Triangular Ear Bass 21 (Sansamp BD) mystery!

[luckis]

Hello all.

I´ve been building pedals a lot for some years now. I proud myself in being very tidy and exact, and so, i have only encountered very few problems in my builds. They usually work perfect at the first try.

But there is a mystery with this build that haunts me to this day 

I started building two of these, to find that one of them had a magnificent sound, almost identical to the original, and the other was very different. It lacked mids, presence, volume, and the drive sounded weak and muddy.

At first i thought a problem with componets of course. But i studied the board a hundred times, everything was good and working. No differences with the other one. I replaced IC, reversed them with the other pedal, changed pots, jacks, switchs, everything. To no avail.

Furthermore, i´ve built two more of them and they all sounded as the second one too  I´m starting to think that the peculiar one was the good-sounding one 

any thoughts on this??

[garcho]

Read this.

[luckis]

Right. Will do the homework and report back

[duck_arse]

post photos!

[luckis]

Ok, here we go, tidy tidy. Used the only one of three different boards with the same problem i built that is still assembled whole.

Project: Tech 12 bass driver (PCB by 12afael)

Link: http://sites.google.com/site/plexilandia/tech12bassdriver.zip
Tried both this pcb and the relayout done later by Ruz guitar Gear, same problem.

Mods: Tried both tl071 and 74 as the schem says and also tl2262 and 2264.

No bridges or bad traces, checked a thousand times in the two or three board i made

Substitutions: TL2264 and 2272 instead of the TL072 and 074, but also checked before with original ics, same problem.

IC1
1= 4.37
2= 4.37
3= 3.97
4= 8.79
5= 4.29
6= 4.51
7= 4.39
8= 4.37
9= 4.40
10=4.38
11=0
12=4.20
13=4.37
14=4.38

IC2
1= 4.37
2= 4.37
3= 4.34
4= 8.74
5= 4.38
6= 4.37
7= 4.34
8= 4.37
9= 4.36
10=4.34
11=0
12=4.35
13=4.37
14=4.36

IC3
1= 4.37
2= 4.37
3= 4.36
4= 0
5= 4.34
6= 4.37
7= 4.34
8= 8.76

IC4
1= 4.37
2= 4.37
3= 4.36
4= 0
5= 4.34
6= 4.37
7= 4.34
8= 8.76

VOLTAGE OF dc at the board: 8.76

Another thing i vaguely remember, on which i will have to report later, is that the pots on the failing units seemed to give lower values than on the good one, like, 10, 15k lower (they are all 100k pots) but i have no exact numbers on this.

[pappasmurfsharem]

Pots generally have a 20% tolerance. So that can explain your seen values.

[luckis]

Yeah, but strangely i swapped all the pots with the ones in the unit that sounds good, and even bought a new set, and the all seemed to lower the values when connected to the pcb   

[induction]

Do you mean you measured the resistance of the pot while it was connected to the board? If so, it's not surprising that the value would go down because you're measuring it in parallel with whatever other components they connect to. Does that not happen on the good sounding one?

[luckis]

Right. I just double checked this and came up with the following values.

                  Good one            Bad one

Level          103.5/104           88.4/80.6
Blend         102/101.7           93.1/92.6
Treble       102.7/102.8         96.3/96
Bass          106.6/96.3          103.5/94
Drive         88.2/0                 76/0
Presence   106.4/0               83.5/0

The values are "pot on 0/pot on 10"

As you can see there is a notable difference in general. And this may be a coincidence or not, but the pots that have the most difference (presence and drive) are the ones that control the parameters that sound different to the ear (as i said, the bad unit sounds muddy and the drive is less notable)

Why could this be? I changed pots a lot of times, even swapped them between units, they read fine when not connected (100k) but they change the values when connected.

[PRR]

> change the values when connected

Then not the pots. Whatever they connect-to.

[mremic01]

I have the same issue with pretty much every build. They tend to sound different from each other. Most sound kind of the same, but some sound way off. Sometimes that's a good thing, sometimes not. The only explanation I've ever heard for this is component tolerances.