Blackstar HT-DISTX taming

[tbonuss]

Howdy,

I just picked up a Blackstar distortion pedal as per subject, and man this thing is sweet. 75 bucks on Stupid Deal of the Day.
Oh...looks like they still have it for 90 bucks.

Blackstar HT Series HT-DISTX Tube High Gain Distortion Guitar Effects Pedal | Musician's Friend

Pedal is great. But, as far as I can tell its fully saturated at 50%. It literally has all the gain I need at 10%.

I'll be perfectly happy with it if I can't "adjust" this, but I'm wondering if I just put a different tube in it, I might get a little more range of adjustment.

It comes with a Sovtek 12AX7WA. Thoughts?

Thoughts on this chart for tube selection?

https://www.amplifiedparts.com/tech-...ent-made-tubes

Thanks in advance for anything at all.

[oc disorder]

G'day Tbonuss,
My initial thoughts on that tube chart are twofold.
You won't get the 90% reduction you are hinting at just by swapping different brands.
Those results are from tests on a tube which is placed in a typical guitar amp with all the high
voltages etc.
In your case who knows how they have configured the valve.
In previous "tube in a pedal" units it seems to me they deliberately starve the tube of HT.
The results on the page probably wouldn't replicate using your pedal as a test bed if you see what I mean !

I think you should step back and have a look at the whole "12A" family.

By that I mean ... 12AX7,12AT7,12AY7,12AV7 ,12AU7

Swapping for a slightly different type with the same pinout will get you more gain reduction
than subtle differences in gain from the same type.

Here's some links that may help

Preamp Tube Gain Factors And Substitution Chart - 300guitars.com

"12AX7 Family Tube Substitution

The 12AX7 family of dual-triode preamp tubes consists of the 12AX7, 5751, 12AT7, 12AY7, 12AV7 & 12AU7. These are all pin compatible with one another, the only differences being the gain factor of each tube. A common substitution is to replace a 12AX7 with a 5751 or a 12AY7 to tame a preamp that tends to overdrive too easily, allowing you to get a better ‘clean’ sound out of your amp."

---------------------------


http://www.worldtubecompany.com/mm5/...vc?Screen=TF-2

" Question: What tubes can you substitute or replace for a 12AX7?
ANSWER - You can substitute a 12AX7 for a 12AT7, 12AU7, 12AY7, 5751 or a 7025. But what are the differences? It depends on which tube you are replacing. Let's assume it is the first preamp tube.

12AT7 * * * * The 12AT7 is a clearer sounding tube than a 12AX7 but with a little less gain.

12AU7 * * * * The 12AU7 sounds like a 12AX7 but produces a lot less gain in the preamp circuit. Arguably the Best sounding American 12AU7's ever made are the RCA Clear Tops and Tung-Sol's.

12AY7 * * * * The 12AY7 sounds warmer with more bottom end to it than a 12AX7.

5751 * * * * The 5751 sounds smooth with nice mid range tones. It is warmer with good bottom end to it.

7025 * * * * The 7025 has a higher gain than a 12AX7 tube. It is also a crisper sounding tube. This is the industrial version of the 12AX7. You can beat the crap out of it and it will still go! "
-------------------------

www.thetubestore.com - Preamp Tube Gain Factor

"Choosing pre-amp tubes by gain factor
One simple tweak that is favored by guitar amp users is to plug in a pre-amp tube with a slightly different gain factor.
The gain factor of a tube simply measures how much it amplifies the input signal. For example, the common 12AX7 tube has a gain factor of 100, while a 5751 tube (which is often used in place of a 12AX7) has a gain factor of 70. This means that if you plug a 5751 into a socket that expects a 12AX7, the pre-amp will have about 30% less gain."

[tbonuss]

Perfect! Thank you so much. I'll be out for a while, but when I get a chance, I'll buy a few and try to record some samples for comparison--assuming they'll fit into the narrow slot.

BTW: according to the manual-

Operates at 300V HT

So not "starved"?

[oc disorder]

"So not "starved"?" No .. more like "Bloated" from what you said

Here's Karmadog777 and others experiences with a few pictures on the Seymour Duncan forum.

He relates his had a Sovtek tube which he swapped for a JJ then settled on a Tung Sol !

http://www.seymourduncan.com/forum/s...ics-documented

Would be interested in your experiences when you get to it.

[tbonuss]

"So not "starved"?" No .. more like "Bloated" from what you said

Here's Karmadog777 and others experiences with a few pictures on the Seymour Duncan forum.

He relates his had a Sovtek tube which he swapped for a JJ then settled on a Tung Sol !

Inside a Blackstar (HT DistX) pics/documented

Would be interested in your experiences when you get to it.

Thank you for the link! My experience so far seems to be a bit different than that thread. That is, I REALLY like the way this sounds.

Also, I can't believe he pulled the whole thing apart. The tube is accessible from the top. I can almost hear the sound of his palm smacking his forehead. Doh!

Bottom line, I believe this thing is an absolute steal at less than 100 bucks, I'm just trying to see if I can get a tad more versatility out of it.

So...from my reading it seems that the 12AU7 Tung Sol is a good start (the RCA Clear Top stuff is too overwhelming) I'll sample some chords and leads and record the sample through the pedal into an audio interface with the different tubes.

[tbonuss]

Bottom line, the Tungsol 12AU7W did the trick for me. I worked it out this weekend, and its got a broader range of overdrive -> distortion. It goes to what I think is the max saturation that I would use.

Couple of obserations:

1. Its had some kind of effect on the ISF, or I should say where *I* want the ISF. If I understand correctly the ISF basically shifts the central frequency for a mid-scoop. American is lower; British is higher. Anyhow, with the 12AX7 I kept ending up with full American, and with the 12AU7, I keep ending up on the British range. Again, I'm not saying that makes it sound the same, just that thats what it seems to "want" to me...

2. It gets hotter than it did with the 12AX7--I think.

3. Like with the 12AX7, there still isn't a big difference between 50%-100% on the gain knob. Its definitely having more effect than before, just not as much as I would expect.

4. FWIW: It now compares favorably to my original Marshall Guv'nor, hands down. For me.

I will make some recordings when I decide exactly which comparisons I will make--I had thought that I would need to swap the tubes out a few times to do the tests, but I don't think thats a good idea. I can get the tube out without too much stress on the socket by putting counter pressure on the socket (carefully) with a screwdriver, but when pushing them back in, its pretty much all the pressure on that little vertical PC board. It doesn't feel good--so I think I'll avoid doing it.

So, I'm trying to make sure I think of all the comparisons that would be helpful before I switch the tubes out again.

Compare different gain settings.
Different ISF settings across gain settings.
Different gain settings while compensating (if necessary and possible) with volume knob for roughly the same amplitude o/p.

Get not only audio samples, but also some kind of Crest factor to try and quantify things. I'll really have to think about how to make that a meaningful comparison.
Sinewave on the input, two current clampmeters on the output, one peak, one RMS and record the ratios from the comparisons above?

[tbonuss]

Had a few minutes today, so I took a shot at setting up some tests, or at least trying to think my way through it...
I would appreciate any guidance with this.

This isn't very well controlled yet, I just picked an open d string and adjusted the gain settings.
I used the emulated output from the Blackstar through a cheap Behringer inline into GarageBand. This doesn't seem to be a good representation of what is coming out of the amp (it seemed to saturate more quickly) so I'll have to do that a different way.

The guitar is a partscaster with a Dan Altillio rail humbucker that I got in 1986 or so.

I ran the blackstar into a Peavey Classic 100 head into a Power Soak, and put two clampmeters on the amp output line (one reads true RMS, the other just multiplies peak by .707 as if its a sine wave. The difference between the two gives a sense of the flattening of the wave, as RMS rises at a greater rate than peak.
I use the ratio of the two (crest factor???) to put numbers to the phenomenon. On the graph I just multiplied the ".707" meter by ~1.41 to get peak.

So, this is just a first shot, admittedly not well controlled, but I'm just dabbling and trying to learn something. Any suggestions would be appreciated. Once I figure out what exactly I'm doing, I can compare different tubes in this thing.


Dadgummit. I don't see how to upload a sound clip and I'm out of time for now. I'll check back later to do this.

Later...Okay. Maybe this will do it. Its just two sets of four open d strings for each gain setting. Starts at bypass, then 0, 20, 40, 60, 80 and 100. The gain and volume jump on the emulated output is more pronounced than through the amp.

http://www.soundclick.com/bands/defa...bandID=1406839