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What To Do With This Amp?
What To Do With This Amp?
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Old 7th October 2019, 06:31 PM   #21
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by Tubelab_com View Post
...run the field coil from a small Variac, an isolation transformer, and a suitable rectifier / filter cap...
In another thread a year or so ago, somebody posted a link to an extremely expensive current-production guitar speaker that has a "dial-a-sensitivity" knob on the back. It is not a field-coil speaker, and uses a permanent magnet.

It wasn't clear to me how it works, but my guess is that it either moves the rear pole-piece away from the magnet axially, or shunts part of the magnetic field away from the voice coil gap by moving a low-reluctance chunk of iron to partially bridge the magnet poles.


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Old 7th October 2019, 11:35 PM   #22
Tubelab_com is offline Tubelab_com  United States
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I remember the thread, and remember chasing it down to find one of several Eminence speakers that have a permanent magnet with some means to adjust it's strength. I couldn't find a clear explanation anywhere as to how that works, but I did find the words "magnetic shunt" used a couple times. Depending on which speaker one chooses, the reduction in SPL is only 8 to 10 dB at full reduction.

While searching I found another "patented" system called flux tone....guess what, it's a field coil speaker with a variable power supply. SPL reductions of up to 25 dB are claimed.
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Old 8th October 2019, 01:09 PM   #23
Printer2 is offline Printer2  Canada
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It creates more of a gap in the circuit.
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Old 8th October 2019, 04:21 PM   #24
wiseoldtech is offline wiseoldtech  United States
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And a larger "gap" in the wallet of some.

It's just another "invented gimmick" designed to attract the easily swayed crowd.

What cracks me up is those "musician" blogs - the guitar/band types. Musicians discussing how to "mod" or "improve" their amps, etc. Swapping tubes, doing all sorts of goofy things. STICK TO PLAYING MUSIC and leave the electronics to knowledgable professionals.
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Old 8th October 2019, 06:42 PM   #25
Printer2 is offline Printer2  Canada
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The gimmick is suppose to work well. Another gimmick is a VVR, both allows a musician to practice with a more distorted sound at a lower volume. Some actually like the effect.
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Old 8th October 2019, 09:15 PM   #26
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by wiseoldtech View Post
STICK TO PLAYING MUSIC and leave the electronics to knowledgable professionals.
I understand where you're coming from, and there is far too much looney-tunes nonsense surrounding gear for musicians these days.

That said, IMO the right collaboration between artists / musicians and engineers / scientists can often produce better results than either of them working by themselves.

Engineers try to keep their creations from breaking. Artists have a way of pushing technology until it breaks, and then creating their most interesting art from the chaos that ensues.

The evolution of guitar amps is a simple example - engineers and techs building amps to be "clean", using Hi-Fi designs taken from the back of the RCA catalogue; guitar players discovering that if they turned up those clean amps loud enough, they suddenly got more sustain and a singing vocal-like guitar tone, great for early electric blues.

Eventually guitar amp designers caught up with the artists and started to design amps that distorted on purpose, not by accident. But it was the artists that taught the engineers that this was how you make a better guitar amp...not by following existing Hi-Fi principles, but by violating them!

I think Photoshop (TM) is another excellent example. The average software jockey doesn't know what visual artists need; the average visual artist has no idea how to write a computer program. Put them together, and a whole new genre of software emerged, one that shook up the worlds of photography, advertising, publication, and more.


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Old 8th October 2019, 11:04 PM   #27
Tubelab_com is offline Tubelab_com  United States
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Back in the late 80's and early 90's I fixed things for coworkers and friends, most of those things were guitar amps or computers. I even made some guitar amps back then.

So this guy who I barely knew brings over a sick guitar amp. It drank some beer, too much beer. I rip it open for an autopsy......UH, why does a Bandmaster have one 6L6GC and one EL34 in it? He said that he and his friend who had a Marshall got to trading tubes back and forth with each other's amps, and they both liked what happened.

So I find that one of the output tubes had a carbon tracked socket, which resulted in blown diodes in the power supply. Easy fix, not so easy clean up...Beer + dust makes mess.

UH, this thing had a neat sound, but it was a "one trick pony."

This led me to create a a three headed monster, then a 4 headed monster.

One amp, 4 output tubes, big switch. There were two tubes on each side of the P-P OPT. Each had it's own bias pot, and they were wired in parallel....
except for the grids. Each had it's own coupling cap connected to the big switch. There were several combinations of none, one, or two tubes per side, and often the tubes were different kinds. There were some selections where one tube got full drive, while the other got reduced drive. I think one selection drove one tube with the wrong phase drive.

I wound up making a few of these, but that game kinda died when the first DSP boxes came out.....I even bought one, a Zoom 505, still have it somewhere.
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Old 9th October 2019, 03:34 AM   #28
Gnobuddy is offline Gnobuddy  Canada
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...that game kinda died when the first DSP boxes came out...
I was not a fan of any of the DSP boxes until a couple of years ago, when the Boss Katana line came out. To me, they were a stunning improvement over every previous product in that general category.

Boss is now introducing a "New and improved" Katana lineup. This video starts off with a minute and a half of silliness, but IMO, it's worth waiting through it to hear Danish Pete play: YouTube


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Old 9th October 2019, 01:46 PM   #29
Tubelab_com is offline Tubelab_com  United States
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I was not a fan of any of the DSP boxes until a couple of years ago
The processing power of the mid 90's chips was pretty wimpy compared to what exists today....and people have had 25 years to figure out the algorithms.

I got the 505 because it was cheap and unique. Some of the reverb's werent too bad, but I grew tired of it quickly and it's in a box somewhere. I haven't seen it since I left Florida.....just hope that I took the battery out of it before the move.

When my wife is home, I usually play my guitar through headphones. I just plug the guitar cord into my audio interface on the PC and run a TH3 amp / FX simulator. It's kinda weird hearing a 60's surf twang in one ear, and a cranked Marshall stack in the other.
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Last edited by Tubelab_com; 9th October 2019 at 01:48 PM.
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Old 9th October 2019, 06:05 PM   #30
Gnobuddy is offline Gnobuddy  Canada
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Originally Posted by Tubelab_com View Post
...Some of the reverbs weren't too bad, but I grew tired of it quickly and it's in a box somewhere.
That describes exactly what happened to me as well. And, I suspect, a lot of others too.

I still have a Zoom G3 and a Zoom G5 "in a box somewhere". That's after giving away a Digtech RP-something, giving away a Line 6 Pod 2, and re-selling a couple of Line 6 amps. Clearly, I was a slow learner.

Now I have a Katana 50. That one isn't in a box - it's sitting by the couch in the living room, right next to the beater Epiphone electric guitar that gets picked up every evening after work.

The Katana is more than good enough for 99% of what I play, but I feel another oddball tube guitar amp project coming on, just for fun...

-Gnobuddy
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