Taming a rogue Highway 89.

[RobB]

I’ve built Doug Hammond’s Hwy89.  The overall tone is correct but the output level and distortion controls of my build are almost unusable.  It’s way to loud and distorted.  Doug’s said his sound clip was recorded with the gain control turned up full but my build produces that sound at about 9 o’clock.  Also, I seem to get unity gain with the level control at about 9 o’clock.  The controls are very touchy, this doesn’t seem right.  Think I’m going to need some help with debugging.  

I’ve double checked all the component values.  DC voltages at the (collector, base, emitter) transistors are as follows.  
Q1 (5.1,1.7,1.0)   Q2(9.6,1.6,1.2)   Q3(4.2,1.2,0.5)

With all controls set at 12 o’clock and a 10mVrms sinusoidal signal being fed in I measured the following (rms) voltages.  
250mV at the junction of C3 and C4.
147mV at the emitter of Q2 (still fairly sinusoidal)
3.3V at the level pot (very clipped at this stage)!

Typical gains of my batch of 2N5089s are around 650.

I’m looking for a warm moderate gain "blues" overdrive, which I’m sure this pedal can deliver.  Any ideas/suggestions?

[petemoore]

Is that connected to the pos power rail?
 if not it looks misbiased...

[RobB]

Yes, the collector of Q2 is connected directly to 9V as per schematic.

[csj]

deleted

[Chico]

I have a similar problem.  The treble, bass and gain sound about on the mark, but the output volume is incredible.  To get the output approximate to the bypassed volume, my output pot is barely cracked (between 8-9 oclock)

Have others addressed this issue?  I have heard of a revised schematic.  Can anyone characterize the changes?

Thanks

[Doug H]

Make sure you are using a log taper pot for the output pot.

Doug

[RobB]

Thanks Doug.  Just double checked that.  It's log 500k.

I've socketed some of the resistors and I'll have a play around with biasing some time this week.

Is there a way to tone down the treble boost of the input section?  I'd like to experiment with this at some stage too, but haven't found any posts regarding mods or alterations to the Brian May treble boost anywhere.  I suppose altering the value of C3 will make a difference here.

By the way, yes I am working from the corrected schematic.  

Looks like I'm not the only one struggling with this build.