# Yba-2 bass mate modding



## Mikev7305 (Jan 6, 2020)

I recently picked up a bass mate head (6V6) from a forum member and I want to possibly adjust a couple things about it and I'm looking for your expertise. 

It sounds great for the most part, but there is a bit of a spikey high end when I put the treble up past 5. Now typically I'd just keep the treble below 5, but there is a ton of gain that gets added once it's above 5 and I'd like to be able to use it. 

I'm wondering what things I could change to try and tame that shrill high end spike? My first guess would be the treble cap value. But I don't know which one that is... 

Also, the first thing I did on my yba-1 and ygm-3 was change the first coupling cap from .1uf to .01/.02. This one has a 22uf cap on it? It doesn't sound crazy bassy, but I wouldn't mind bringing it down a bit from where it is. 

I'm very interested to hear your thoughts on what I could do. And keep in mind, I'm pretty new to this so be gentle...


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## ga20t (Jul 22, 2010)

I posted a thread here asking pretty much the same but had no bites. Subscribed for discussion/info about these not often discussed amps.


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## stormbringer (Aug 27, 2014)

first coupling cap is 22uF? Can you give me the component number on the schematic, because I don't see it. C2 is .05uF...


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## stormbringer (Aug 27, 2014)

simple spikes solution: add a cap between pins 6 and 8 on the V1 tube socket. This will act as a low-pass filter. Try 150 pf for starters. Reduce to 100 pf if it is too dark. 47-68pf after that.


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## Mikev7305 (Jan 6, 2020)

On the schematic the C1 value is ripped so I can't tell either. But I'm pretty sure it's that blue one in the pictures I posted. I might just change that to .01 anyways since I'm in there. 

The simple low pass filter on V1 is a great tip! Thank you!


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## Mikev7305 (Jan 6, 2020)

I believe my version of bass mate only uses one half of V1, so would something between pins 6-8 even do anything?


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## dtsaudio (Apr 15, 2009)

First off, C1 is NOT a coupling cap. It is a bypass cap for the V1 cathode. Making that .01uf will roll off bass alright. Probably at about 10khz and below. You can lower it in value to thin out the sound, but maybe try 1ufd, or 10ufd.
Your coupling cap before the volume is .05ufd. One of the little beige brown square caps.
From your pictures it looks like someone has already changed the tone cap. It's mounted right on the tone pot, and is .01ufd.


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## Mikev7305 (Jan 6, 2020)

dtsaudio said:


> Your coupling cap before the volume is .05ufd. One of the little beige brown square caps.


Would it be this one? Maybe the colour looks off but it's pretty yellow to me (I've actually been told I'm a bit colour blind). The picture is a bit blurry but it is .047


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## dtsaudio (Apr 15, 2009)

Yes, that is the one. And yes, they're yellow. Try 0.02ufd (same value as the Guitarmate.
That coupling cap is designed into the amp for good bass response (after all it's a bass amp). There are two more coupling caps leading to the 6V6 tubes. Interestingly, the ones in the Bassmate are smaller value than the ones in the Guitarmate.


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## Mikev7305 (Jan 6, 2020)

Ok so coupling cap is figured it and I'm gonna do it tonight. Next thing is the treble spiky thing. I'll put a 100pf cap on the tube pins and hopefully it works. Any ideas on changing that tone cap? Or the resistor going to ground on the treble pot?


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## Mikev7305 (Jan 6, 2020)

One more for you guys, which one is my slope resistor? Pretty sure it's the red one but the blue one is the same value


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## stormbringer (Aug 27, 2014)

Mikev7305 said:


> I believe my version of bass mate only uses one half of V1, so would something between pins 6-8 even do anything?


between the anode and cathode pins, which have the yellow wires leading to the board.


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## jb welder (Sep 14, 2010)

Mikev7305 said:


> One more for you guys, which one is my slope resistor? Pretty sure it's the red one but the blue one is the same value


Yes, the one you circled in red looks to be the slope resistor.
The one circled in blue appears to be the plate resistor for V1, which is shown as 100K stock value on the schematic.


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## Mikev7305 (Jan 6, 2020)

Perfect thanks. Might change that one to 100k or less. The plate resistor has the colour code of a 220k resistor. I have no idea what that change would do tonally from the 100k that's on the schematic


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## Mikev7305 (Jan 6, 2020)

Last question, if I change the value of that little .0047 capacitor on the treble pot, which value could make the amp darker? Would .0022uf make it darker? I'm just trying to find a solution with the caps/resistors I have at home


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## stormbringer (Aug 27, 2014)

Mikev7305 said:


> Perfect thanks. Might change that one to 100k or less. The plate resistor has the colour code of a 220k resistor. I have no idea what that change would do tonally from the 100k that's on the schematic


It would give you more gain.


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## dtsaudio (Apr 15, 2009)

Mikev7305 said:


> Last question, if I change the value of that little .0047 capacitor on the treble pot, which value could make the amp darker? Would .0022uf make it darker? I'm just trying to find a solution with the caps/resistors I have at home


The smaller cap will raise the frequency of adjustment, so most likely no. You'd need to make the value larger.


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## Mikev7305 (Jan 6, 2020)

Awesome thanks fellas!


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## dtsaudio (Apr 15, 2009)

stormbringer said:


> It would give you more gain.


And less headroom before distortion


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## Mikev7305 (Jan 6, 2020)

Got er running! Changed the slope resistor to 50k (two 100k in parallel is all I had) and changed the first coupling cap to .01uf. I'll crank it up tomorrow and see what it's like. The spike can be tamed with an EQ pedal until I get a hold of some caps between 50pf-150pf. Thanks again guys I REALLY appreciate it!


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