PT 80 Delay Volume Tone Issue

[jcbak]

Recently built the PT 80 Delay from GGG.com.  Works fine with the exception that when engaged, there is a slight drop in volume and a thinning of the tone.  It's not huge, but noticeable.  The pedal seems fine in every other way.  Any suggestions?

[oskar]

Ok. From the GGG-schematics there is a 10k resistor providing feedback on the last OP-stage. If you want to increase volume
increase the value of this one or put in a trimpot and tweek it.
This fix doesn't take into account possible errors in your circuit making it sound lower than it should, maybe it's operating just
as it should, it merely provides gain.

[jcbak]

Thanks for your response.  I'm too new at this.....(2nd pedal).  I'm still trying to learn how to read a schematic and match it to the layout diagram and identify what is what.  I'm not sure what resistor you're referring to....sorry.  If I can figure out which one it is, do you have a suggestion for its replacement?  As an alternative, I have a small trim pot but have no clue how to integrate it with the pcb since there is no spot for it.  (I know how stupid I sound.  I apologize). 

[oskar]

I'm not sure what resistor you're referring to...

If I can figure out which one it is, do you have a suggestion for its replacement?

If you double the size, you'll double the output. probably 12 - 15k is a good place to start.

As an alternative, I have a small trim pot but have no clue how to integrate it with the pcb since there is no spot for it.

Glue it!        ...or just go with a fixed resistor.

[oskar]

Hi again and wait a minute!
The way I interpret the schematic, there should be plenty of gain through the circuit ( I haven't tryed this pedal myself ).

If you compare the signals.
1. Bypassed
2. Effect on. Delay level all the way down.

Signal 2 should be an amplified clean signal audibly stronger than the bypassed

[jcbak]

Nope......tried it......it is somewhat lower in volume.  Like I said the difference isn't huge....but it is noticeable....

[jcbak]

Changed the resistor to a 12K....no luck.  There is still a drop in volume.  It must be somewhere in my build, but I don't know where it could be.   Any suggestions??  Anyone??

[Thomeeque]

Hi again and wait a minute!
The way I interpret the schematic, there should be plenty of gain through the circuit ( I haven't tryed this pedal myself ).

From dry signal point-of-view there's not much gain between very input and output of circuit. Input buffer boosts only high frequencies (which output buffer cuts back)*, resultant gain should be approximately 1 (frequency responses of input and output buffers does not match exactly, but difference is probably not very dramatic**).

*This is often used added-noise reduction trick, mentioned even in PT-80 building instructions. Btw. by changing "This one!" 10K resistor you de-tune this mechanism, changing (lowering) of input 10K resistor (between [A] pad and (-) node of op-amp) is the save way, how to boost dry signal.

If you want to simply count gain for concrete frequency, replace 0.015 caps by resistors with R = 1000000/(2*pi*0.015*f) (e.g. cca 100K for 100Hz; 10K for 1kHz; 1K for 10kHz)

** EDIT: I have made mistake, frequency responses of input and output buffers match exactly (or better said are in exact contradiction - the level of treble boost of input buffer is exactly same as the level of treble cut of output buffer at each frequency..) 

[Thomeeque]

Recently built the PT 80 Delay from GGG.com.  Works fine with the exception that when engaged, there is a slight drop in volume and a thinning of the tone.  It's not huge, but noticeable.  The pedal seems fine in every other way.  Any suggestions?

Hmm, dry signal path is very simple, just input buffer with treble boost and output buffer with treble cut (read my previous post for details). So maybe start with simplest thing, try to replace dual op-amp used by these buffers (TL072). Then check values of parts around these buffers.. maybe post sound sample (bypassed and engaged with delay level at 0), we'll see.. good luck!

[oskar]

Btw. by changing "This one!" 10K resistor you de-tune this mechanism, changing (lowering) of input 10K resistor (between [A] pad and (-) node of op-amp) is the save way, how to boost dry signal.

-Oops!

[oldschoolanalog]

Try putting a 1k resistor in series with the output. Right at the board. I had the same volume drop problem w/my PT80 and this worked. Use the search function; PT80 volume drop. The explanation is in there somewhere.
Dave

[jcbak]

The thread dealing with the PT80 volume drop addresses issues with an effects loop.  I'm not using one.

[oldschoolanalog]

I wasn't either. Trying that suggestion would take you less than 5 minutes.
Your call.

[jcbak]

Are you referring to this fix:  On the schem look above the opamp you will see

"1K series with .015 uF
10K
47 pF

Change these to

5K series with .003 uF
50K
10 pF"

or this one:

"Another thing to try is insert a 1K series resistance between the PT-80 board and the output jack."

[oldschoolanalog]

"Another thing to try is insert a 1K series resistance between the PT-80 board and the output jack."

This one.

[RDV]

FWIW mine actually boosts and beefs up the tone as well. I've been using it live since I replaced a defective switch. Mine is an older version with the Millenium 1 bypass.

RDV

[jcbak]

Forgive my ignorance.  Where on the board does the 1K resistor get inserted???  I know...I'm a idiot.

[jcbak]

Unless I'm reading it incorrectly....the output from the board (labelled "O") goes to the footswitch then to the output jack.  Would I insert one side of the resistor in the board at what I think is the output and attach the other end of the resistor to the wire running to the footswitch??

[oldschoolanalog]

Unless I'm reading it incorrectly....the output from the board (labelled "O") goes to the footswitch then to the output jack.  Would I insert one side of the resistor in the board at what I think is the output and attach the other end of the resistor to the wire running to the footswitch??

Yes, that should do it. 

[jcbak]

Tried it.....didn't change anything.  I obviously screwed something up in the build somewhere.