# Boss CH-1 Tone Suck?



## LydianGuitars (Apr 18, 2013)

I've had a few Boss pedals and out of all the ones I've had, I've only kept the CH-1 (Black Label Taiwan, Analog) and the SD-1 (Black Label, Japan).

The CH-1 replaced the older CE-2 I had because the CE-2 would distort easily, even with the guitar plugged straight into it. It was fine with lower output pickups but with something like a DiMarzio Tone Zone or Super Distortion, the CE-2 was overpowered.

Lately, I added the CH-1 back in the signal chain, more specifically in the effect loop of the Silver Jubilee Marshall 50w head. I kept tweaking the knobs on the amp thinking that something just wasn't right. I struggled with the tone. It lacked all clarity, lost top end, the mids were muddy. Just not the usual tone. I tried a few different guitars and had the same problem. 

Then, I removed the CH-1 from the loop and voilà! Tone was restored. I tried the CH-1 before/after the TC Nova Delay in the loop and it made no difference. 

In front of the amp, the tone difference is slightly noticeable but definitely liveable. Sounds much better this way but I really prefer to have chorus in the loop for when I have more distortion. 

Has anyone else noticed this? I wonder if its the nature of the Jubilee's effect loop impedance or levels. Seems very odd. I haven't tried the pedal with another amp yet because its at the rehearsal room and the 2204 and 1987 don't have effects loops.

I haven't looked at the schematic but there must be a way to improve the input buffering.


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## mhammer (Nov 30, 2007)

The CH-1 has a 1k input resistor and a 1k output resistor in series with the signal. I wonder if bypassing them (by soldering a little piece of wire on the copper side of the board, rather than outright removal), might help the situation.

Note, as well, that, like all Boss pedals, the CH-1 assumes that once you plug in, the connection to the input will never be lifted, even for a msec. So it lacks any terminating resistor to drain off the .047uf input cap. I don't know anything about your amplifier FX loop, but there may be a risk of switch-popping due to the input structure of the CH-1, that can be remedied by simply adding a 1M-2M2 resistor from the pedal's input jack to ground.


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## LydianGuitars (Apr 18, 2013)

I just found the schematic for it. 
http://www.freeinfosociety.com/electronics/schemview.php?id=2290

Bypassing the 1k input won't do much, at least I don't think so. From what I can understand, that's just to remove parasitic signals. 

Looking at the schematic, I found that the "B" output is just the buffered signal. When I use output "B", the signal sounds better, although I do think it could be improved. That being said, the problem with the headroom is really after the non-inverting unity gain IC 1-B input buffer. Beyond that, I'd have to scope it out to see when the distortion comes in to play. 

The clipping could be happening as early as IC 1-A where the signal limiter comes into play.


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## cdayo (Jan 28, 2014)

I use a 2205 and have found some pedals to finicky even within that EL - some say there are flaws in its design. When in introduce pedals after my guitar and before the amp, i usually overcompensate treble and roll back my tone to find a balance...its a tough balance when wearing earplugs.

I have been doing some reading on the CH-1...I currently have two, one is a pink label (possibly analog - yet to be confirmed) and the other i believe a black label ( i just bought it and there was no label on the bottom but it looks newish.) I intend to mod the newer one but I am wondering if upgrading some of the cheaper caps in the signal chain would have a increase on sound quality. I am in the process of acquiring parts for a DS-1 mod and much of the info I have come across is to upgrade the caps in the signal chain for increased clarity. 

I am really new to this so I guess this comment probably wont be the best help as looking at the schem I now see there is the one lowly .047uF cap MH referred to even before output B...would upgrading to better caps increase fidelity on this pedal? I wouldnt think so if you are experiencing signal loss in just the buffered circuit

*edit - after examining the schem further, replacing the caps might be a pricey option as there are many in the signal chain.


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## LydianGuitars (Apr 18, 2013)

In my experience, replacing a cap of the same value to a different type won't give you much of a difference in tone. Most of the time, the difference comes from wide tolerances. The same thing applies to stuff like amps, really. Many will say that different caps sounds different but whether they sound better is another story. There's a lot of placebo effect in the world of audio, but I digress. Some caps are better than others and some have better audio characteristics, but, the bottom line is: You won't turn the Boss buffering into a hi fi buffer just by replacing a few caps. 

For a pedal that's 25 or 30 years old, replacing the electrolytics is a good idea. Changing them out for Wima or MKTs when possible is a step in the right direction. When staying with electrolytics, I like Nichicon and Panasonic caps. The Nichicon muse series is ideal for audio applications because their internal construction is less likely to have microphonic behaviour.

I think that the main problem with the CH-1 is maybe IC 1A, like i said earlier and also, the fact that the opamp used for buffering is a cheapo general purpose opamp. 

I did bit of research and found that "monte allums" has a kit that might solve the issues. First, I want to see where the clipping is happening. This seems to be a recurring problem for Boss pedals.

For caps, they're just a few pennies each, at most under, a dollar. I'll be ordering some parts from Mouser pretty soon. I can buy some extras and send 'em your way if you want.


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## mhammer (Nov 30, 2007)

LydianGuitars said:


> I just found the schematic for it.
> http://www.freeinfosociety.com/electronics/schemview.php?id=2290
> 
> Bypassing the 1k input won't do much, at least I don't think so. From what I can understand, that's just to remove parasitic signals.
> ...


D3/D4 are unusual. The circuit ought to work just fine without them, and in fact the beloved CE-2 has the same stage without those diodes, and is near identical to the CH-1 up to the EQ stage.

Though tailored to address a different problem (excessive levels due to recirculated/feedback signals, not excessive input signals), the BF-2 employs a similar pre-emphasis/de-emphasis circuit (what I like to call "the poor man's Dolby"), and has diode-limiting in a pre-BBD stage. However, it uses a pair of back-to-back diodes, in series with a 4k7 resistor, to produce a "softer" limiting.

Another thing that occurs to me is that the two output jacks on the CH-1 employ a TRS switching arrangement. When output B is used for dry, the ring connection on the B jack is shorted out to ground, via the mono plug inserted. That, in turn, ties the emitter of Q4 to ground, through D2. When it does that, Q1 is turned off. Q1, meanwhile, governs the flow of the dry signal to the mixing stage (IC5b). So, insert a plug into output B and all IC5b has to "mix" is the wet signal.

But what if there were something a little "off" with that FET (Q1), such that it never really reached its minimum drain-source resistance? Boss switching FETs have been known to fail, or be wonky, before, and this often comes up in "I can still hear the distortion even in bypass, what's up with that?" comments.

So, let's ask a couple of questions. What is the difference to the clean signal, between coming out of Output B and Output A. If B, the dry signal has passed through the input buffer, and passed directly to the output jack. If A, it goes through the pre-emphasis circuit (IC1a), then through C28, R53, Q1, and then to the de-emphasis/mixing/output stage (IC5b). Imagine there was something suboptimal in the manner that the switching circuit worked, such that the drain-source resistance of Q1 never hit its minimum. That would mean that in effect mode, there would be wet+dry, but a dominance of wet over dry signal, with the wet signal being duller from all that necessary lowpass filtering. It would also mean that when the wet signal was cancelled (Q2 is turned off) in bypass mode, there might be a bit of a volume drop.

I don't KNOW that this is happening, merely trying to consider alternate possibilities within the realm of the feasible.

As for clipping, do consider that the CH-1 uses a fixed, rater than adjustable input bias for the BBD. Look at the CE-2 ( http://www.hobby-hour.com/electronics/s/schematics/boss-ce2-chorus-schematic.gif ) and you'll see that the DC bias required for the BBD to pass audio signal, is set by VR3 (over on the left). In the CH-1, it is set by the network formed by resistors R14 through 17. That bias could be spot on. On the other hand, we know that the degree of distortion in a BBD is a function of how close to the optimal bias voltage one is. If you were tweaking VR3 on a CE-2, you'd find that you'd go from no delay signal at one trimpot extreme, through a zone with weaker and distorted delay, then louder and distorted delay, then clear/clean delay, back to distorted, then weaker and distorted, and finally no delay. Is it remotely possible that, through some combination of use of 5% resistors to divide down the supply voltage, and whatever you're powering the CH-1 with, the bias is _just _a little off? Yes.

Sidenote about the MN3007 and MN3207: One of the advantages of the 3207 is that it will run off lower supply voltages. This allowed manufacturers to power it through a 5V regulator which, in turn, was dropping 9v from a battery, down to a stable 5V. That 5V regulator could continue to do that until the battery had aged down to around 7VDC, by which point there probably wasn't enough juice in the battery to power the pedal anyway. Why was this good? Because it meant that, unlike the CE-2, where the "best" bias setting might change as the battery aged, whatever you set the bias to for a 3207, using a stable 5V supply, _would be valid _for as long as the battery was strong enough to power the pedal. So the 3207 chips, and entire 320x series of chips, were a way of keeping distortion to a dependable minimum, in the primarily battery-powered world of the 1980s.

The CH-1 still uses the earlier-generation 3007, that runs off higher supply voltages and has slightly better headroom. But there is no adjustable bias, such that if your battery has dropped from, say, 9.4V out of the wrapping, down to a still respectable 8.3V, the bias could be a little off, and distortion ensues.

Again, not definitive, but within the perimeter of the possible. Given that you have it in your amp FX loop, is it powered by battery or something more stable?


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## cdayo (Jan 28, 2014)

That is some mighty fine analysis. Just what I like to read after a long day at work


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## LydianGuitars (Apr 18, 2013)

@mhammer, I think you need to take a step back for a sec. The bucket brigade hasn't come into play yet since the pedal is "off". That's great info on the bias of the BBD chips. I haven't looked much into those (never had to).

The "bad tone" problem happens while in bypass mode, output A. Its a combination of lo fidelity and bad distortion. 

When using output A, you're going through the buffer, pre-emphasis/limiter/high roll off (why is the high roll off so high?), the FET switch and the de-emphasis. 

I checked the specs on the voltage limiting zener diodes on the pre-emphasis opamp and they're rated to about 3.0v. That means that the AC voltage the pedal can handle is 6vac peak to peak. With the gain dimed on the jubillee, I'm going full throttle into that pedal (the master vol on the Jubilee is after the loop), which isn't designed for *line level* signals.

That's the real problem. What I need to do is find a pedal that handles line level, like the TC Nova series, which I love.

In saying that, I do think that the buffering could be improved with a better input buffer opamp. Same goes for the pre/de emphasis opamp, which would greatly benefit from caps/resistors of higher tolerance around the emphasis circuit. To replace the opamp, I'd need a SIL to DIP adapter and those SILs aren't made anymore.


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## LydianGuitars (Apr 18, 2013)

....deleted....


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## mhammer (Nov 30, 2007)

Yeah, the pre/de-emphasis is really intended to address noise from the delay path, but it ends up getting applied to the entire signal. Ideally, the signal would be split before the pre-emphasis, and mixed back together after the de-emphasis, such that the pre-de was applied ONLY to the delay signal. That way, any component-tolerance-related monkeying with the spectral content would apply only to the wet signal and not the dry. Of course, that would have meant a more complex and costly circuit.

As for handling higher input signal levels, there are clearly going to be limitations imposed by the BBD itself. But, that part aside, I suppose one could reduce the value of R5 (say, from 47k down to 33k), and increase the value of R55 from 47K to something like 62k or 68k. The basic idea is that IC1a could have its gain reduced below unity, for a bit of attenuation and immunity against clipping of larger amplitude signals, and the output stage at IC5b would have a complementary increase in gain to compensate and yield bypass/effect volume balance.

But that starts to monkey with the pre/de-emphasis response, so, likely other component values would need to be calculated and replaced...all of which starts to be more trouble that it's worth. I'm getting the sense that maybe this is best addressed by simply having an attenuator on the front end of the pedal, and a simple single FET gain-recovery stage on the output....assuming you still want to keep it in the amp's effect loop.

BA/M5218Ls are actually pretty good opamps. If the one in your pedal is bad, I may actually have some SIL versions in addition to DIPs. You're welcome to either.

Mark


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## LydianGuitars (Apr 18, 2013)

I did think of doing the level adjustments but I'd end up having issues at the de-emphasis stage later on. Its not worth the trouble or hassle. I think that I simply won't use this pedal in the line level loop of the Jubilee. 

I checked the specs on the 5218 opamp and you're right. On paper, the specs are nice. Good input impedance, noise characteristics, output voltage amplitude, slew rate is more than sufficient. The input current is decent too. The OP2134 does have better input impedance and input bias current but I'm not sure that there would be an audible difference.

The switching Q1 FET could be getting old or colouring the tone too much. I could switch it out for a 2N5484 and see what happens. I do think that getting the pre and de emphasis circuits as close as possible would be part of the solution in getting better transparency from the pedal. Its just a few resistors and caps. I could go with tighter tolerances and match them between the input and output.


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## mhammer (Nov 30, 2007)

Just out of curiosity, where is the pedal in relation to the amp loop? Is it sitting atop or beside the amp, or are you running long cables from send out to the pedal and back to receive?


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## LydianGuitars (Apr 18, 2013)

Its on a pedal board. short loop. about 15'.
On stage, I use 25' loop cables.


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## mhammer (Nov 30, 2007)

Hmmmmm.... try it with the shortest possible patch cables, and tell me if you notice a difference.


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## LydianGuitars (Apr 18, 2013)

Nope. Its not the cables. I tried 10' -> CH-1 -> 10' amp. That's a pretty short leash.
The problem isn't with long cable runs.


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## mhammer (Nov 30, 2007)

10 feet is still pretty long, compared to a 1-footer. But still, I guess we can cross that one off the list.


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