zw44 volume too low

[sfb]

Just finished an Zakk Wylde OD and it´s too quiet. What could be the problem. I checked all components and they seem to be ok. I used MPSA13 and TL072.
All pots dimed i get about half of output than bypassed. Battery voltage is 9.06
Here´s the schematic:

http://analogguru.an.ohost.de/193/schematics/Mxr_ZakkWylde.gif

[Govmnt_Lacky]

Pictures are worth 1000 words! Pictures of the PCB/Vero would help. 

[sfb]

Sorry. There´s no camera in the house.

I used this layout (and pcb).

http://2.bp.blogspot.com/_XBLxtjUxez0/SZwCdQS6yQI/AAAAAAAAAC8/NkQ3SfFs7Vo/s1600-h/ZW44.bmp

[Govmnt_Lacky]

You mention that you get half of the bypassed volume with "All pots dimed." Could you define what you mean? Do you mean with ALL pots turned all the way down? What does "dimed" mean?

This circuit was designed around the MC33718 chip. Might be that chip has a higher output than the TL072 that you subbed.

Also, this might just be a matter of adjusting the Volume out pot to unity match the bypass.

Need more details (i.e. pot positions, gear, setup, etc.)

[anchovie]

What does "dimed" mean?

A dime is ten cents, so it means the control knob is set to 10.

I doubt it's the op-amp substitution as gain is set by R4 and VR2+R6.

Is it actually distorting, or is it clean as well as quiet?

[sfb]

Pots are maxed. I also tried 4558 but no help. What do you mean adjusting volume pot? Swapping it? 100kA?

Oh. New post. It has distortion but i think there should be more.

[anchovie]

Read the "What to do when it doesn't work" sticky topic and post voltages as requested.

[petemoore]

  Anchovie's suggestion: For quickest, easiest results, for reliable problem locating, solution finding.
  Electronics is about reference points and potentials, bias voltage measurements allow analysis of whether they could operational [locating the problem].
  Solution generally pops up about this time, or, another reading or probing is required and provided first.

[sfb]

Voltages:

TL072
1: 4,21
2: 4,21
3: 4,20
4: 0
5: 4,13
6: 4,18
7: 4,17
8: 8,35

MPSA13
1: 7,02
2: 8,01
3: 8,45

Seems funny to me. I rotated MPSA13 180deg. and it still works? I watched some videos on youtube and I don´t have that much distortion.

[petemoore]

  MPSA 13 MPSA13 Datasheet pdf - Darlington Transistors -
www.datasheetcatalog.com/datasheets_pdf/M/P/S/A/MPSA13.shtml
 Darlington bipolar, has two diodes, when biased the Base will be above emitter by at least 1 diode drop and the collector is connected to V+.
 This is an emitter follower, so the emitter should be well above Gnd. to allow signal voltage swings in both directions from the in-the-middle-ish of supply bias point. If 9v battery is used, that'll be somewhere near-ish 4.5v, or 1/2v of supply.
 V+ potential from ground is the reference point by which all other voltages are some...smaller number, the battery or supply voltage allows calculation of all the other voltages and is required, although it can be assumed it is at least at least that of the highest measured...
 Measure each resistor ''as far away as possible'' [follow the schematic and find a distant-point contact, this includes the debugging of cold solders at the same time the resistor value is measured], and compare measured value to what's shown on schematic.
 No swing room on the darlinton [the emitter is near supply] is blocking signal path, a good place to concentrate efforts.
   The voltages on the opamp look to be operational [the inputs and outputs are around 'middle' of the supply = 1/2v supply].

[Govmnt_Lacky]

Not to get off point but, I noticed on the layout that the GAIN calls for a 1MD pot. What kind of taper is "D"? I have not heard of that.

sfb,

Are you using a "D" taper pot?

[sfb]

I´m using 1MA pot. Whats the difference?

[Govmnt_Lacky]

I do not know, off hand, what the difference is but I am just wondering if this may be contributing to your problem.

[sfb]

Reality check. It seems that there is not enough gain. I can get clean sound out of it on low settings. Low gain causes low output. I checked all soldering and they were fine.

[Govmnt_Lacky]

I am going to have to side with pete on this one. Verify your trannys are in the right spots, properly oriented, and you may want to include the voltages of the 5088 as well. If you socketed your trannys and all the voltages work out and you are running out of options.... swap them bad boys out.

[Govmnt_Lacky]

Also, according to your layout, I am having a hard time understanding what the switch is for between the 5088 grounded emitter and it's base. Can anyone chime in here and answer that?

[petemoore]

  As long as you have a range between 0.0ohms [or so] and 1meg [or so], the circuit will have full function of gain range, the knob might 'work funny'...gain increasing near one end of rotation.
  Otherwise the MPSA 13 is still blocking signal path ?
  Something is pulling the Base/emitter up by the V+, perhaps emitter resistor is floating or wrong value ? Some erronious connection to V+ ?
  Measure all resistors around transistor that is misbiased.
  View the data sheet of MPSA13 to re-verify it's pinout is correct.
 

[CynicalMan]

If you can't get this going, I'd just take out the MPS-A14 and related parts and wire the input directly to the 18n cap. The input impedance will be 100k, which isn't low enough to make a noticeable problem in a circuit like this.

[sfb]

I am going to have to side with pete on this one. Verify your trannys are in the right spots, properly oriented, and you may want to include the voltages of the 5088 as well. If you socketed your trannys and all the voltages work out and you are running out of options.... swap them bad boys out.

I don´t have 5088 at all. I have tbp so left those parts out. Sorry I forgot...

[sfb]

If you can't get this going, I'd just take out the MPS-A14 and related parts and wire the input directly to the 18n cap. The input impedance will be 100k, which isn't low enough to make a noticeable problem in a circuit like this.

I tried this and gain and vol increased. But I like to have all those parts in circuit working as they should.