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Old 11th October 2017, 10:53 PM   #31
turk 182 is online now turk 182  Canada
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just got a tip from a guitar player friend check this out....Iconoclast Speaker Emulator | Neunaber Audio Effects
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Old 11th October 2017, 11:56 PM   #32
Printer2 is online now Printer2  Canada
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Guitars have little use for anything above 5 kHz and act as a bandpass filter. Another reason we mike the side of the cone rather than the center. Just reducing the signal out of the amp is not enough, rolling off the highs is part of the sound.

Tube amps are nor known for their dampening and the less control of the speaker the more alive it will sound (within reason). Unless I am reading it wrong with the advice of expoying the voice coil in place (solid in place) would remove half of the reason for driving a voice coil. I would like the spider to hold it in place and maybe having some foam stops to limit the excursion so it does not fly apart.
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Old 12th October 2017, 02:35 AM   #33
famousmockingbird is offline famousmockingbird  United States
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This schematic could be simplified as a speaker simulator.
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Old 12th October 2017, 03:02 AM   #34
Tubelab_com is online now Tubelab_com  United States
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Quote:
George, how did the amp bring the LTP down and not the previous gain stage?
I don't remember where the original idea came from. I saw a schematic for some popular amp that had a "Power" knob that was a VVR connected only to the PI, so I tried it on one of my long lost prototypes from the old HBAC.

The schematic is included below (HBAC_5T). It was an experiment in building the most amp I could for $100 in parts. I think this came in at $99 and change including transformers and the L-pad, but no cabinet or speaker, as per the original rules. Most of the Mosfet stuff is now gone, only the buffers feeding the tone stack and master volume remain. The unconnected end of R53 is wired to the OPT secondary through a shaping network to form a presence control of sorts. The amp had too much gain so the last gain stage (V2B) has been eliminated.

The LTP VVR was added by simply removing R48 and R49 from the board, hanging two new resistors from the plates with their other ends connected to the VVR. The VVR is simply an N-channel mosfet with the drain connected to the + end of C18, the source connected to the two plate resistors and the gate connected to the wiper of a 1 meg pot wired from B+ to Ground.

I could get a good tone by playing the master volume against the VVR knob up to the point where the LTP started really starving for voltage and sounding sick. So, back up a bit and dial back the scream with the L-pad.

Note, I tended to play this thing cranked......think Soldano in the high gain mode. At 25 watts or so it was loud, and the HBAC was about low powered practice amps, so the dual dial-back's sounded pretty good when cranked, yet turned down.......

It sits in a box awaiting further action because the little 4 watt screamer I made about 2 years ago for the HBAC reprise (GTA_4T_11-10-15) still gets my use whenever I play the guitar, which isn't too often any more. Serious nerve damage has left me with numb fingers, making guitar playing nearly impossible, and soldering very frustrating.
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File Type: pdf GTA_4T_11-10.pdf (22.6 KB, 19 views)
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Last edited by Tubelab_com; 12th October 2017 at 03:08 AM. Reason: Wrong schematic included....fixed now
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Old 12th October 2017, 03:44 AM   #35
famousmockingbird is offline famousmockingbird  United States
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Quote:
Originally Posted by Tubelab_com View Post
The LTP VVR was added by simply removing R48 and R49 from the board, hanging two new resistors from the plates with their other ends connected to the VVR. The VVR is simply an N-channel mosfet with the drain connected to the + end of C18, the source connected to the two plate resistors and the gate connected to the wiper of a 1 meg pot wired from B+ to Ground.
I get the idea thank you for sharing. I have some IRF830's in my bin, I also think I have some FQPF2N70's. I am not looking to get the amp into Eddie Van Halen territory, I just want to lower or eliminate the speaker volume while keeping the tube amp in the sweet spot..... The sweet spot for me is before clipping where it's still relatively clean but really rich and full sounding.


I would love to hear your 4 watt screamer. That schematic looks very interesting with some neat ideas and cool tube selections.
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Old 12th October 2017, 10:17 PM   #36
Tubelab_com is online now Tubelab_com  United States
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I would love to hear your 4 watt screamer. That schematic looks very interesting with some neat ideas and cool tube selections
I never posted any sound files since I have become rather frustrated with my current inability to play the guitar. Both of those amps were designed for the Hundred Buck Amp Challenge. The very long and sometimes heated thread actually started when another forum member bragged about a kit he was selling on Ebay at the time and stated that nobody could build a better or cheaper kit (or something like that) and I replied "wanna bet." A third forum member proposed the challenge, and it started. The original challenge asked for a tube guitar amp design for less than $100 parts cost.

The 4 tube "screamer" design started out as a 3 tube design, and was my attempt at absolute minimum parts cost. The original prototype used a 6AU6 and a pair of 6AQ5's because I had plenty of them. A 4th tube (a 6AV6) was added for more gain early on. The original rules allowed for silicon in supporting roles, but that got protested several times throughout the entire thread. The 4 tube design as submitted during the active contest had no silicon except in the power supply, which was allowed.

Once I had a working prototype I performed the same task I learned as a cell phone designer at Motorola, I made a spreadsheet of parts with costs, sorted by cost, and started attacking the biggest cost parts first.

I got the idea to use a series heater string in both amps because it reduced the power transformer and tube costs by half. The series string tubes used in the 4 watt amp were on the dollar list at the time, and still are. I used a 70 volt line transformer for the OPT in that amp. It was $4, now around $5. I think the total amp cost was about $45.

As the challenge was ending, my engineering career was on life support requiring long work hours. I didn't have the time to work on it any further, so it all got pushed aside. All of the HBAC stuff wound up tossed into random moving boxes when we packed up to move out of Florida on 3 weeks notice. I sold or even gave away all of my working guitar amps since they were all too big to move.

Over two years later, the challenge had ended, we had moved everything twice, and finally settled into our "retirement" home. The "stuff" from Florida, however was scattered randomly in 3 different places, and several key items still have not been found.

My wife and I used to go "box shopping." We would open up a random box and be surprised by what we found. One such box contained the remains of the little 4 tube amp along with Sherri's other non related craft items. The amp probably got packed in the box with the sewing stuff used as padding.

I was never really happy with the sound of the amp, so I ripped it up, added a pair of mosfets, and the real screamer was born. As it is now it can go from clean to full metal racket just by rolling into the volume knob on the guitar, or as I use it with a Strat, by flipping the pickup switch.

The whole thread should be required reading for any guitar amp builder since there were many novel ideas discussed by several good amp builders, but it is long and often full of unneeded noise. The thread had gone silent (as it has again) for about 6 months when I discovered my old amp, so I woke it up for the amps rebirth. That started in post #1605:

The Hundred-Buck Amp Challenge

I have since found the 5 tube 20 watt prototype, so I will re-spark the old thread when I get time to play with that one. There were actually two of the 5 tube amp designs, one with all 9 pin tubes, and the other with octal output tubes. Somewhere in the original thread I hacked the octal version to run with 12AX7's and EL34's and a real guitar amp OPT. It ROCKED, but I haven't found that board yet. It's in a box somewhere near me.......
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Old 13th October 2017, 05:41 PM   #37
famousmockingbird is offline famousmockingbird  United States
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Sorry to hear about the nerve damage, I hope things improve for you. My father had surgeries in both wrists because he couldn't use his hands due to something similar. That was about a year ago and he is doing much better now. He isn't a plucker but before the surgeries he couldn't even pull the trigger on a Ruger 22.


The heater string is probably my favorite idea from that amp, I have some 50C5's I want to do something similar with, use back to back salvaged wall warts and string together some tubes. I have some 70v transformers too but haven't tried them, I am thinking I will need to splurge for some real iron. BUT a new amp is not on the list of things to do now and I do want to get something up and running for next weeks practice.

I did get the blessing to use the amp so long as it doesn't output any volume. I am told the drummer uses electronic drums although photos showed acoustic drums, probably old pictures on their web page.

The next two days I have time to mock something up so I have to get err done so they say. I am going in the basement to dig out some speakers for the cause.
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Old 13th October 2017, 06:48 PM   #38
AquaTarkus is offline AquaTarkus  Canada
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Quote:
Originally Posted by Markw4 View Post
Kemper Profiler Rack would seem to be the hot setup nowadays. Not cheap though:
We hateses nasty digital modeling ampsss!

Click the image to open in full size.

BTW I have a Line6 Floor Pod modeler, and find it isn't pick-sensitive anywhere like a real tube amp. It's kind of all or nothing when it overdrives.

Quote:
Originally Posted by famousmockingbird View Post
I have some 70v transformers too but haven't tried them, I am thinking I will need to splurge for some real iron.
The OT is the foundation of a tube amp's tone. You will never get good tone with a cheap OT.

Last edited by AquaTarkus; 13th October 2017 at 06:52 PM.
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Old 13th October 2017, 07:28 PM   #39
famousmockingbird is offline famousmockingbird  United States
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Yes we do hates digital modeling amps lol. I need my precious tube amps


I agree the OT is an integral part of tone.


I did manage to find a driver that had an already destroyed cone so I cut it off and put it upside down with a piece of foam to maybe minimize excursion. Some sound does come out but not too much, I think it will pass. I can mount it on the bottom of the amp facing down. I still will need to make a low pass filter to tame the highs. Or I can try and just turn the treble way down on my amp or mixer. I think I can make a filter on the divider across the direct output. Say 100R/10R and parallel a cap with the 10R?
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Old 14th October 2017, 12:14 AM   #40
turk 182 is online now turk 182  Canada
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hope the line input on the mixer can play nice with your amp.

hope you don't run into grounding issues with a single ended connection. (does your amp's OT secondary have a connection to chassis?)
i would rather have something transformer isolated feed to mixer. i've made use of a Hammond 324 for this purpose worked well.
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