AMZ Muffer Troubleshooting

[Flynn]

I've breadboarded the muffer circuit (this one:  http://www.muzique.com/schem/muff.gif) three times today.

Double-checked transistor pinouts and connections. 

I did not include the diodes and C3 so it should be a clean boost.  But it's coming out seriously distorted even with volume backed down.

(Yesterday I did a tape sim circuit with dual power and 3-4 times the part count and no problem...but this little guy is taxing me!)

From ground i measure the following on the 2n3904:

Collector -  7 volts
Base -       .63 volts
Emitter -    .02 volts

Using polarized tantalums for the input and output caps.  Checked polarity.  Even bypassing them doesn't change it much.

Strong 9volt battery through a 10k resistor to the Collector.

Would love any suggestions on how to troubleshoot this guy...

[Quackzed]

make sure r4 is 150 ohm not 150k? double check the pinout of your npn transistor? though the voltages look ok. r1 could be a cold solder joint? might mis-bias the base and cause the issue...

[Flynn]

Thanks Quackzed,

Definitely a 100 ohm (not 150 ohm like on schematic).

Working on a breadboard so no solder yet.

Checked the NPN several times.

So those voltages do look ok?

[Quackzed]

yea, generally the bass will be @ a diode drop above the emitter, since the emitter is very close to ground as it should be with 100 or 150 ohm resistor, the base at .63v looks right on. and the collector will be a little less that the battery + due to the series 10k resistor... i might try swapping the 100 ohm with a 1 k just to see if that changes anything, if not i'd try some different caps .01 or .1 or whatever you have handy just to see if the tants are shot. i believe they're not very tolerant of reverse voltage, so they may be a likely culprit if everything else checks.. .

[PRR]

Check values *and ratio* of R2 and R2.

Your voltages suggest if R2 is 470K as planned, R1 must be nearer 50K than 100K.

[Rob Strand]

Check that you haven't got C an E reversed.  (When you look at the pinouts make sure you are view from top or bottom.)

[Flynn]

Hey thanks to you all for the input.

I broke it down again and tried things in different holes on this old breadboard.
Changed 100ohm to 150, also found my 10k was the wrong value.
Placed a 10uf electrolytic on the input.
Put a non-pole tantalum on the output.

Things are working MUCH better, though I do have a couple of questions...

When I max the clean boost it starts to sound like a bit-crusher.
When i engage the distortion there is a significant drop in level.

I also added an extra layer of 1N34A diodes after the 1N914s.  This increased level slightly and compressed things more.

Here's an audio clip i just did.  I put notes there, but here's a rundown:

1st Segment - clean boost and i increase the level as it progresses.  You can hear the bit-crushing at the end of it.
2nd - Distortion engaged (per schematic), increasing boost as it goes
3rd - Extra diodes, increasing boost as it goes

https://soundcloud.com/user-342548702/muff-test-11-20-16

Transistor now has the following voltages:   

E = .06 
B = .6 
C = 4.84

[Flynn]

By the way, added a 1.5k resistor in series with the diodes and it boosted the volume a bit and removed some of the 'splat-iness' of the distortion.

[Flynn]

Hello All,

Mr. Orman was kind enough to make some suggestions regarding the questions I had and I wanted to re-post them here in case they're of help to others:

>>When I max the clean boost it starts to sound like a bit-crusher.

You are running out of headroom. The signal level is larger than the transistor can supply on a 9v battery. Use two 9v batteries in series for 18v and it will sound cleaner.

You could also add a 33k resistor in series with the input and this will reduce max gain and spread it over a more usable range.


>>When i engage the distortion there is a significant drop in level.

The diodes are clipping the signal peaks as they are meant to do. This is normal with any diode clipping circuit. Not much can be done but add a second gain stage after it to boost the signal level.

More reading: http://www.muzique.com/lab/boost.htm and http://www.muzique.com/compress.htm



Thanks to Mr. Orman and to all of you who have chimed in.  I'll keep tweaking and report back...

[tlite]

Zombie thread thank you!  I just was having the same issue with a Muffer and because you posted the bit about the resistor in series with input it totally solved my issue.  (I went with 22K instead of 33K as I wanted a little bit of breakup at higher levels).

Great info in here- thx!

[antonis]

Quite natural..

As it is, stage's gain is dependent on signal source output impedance (approx. 470k/Zout)
Adding a series resistor lowers down the gain 'cause its value is added on Zout..