# Mods for the Blackheart Little Giant?



## Greg Ellis

Has anyone had success in modding their Blackheart Little Giant?

I'm finding a couple of things lacking:

1. Insufficient bass output. With the amp's bass control at max, I get a decent bass output on my neck-position humbucker, but on my bridge pickup it's pretty much completely gone. Need more bass.

2. Need more clean headroom. I'm not exactly in love with the amp's distortion, and I'm wondering if it might be more productive to play it clean and add dirt up front with pedals.

Has anyone modded the Little Giant on their own?

I'm aware of the Bitmo kit that costs about $40. Also the british ones (stage 1 and stage 2) that mostly clean up the buzz and hum by swapping in better components).

The Little Giant is quite a simple amp - 1/2 a 12ax7 into a 3 way tone stack, volume control, another 1/2 12ax7 and then the single el84 as a power amp.

Could I make some simple changes in the tone-stack to help me get where I want to go?

Schematic is available online if anyone's interested:

http://www.blackhearttalk.com/pdf/BH5_schematic Rev 20070611.pdf


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## Greg Ellis

No interest?

Here's what I've researched so far...

1. Input - play around with the series input resistor to change the stage 1 input level. Blackheart uses 33k here. 68k seems to be a more common value. Raising this value will reduce the signal hitting stage 1, keeping that stage cleaner. 

I've played around a bit with both boosting and attenuating the input signal (external to the amp), using a combination of guitar volume and some pedals. Boosted, it gets kinda fizzy and unpleasant, but attenuated (with the amp volume cranked up to compensate) it sounds a lot better. I'm not sure how high I can safely go on the input series resistor - I guess 68k is a good place to start. Is there any danger in using higher values here? I mean aside from losing volume.

2. 1st stage - 100k on the anode, 1.5k on the cathode and .22uF bypassing the cathode resistor - those values all look pretty standard for a 12ax7. Reducing the 100k anode resistor seems the simplest way to reduce gain in this stage. Not sure how low I can go without getting into trouble with excess current. I've got a 2W 22k pot, maybe stick that in there with a 75k resistor and mess around a bit. Stage 1 anode drives the tone stack.

3. Tone stack - this is a blackface-style, anode-driven tone stack, using a Fender value for the slope resistor, and Marshall values for the caps. The tone stack feeds the only volume control in the amp.

Fender (e.g. Twin Reverb): slope resistor = 100k, treb = 250pF, mid/bass = .1uF/.047uF
Marshall (e.g. 1987, 2203): slope = 33k, treb = 470pF, mid/bass = .022uF
Blackheart: slope = 100k, treb = 470pF, mid/bass = .022uF

If I understand the tone stack correctly, I can increase bass response by adding more resistance between the signal and ground. Not sure exactly where to put this, though. Between the bass pot and the mid pot? Between the input lug and the wiper on the bass pot? I'm guessing that the pot lugs would be the easiest access point, but I haven't opened the amp to look yet.

I'm not really sure I understand how the slope resistor works - Marshall tends to use a much lower value, which supposedly creates a more "midrangey" sound. Not likely to help my with my lack of bass problem, as far as I can tell.

Tone Lizard mentions that this style of tone circuit suffers from a "huge insertion loss" (that's what SHE said :lol, and mentions a mod which lifts the ground from the mid resistor to create a huge boost (and completely bypass the tone stack). I'm not sure what that might do to stage 2 - it seems a bit extreme, but might be fun to try. 

As a pie-in-the-sky sort of idea, I could convert to a Tweed-style tone stack (e.g. Ampeg SVT), but that seems like a whole lot of surgery for unknown benefit.

Stage 2 - 100k on the anode, 1.5k on the cathode, and 1uF bypassing the cathode resistor. Nothing really unusual that I can see. 

What confuses me here is the 1.5k series resistor between the volume pot and the input to stage 2. If I understand the circuit, this resistor is attenuating the signal input to stage 2, after it's already lost a bunch of vinegar passing though the tone stack. That seems like an odd thing to do.

Maybe it's just there to keep the stage 2 grid off the ground? If that's the case, why not connect the resistor between the volume pot wiper and the ground, allowing the signal to pass unaffected into the stage 2 grid? As it's wired, not only is the series resistor attenuating the signal, but the volume pot seems to be changing the input impedance on stage 2. What the heck? Forgive me if this is a stupid question - I'm kind of new at this stuff.

I see the same thing coming off the stage 2 anode and into the power stage. There's a .022uF cap in the signal path, with a 220k resistor to ground, that seems pretty normal. But then the signal passes through another 1.5k on its way to grid 1 on the EL84.

Does anybody understand what's happening with these 1.5k's in the signal path?


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## Wild Bill

Greg Ellis said:


> No interest?
> 2. 1st stage - 100k on the anode, 1.5k on the cathode and .22uF bypassing the cathode resistor - those values all look pretty standard for a 12ax7. Reducing the 100k anode resistor seems the simplest way to reduce gain in this stage. Not sure how low I can go without getting into trouble with excess current. I've got a 2W 22k pot, maybe stick that in there with a 75k resistor and mess around a bit. Stage 1 anode drives the tone stack.
> 
> What confuses me here is the 1.5k series resistor between the volume pot and the input to stage 2. If I understand the circuit, this resistor is attenuating the signal input to stage 2, after it's already lost a bunch of vinegar passing though the tone stack. That seems like an odd thing to do.
> 
> Maybe it's just there to keep the stage 2 grid off the ground? If that's the case, why not connect the resistor between the volume pot wiper and the ground, allowing the signal to pass unaffected into the stage 2 grid? As it's wired, not only is the series resistor attenuating the signal, but the volume pot seems to be changing the input impedance on stage 2. What the heck? Forgive me if this is a stupid question - I'm kind of new at this stuff.
> 
> I see the same thing coming off the stage 2 anode and into the power stage. There's a .022uF cap in the signal path, with a 220k resistor to ground, that seems pretty normal. But then the signal passes through another 1.5k on its way to grid 1 on the EL84.
> 
> Does anybody understand what's happening with these 1.5k's in the signal path?


Be careful screwing around with plate resistors. Stop thinking of them as just throttles for how hot the tube runs. That's not the way the circuit works at all.

Every tube has an optimum plate load resistance (or impedance) where it will work properly, not just for gain but for operating in the right portion of the signal cycle. Along with the cathode resistor to set the bias the preamp tube will be set to operate without clipping either side of the wave and for best gain.

You can play a bit with these resistors but only in a certain fashion. First off, never reduce the value! That's asking for trouble. You can change that 100k for a 12AX7 to 220K and you will get more gain, since now you can develop a greater voltage swing across that resistor, which is the output load for the stage. Higher values lead to instability - squeals, big time!

One old (and stable!) trick to reduce gain in a triode stage is to use a "split load", where instead of a 100k resistor for the plate you use maybe two 47k's in series to feed the plate and take the output from the tap in the middle! This is just like using a volume control. Some old Fenders used this trick.

As for those 1k5 resistors at grid inputs, it sounds like you're describing "grid stoppers". The impedance of a grid input is over a million ohms. 1K5 is mice nuts, so it won't reduce the signal by any measurable amount. However, it tends to protect the grid input from "hanging free", picking up noise and other bad stuff. It also keeps strong signals from "blocking" the tube on strong signal peaks, causing distortion.

There's a really great FAQ here:

http://www.aikenamps.com/

Go to "Tech Info", then "Advanced". You'll find explanations about "Grid Resistors - Why Are They Used" and "Designing a Triode Amplifier Stage".

Mr. Aiken's site is invaluable!

:food-smiley-004:


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## Emohawk

Hi Greg,

Those are some pretty common gripes about the low-wattage SE amps in general, at least the lower cost ones like the Little Giant, Valve Junior, AC4TV, et al.

I defer to Bill (and Aitken, ToneLizard & others) for the really involved stuff, but I will tell you that a big weak spot in these amps is the output transformer. If you want some more bottom end (and overall clarity with possibly a little more headroom), an OT swap is a good place to start and it's a relatively simple mod. The Hammond 125?SE series is very popular with these amps. I currently have a 125ESE on the way for my VJ, but the 125DSE is also popular. I plan for this to be the last mod for the VJ...but I keep saying that...

Kirb


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## Greg Ellis

Thanks guys. I've definitely got some more research to do before I start soldering.

That trick with the pair of 47k's sounds promising - I might give that a shot if raising the input resistor doesn't get me where I want to be.

Kirb, thanks for the idea, but swapping the OT seems kind of extreme (and premature) for my current situation. I can get the amp sounding the way I want, just not on my bridge pickup, so I know that the stock OT can deliver "the sound". If I can't solve it in the tone stack, maybe I just need a different pickup. I don't have an EQ pedal here, or anything that would boost the bass on the way into the amp - that would be a good way to test out a few things.

Come to think of it, duh, I should have tried a different guitar or two today when I was messing around. Too late at night now.

Any other comments are very welcome, especially about modding the tone stack.


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## Greg Ellis

I swapped out the EH 12ax7 for an old GE 5751 that I found in the garage. That has cleaned things up considerably, although I'm still tending to attenuate the input in order to get the amp sounding the way I want.

If I understand the tube data correctly, 5751 runs very similar to 12ax7, but produces somewhat less gain (~70, instead of 100?).

Only problem with the 5751 is that the bass gets a bit "flubby" at certain settings and volumes. Maybe I need to dig up some other tubes to try.


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## mrmatt1972

WHat speaker cab are you using? I have lots o bass with mine through a homemade, but deep and semi open, 1 x 12.

Also, where is the amp situated. An amp beside or between upholstered furniture will sound muffled and weird.


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## Greg Ellis

I'm playing through a close-backed 1 x 10" - the speaker is an Emminence Ramrod. Ridiculously high efficiency - it's very loud even with a 5 watt amp. I'm using an attentuator (most of the time) to keep the volume under control.

http://eminence.com/guitar_speaker_detail.asp?model=RAMROD&speaker_size=10&SUB_CAT_ID=4

I've tried a few different rooms and placements - no big changes really, aside from some natural reverb in some of the rooms.

I think part of my problem might be that I've never owned an amp that so faithfully reproduced all the garbage I feed in (fretting noise, string touches on the pickup, etc.). It sounds remarkably different as I try different pickups, guitar volume levels. Even the tone control on the guitar has an enormous impact. Most amps I've played colour the sound a lot more.


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## Emohawk

Greg Ellis said:


> I think part of my problem might be that I've never owned an amp that so faithfully reproduced all the garbage I feed in (fretting noise, string touches on the pickup, etc.). It sounds remarkably different as I try different pickups, guitar volume levels. Even the tone control on the guitar has an enormous impact. Most amps I've played colour the sound a lot more.


That's true in a way. The big difference is tube amps tend to be far more responsive to your input - small nuances in your playing can have huge impacts on the tone. It's a much more interactive thing. A tube amp is an instrument in and of itself really. It can be a bit of an adjustment learning how to "play" it!

Tube amps still color the sound, just in a sweet tubey way.  That coloration & the interactive nature of tubes is what makes them special.

Oh - and it's not a "problem", BTW. It just opens doors to new nuances of your style.


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## Robert1950

If you are feeling really ambitious - http://www.allenamps.com/blackheart.php


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## Greg Ellis

Robert1950 said:


> If you are feeling really ambitious - http://www.allenamps.com/blackheart.php


Yeah, I read that a couple of days ago. Interesting ideas, but...

It's a $200 kit, on top of an almost-$200 amp. Puts the amp price up to almost $400.

I've seen an awful lot of Peavey Classic 50's, Sovtek Mig's, Traynor YCV40's, YCV20WR's and similar amps selling used in the $400-500 range. Some of those have great gobs of desirable features (reverb, footswitched dual channels, more power, etc.) on top of the Little Giant.

If I had the extra two bills to spend, I would think I'd be WAY better off selling the Little Giant and buying a $400-500 amp, rather than sinking another $200 into it.

Don't get me wrong, I'm not unhappy with the amp, far from it. To a large extent, I'm still learning how to use it. If there are things I can do for a few dollars here and there, I'm certainly ready to try. But investing a big chunk of extra cash into this particular amp? I just don't see the point.


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## jammers5

*Bitmo mod for BH Little Giant*



Greg Ellis said:


> Has anyone had success in modding their Blackheart Little Giant?
> 
> I'm finding a couple of things lacking:
> 
> 1. Insufficient bass output. With the amp's bass control at max, I get a decent bass output on my neck-position humbucker, but on my bridge pickup it's pretty much completely gone. Need more bass.
> 
> 2. Need more clean headroom. I'm not exactly in love with the amp's distortion, and I'm wondering if it might be more productive to play it clean and add dirt up front with pedals.
> 
> Has anyone modded the Little Giant on their own?
> 
> I'm aware of the Bitmo kit that costs about $40. Also the british ones (stage 1 and stage 2) that mostly clean up the buzz and hum by swapping in better components).
> 
> The Little Giant is quite a simple amp - 1/2 a 12ax7 into a 3 way tone stack, volume control, another 1/2 12ax7 and then the single el84 as a power amp.
> 
> Could I make some simple changes in the tone-stack to help me get where I want to go?
> 
> Schematic is available online if anyone's interested:
> 
> http://www.blackhearttalk.com/pdf/BH5_schematic Rev 20070611.pdf


I know I am late in this conversation but I purchased the Bitmo Triple Bypass mod for mine that sounds fantastic. My brother was a tv/vcr repairman in his previous career and did all the snipping and soldering. The result? fantastic!


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## parkhead

Based on what you've described here's what I'd do 
step 1 
Change the slope resisitor to the 33k marshall value this gives you more bass and mids ...

step 2 
I'd also look at changing the .02 tone caps to .01 or .0056 
this will boost both the mids and the bass while focusing the bass into the mids 

since you are dealing with a SE low powered amp what you really want to do is add the illusion of bass 
since bass requires power ...

Step 3 
Change the first B+ Filter cap to the biggest value you can find that will fit the board 
this will add bass potential in the power supply 

Step 4 
change the OT to the hammond 125ese if it will fit 
the difference is shocking you will lose some distortion 
but the punch and dynamics will be astounding 

I did a valve JR somewhat like this 
bypassed the pre set tone controls 
Used smaller value .01 coupling caps to move the bass up slighly 

bumped the First Filter and slammed the 125ese (60 bucks) in there 
I can play clubs with this amp and almost be loud enough 
If I played harp the amp would be perfect 

for slide its killer...
since doing this amp up I use it for my Lead tone 
with an A B Y "BOTH" box 
and kick the 5 watt thing in for leads it screams 

this is the amp without the hammond 
YouTube - Epi vj Billy Gibbons tone

with the hammond the clean volume and the bass response went way up 



P


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