Amptweaker - Tight Metal  [traced]

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Pruttelherrie
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Post by Pruttelherrie »

bajaman wrote:I do like zener diode clipping behaviour soundwise - and the different vref bias voltages definitely play a large part in this circuit's operation. :!:
Is there an asymmetric Vref (with which I mean not equal to 1/2Vsupply) on the stages with the zener in the feedback loop? If so, is that to get the 5.1V zeners to work 'correctly' in this application? With Vref=1/2Vsupply they would never conduct, but if you shift the Vref a bit they would conduct before opamp clipping occurs (as mentioned somewhere above). In that case I think you would get asymmetrical clipping: ~0.6V forward voltage and 5.1V reverse voltage. Is this what you mean with 'zener diode clipping behaviour'?

Also, with respect to the gate: with a higher gain setting you get more gating action, but also more 'crossover-distortion'-like behaviour of those diodes, attributing to the total amount of distortion. Neat!

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Post by Pruttelherrie »

azrael wrote:
J0K3RX wrote:The FX loop is before and after the effect via a switch on the bottom of the board... Just one loop that toggles to the front or to the back
Ah, I see! Man that one at the end is kind of useless, no? Might as pull the effect after the actual pedal at that point haha.
Well, the thing is that the loop switches along with the pedal. That wouldn't work when you put the effect after the pedal.

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Post by azrael »

Ahh, that's a fair point. :)


Looking forward to the corrections, I have a layout that is pretty much done. Just gonna fix it with the corrections. No PCB mount pots this time, but the pots are all by the edge for easy wiring.

I have to say, the VREF going to the volume pot is quite annoying. It's killing my ground pour. Any reason we couldn't just reference it to ground?

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Post by jymaze »

Well, you need a Vref at the input of the opamp anyway. Actually, I found it quite clever to use the volume pot for that purpose so you don't need the usual high value resistor to Vref.

Also, yes, it is asymmetrical Vref (with 2 different Vref, 100k/150k and 18k/47k).

It is a nice clipping principle, but actually the first to pioneer that principle was CARVIN in their SSX line in the 80s. Today, there clipping stage on the SSX is even more complicated and I think it sounds great. Basically it is based on serial stages of inverting very asymetrical clipping stages (wait... just like cascading tube stages! Damn...).

Then here you have a BMP tonestack almost flat (just a little dip around 250 Hz to make it tight) then a big scoop with a T notch filter. Nice stuff!

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Post by J0K3RX »

jymaze wrote:Hey Jok3rx,

Sorry to ask again, but I have a problem with that track:
The attachment WeirdTrack.PNG is no longer available
I cannot see it on your pics. You are sure it stand like that? Confirmed with a meter? Why would they just put 2 resistors in series when you can just put one?

Ok, one thing at a time... sorry, long day at work.

jymaze, good eye... but we were both wrong. I missed a trace that connects between those two resistors from the 100n cap below... I drew it in with paint shop pro right below your yellow loop
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Post by J0K3RX »

azrael wrote:Ahh, that's a fair point. :)

I have to say, the VREF going to the volume pot is quite annoying. It's killing my ground pour. Any reason we couldn't just reference it to ground?

Any reason you can't connect it using a jumper?

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Post by jymaze »

Great Jok3rx,

That is what I thought. The tone stack makes perfect sense now.

I will update the schematic tomorrow, there was a couple mistakes. I am 99% sure about this circuit now. Then we will just have to proof your layout and maybe have a fabbed run of these boards! I want one!

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Post by J0K3RX »

Wow!! bajaman's layout is insanely good!!! I think better than the original... :lol:

bajaman - I sent you the corrections as best as I can tell..

I would still like a one sided board for this without the light up knobs and FX loop to keep it minimal! Pots don't have to be on-board but it damn straight will need shielded cables!!!

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Post by azrael »

jymaze wrote:Well, you need a Vref at the input of the opamp anyway. Actually, I found it quite clever to use the volume pot for that purpose so you don't need the usual high value resistor to Vref.

Also, yes, it is asymmetrical Vref (with 2 different Vref, 100k/150k and 18k/47k).

It is a nice clipping principle, but actually the first to pioneer that principle was CARVIN in their SSX line in the 80s. Today, there clipping stage on the SSX is even more complicated and I think it sounds great. Basically it is based on serial stages of inverting very asymetrical clipping stages (wait... just like cascading tube stages! Damn...).

Then here you have a BMP tonestack almost flat (just a little dip around 250 Hz to make it tight) then a big scoop with a T notch filter. Nice stuff!
vref at the opamp is easy, that doesn't mess up the layout at all haha.

Wait, did bajaman post a layout? I'd like to see!

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Post by J0K3RX »

coldcraft wrote:does anyone think the tight rock is just the metal with maybe a 250k Gain knob and different tone stack values?
No, but I bet they are very similar!

Some cool stuff in these pedals that can be used in other designs...

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Post by J0K3RX »

azrael wrote:
jymaze wrote:Well, you need a Vref at the input of the opamp anyway. Actually, I found it quite clever to use the volume pot for that purpose so you don't need the usual high value resistor to Vref.

Also, yes, it is asymmetrical Vref (with 2 different Vref, 100k/150k and 18k/47k).

It is a nice clipping principle, but actually the first to pioneer that principle was CARVIN in their SSX line in the 80s. Today, there clipping stage on the SSX is even more complicated and I think it sounds great. Basically it is based on serial stages of inverting very asymetrical clipping stages (wait... just like cascading tube stages! Damn...).

Then here you have a BMP tonestack almost flat (just a little dip around 250 Hz to make it tight) then a big scoop with a T notch filter. Nice stuff!
vref at the opamp is easy, that doesn't mess up the layout at all haha.

Wait, did bajaman post a layout? I'd like to see!
He didn't post yet... I have it so I could check the switches etc.. but it's his and he will post when he's damn good and ready :lol: By the way, I am just being a smart ass, I can't help it... :mrgreen:

By the way - it's double sided so carry on with the single layer if you were working one up!!

Sprint 6 is the bomb! need to purchase...

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Post by bajaman »

I will post all the files - (gerbers as well) very soon. :wink:
cheers
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Post by azrael »

Oh, of course, bajaman. I thought I had missed something awesome again hahah.

Yes, I'm working on a single sided layout, been a while since I've done them, since I've been fabbing double sided boards lately. Doing single sided is good practice every now and then hahah. Right now I have one jumper, and I hate jumpers, so just waiting on corrections, maybe I'll get a good new idea on how to lay it out.

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Post by bajaman »

Hi Azrael :D
My layout is merely a tidied up version of Jim's original trace of the actual Tight Metal PCB layout.
I have changed (shortened) some of the tracks and some have been changed layer wise.
I am sure there will be many folks here who would love a single sided layout (did I here vero board layout from someone? ).
A good example of FSB in action and special thanks to Jim for his purchase and dismantling of this interesting pedal.
Once the circuit is finalised i will run some simulations with Multisim 12 and of course publish my findings for all. :wink:
cheers :thumbsup
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Post by jymaze »

Hello,

Here are some hand drawn corrections to the tonestack and a breakdown of the PSU with the asymmetrical and 2 tiered biasing in all its glory. I think the schematics can be considered final now. I trust someone will update the last Eagle schematics accordingly.

These schematics are all based on the pictures that Jok3rx originally posted and not the board layouts that have been floating around lately. Maybe someone wants to proof the layout versus the final (I think so at least) schematics?

Thanks guys!
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Post by apollomusicservice »

According jymaze new tonestack sketch I made new Eagle file with this corrections. Mod you can del my previous Eagle file in order to avoid any confusion.
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Post by apollomusicservice »

Ooops, I almost forgot, for those who like SMD technology this is a SMD PCB of Amptweaker Tight Metal.
Good luck in building :D
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TightMetal SMD layer.pdf
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TightMetal SMD components1.png
TightMetal SMD components.png
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Post by bajaman »

Hello Apollo :)
Nice SMD layout :thumbsup
Unfortunately your Eagle schematic still has many mistakes :(
Power supply is wrong, notch filter has missing 22u cap, no gate switch etc.
cheers
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Post by J0K3RX »

What, nobody made a single layer through hole yet? :? Is it because it doesn't have Wampler tattooed on it? :mrgreen:

Don't make me do it! We will be debugging till the cows come home... :roll:

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Post by apollomusicservice »

OK bajaman thanks for notes, I dont have Sprint-Layout software but if someone has a schem as pdf, png, gif, jpg
I'll make correction in my Eagle files and SMD pcb.

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