Ah, I see - thanks Phil and JM.  So just by sheer luck, my clamp is "working" but puts the Zeners and my PT at risk.  I'll take it out and I'll have live with the over voltage.  Or how about some small value resistors? 

When I do the math for this I'm getting weird results: 

R=V/I so

R=.7v/3A
R=.233 ohm?

Can't be right - never heard of a .233 ohm resistor???  I must be doing something wrong here...any help is appreciated.

Or should I just insert a voltage regulator of some kind - recommendations?

Jim

Just checked, they are 5 watt Zeners (1N5339B) - so they should be ok for clamping that small amount (.7v).  The Zeners for clamping the 12v down to 6.3 was a bad suggestion - don't do it.  Run the heaters in series and use the 12vac and that will be simpler and work without issues. 

Jim

So based on your answer, the Zeners won't take it and if they don't fail it could cause the transformer to fail?  So in reality, the example I showed is pretty flawed.  Or is it only usable when say the voltage being clamped/clipped is not significant or is it the current that would cause the failure?  Would larger zener's work - say 5 watt?  It seems to work fine for dropping the less than 1 v in my usage but in this usage (dropping 6vac) it would basically be a failure waiting to happen, if I'm understanding you.  The 6 vac at 1 amp would be 6 w - much more than the 1 watt resistor or 2 in series.  I see what your saying.  In my usage if the voltage drop is .7 (or so) and I have 2 x 1 watt 5.6v Zeners, they must be seeing about 2.1 watts or more as that circuit is a 6.3vac 3 amp filament - does the Zener get hit with the current if it's not actively clamping the voltage?  Maybe I should swap these for 5 watt Zeners.

Thanks for the insights -

Jim

But wouldn't this do the job -

http://www.electronics-tutorials.ws/diode/diode_7.html

About 3/4 way down, Zener Diode Clipping Circuit.  I used it to regulate 6.3v AC heaters since I was reading over 7v due to the way the PT was wound - 115v pri where we get 124v normally.  With 2 Zeners configured Cathode to Cathode and the Anodes attached to the 2 sides of the heater filaments (I put them at the start of the circuit just after the PT), I could get 6.3v pretty steady.  I used 1 watt 5.6v Zeners since .7v is forward bias voltage giving a total of 6.3v (still I wonder if someone actually made the 5.6v Zeners just for this purpose since they are perfect for it). 

Anyway, this is what I thinking about when I mentioned Zeners - I guess I wasn't clear. 

Jim

Hi Juan, 

Good points.  I was thinking that the transformers would have to be rated high enough but didn't realize that the first would have to be so high (double) in terms of current.  But I suppose it has to come from somewhere!  And that would make sense if you are "stealing" the filament source from that one, it would have to be high enough to still provide enough current for the rest of what you're doing with it.  Not trying to argue with you but, I'm trying to understand your statement that it would be "incorrectly mixing AC and DC circuits".  In the tube amps I've built (2 completed and working on #3) the filaments were all AC but the rest of amp was all DC.  This was at 6.3 VAC and the heaters were wired in parallel.  I was thinking they could also have been DC at 6.3 in parallel since he's got 12v AC to work with is this ok?  So I guess my thinking is wrong here, can you explain since I'm not understanding why.  And yes, your right, he could do 12VAC heaters as well with probably less work just wired in series, but I'm just used to thinking about heaters at 6.3v! 

Hey, maybe you were thinking that I meant that the second wall wart was DC?  If so, I apologize for not being clear, BOTH have to have AC secondaries, or this won't work. 

Thanks - and as always, appreciate your insights,

Jim

Quote from: jcgss77 on November 13, 2011, 03:15:05 PM
Have you heard back from Line6 yet?  I am curious to hear what they have to say from a technical standpoint about this. 

I do think, however, that since you are designing a speaker box for these amps, that you should experiment with lower wattage speakers than what the amps put out.  I have found that going with a lower wattage speaker can color your sound in interesting ways, that aren't always unfavorable.  Of course, it all depends on what sounds good to you.  A lot of people actually use a total speaker wattage of half of the amp output.

:lmao:

Good one! 

Wait, unless your serious then all I have to say is:  WOW!  Oh, and please clarify.   Would the "color" include the sound of the speaker self destructing?  I must have been living in ignorance as I've always understood the rule of thumb is that the speaker should be rated for double the amps rated power.  I wonder if I've been doing it wrong all these years...

Jim

It's super dangerous to do it that way without a transformer.  What you want is a an isolation transformer that has seperate primary and secondary windings.  Believe it or not this was actually done on some old tube amps - I believe even models that Sears sold (Silvertone, for example).  They were just being cheap and pretty reckless.  Don't be cheap and foolish - get a transformer and do it right. 

For a cheap solution, get 2 wall warts that put out about 12v AC or so (more or less is ok so long as they are the same).  Also whatever kind you choose and make sure you get some with enough current output to handle your complement of tubes and the rest of the circuit.  Then wire them back to back - like this:

(input) 120VAC -> WW1 -> 12VAC - 12VAC -> WW2 -> 120VAC (output)

A tricky way to do this would be to have a jack on the outside of pre-amp that accepts the 12v output of the first WW (WW1) then wire that receptacle to the other WW (WW2) that's inside your pre-amp housing. 

This will provide isolation since each of the wall warts is isolating the mains from the output (so actually double isolation).  One thing you will need is 6.3V AC for the heaters.  You could tap into the 12V from the output of WW1 and with dropping resistors or even with a pair of ZENER Diodes (use 1 watt 5.6V Zeners) to get it down to 6.3v -or if you want you can rectify that too (plus filter) and have DC heaters - do the rect before the Zeners and you will only need 1 to clamp the voltage to 6.3v - but you'd still use 5.6v zeners though.   

Jim

Well, if this example is any indication I'd say it's more -

So as Mexi pointed out, we have:
80w at 8 ohms
What is the wattage at 16 ohms given that doubling impedance will reduce the wattage at 8ohms by 31%. 

So 100% - 31% = 69% so the reduced wattage is 69% of 80w so:

.69 * 80= 55.2

But to go back:

X% of 55.2=80

And we solve for X:

(55.2 * X) / 55.2=80 / 55.2

Then simplify:

X=80 / 55.2
X=1.449275362318841

So let's just say it's 1.45  - so going the other way is 45% more (if I did that right - and that would be amazing as I'm pretty math challenged)

I think that the danger is that if you drop it further than the rated impedance, it tends to have a run-away condition when the actual impedance drops even lower.  Keep in mind that the 8 ohm impedance is "nominal" meaning it can vary - less and more depending on frequency.  So really at certain points, if it drops too far, poof, there go the output transistors:  crackle, roast, melt...

So if we go a head and do the last part:

1.45 * 80 = 116

So 116w at 4 ohms

What about 2 ohms (which it will hit at various frequencies)?

1.45 * 116 = 168

So double the wattage at 2 ohms!   It all really depends on what the transistors are rated for.  I'll have look them up. 

Jim

Phil,

Looks like I'm going to end up building your PhABBTone -    - read a lot of the other threads and like the sounds in the clips.  Still working on getting some that I can show you what the sounds are like now and after I get it tweaked. 

The Jet City worked well - for almost the whole practice I used it with my HO - SE all tube, about 10 watts.  The amp was barely able to keep up as the other guitar player had it volume up.  It did ok.  At the end of practice I tired the Marshall and it really does improve the sound - deeper and fuller.  Also, because the speaker is 16 ohm, it is less volume at the same settings but that's good as I'll have more lee way in adjusting it - if that makes any sense.  I did try backing off the gain and getting cleaner signal even on the OD channel and that seems to also help with the "cutting through".  I'll have to retrieve the Marshall as it's still over at the drummer's house and play with it at home where I can work on the EQ settings and trying to tweak that.  So progress is being made but there's more work to do to get it optimized and I'm sure I can get killer sounds out of it with the right EQ - I'm going to build the PhABBTone and try that out too! 

Many thanks to all for the great insights - ROK ON ! 

Jim

Ok - thanks Phil.

Man, I've got some reading to do.  Been chasing down all your posts you linked to and then links inside of them.  Got it all downloaded and I'm going through it - this is so cool!   

Thanks so much,

Jim

Phil,

Wow - thanks for the detailed descrip and pic.  I have a few questions - can you lay out the single chain for me?

Is it something like: 

Guitar ->  GEQ -> PHABTONE -> AMP

Are your effects in parallel to both the GEQ and PHABTONE or just the GEQ?

I think I might be able to find GEQ like that for cheap somewhere - online, thrift shop or even my local pawn shop.

Jim

Erokit - Thanks for the ideas.  I appreciate any input on speaker selection as I don't have any real identifiable speakers right now to form an opinion on.  The one that came in the Valvestate is a "non-specific" model OEM Eminence.  I might as Eminence if they could tell me how they would describe the voicing that they used for that speaker. 

I've considered the Celestians but as you point out they are pricey but there's Warehouse speakers and they are supposedly some very good clones of Celestians for a very good price.  I'll be looking into those for sure - probably 75 watt model. 

Update on what I've been able to do with the Jet City cab - finished running it with the 6.3 heater supply of PT for the in progress TD.  Since the Marshall is at the drummers house (he took all the equipment in his truck to the gig and brought it all back to his house, which is where we practice anyway), I hooked it up to my AX84 HO SE tube amp.  It's only about 5 -10 watts (depends on which tube I use).  I've tried it with my Ibanez and man it pumps out the Bass - I can play my marshall at pretty good volume levels in my basement but with this my wife came down and told me me turn it down - I think it's the whole lower harmonic content that you get with tubes.  My Marshall NEVER has this much bass - in fact I had to turn it down as it was almost too much bass.  I'm going to try some different tubes as this is an SE amp that has adjustable cathode bias (uses a pot in series with a small cathode resistor) .  So far I've tried an Old Stock Sylvania 6L6GC that has killer bass but it's almost too much.  I'm going to take it tomorrow to practice and see how it does.  I'll also hook up the Marshall to see how it does with the Jet City and report back - maybe I can record the practice.  I'll ask the drummer if he has any way to record us.

Jim

Quote from: mexicanyella on April 02, 2012, 07:05:21 PM


I would suggest backing off that bass. You're probably fighting a losing battle (and eating up headroom) trying to get all that bass going. But the stuff people are going to hear offstage is not the pants-flapping low-end chunk (especially with a 1 x 12 open-back), however they will hear mids and highs, and that's where a lot of the tonal character resides anyway.

I have found that while it seems counterintuitive, sometimes small amps can make some righteous sounds if you run the eq knobs pretty low and slam the signal elsewhere in the chain. For example, I have a one-channel Peavey with pre and post gain, plus bass/mid/treb. With my single-coil guitar, with pretty low-output pickups, I can get a nice rhythm grind that's bright and cutting but not harsh if I run the bass on 2, mids on 3, highs on 4...but make up the gain by pushing the post gain hard, like 6 to 10, and then setting the grit level to taste with the pre gain...in my case, I like it about 6. This makes a surprising amount of noise from a 12-watt SS amp, with light speaker breakup but it sounds bluesy, not "about to catch on fire." A similar approach might work for you; try backing all the eq down and cranking the channel's post gain and master harder and see what that does. Maybe knock the pre gain back a number or two and see if shifting the gain boost later in the chain, with less in the EQ, sounds "rootsy and organic and cool" or just "stupid." Can't hurt to try it.

From the music you listed, I think this could work for you; none of those bands relied on large amounts of chunk coming from the guitars.

Keep in mind that the bass guitar and drums have physics on their side for producing low frequencies, and if you step out of that realm somewhat you are making it easier to hear them do their thing, while keeping your efforts in frequency bands your equipment's better set up to deliver. Again, even if the sound you get is not ideal to your ear when soloed, it's how it sits in the mix that counts, if you're in a band.

Keep us posted on how the experimenting goes. Maybe you'll find that you just don't like your amp, but if you can make it work for you it's cheaper and easier to carry...

Mexi - Thanks for the ideas - I'll check out your suggestions - I suppose I just thought that I was too bright and wanted to "warm" up my sound so I ran up the bass and dropped treble and recently I've been playing with the mid trying various settings and that's where I last had it.  I've also been trying various gain/volume/mv settings.  I should probably explain - and this would also go to Phil's post - some more about what I'm using as far as guitars and amp. 

Guitars: 

- 1982 Ibanez Artist (AR-100) with Humbuckers - this is my "main" guitar and use it for most things. 
- 1993 Charvel Strat copy with single coils - - this is my "single" coil guitar for use on the songs that need a single coil sound
- 1993 Fender '57 Vintage reissue Strat - I don't use this right now as I need to do some work on it

Amp:

1992 Marshall Valvestate - 2 channels, Clean and OD - Clean has Gain, B, M, T:  OD has Gain, B, M, T, Contour, Vol, - There's in/out effect loop with effect mix (dry/wet), Reverb, Master Vol.  Also, each of the channels has a OD level switch - in the clean it just adds a little grit but on the gain channel it takes it from pretty good crunch/dist to "JCM-900ish" scream.  Some people don't like the JCM setting because they say it gets buzzy but if you adjust the eq it tones down the buzz.  Now the contour is pretty cool, if you max it you get a really scooped out sound and at the minimum setting the opposite - it gives it a really good mid boost/peak.  I don't like the minimum setting and the scoop can be good for some stuff (metalish or just really high gain lead sounds).  I usually run it at around 6 of 10. 

Overall, I play both rhythm and lead - more rhythm probably.  Lately I've been switching between the Charvel and the Ibanez when I need to but I really don't change the amp settings other than to switch to the clean channel.  I usually don't run the Charvel on the OD channel as it's not shielded (something I need to do) and can buzz/hum a bit if the gain is up.  I tend to use an old Boss OD-1 to boost the clean channel with the Charvel if I do a lead.  I also have a dist box that I use on the clean if I want some more dirt for lead but for rhythm I just use the basic amp - sometimes the boost and just control volume with my guitar.  I tend to use the Ibanez more for the OD/higher gain stuff - we do some Santana and it works well for that.  One thing I should say is that I tend to play a lot of stuff, even my leads, on the neck pickup of both guitars - I like a warmer/mellower tone that's not so trebly/biting/buzzy - I guess it's the Santana influence, trying to get the "woman" tone.  ;-)

Phil, I'd been thinking about building a small eq since I saw some plans and a PCB someone sells to make one.  Where do you find the graphic EQ you mentioned for that cheap?  Aren't they rather large?  Where do you put them while you're playing?  Parametric is also interesting.  Oh, as far as pickups, all stock - I was considering changing out the Charvel ones for some SD and possibly getting the stacked humbuckers for the bridge - I'd like them to be switchable between SC and HB mode.  Still, to change them all out would be a chunk of change too.  I really don't want to mess with my Ibanez as I've read they are now rather sought after and mine is in really good shape - I got all my equipment new and have been the only owner/user.  I tend to take good care of my stuff - other guitar players are amazed that they have so few scratches/dings in them for their age, well, I don't to drink to excess, don't do drugs and I put them back into their cases when I'm done using them - no extraordinary measures.  Maybe it's the hard shell cases - I like to get hard shell with my instruments and "back in the day" lots of music stores would throw in a case to sweeten/close the deal. 

Joe - your post hit as I typing this.  That's a good plan but I"m no where near the 4 x12 in terms of ability to build or buy.  I think I'm going to replace the internal speaker with a 16 ohm and in parallel with the external 16 ohm that should be 8 ohms right?  I was thinking an Emi Wizard but it says on the Eminence site that it's more for closed back cabs not open so I'm looking for something with super high efficiency like the Wizard (103 db!!!) so I won't loose so much "volume" when I put the 16 ohm load on the amp.  That way, I can use my Jet City cab with the 16 in there in parallel with the internal for 8.  I suppose another option is to replace the Jet City speaker with the 16 ohm Wizard and move the Jet City into the Marshall to see how it will sound.  That way I can parallel the 2 or use the ext or internal - with some reduction in power output.  - I think that's my plan. 

So for now, I'm going to do the following - work on the eq settings, as I beleive and as Mexi has pointed out, this is core to my sound.  Try to get/make a low cost graphic or para eq per Phil's idea.  Continue with breaking in the Jet City speaker and getting the cab put back together to use with my Marshall for now.  Order the Emi Wizard when I get my Tax refund!!!  I've already done the jack as Juan recommended, it was super easy - there was already the perfect sized hole in the bottom of the chassis where a wire crimp/holder thing was installed to hold the hardwired speaker wire.  I just removed the wire from the speaker (spade connectors) cut off the ends and installed a 1/4 cliff type jack (hole is perfect fit -no drilling required).  Made a speaker wire from some 16awg speaker wire I had (stuff that you use for stereo speakers - 2 parallel, copper/silver leads in red/black plastic) and attached spade connectors and a 1/4 plug to the ends.  Works good.  Now I can run a speaker wire to the ext cab and play through that or plug in the internal speaker.  I could also make a "Y" cable to run both the internal and external at the same time - in parallel.  But that will be after I get the other 16 ohm speaker - which ever one I decide on.  Right now the Wizard looks like a good candidate.  I'll look at Juan's list of speakers and see if any of them might be good for the open back Marshall or the Jet City.  Not sure if he really only meant them for the 4 x 12. 

Lastly,  in light of the size and cost of getting and fitting out a 4 x 12, would a 2 x 12 be worth considering? or would it be case of just a "bit more" and you'd have a 4 x 12 so why not go for it.  One very big consideration is the size and weight issues of lugging it around. 

Thanks again for all the great input - really helps me to figure this out.

Jim

Oh, one thing - I've never used the Jet City cab as I bought with the intention of converting it to a combo - putting my Tweed Deluxe (TD) into it.  Since I'm not so good at wood working I figured that I could maybe cut here and there and get the tweed chassis to fit into it.  I measured everything and it seemed like it would fit.  So I took it apart and it's been that way since.  So to break in the speaker (which is brand new) I took the PT destined for the to be completed TD and capped of all the secondaries except the Heaters and the CT's.  The Primaries I wire nutted to a power cord (with 3 prong plug).  I got a jack and attached 2 wires to it and twisted them and wire nutted them to the heater leads.  The CT's I attached to the power cord ground.  I plugged the speaker into the jack and it's been humming along for about 12 hours.  How long should I run it like this to break it in? 

Jim 

Thanks for the replies guys - I appreciate you taking the time. 

Mexi:

Since I posted I've spoken with some other guitar players and they pointed out some of the points you've made.  The closed/open back cab is definitely a factor.  And I'm definitely with you on the eq settings - right now my Amp settings EQ wise are Bass=10, Mid=8ish, Treb=4-6 (depends on the song).  Gain wise I'm at about 6 (out of 10) so I'm not maxed out and the way I've found sounds good is to put the MV at around 8 or so and control the level with the channel volume.  On the Clean channel the Gain=volume but on the Lead Channel there's a sep gain and volume for that channel.  On my Guitar I'm running it mostly on the neck pickup and even then I turn the tone down to about 7 or less.  If I use the bridge the treble/tone is down even more but that could depend on the song.  I'm going for beefy, meaty tone but everything I've tried just doesn't get it.  Reason I was lamenting about the amp is that it's a MOSFET back end and you know the old saying about tubes and the lower/deeper bass they can get because of the harmonic content.  I really beginning to think this is true.  That said, I'm still going to tweak the eq and see if I can't get it to sound better.   Oh and we play mostly classic rock - CCR, Grand Funk, some country, Seger, Skynyrd, stuff like that. 

JM: 
Yes, I'd love to get/steal/make a 4 x 12 but not with my money situation at the moment.  As for the making option, I'm "wood working challenged" so that would take me 3-4 times as long as someone with those skills.  As I mentioned, I have that un-used cab with the 16 ohm and I've already started the work to install the jack.  And yes, how you describe is how I'm planning to do it - jack in the chassis and solder a plug to the short cable attached to the speaker (using spade lugs) then plug it into the jack as needed.   One question about your comments: Yes I found out I had calculated the parallel impedance wrong - just by simple logic I should have seen that since 16||16 is 8 ohm 16||8 has to be less than that - Doh!  But IF (when), I replace the internal speaker in my Valvestate with a 16 ohm speaker, I can run that in parallel with the Ext Cab without any issues right? 

Again, thanks for all the great input. 

Jim