<![CDATA[Music Electronics Forum - Theory & Design]]> http://music-electronics-forum.com/ en Fri, 20 Nov 2009 21:24:27 GMT vBulletin 60 http://music-electronics-forum.com/images/misc/black/rss.jpg <![CDATA[Music Electronics Forum - Theory & Design]]> http://music-electronics-forum.com/ Orange Rockerverb 100 http://music-electronics-forum.com/t16202/ Thu, 19 Nov 2009 03:30:24 GMT Id like to incorporate some of the preamp of this fine sounding amp into a home brew. I have the scem here but its kinda confusing... Looks to... Id like to incorporate some of the preamp of this fine sounding amp into a home brew.

I have the scem here but its kinda confusing...

Looks to have 6 pre tubes.

1 loop
1 reverb
1 pi

3 for clean/dirty

Id like to use the Dirty circuit without the rest . (no loop / clean ch. / verb)

Would this be ... V9a-b , V8a-b , and then just out to the PI tube?
The output being the 500K pot RV8 ?

Would anything have to be between the pot and the grid of the PI ? Maybe a 1meg


sorry--i just have the paper schematic here ]]> Valvehead http://music-electronics-forum.com/t16202/ Mixing power tubes http://music-electronics-forum.com/t16199/ Thu, 19 Nov 2009 02:25:39 GMT So here's my amp I've been building and tweaking now for 6 months. It sounds great, however I'm curious. The 6V6 (cathode biased 32v) grids are clipping before the 6L6 (fixed bias -47v) are. I'm not TOO concerned, however it's caused some new brainstorming. I've thought about 2 separate PIs for the pairs. Maybe a LTP for the 6L6 and keep cathodyne for 6V6. I've also considered changing the cathodyne to clip later by increasing the supply voltage and the load resistors (Ra and Rk), however I don't really want to change this as far as the clean channel is concerned when the 6L6 tube-cancel switch is engaged and only the 6V6 are running. I've also considered cathode biasing the 6L6 and getting them to run at a Vgk that is closer to the 32v on the 6V6, and considered biasing the 6V6 colder up towards the -47v that the 6L6 are at. Hope you're still w/ me here. I guess essentially I don't want to change anything except for the fact that the 6L6 aren't seeing a big enough drive voltage. Is there another way I could up the drive voltage to just the 6L6 grids aside from adding another tube and PI? Or maybe someone has a better way to arrive at my solution?
Attached Files
File Type: pdf ampage11_09.pdf (45.1 KB)
File Type: pdf power_supply_ampage.pdf (30.5 KB)
]]> lowell http://music-electronics-forum.com/t16199/ Measuring wattage http://music-electronics-forum.com/t16197/ Thu, 19 Nov 2009 00:16:25 GMT I have 60v p-p unclipped on my speaker output at 8ohms with my scope. This seems insane. (60x60)/8=450watts. I have calibrated the scope. When I... I have 60v p-p unclipped on my speaker output at 8ohms with my scope. This seems insane. (60x60)/8=450watts. I have calibrated the scope. When I use an AC voltmeter it's 20v p-p. Anyone know what's up w/ my scope measurement? It's set at 1v division and the probe is at x10. On the screen it's showing 6v p-p. ]]> lowell http://music-electronics-forum.com/t16197/ Blender pot on effects? http://music-electronics-forum.com/t16190/ Wed, 18 Nov 2009 13:24:15 GMT Hi, as I am contemplating my next build, as was wondering if anything has been done with a blender for effects loop. I have been using a reverb pedal... Hi, as I am contemplating my next build, as was wondering if anything has been done with a blender for effects loop. I have been using a reverb pedal with a tweed deluxe type head, 2 channel. By looping the 2 channels and putting the pedal in the loop I have been controlling the effect volume with the second volume pot, while maintaining a pure tube path on the first channel. I find this very desirable as I never liked having the total signal passing through a solid state pedal. I am now looking at building something similar to an Orange Graphic amp (1970's) which is single channel. I am looking for ideas or plans on using some type of blender pot in the effects loop so as to allow the original signal to also be present. Any and all help would be appreciated.

Also, and as a second question; I will have a busy front panel. I was thinking of using a DPDT center off switch as power and standby combined in order to save space. Has anyone done this? Any problem with this?

Again, many thanks to all

D ]]> DaBreeze http://music-electronics-forum.com/t16190/ primary impedance Gibsonette http://music-electronics-forum.com/t16188/ Wed, 18 Nov 2009 10:38:59 GMT Hi all - after lots of reading in this great forum I finally have a question. I am recreating a Gibson GA8 (Gibsonette with the self splitting... Hi all -

after lots of reading in this great forum I finally have a question.

I am recreating a Gibson GA8 (Gibsonette with the self splitting PP-power stage - not the dual SE) circuit and chasing for the corresponding OT.

Does anybody here have an idea when it comes to the primary impedance used in this circuit?

Thanks and greetings! ]]> pentatone http://music-electronics-forum.com/t16188/ Amp Builder new on the scene http://music-electronics-forum.com/t16165/ Tue, 17 Nov 2009 03:03:13 GMT Hey guys... I am INCREDIBELY interested in getting to know how to build amps as well as repair existing amps and mod and design effects pedals.... Hey guys...

I am INCREDIBELY interested in getting to know how to build amps as well as repair existing amps and mod and design effects pedals. The problem is although I have a good general understanding on soldering and electronic boards etc I have absolutely no experience on how it relates to sound and guitars specifically. Basically, I am looking for some reading material that can take me from green to somewhat knowing. I have a very fast learning curve and would like some material that isnt going to spend an hour teaching me something I can learn in 5 minutes so I dont get frustrated and bored. I ordered the book/dvd combo called Understanding Vacuum Tube Guitar Amplifiers from kendrick amplifers a few weeks ago and it never came in the mail so I'm getting frustrated and looking for other avenues to travel. Any suggestions would be greatly appreciated.

Dan ]]> dwfender http://music-electronics-forum.com/t16165/ Output tube impedance http://music-electronics-forum.com/t16154/ Mon, 16 Nov 2009 12:38:03 GMT Is there a chart somewhere showing the output impedance for various power tubes in push-pull. I've seen various differing opinions in other forums, just would like to have a chart for reference on future projects

Thanks

D ]]> DaBreeze http://music-electronics-forum.com/t16154/ Fender AB763 Style Optocoupled Tremolo Circuit Question http://music-electronics-forum.com/t16134/ Sun, 15 Nov 2009 02:06:11 GMT Hey guys, I'm an amp builder that primarily deals with Marshall stuff. I've done a Fender AB763 circuit once, but don't have LOTS of experience with them.

I have a couple of questions regarding the LDR coupled tremolo circuit in the AB763 Twin Reverb amp.

1) In regards to the 10M plate resistor in the lamp driver circuit that the LDR/100K resistor hooks up across, would it be OK to use another high value such as a 2.2M or a 3.3M, or would that bypass too much current and lower the voltage drop across it too low to fire the neon lamp?

2) In regards to the speed & intensity pots in the oscillator circuit, what is the reason for the circuit calling for a reverse audio taper pot? Is it absolutely critical that these be a RA taper? How will the trem circuit respond if one were to use regular audio taper pots?

3) Would it be OK to use a 250K pot in place of the normal 50K Intensity pot?

Any input on this would be greatly appreciated. ]]> Wilder Amplification http://music-electronics-forum.com/t16134/ screen supply pot? http://music-electronics-forum.com/t16119/ Sat, 14 Nov 2009 11:11:48 GMT anyone try a 2w pot in series w/ the screens after the supply node for power scaling? I have a 2 6v6/2 6l6 amp and I'd like to try this. The screens/plates are around 460vdc. I'll leave the 470ohm screen resistors in there so when the pot is essentially dialed "out" of the circuit the 470s will still be in. Thinking of using a 2watt 5k pot. Any thoughts please contribute, but I might just order the part, try it and see. ]]> lowell http://music-electronics-forum.com/t16119/ Loading a gain stage with a constant current source http://music-electronics-forum.com/t16110/ Fri, 13 Nov 2009 22:53:37 GMT I was reading the preview chapter of Merlin's book again, and was going over the section towards the end when it talks about baising. Normally with a preamp gain stage cathode biasing is used because it it simple and straightforward. But when using a resistor as is normally done, the cathode current feedback reduces the gain of the tube. Thus cathode bypass caps enter the picture, to partially or fully bypass the cathode current, and boost the gain of the stage back closer to what it could be if there were no cathode current feedback. Okay, so far so good, but now we have the new problem that adding the capacitor creates a filter which messes with the frequency response of the stage, making gain frequency dependent. Whee.

In the same section, Merlin mentions using one or more diodes with the correct forward voltage drop to bias the tube. Since diodes are not ohmic devices like resistors, once the forward voltage is reached, the current can change all it once, and the voltage across the diode is going to change negligibly, if at all. Cool! Now we've come up with a constant voltage source to bias our gain stage with, eliminating cathode current feedback and allowing us to get both the full gain of the tube, but also across the full frequency response of the tube. Yay!

This got me thinking about tricks that could be done on the anode of the tube. Loading the tube with a constant voltage source would be counter-productive, as the whole point of the stage is to get voltage gain -- a larger voltage swing out the anode than went in at the grid. But what about using a constant-current source to load the tube with? If I'm understanding the wikipedia article on current sources correctly, a constant-current source flows the same current, regardless of whatever voltage is across it. Considerations of unnecessary complexity aside what effect would this have on a gain stage? Best I can figure, the load line for that stage would be a flat line with no slope, but I'm not sure what the implications of that would be. Best I can figure, it probably doesn't have enough benefit (if any) to be worth it, or someone somewhere would have done it already.

Could someone who knows more about this than I do chime in and help me figure out what would happen in this scenario and why? ]]> Koreth http://music-electronics-forum.com/t16110/ Reverb 12AT7 Tube Heat ? http://music-electronics-forum.com/t16101/ Fri, 13 Nov 2009 14:18:07 GMT Do any of you back off the voltage on the 12AT7 in the Fender reverbs ? If you do a touch test those tubes they just run so freaking hot that it... Do any of you back off the voltage on the 12AT7 in the Fender reverbs ? If you do a touch test those tubes they just run so freaking hot that it bothers me as it seems it would burn out way faster than the others. I realize the 12AT pulls more current than a 12AX by Siemens but does it kill the tube quicker I guess is what I'm getting at ? ]]> Amp Kat http://music-electronics-forum.com/t16101/ Voltage dividers - calculating resistor values for tube substitution? http://music-electronics-forum.com/t16085/ Thu, 12 Nov 2009 02:37:06 GMT I've been kicking around plans for this project for a while now: building a clone of an old Gibsonette GA-8 (parallel single-ended 6V6 design), but using Russian 6P1P tubes, of which I acquired a significant quantity at a bargain price. The 6P1P is a 9-pin tube like an EL84, with characteristics roughly equivalent to a 6V6 except that it uses lower plate and grid voltages (+250v on each, similar to a 6AQ5).

My donor chassis is a Hammond AO-39 power amp from an A100 organ, with sockets for 2-EL84s, a 12AX7, and a 5U4GB rectifier. If I use this for the Gibsonette clone project, I'll gut it, put in a new SE output transformer, and build the new circuit from scratch. The power transformer on the AO-39 puts out 350v, about the same as that on the Gibsonette schematic.

I'm a noob at this, but I think i understand that I can get the plate and grid voltages down from the specs on the Gibsonette schematic (+320v on the plate; grid is not labeled) by substituting higher dropping resistor values in the power supply voltage divider (R13 and R12 for plate and grid, respectively, on the attached annotated schematic) for a larger voltage drop at each of those stages. Correct so far?

If my limited understanding of voltage dividers is correct, I'll also need to use lower dropping resistor values after the ones for the plate and grid, so there is less voltage drop across each of those, in order to keep the downstream voltages the same as spec. That would mean R9, R7, and R5 on the attached schematic, correct?

And that is about the extent of my understanding. I'm now at a loss as to how to calculate what values of resistors I would need to substitute to get lower voltages at those two stages of the divider network while keeping the further downstream voltages the same. Any ideas, or links to a good reference source that will help me make the calculation?

Thanks!
Attached Images
File Type: jpg GA-8 schematic - annotated.jpg (783.7 KB)
]]> Alex_SF http://music-electronics-forum.com/t16085/ Is 2 Watts enough for power resistors? http://music-electronics-forum.com/t16084/ Thu, 12 Nov 2009 01:06:44 GMT I know a lot of power resistors are 3W metal oxide, 5-15W ceramic and even wirewound. Will 2W be enough for a typical 2x6v6 build (20-40 uF filter... I know a lot of power resistors are 3W metal oxide, 5-15W ceramic and even wirewound. Will 2W be enough for a typical 2x6v6 build (20-40 uF filter caps)? ]]> Natman http://music-electronics-forum.com/t16084/ My Vision of the Future Guitar Amp http://music-electronics-forum.com/t16075/ Wed, 11 Nov 2009 21:27:50 GMT Let me start by saying that I fully understand there will always be a percentage of players that will never give up tube amps and analog effects. I... Let me start by saying that I fully understand there will always be a percentage of players that will never give up tube amps and analog effects. I don't know what that percentage of the market is, but I believe that as technology improves & prices come down over the next 5 years or so, 2 things will combine to dramatically change the typical new guitar amp. More refined, modify-able modeling technology & multi-touch screens could provide the features & user interface that push the vast majority of players over to digital modeling for good.


Here's what I envision for the evolution of the common guitar amp:

The "faceplate" will be a multi-touch flat panel screen that runs the width of the amp.

The screen will allow you to choose pre-amp effect(s), the amp sim, and post-amp effect(s).

You will "flip" through pictures of effects boxes & amps with a swipe of your finger ala the iPhone.

Once selected, the screen will display visual controls that match the original effects & amp models' faceplates.

You will "grab" virtual knobs with 2 fingers & turn them like you would a real knob for adjustments.

Higher models will have an "Advanced" button for the modelled amp or effect that adds more virtual knobs for parameters that the original didn't. Players who want simple interfaces get what they want & players who want more options get what they want, too.

Foot controllers could be as simple as switch & light units that correspond to the pre-fx, amp, and post-fx displays - keeping all the controls up on the amp. No more bending down to the floor to adjust effect controls.

The amp could have only guitar speakers or it could have FRFR (Full Range Frequency Response) speakers, enabling it to be used with electric or acoustic guitars or even with guitar synths. The amp sim & effects can be suited for any use at that point.

The number of effects, amp models, preset banks, etc., can be varied for different sizes & price points, but the undelying technology can be reused from model to model.

Since power up is essentially a computer boot, the display could show the amp in "Standby" until the computer is ready, when it shows "On".


Here's where I think it gets very interesting. If manufacturers adopt an open software model for their amps, modders could begin modding the sims or creating new ones - including your own custom faceplates (Line6 already has software available that you can use to create your own effects). The ability to create your own sound AND look would be very compelling, I think. ]]> Phostenix http://music-electronics-forum.com/t16075/ Amp to Speaker/Cab Simulation - Your Experience? http://music-electronics-forum.com/t16073/ Wed, 11 Nov 2009 19:34:27 GMT Here is what I have. I've been comparing two setups.

My first setup is a full-up amp modeling floor unit with amp models, cab sims, and effects. Although for the sake of testing, I turn off all the effects leaving it with a 57 Tweed Deluxe amp sim and 1x12 Tweed Deluxe cab sim enabled. My second setup is a real 5E3 clone amp with the speaker-out connected to a Palmer PDI-09 and the speaker-out of that driving a home-made resistive load @ 8 ohms. In both cases, I'm sending the XLR signal I want to a simple powered PA monitor.

Tonally, these setups both sound pretty close to each other working with them at home. I have not tried gigging the Amp + PDI yet. I started playing with the PDI because I wasn't happy with how cold and weak the sound from the modeler was in my in-ear monitor.

In my comparison test at home, both have a bit of a cold and metallic sound as compared to the 5E3 directly to its own Weber 12A125A speaker. I would roughly expect this result, but was looking for ways of improving it. A guitar speaker has this interesting mix of warmth yet sparkle that you don't get through basic EQ techniques. If I could find a little green box that sounded more like my Weber speaker, I would be happy.

Let me know what you know. :) For example, would using an inductive load, instead of resistive, help? Or do I need to get into much more expensive speaker simulator units? ]]> mbratch http://music-electronics-forum.com/t16073/