Dowtown fuzz/EHX octave multiplexer : how to increase 1st sub octave volume ?

[eh la bas ma]

Hello,

I built a Dowtown Fuzz sometime ago :

https://lectric-fx.com/wp-content/uploads/2019/09/Downtown.pdf

I am looking for a mod, to control the 1st sub octave volume, if it is possible.

Even with the Blend fully CW, I find the 1st octave to be too quiet, not enough presence.
If I switch on 2nd octave, I can definitly feel the difference, the octave signal is much more noticeable.

I'd like to be able to hear the 1st octave just as clearly as the 2nd.

The schematic is big and complex, I don't understand where the first octave is "made"  and how to boost the effect.
What would be the simplest way ?

Any help would be welcome !

[Scruffie]

A couple of people mentioned an overall lack of volume in which case I recommended changing R4 to 62k and someone did say it helped with the feel of the overall blend.

If you watch demos of the original, that is sort of how it works, IIRC we did try tweaking the level of the individual octaves (R44 for the lower) but the octave blend would be uneven afterwards.

[amptramp]

On the right-hand side of the schematic, you will see a CD4013 dual D-type flip-flop.  Every time it gets a clock pulse from the LM311 comparator, the Q and /Q outputs change state.  Since two puises take the output back to where it started, this gives an octave down.  The upper flip-flop give the first octave down and the lower gives the second octave down since it is triggered by the output of the upper one.  The first octave output is labeled "B" in the schematic and it goes to a voltage divider made by R40 and R41 that drives a JFET.  The JFET output goes to an op amp that drives the subharmonic pot.  The first thing to do is check whether this pot is adjusted properly since if the slider is in the low position, it will favour second suboctave over first.

Changing R41 and R42 values may help or maybe swapping the 2N5485 JFET's would give you the opposite problem - more first than second suboctave.

[eh la bas ma]

Thanks for your replies!

I tried to change R4 (120k) to 68k (no 62k on hands). It felt like something was off-balance, I think the octave tracking became worse than usual, even more glitchy. No obvious improvement anyway, I put the 120k back...

I reflowed the sub harmonic pot, while it was screwed in position on the enclosure.
I didn't try to change R41 or R42 yet.

I forgot to put back Q1 during a test, I noticed it didn't make any obvious change with or without it...Could it mean there is an issue somewhere on my build ?

Edit : readings on Q1, pedal powered and switched off :

C= - 8.28 V
B= 0 mV
E= 0 mV

[Scruffie]

Thanks for your replies!

I tried to change R4 (120k) to 68k (no 62k on hands). It felt like something was off-balance, I think the octave tracking became worse than usual, even more glitchy. No obvious improvement anyway, I put the 120k back...

I reflowed the sub harmonic pot, while it was screwed in position on the enclosure.
I didn't try to change R41 or R42 yet.

I forgot to put back Q1 during a test, I noticed it didn't make any obvious change with or without it...Could it mean there is an issue somewhere on my build ?

Edit : readings on Q1, pedal powered and switched off :

C= - 8.28 V
B= 0 mV
E= 0 mV

R4 increases the input gain so you would need to adjust the sensitivity control after adjusting it, but perhaps it just wasn't for you. I can't see why it would help balance, it was just what someone else reported 

Q1 feeds the current in to the compressor section (CA3080) of the fundamental extractor, that section is important... if you audio probe IC1 pin 7 with it installed you should hear, well, a compressed version of your input signal.

[StephenGiles]

Thanks for your replies!

I tried to change R4 (120k) to 68k (no 62k on hands). It felt like something was off-balance, I think the octave tracking became worse than usual, even more glitchy. No obvious improvement anyway, I put the 120k back...

I reflowed the sub harmonic pot, while it was screwed in position on the enclosure.
I didn't try to change R41 or R42 yet.

I forgot to put back Q1 during a test, I noticed it didn't make any obvious change with or without it...Could it mean there is an issue somewhere on my build ?

Edit : readings on Q1, pedal powered and switched off :

C= - 8.28 V
B= 0 mV
E= 0 mV

The octave tracking should be excellent and fast - at least it was using CA3094s in my guitar synth build adaptive filter, so something may be amiss in your build.

[eh la bas ma]

Here is a sound sample of my build.

https://soundcloud.com/ehlabas-ma-chaussure/dowtown-samplewav

Can you please confirm if something sounds weird ?

First clean guitar, then 1st octave (Sub at 9', Blend and Sens. are fully CW), playing a bit with Tone, then fuzz, then 2nd octave (Sub at 12')... bass switch always down exept for the last few seconds in the end (1 : 35).

[StephenGiles]

Ah yes, you see there isn't a frequency control loop as in the guitar synth, so you are going to get poor tracking. You need the 4030 frequency doubler, those 4047s with VCO 1 and VCO 3 from the guitar synth for the control loop to provide a stable signal for octave dividing - what do you think Scruffie?

[Scruffie]

Here is a sound sample of my build.

https://soundcloud.com/ehlabas-ma-chaussure/dowtown-samplewav

Can you please confirm if something sounds weird ?

First clean guitar, then 1st octave (Sub at 9', Blend and Sens. are fully CW), playing a bit with Tone, then fuzz, then 2nd octave (Sub at 12')... bass switch always down exept for the last few seconds in the end (1 : 35).

It's difficult to hear, but it does seem a bit thin and buzzy...

What output are your pickups? Usually you wouldn't need the Sens cranked up unless they were quite low output.

Did you manage to audio probe the compressor section?

Ah yes, you see there isn't a frequency control loop as in the guitar synth, so you are going to get poor tracking. You need the 4030 frequency doubler, those 4047s with VCO 1 and VCO 3 from the guitar synth for the control loop to provide a stable signal for octave dividing - what do you think Scruffie?

The tracking in the Deluxe is quite good, not identical to the guitar synth but comparable, the 311 after the fundamental extractor is set up as an oscillator and the 311 from the compressor envelope mutes it off so it sort of works in a similar fashion.

[eh la bas ma]

I can confirm i have a signal on IC1 pin 7. It is quite louder than the signal on the IN jack's tip, and slighly distorted.

The guitar i am using on the sample has active hambuckers pickups.

I don't need to set Sens. fully CW, 9' would work. I set it fully CW because the octave sounds a bit more noticeable.

Are the voltage readings on Q1 looking ok ?

[Scruffie]

Should be loud and hopefully noticeably compressed? But Q1 is fine, yes.

Pretty late here so I'll come back to this thread tomorrow.

[eh la bas ma]

Should be loud and hopefully noticeably compressed?

I think so, but here is an other sample, just to make sure :

https://soundcloud.com/ehlabas-ma-chaussure/audio-probe-pin-7-ic1wav

First, I audio probe the IN jack's tip and then IC1 pin 7. Caution, big volume boost at 0:29'. Sound is a bit scratchy because my hand isn't really steady this afternoon, the probe is slighly moving, so it 's not always clean.

Controls are set : Sens at 12'  Sub = 9' Blend = 2' Tone = 11' Fuzz = fully CCW (no fuzz)

[Scruffie]

Should be loud and hopefully noticeably compressed?

I think so, but here is an other sample, just to make sure :

https://soundcloud.com/ehlabas-ma-chaussure/audio-probe-pin-7-ic1wav

First, I audio probe the IN jack's tip and then IC1 pin 7. Caution, big volume boost at 0:29'. Sound is a bit scratchy because my hand isn't really steady this afternoon, the probe is slighly moving, so it 's not always clean.

Controls are set : Sens at 12'  Sub = 9' Blend = 2' Tone = 11' Fuzz = fully CCW (no fuzz)

Can't quite hear the delayed attack I might expect from the compressor, but I think it's working from that clip.

Have you tried any of the suggestions earlier in the thread yet? If you either increase R44 or decrease R42 (same effect) that should give the 1 octave a bit more level.

Amptramp also suggested reducing R41, not something I've tried but worth a shot.