New Effect: Microtubes 2k (Cmos Design)

[snap]

ZC: how did you wire them as a buffer?

[gigimarga]

Sorry, but i was very busy at work today so i have no time to upload some clips.

I used a regular Squier Affinity (i'd paid for it 250-300$ new in box)  and an old 20W full-tube romanian amp with one clean channel (modified by a friend of mine to sound fender-like).

Yesterday, when i reported the oscillation, i tested Microtubes at a very low volume setting (it was 2:30AM and my child was sleeping ).,
Today i retested it at a high volume (half the power) and, strange, no oscillations!!!
I think that i'd stayed too close to the amp yesterday, so my apologies!

I will try tomorrow to add a DPDT for the LPF and i will write here the result!

About ICs i only want to say that i had very BIG problems with HCF4049UBE...a really nightmare!

[zencafe]

Hehehe, nice that it didn't oscillate... I began to worry hehehe.
I'd really like to your opinion, I mean, a critic... in order to improve whatever you may feel needs to... I'm really open to commentaries and constructive critics since I'm not a guitarist myself, I'm a bassist, so eventhough I've studied a lot about distortions, my point of view my be different than many guitarists...

Here's the pic of the buffer I used... R1 and R2 are the same value (I think I used 10k), I know is pretty basic "design", but I was just experimenting...




I've seen other kind's of buffers with inverters in this forum, don't remember exactly on which threads, but I'll do some search when I arrive home.
It maybe that the type of buffer I used is specially noisy compared to other designs, I don't really know, so if someone has experimented with these, let us know!

Best Regards

D.

[bool]

@zen: yes, the linkwitz circuit could be translated easily. In my quick drawing it has the NFB loop bypassed with a cap for higher freqs, so the noise should go down (functions as a lowpass with a peak). As a matter of fact, I _was_ looking at DoubleD @ROG, wanting to roll something similar for my use (with mosfet input) but use the remaining buffer for a "sim-filter".

Unfortunately, I can only get (problematic ?? ) HCF chips here atm., so I can't either put together a prototype - or simulate it because afaik there isn't analog models for 4049 or 4069 available.

for the record: there are some notes from the "old world":
http://www.harmony-central.com/Guitar/Faqs/faq/faq.tubeSoundFuzz.txt

[gigimarga]

Today i have a little time to record few soundclips using this setup Squier Affinity ->Microtubes->cheap soundcard (less than 10$)->Audacity. I didn't made any post-processing!

Unfortunately, my computer is not grounded, i was very tired (a stupid excuse for my poor playing) and, from mysterious causes, i got on some settings a strong feedback (even i shutdown my speakers!!!).

On all soundclips the switch SW2 was off (the whole LPF was connected) because i couldn't here serious differences with it on or off and the gain pot was at maximum.

The soundclips:

1. SW1 off (low gain - 1M resistor is not shorted) and guitar volume at 10: http://www.aronnelson.com/DIYFiles/up/low_01.mp3
2. SW1 off (low gain - 1M resistor is not shorted) and guitar volume at  5: http://www.aronnelson.com/DIYFiles/up/low_02.mp3
3. SW1 on (high gain - 1M resistor is shorted) and guitar volume at 10: http://www.aronnelson.com/DIYFiles/up/high_01.mp3
4. SW1 on (high gain - 1M resistor is shorted) and guitar volume at  5: http://www.aronnelson.com/DIYFiles/up/high_02.mp3

[gigimarga]

I forgot to say that on every clip i cycled through all the positions of the pickup switch.

[dschwartz]

it sounds fantastic , even directly to the sound card..
did you boxed it up?

[gigimarga]

Yes, it sounds fantastic...i've tested it today on a full tube amp (a clone of a Soldano) of a friend of mine, using a mexican Fender Strat at 50-70W and sounded amazing.

I didn't boxed it yet because i don't have any boxes and footswitches (it's impossible to find here these...) and because i've built it on a Hot Harmonics PCB and it looks very strange (some resistors/capacitors are soldered on the legs of the pots)...i'm waiting for an official PCB

[zencafe]

Sweet!!

Thanks a lot for the samples! I'm really really glad if you liked my distortion... specially after reading that you were a bit disappointed with some 4049 projects.
I'm a bit consurned about the oscillation though... you could try changing the 4049UBE.
I'll post the PCB soon, I'll update it as soon as possible!
It maybe that since your guitar doen't have a too hot signal, you don't generate enough harmonics saturating the cmos, so the difference between the LPF is not that big...

Didn't you dschwartz get a very strange and strong oscillation with a Hot Harmonics too?
Wired, since I've haven't had any issues with that, even in breadboard and with very hot signal pickups

Regards.

Doug.

[dschwartz]

yes, i had an oscillation near max position of the "octave " control of the hot harmonics, it was excess of highs, since when that pot is set to max, well it seems to bypass the treble cut cap. well, that Octave pot has a very akward configuration.. can someone explain it a little?

i used this schem from Gauss-god-markov:

[zencafe]

What do you mean by configuration?

As far as I see, is connected in the same way as the gain control: On one position the pot acts as a 100k feedback and 0 ohm input resistor, that mean lots of gain (Av = Rf/Ri) and in the "other" it acts as a 100k input, and a 0 ohm feedback resistor. I've seen the same configuration in many op amp based pedals.
I think the oscillation must be related with the feedback... did you try removing that 2M2 feedback resistor?

Saludos Daniel!

[snap]

Remove R7: even more gain!

[zencafe]

Mhh, never said that it oscillated because of an excess of gain, honestly doubt it.
If you see the Microtubes has much bigger feedback resistors, and at least, It hasn't oscillated in any tests I've made...

[gigimarga]

I can't understand how near my computer speakers, at a very low level (maximum 1/2W!!!) i get the oscillation and on my friend's amp, at 50-70W, i don't get it!!!

[zencafe]

Mhh wierd... did you use shielded cables?

[dschwartz]

i heard that oscilation on the demos..probaly RF noise induced by single coils , also near a PC monitor..if you hear well, oscilation is greatly reduced on intermed positions (2, 4)

[zencafe]

Yeah, It must be that... I've tried it with a Squier Strat with fender pickups, even though the noise level was high, it didn't oscillate...
I think it could be some RF leaking somehow... but the feedback caps are big enough and should cut them.
I'm now working on the PCB, I'm having some trouble with the Eagle 2 PDF part...  .

[gigimarga]

dschwartz you're great!!!
I have the same problem with another effects and now i know why: the PC monitor!!!
On the 2/4 positions there was almost no oscillation...
So, no problem with the oscillation...only a stupid mistake of mine!!!

Great sounding effect...it's no.1 in my top of 4049...thx a lot zencafe!

[zencafe]

Thank you for building it, and uploading samples .

[WGTP]

Thanks gez for the output Z info.