Sound shut down when raising gain on a Markbass

[Lorenzo Ponce]

Hey there felLOWs !

I have a very strange issue with my amp. I use a MarkBass Little Mark Vintage Gold Line head - yes, the one with the fancy little tube upfront. This is plugged into a Phil jones Piranha 2X7. I have used it with a P Bass, a J Bass, a Yamaha 5 strings, no problemo. Last Friday I made this HUGE - and very beginner level - mistake : use it with my upright bass without making proper tests before. Assuming it would work fine. It did not. Here's the issue : I use a David Gage The Realist piezo direct into the amp. When I plug it, no problem, all good. But as soon as I turn the gain up - or even switch the preset knob - the amp makes a very small "blip" and the sound is simply shut down. Everything is on, the power is not cut, there is simply no sound anymore. If I restart the amp, it works again so nothing is "broken" in the process apparently. Soundcheck was a mess, I ended up playing direct into the PA. Back home I replicated the experience same thing : I can raise the volume through the roof with my P Bass, no issue. But when I do the same with my upright, it shuts down - approximately after 1/3 of gain course. Stranger thing is : it does not always cut. Sometimes it can handle gain raise, sometimes not. I tried to identify it this was linked to a specific setup position - there are three - but no correlation. Looks like random, but there is no "randmoness" in amps tech.

I'm not a tech, so I have no clue. The David Gage piezo was given to me pretending it was not working, but it works fine in other configurations - I played it through a Fender Rumble, another MarkBass head, etc. without any issue 100% of the time. And my amp works well with other basses - although I haven't tried another upright with another piezo... could it be that the input level is too high ? anything else that comes to mind ?

I would like to avoid taking it to a tech, there are not much in the area...

 

[Geogio]

Take what to the tech? The amp or the piezo?

But your amp plays fine with your other basses, correct?

And your piezo so plays good in your other amps, correct?

Have you checked with the support at the Mark bass web site? Maybe a chat box.

I am not an expert, but digital equipment sometimes senses anomalies and will go into a protection mode. Those features are hard coded on a chip, thermals, input voltages etc...

 

[Lorenzo Ponce]

Take what to the tech? The amp or the piezo?
But your amp plays fine with your other basses, correct?

The amp. Yes correct.

I've been reading elsewhere meanwhile that it could just be the jack input of the amp that is dirty / corroded - bought it second hand so who knows where it has been stored - that triggers some kind of protection mode. Fact that it only clipped with the piezo may just be random - because as we know, correlation is not causality...

 

[Geogio]

The amp. Yes correct.

I've been reading elsewhere meanwhile that it could just be the jack input of the amp that is dirty / corroded - bought it second hand so who knows where it has been stored - that triggers some kind of protection mode. Fact that it only clipped with the piezo may just be random - because as we know, correlation is not causality...

Qtip and 93% rubbing alcohol... although I prefer everclear... a can of CRC Electrical Contact Cleaner is handy too. Be careful swabbing out the female input, wet the Jack and work it a few times.

A more invasive cleaning is accessing the connector on the inside the amp and cleaning any patina off with a tool or abrasive pad using the CRC.

It might be just be the piezo jack. But a cleanup all around would be good.

 

[agedhorse]

Before guessing on a “cure”, correctly identifying the actual cause is helpful.

What’s more likely is that the signal level from the piezo pickup is much hotter, or that it’s capacitive source impedance is causing an oscillation (or instability) with the input gain stage of the amp.

This is not unheard of, and something a very skilled, qualified technician can identify. The cure may not be obvious however, MarkBass may need to be involved. Perhaps they have seen this before.

 

[Aloe]

uhm, got some buffer to try (like just any pedal turned on)?

the Realist's output impedance is 10M, and LM Vintage's input impedance is just 500k, they might not work together without an extra buffer, as basically Realist wants at least twice bigger impedance to work good (but sounds better if it's even larger).

your 'another Markbass head' likely has an 1M impedance, so does Rumble.

 

[Redbrangus]

This does sound like an interface issue; I'm with @Aloe that just about any sort of pedal or preamp could serve as a buffer stage to isolate the source from the load. Just doing so temporarily, as a test, would identify whether that's the problem or not.

 

[Jon Burnet]

so not sure if this helps, but my LMtube800 does a thing where if the tweeter is cranked and the treble is cranked and you pop, the entire amp shut off output until you turn the amp off and on again. apparently some sort of protection circuit. i play with the tweeter turned almost off and normal treble, so its never an issue, but i am aware it exists.

 

[agedhorse]

uhm, got some buffer to try (like just any pedal turned on)?

the Realist's output impedance is 10M, and LM Vintage's input impedance is just 500k, they might not work together without an extra buffer, as basically Realist wants at least twice bigger impedance to work good (but sounds better if it's even larger).

your 'another Markbass head' likely has an 1M impedance, so does Rumble.

The output impedance is nowhere near 10M

 

[Aloe]

The output impedance is nowhere near 10M

of a Realist? they spec it like this:

Realist FAQ
Link Removed
The Realist is a high impendence transducer. The Realist is rated at 10mg ohms.

 

[agedhorse]

of a Realist? they spec it like this:

Realist FAQ
Link Removed
The Realist is a high impendence transducer. The Realist is rated at 10mg ohms.

No sir, that’s the INPUT impedance that works best for the Realist, not the OUTPUT impedance.

 

[Aloe]

No sir, that’s the INPUT impedance that works best for the Realist, not the OUTPUT impedance.

I thought, the second is a shortcut for saying the first one.

but you've corrected this error and we're now again good. thanks!

 

[agedhorse]

I thought, the second is a shortcut for saying the first one.

but you've corrected this error and we're now again good. thanks!

In all fairness, there is a LOT of incorrect information on the web about how piezo pickups work, some of which is provided by manufacturers that market and sell products to "fix" problems that don't really exist via grossly inaccurate marketing claims and promises.

 

[Lorenzo Ponce]

Yeah.. I should definitely learn a bit about electronics theory I guess.
Thks for the tip. I don’t understand fully but I’ll investigate - however does not explain why it actually works fine sometimes…

 

[Lorenzo Ponce]

So… in short :
- might be just about cleaning up the jack input (ideally without opening anything)
- might be an impedance problem ( I don’t really understand the theory, I’ll do my homework) but if The Realist requires a 10m input and my head is 500k, what am I left with ? What should be done to align ? i have a compressor pedal I could use as a buffer, still helpful ?

i have contacted MarkBass they redirected me to local distributor and I don’t have an answer yet…

thanks again to all of you

 

[Aloe]

i have a compressor pedal I could use as a buffer, still helpful ?

likely, look up it's input impedance and if it's 1M or greater, you're good. if the pedal is 'true bypass', you need to have it on to actually buffer your signal. at least try this to conclude if your problem can be solved by a buffer.

another buffering option is using a HPF (the Thumpinator has 2M input, I believe) or using a buffer in your pedal tuner (Peterson Strobostomp HD has a 4.7M input impedance per specs).

 

[Pings Bass]

I also have a David Gage Realist and always use a buffering preamp FWIW. I admit to being confused about how piezo pickups interact with amp inputs. Sounds like there's maybe a fault in the pickup the amp is protecting itself from?

The David Gage piezo was given to me pretending it was not working, but it works fine in other configurations

I mean ... maybe it has an intermittent fault, and the markbass is just more sensitive/better at protecting itself?

 

[agedhorse]

So… in short :

- might be an impedance problem ( I don’t really understand the theory, I’ll do my homework) but if The Realist requires a 10m input and my head is 500k, what am I left with ? What should be done to align ? i have a compressor pedal I could use as a buffer, still helpful ?

It's NOT an impedance issue, it's almost certainly a stability issue with input of the MarkBass. A buffer MAY solve the problem (not because of impedance), if it does it's the easy fix.

 

[Engle]

The

I also have a David Gage Realist and always use a buffering preamp FWIW. I admit to being confused about how piezo pickups interact with amp inputs. Sounds like there's maybe a fault in the pickup the amp is protecting itself from?


I mean ... maybe it has an intermittent fault, and the markbass is just more sensitive/better at protecting itself?

The Gage site says you shouldnt need a preamp.
I was given a dead Realist pickup and found it had a couple of resistors built into the output jack. I assumed they were for impedance matching. There was an open at that point. I just wired it direct to the jack and got it working.
I always use an FDeck HPF with upright bass anyway.

 

[Redbrangus]

The Gage site says you shouldnt need a preamp.

Well, you shouldn't, but maybe sometimes you might -- not for the gain, but to isolate the input from the exceptionally high source impedance, which must be about 1MegΩ if they're recommending a 10Meg input impedance for the following stage. If the LM Vintage's input impedance is indeed 500KΩ, it's likely it is loading the output of the pickup, if only somewhat. But as @agedhorse pointed out, this isn't actually an impedance problem -- it's more likely to be the highly capacitive nature of the source that's setting up the conditions for inaudible oscillations in the amp and tripping the protection circuitry. This is why we've suggested trying a pedal or something between the pickup and the input -- it doesn't have to have gain, like a preamp, but it does need to present a relatively high input impedance, so as to avoid loading down the pickup.

I'm not terribly familiar with the current range of amps in the market; I suspect there are a lot of amps out there with a 1MegΩ input impedance, but dang few with a 10MegΩ one. I'm not sure the builder isn't doing himself a disservice by stating flatly that the user doesn't need a preamp without providing at least some information about the implications of the exceptionally high source impedance.