Cheers
Title: Re: Intersound IVP layout
Post by: iainpunk on February 14, 2021, 03:25:35 PM
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
Title: Re: Intersound IVP layout
Post by: jimladladlooklike on February 15, 2021, 08:03:59 AM
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
Title: Re: Intersound IVP layout
Post by: jimladladlooklike on February 15, 2021, 08:17:02 AM
Also, I just noticed that before and after the t former there are two separate 4558 ICs, both of which are only having one half used. Would it be possible to use both halves of one 4558?

Thanks
Title: Re: Intersound IVP layout
Post by: iainpunk on February 15, 2021, 03:31:52 PM
ow, yeah the effects send is the new output, and that is the output amp, since you probably dont want to stack buffers, that's a waste of components, power and board real estate.

i recommend merging halves, independent of the circuit, there are very few cases where you actually need to keep the opamps in their original pairing, most of the time you can get away with shifting that around a bit, in this case you can too.
if you can work out a layout, i recommend using quad opamps, they are generally cheaper per opamp, and it saves a bit of power management since you only have half the amount of chips.

cheers, Iain
Title: Re: Intersound IVP layout
Post by: jimladladlooklike on February 15, 2021, 04:17:47 PM
Okay got it.

Makes sense about the quad op amps! Wish I'd thought to ask sooner as I've done most of the layout with dual op amps. Chalk it up to experience I guess.

Thanks a bunch for your help. With any luck I will have the full layout ready to post soon.

One more thing I'm curious about is whether I can avoid having to use 240v mains power and just use a 9v to 16v converter?

Cheers
Title: Re: Intersound IVP layout
Post by: PRR on February 15, 2021, 08:24:06 PM
OTOH quad opamps lead to a lot of wiring in a small area and increased leakage between stages. (R.G. may have notes on this.)

Neither way is wrong. Duals are very popular.
Title: Re: Intersound IVP layout
Post by: jimladladlooklike on February 16, 2021, 08:28:27 AM
Yeah I suppose that also makes sense, thanks.

I'm up to the point in the layout where I need to place the xfrmr. Could anyone tell me which 4 wires to use if I use the following xfrmr?

https://www.mouser.co.uk/ProductDetail/42TM018-RC/

Cheeeeerrs again.
Title: Re: Intersound IVP layout
Post by: jimladladlooklike on February 16, 2021, 08:32:41 AM
Wait never mind I think I've got it. I'm presuming that wires 2 and 5 are centre taps? So I'm also assuming that I need wires 1, 3, 4 and 6...
Title: Re: Intersound IVP layout
Post by: iainpunk on February 16, 2021, 11:27:51 AM
i haven't had much experience with chare pumps and changing 9v to higher voltages, but i don't think the circuit will draw a lot of current so that might not be a problem.
something like this could be something to experiment with:
https://www.ebay.co.uk/itm/12V-Dual-Output-DC-DC-Converter-Step-Up-Voltage-3-3V-5V-9V-to-12V-Boost-Module-/253029625315
a nice large capacitor from both the + and - to ground is important to filter the switching noise.

cheers, Iain
Title: Re: Intersound IVP layout
Post by: ElectricDruid on February 16, 2021, 02:21:23 PM
Okay got it.

Makes sense about the quad op amps! Wish I'd thought to ask sooner as I've done most of the layout with dual op amps. Chalk it up to experience I guess.

Opinions differ, but I prefer duals for layout because then all the op-amps "point in the same direction". This helps signal flow around the board. On a quad package everything points out from the middle, which I find more difficult to lay out. Plus the power pins are reversed with respect to virtually everything else, which makes it awkward to put them on a board with other parts (unless you add them in upside down, which I also don't like).
If you play around with both, you'll find which you prefer. Depends a bit on your design style, I guess.

Quote
One more thing I'm curious about is whether I can avoid having to use 240v mains power and just use a 9v to 16v converter?

How much current does it draw? Usually voltage boosters are ok as long as the current drawn if fairly light. Big loads make that a lot harder. But doesn't this thing have a +/-16V bipolar supply? In which case, you'd be doing a lot of gymnastics to get that from a +9V input...not impossible, just tricky.

You could think about running from an 18V input and then just adding a rail-splitter op-amp to give you a +/-9V supply. That'd let you use the circuit without making any serious modifications, and 9V isn't so massively different from 16V that you'd notice much. At least, not in this circuit for this application. Yes, you lose a bit of headroom (18V vs 32V), but if we're turning it into a pedal, we don't want mixing desk levels anyway.


Title: Re: Intersound IVP layout
Post by: jimladladlooklike on February 17, 2021, 07:53:21 AM

How much current does it draw? Usually voltage boosters are ok as long as the current drawn if fairly light. Big loads make that a lot harder. But doesn't this thing have a +/-16V bipolar supply? In which case, you'd be doing a lot of gymnastics to get that from a +9V input...not impossible, just tricky.

You could think about running from an 18V input and then just adding a rail-splitter op-amp to give you a +/-9V supply. That'd let you use the circuit without making any serious modifications, and 9V isn't so massively different from 16V that you'd notice much. At least, not in this circuit for this application. Yes, you lose a bit of headroom (18V vs 32V), but if we're turning it into a pedal, we don't want mixing desk levels anyway.



Oh right, thanks for pointing that out. It hadn't dawned on me that I would need to get both +16v and -16v from +9v... Will do some research on how.

I don't know how much current it draws, honestly. How would I calculate that? Watts/Volts? How do I find out the wattage? Excuse my ignorance.

Thanks
Title: Re: Intersound IVP layout
Post by: iainpunk on February 17, 2021, 09:38:54 AM
an educated guess: it uses less than 150mA

you might also want to look at the transformer voltage/freq rating. i expect the transformer to be slightly overdriven, but at a lower voltage, you might not get that, so trying lower voltage transformers might be a good idea here.

cheers
Title: Re: Intersound IVP layout
Post by: jimladladlooklike on February 19, 2021, 08:04:17 AM
Right, so I think it may be best to abandon the idea of powering with a +9v wall wart.

Instead, would I be able to power it with +32v DC and split the voltage somehow?
Title: Re: Intersound IVP layout
Post by: iainpunk on February 19, 2021, 11:07:20 AM
you can probably get away with only using 18v to 24v, i think 32v might be overkill here, the gain isn't that high, and the circuit will most probably work just fine on + and - 9v or 12v.

i suggest looking in to charge pumps and other boost converters like the Ebay link i posted earlier, this makes 9v in to a higher voltage

cheers, Iain
Title: Re: Intersound IVP layout
Post by: jimladladlooklike on February 19, 2021, 06:29:11 PM
Okay, thanks again. Still getting to grips with power supplies and what different circuits require/whether they are affected by a differing voltage.

But, I have finished the vast majority of the layout... I think.

A quick note: I like to drill a larger hole through one of the holes in the strip board to create a trace cut which I then tidy up with a tool afterwards. The DIYLC software only allows lines to be drawn between said holes, so each of these lines represents a hole that will be drilled to the RIGHT of it.

Here we have the input preamps. There are two input jacks on the IVP, both with a lo/hi impedance switch on them. I've simplified it slightly so there is one low and one high, neither of which you can change with a switch. (Also, with regards to the PS decoupling network, I'm not sure I will need this if using a charge pump? I'm guessing this is to eliminate DC ripple? I left it in just in case it's necessary.)

(https://i.postimg.cc/zbhDjgnp/Intersound-IVP-input-preamp-stage.png) (https://postimg.cc/zbhDjgnp)

Following that we have the elaborate EQ section:

(https://i.postimg.cc/4HZGQF4N/IVP-Equaliser.png) (https://postimg.cc/4HZGQF4N)

And finally the tube voice part:

(https://i.postimg.cc/fkFpsPQ3/IVP-Tube-Voice-Circuit.png) (https://postimg.cc/fkFpsPQ3)

As you can see, especially with the EQ, it's a lot of strip board -but I want to put this in some kind of big chassis and use it as an "always on" kind of thing as part of my rig (which it's looking like I will never use again at this rate, but whatever).

Any advice whatsoever would be truly appreciated, likewise if anyone has the time to check it over as per the schematic. I've checked it myself but it's late and my eyes hurt!

PS layout to follow, once I manage to get my head around what to do. Every day is a school day!

EDIT: The resistor on from the emitter of the 2N5210 to -16V on the left of the TV circuit layout is meant to be 36K, oops.
Title: Re: Intersound IVP layout
Post by: ElectricDruid on February 19, 2021, 07:46:30 PM
A quick note: I like to drill a larger hole through one of the holes in the strip board to create a trace cut which I then tidy up with a tool afterwards. The DIYLC software only allows lines to be drawn between said holes, so each of these lines represents a hole that will be drilled to the RIGHT of it.

DIYLC has a "trace cut" option on the "Boards" menu which is the best way to represent a trace cut on veroboard. It looks exactly like drilling a track out with a wide drill bit. Lines don't work well because they're not the way it was designed to be done.
Title: Re: Intersound IVP layout
Post by: jimladladlooklike on February 20, 2021, 09:21:14 AM
Seems I'm using a very old version... will download the new one now!
Title: Re: Intersound IVP layout
Post by: jimladladlooklike on February 20, 2021, 01:42:02 PM
2nd draft:

2n4401 + 2n4403 on EQ board swapped positions and diodes changed accordingly.

Pin 2 of the furthest right 4558 on EQ board now connected to lug 3 of all freq level pots.

Traces now cut using proper tool.

xfrmr added for more accurate size.

(https://i.postimg.cc/s1yWDDmh/IVP-input-preamps.png) (https://postimg.cc/s1yWDDmh)

(https://i.postimg.cc/ppLnzGgV/IVP-Equaliser.png) (https://postimg.cc/ppLnzGgV)

(https://i.postimg.cc/BtgK897w/IVP-Tube-Voice-Circuit.png) (https://postimg.cc/BtgK897w)
Title: Re: Intersound IVP layout
Post by: jimladladlooklike on March 10, 2021, 08:05:14 AM
Hey again,

I've been looking into this power supply situation. I still want as close to the +/-16v bipolar supply as possible, but admittedly don't have the knowledge to get that from and +9v unipolar wall wart. I have come across this schematic for an op amp voltage splitter which utilises an LM741.

(https://i.postimg.cc/1frPgzrP/power-supply-splitter-circuit-min.jpg) (https://postimg.cc/1frPgzrP)

Theoretically, if I found a 32V AC adapter (or an adjustable one that had that setting or, say, +30V) could I use this circuit. The max supply voltage for the LM741 is +/-22V but does that mean it could essentially handle max +44V from a unipolar supply?
Another thing I'm concerned about is the germanium PNP transistor (MJ2555). Could I replace this with a silicon tranny?
Title: Re: Intersound IVP layout
Post by: duck_arse on March 10, 2021, 08:44:41 AM
that transistor should, most likely, be marked MJ2955, which is the compliment to the 2N3055, both are silicon. the same transistor pair comes in different packages with different prefixes, eg TIP3055 or MJE3055, probably others I can't remember. that transistor pair would have been selected for their MASSIVE-ish current handling, probably way more than you would need here.
Title: Re: Intersound IVP layout
Post by: Rob Strand on March 10, 2021, 08:49:07 AM
Quote
Theoretically, if I found a 32V AC adapter (or an adjustable one that had that setting or, say, +30V) could I use this circuit. The max supply voltage for the LM741 is +/-22V but does that mean it could essentially handle max +44V from a unipolar supply?
Another thing I'm concerned about is the germanium PNP transistor (MJ2555). Could I replace this with a silicon tranny?
The transistor is actually an MJ2955 which is the PNP compliment to the 2N3055.

You don't need such large transistors for that circuit.
[Edit: duck_arse just posted the same]

Perhaps you could consider an AC input with a voltage doubler feeding a voltage regulator,

http://www.electricalbasicprojects.com/voltage-multiplier-circuits-half-wave-voltage-doubler/

For the positive supply you use one doubler,
(http://www.electricalbasicprojects.com/wp-content/uploads/2017/11/Voltage_Multiplier_Circuit-768x409.jpg)

For the negative supply you use another doubler except with the diodes and caps flipped.

Connect the input caps from each doubler together then to the transformer.
Connect the "through rail" on the each double together then to the other side of the transformer.

If you start with a higher AC voltage you can use this type of doubler,
(https://qph.fs.quoracdn.net/main-qimg-a8d8bada57a1b7820b49bf949d06a8e3)
Title: Re: Intersound IVP layout
Post by: jimladladlooklike on March 12, 2021, 01:23:03 PM
Cool, thanks for the suggestion, but I don't know where I'd get an AC voltage from. Do such wall warts exist? Also I'm not sure which transformer you mean? I'm trying to steer clear of the need for a PT if that's what you were suggesting. Could I use a version of the schematic I posted but with more apt transistors?

Cheers
Title: Re: Intersound IVP layout
Post by: jimladladlooklike on March 12, 2021, 04:08:38 PM
So I just breadboarded a version of the schematic I posted, except I didn't have an LM741 handy, so opted for an LM386 instead.

It's powered with +9v DC. (The LM386 doesn't can't handle more than 18V, so will have to use a suitable replacement eventually.)

I used two 560r resistors for the voltage divider, hooked up to the two outer pins of a trim pot, the centre pin of which is connected to the non-inverting input of the op amp.

I replaced the transistors with a 2N5088 and a 2N5087.

After measuring, the reading I get are: C1 + terminal = +9v, "ground" terminal = +4.5v and C2 - terminal = 0V. So basically what I have is a voltage divider... I then disconnected the two above capacitor legs and measured there, having noticed that they were connected to +9V and ground, but I don't know what that achieved as the voltages were all over the place. Is there something I'm missing? are the parts I used not the right kind?

EDIT: I was measuring wrong. I was taking the ground reading from the bottom left point of the schematic, not the junction of the two caps.

It works fine! Now I just need to test with an LM741 when I can get some. Thanks for all of your help on this guys, I feel like I'm learning a lot and it's much appreciated.
Title: Re: Intersound IVP layout
Post by: iainpunk on March 12, 2021, 05:04:34 PM
The LM386 isn't a (normal) opamp, its a power amp, with some odd quirks when it comes to biasing, to make it work with less external parts. try any other real opamp, that would probably work better.
if you want to simplify and use the 386, you can leave out the transistors, and put both inputs to ground, this provides a strong, stable Vbias

cheers
Title: Re: Intersound IVP layout
Post by: jimladladlooklike on March 13, 2021, 08:12:40 AM
Oh okay, thanks for the pointer. I was planning on using an LM741 because of it's max input voltage anyway, just wanted to make something similar with what I had to hand. Note to self, always read the datasheet.
Title: Re: Intersound IVP layout
Post by: iainpunk on March 13, 2021, 04:51:58 PM
Quote
Note to self, always read the datasheet.
that shouldn't be just a note, that should be your RULE #4, the other rules will come to you along the way.

cheers