Rebote 2.5 Built! . . . Hiss when activated.

[fazer]

Ok.  I've recently built a Rebote 2.5 delay using a layout from Tonepad.  First attempt did not work.  I reallized that I used 2.4K Ohm Resistors instead or 24K Ohm resistors.  I replaced them and it worked!  The only problem now is that There is a Hiss when the pedal is activated. It is enclosed.  There was also a large boost in volume, which I think is linked to the hiss.

-I removed the millenium bypass and hooked it directly to the dpdt switch.  Still hiss.
-I remelted EVERY solder point.  That helped a little.
-I replaced all the ICs including the 78l05 with different ones (I used sockets). No real change.  Maybe more volume boost . . .maybe
-I bypassed the switch (Carling) directly to the jacks.  Same thing.

Could it be the caps?  there are 6 electrolytics.  3 - 1mF and 3 - 47mF.  I have one Sprague Cap that is the only ~50pF cap I could find around. Everything else is polyfilm. Is there anything else I should be looking for?

I have put an audio probe around the circuit and I noticed that some parts of the circuit seem to be noisier than others.  I have to trace out the signal path to try to pinpoint where this is coming from.

Any help would be appreciated.  Thanks guys.

[Morocotopo]

Funny... when I finished mine, I also noticed some hiss when on. Maybe the delay chip doesn´t have very good audio specs (sample rate, bit depth, dynamic range)? What I know is that the other delay project that uses this chip (PT-80, I think) uses a compander chip, to get better audio specs. Food for thought.

Morocotopo

[DuncanM]

Does it still hiss with the delay level pot turned down?

i.e. does the hiss come from:
a) the delay section or
b) the input section or the output section
So,
If the hiss goes away when the delay level is turned down - check the resistor values around the 2295 pins 13-16.

If the delays come back at a similar level to the direct signal with the delay level maxed - then the problem is with the gain around IC2a or IC2b.
Check the 510k resistors around IC2b and the 24k resistors around IC2a

If the delays come back quieter than the direct signal with the delay level maxed - then the 24k resistor between IC2b and IC2a is too small (maybe 2.4k?).

Too much gain somewhere...

[blanik]

sorry guys, it's not the chip, mine works perfectly without hissing... maybe you got some cap or resistor wrong...

R.

[markm]

sorry guys, it's not the chip, mine works perfectly without hissing... maybe you got some cap or resistor wrong...

R.

I agree.
My suggestion is to double-check polarity on the electros, they hiss when reversed!

[fazer]

All the polarized caps are facing the right way.  I'm trying to trace the signal from input.  I do get a low input signal.  Somewhere along the line it gets boosted.  What should I leave the Level pot at when tracing?  I come at a dead end at the 33k Resistor above IC2.  One side there's signal, the other side of it, I get none.

[DuncanM]

I come at a dead end at the 33k Resistor above IC2.  One side there's signal, the other side of it, I get none.

That'll be normal - one end of the 33k resistor is connected to the inverting input of IC2a which will be a virtual earth.

The signal level at pin 1 of IC2 should be the same as the signal level at pin 7 of IC2.
And they should both be the same level as the input signal.

[fazer]

Well. I made progress.  I replaced the op-amp back to an nte 588 that I had lying around. The 4558 was gaining too much I presume because I was using that when I resoldered all the joints and never went back to the other op-amps.  The nte588 is MUCH quieter.  There is still noise introduced when raising the delay time, but from what I hear it's normal.  The noise is low enough to play a show at this point.  Probably not studio level.

There is still a little volume boost when the effect is engaged.  Is this something related to the opamp or the resitors around it?

[markm]

Mine doesn't have any type of Volume boost, it's unity.
I think you may still have some issues 'cause mine is very quiet as well.

[fazer]

OK.  So do I look across the 5V regulator? I tested all of the resistor values by pulling them out.  I don't have a capacitor tester, but I do Have acess to one at work.  How would I know if it's a leaky cap?

[blanik]

the noise your talking about, i'm not shure how you rate "not studio ready" and "OK for a show", but you got to realize that the PT2399 has noisy repeats, i was a bit dissapointed at first but with an OD or dist. you don't really ear it... the PT2399 is a bit like old tape echoes, it's noisy but damm does it sound tripping!!!! 

it's not wour average clean digital delay à la DD-3 or somethin like that, it's just dirty and cool 

R.

[smank]

The PT2399 it's not a clean delay, but it sounds more like an analog one.
If it appears too noisy, try to check how the chip is inserted into the socket: on mine before insert it better, it was very noisy and distorting.
I confirm my rebote is quiet and unity gain.

I agree with blanik: great delay, far better than "clean digital delay à la DD-3 or somethin like that" !!!

[Pushtone]

What wattage is your amp?

I built the Tonepad Small Clone Chorus. I perceive it as silent with my 30 watt amp
but there is some background hiss with a 100 watt amp.

I find the same thing with PA systems.
An old SPX90 is silent when used in a small PA with less than 2200 watts total power.
But its very noisy when used with a large rig with 50,000 watts of total power.

[markm]

I'm using mine through a Twin Reverb.....there's some power!
But, I also use a Tele and, it's probably got some of it's own noise!

[fazer]

Well.  Right now it's running through a 65 watt fender princeton solid state.  I haven't tried it on a more powerful setup, but maybe that's it too.  It's really not a problem anymore with the noise so much as the volume gain, which is a little lower now anyway.

Don't get me wrong guys.  I love the sound that somes out.  I was just disappointed for a while that I couldn't play it without hearing that noise in the background.  Between repeats there is a little dirt but that's perfectly ok.  I know how cold-sounding other digital Delays can be like and if that's the compromise, then so be it.

[blanik]

there's still something robably wrong about yours, cause the noise is only present DURING the repeats (on the longer delays), it sounds like a slight white noise surrounding the repeated note, between the repeats, it's dead silent, this white noise was surprising (dissapointing at first) cause i was used to the cold and clean DD-3 but after playing for some time on it (and specially with a little "driven" sound) i don't really notice it anymore...

and for the level, when i was playing live i had slight problems hearing it well but i changed the 33k resist (middle lug of level pot --> 1 uF cap --> 33k) to a lower value 20k or 22k so the effect level is louder now so it gives me more control on the level pot...  if you mean your dry signal becomes lower than it's probably something else...

R.

[smank]

I use my rebote trough a 20W 6V6 DIY amp and a 100W Marshall head: I confirm it's quiet.

In order to reduce distortion/noise in larger times, I've increased the value of the 3 caps around the filter before the delay stage (around pin 15-16 of the PT2399).

27n     -->  33n
10n     -->  12n
560pF -->   680pF

The repeats are a bit warmer... but the sound is great!

[blanik]

isn't "warmer" just a positive twist on "tone sucking"? don't they both mean "less highs"?   

R.

[lovric]

blanik - exactly!

hey fazer, too much gain might come either from outside OPAmp or the one inside the PT chip. roughly - the bigger resistor in the feedback loop of an OPA, bigger the gain. you might have to lower those resisstors. check the ground - only one ground wire should connect to the PCB.

[smank]

OK, less highs... 
But this little incresasing in caps value is acceptable (and good sounding), removing a bit of distortion/noise on the repeats.