Roland Bolt 100.

[Mortadelas]

I have this 80s Roland Bolt 100.
My problem is that I am in two bands, one plays blues/rock'n'roll and the other death metal. Now while the clean channel is the best thing to ever happen to my guitar, it's overdrive is horrible.
It's OD channel is SS, 3 Volumes and it sounds harsh, really harsh. Like a 3 volume, more complex, lower drive version of a Boss MT-2.

http://postimg.org/image/vrk5vlhrr/

Anyone has any good ideas before I venture into the long trial and error path?

[mth5044]

Welcome to the forum!

Are you asking for pedal suggestions or a way to mod the amp?

[teemuk]

Not really so much a DIY suggestion but a practical one. Find a good sounding "preamp" -style pedal for the OD, plug it to effects loop. Use the effects loop to "switch channels" instead of amp's own channels.

If you want to mod the amp you will encounter a few drawbacks. The OD channel is not "separate"; at first it cascades a gain stage with diode clippers in feedback loop to signal path of the clean channel, then after that FX loop switching it selects whether the signal is routed through a clean gain stage or another gain stage with diode clippers in the feedback loop.


This means...
a) The EQ'ing of the clean and OD channel is shared (most prominently the tone controls you can tweak, but also the EQ built within those gain stages that OD channel shares with the clean one, and in practice this usually means that you will either get good EQ for one channel and something less ideal for the other, or a compromise which likely isn't that great for either. For overall tone controlling that these very, very different channels require this is actually a major drawback.

b) If clean channel is already awesome this means that you are practically limited to tweaking those two gain stages that distort the signal with diode clipping. You can probably achieve something but overall this is rather limiting. Every tweak that would happen in the sections shared by the clean channel would alter the tone of the clean channel and this is likely not too preferable if the clean channel is already an ideal one.

So... you can try to "polish a turd", heck, it might even work sometimes, or you can take a more practical alternative, which is something along the lines of getting the OD sounds from a pedal/preamp in front, preamp/pedal in FX loop, etc. ...Or perhaps just to buy a better amp for the purpose. Ampeg VH-140C, for example, not only has a clean channel to die for but also a gain channel that fits death metal like torn guts fit the hands of bloodthirsty zombies.

But if you are going to mod the Roland then it might be more helpful for us to know a bit more technical details about what you don't like in the sound. "Horrible", "harsh, really harsh" are pretty generic descriptions and each individual likely interpretes them in their own individual way. Could you provide some more objective terms so we could actually know which areas to focus on instead of trying to guess it?

[Mark Hammer]

Apart from what may be some questionable choices in how the overdrive is implemented, those Bolt amps have a lot of nice bells and whistles and options to them.

teemuk, should I understand that the 3+3 diodes between gate and source are operating in a manner analogous to the diode pairs in a Big Muff?  And if so, this would suggest that:

1) the 82nf cap in series plays a role in establishing the quality/character of the clipping, just as the 100nf cap in the BMP does;

2) the cap in parallel with the diodes and series cap can be varied to round the sharp edges off the overdrive tone.  I see there is such a cap in one of those stages, but not in the other.

[teemuk]

should I understand that the 3+3 diodes between gate and source are operating in a manner analogous to the diode pairs in a Big Muff?

Well, output (drain) hooked to inverting input (gate) is negative feedback....

[Mortadelas]

Thnx mth5044.
If there is a way to mod the amp (no matter how much tweak we are talking about), I'd prefer it. But I haven't heard/seen a single mod done to it and that kinda leaves me in the deep so a pedal seems to be my best bet.

Teemuk:
There seems to be a peak at about 3600hz regardless of eq. Not enough low end gets fed into the OD cirquit. High-end seems more clipped than the low end. Not enough "gain".
Also thanks

There is a three way switch for the effects loop, pre eq, post eq and post vol. Maybe I should take it as hint from roland and go with a pedal in the effects loop. AMT has done wonders.

[Mortadelas]

OK, phase one seems to be
C2 and C7 to .1 and a new 100nF for Q3.

[teemuk]

Not enough low end gets fed into the OD cirquit.

If I calculated correct, the cut-off frequencies of RC filters coupling the first clipping gain stage are about 34 Hz before the first gain control and pretty much below audio bandwidth after it.

The second clipping stage has pretty much identical values.

The very first gain stage has 82nF coupling cap feeding about 1M shunt resistance. The cut-off frequency is about 2 Hz. I can't possibly see how the clipping stages would not receive enough of low frequency content. They way I see it, they receive excessive bandwidth compared to usual modern high-gain pedals that may start to roll off the low frequencies from around 1 Khz.

The way I see it, Roland's scheme in this one is good for making a buzzy, fuzz effect, not modern metal distortion effect.

High-end seems more clipped than the low end.

Try altering the value of the cap coupling those diodes in the feedback loop. What happens when you, say, double the capacitance?

[Mortadelas]

Try altering the value of the cap coupling those diodes in the feedback loop. What happens when you, say, double the capacitance?

OK, will try doubling the capacitance and adding/removing the parralel cap and maybe adding a parallel resistance a la Big Muff.