What do these do ????

[TIMBO]

Hi guy's, Always looking for something different and as i like all things "Jimmy Page" this schem caught my eye and got me intrigued.As we all know there is always a basic Fender/Marshall in most amps and then someone throws a few bits in to make theirs different.

So could anyone enlighten me as to what these bits do:-

The balance pots function
V3a does not appear to be connected for signal to pass,unless it passes via the plate/power supply   Thanks

[kagliostro]

Interesting question

EDIT:

About the tube I can't say

About the pot, seems that is used as some kind of pre-level control to adjust the level from V1a to V2b (as labeled in your example), SW1 seems there to exclude this kind of pre-adjust

as balance pot, in my mind, I see a trimmer and as SW1 a footswitch, but this are only my conjecture

K

[DummyLoad]

sets the bias for the LTPI - about 1/4 of B+ at node D - leave no triode unused philosophy, i guess... 

--DL

[SILVERGUN]

i like all things "Jimmy Page"

 
Can't let that comment pass without sharing this.......one of my all time Page favorite moments (the guy is just bleeding through his Tele)
He says more with these 7 notes than most people say in a lifetime of noodling....30 years ago this September  ....timeless
Sorry for the Hijack, but I'm hoping you'll appreciate this: 

Prelude / Royal albart HD edit...

[Backwoods Joe]

SilverGun that was a great hijack. Loved it. Jimmy sounded almost Beckish for a moment while enjoying a good cig!

[Jack1962]

My I ask a question Timbo ? where did you get the schematic from? I ask because there seems to be a few inputs missing Page's Hiwatts had 4 1/4" inputs and a XLR .

[kagliostro]

http://hiwatt.org/Schematics/DR_Pre2InputJP.pdf



K

[SILVERGUN]

Thanks for that K,
That's a nice looking schematic, and a cool idea for stage....

Am I seeing this correctly...2 footswitch selectable guitars plugged into one amp with a balance control ? 

[TIMBO]

Thanks for all that info guy's, I love these quirky amps. Thanks for the HIJACK Silver, i can't say that i have seen that clip, it got me thinking of when i first heard jimmy (led zeplin) blew me away. When i was 13 my older sister was in a record club and you had to buy a couple of records a month, and when she wasn't around i use to play then. Even at that stage they wern't really my taste (elton john and a few others) anyway a kid at school brought a cassett tape (one of the new gzmos to hit shelves)to school and the only place to play it was in the library in one of the sound proof rooms. Well we had Led Zeplin (led zep four)cranked as much as you can on a one watt cassett player and been hooked (38years) ever since Thanks  

[HotBluePlates]

My guess:
The XLR is not a switch as indicated, because then the Balance control would do the same thing as the Input Volume. If there were a switch on the other end of the XLR cable, all it can do is short out the 1M resistor, or not, which would change the volume set by the Balance control. Also, the name "Balance" doesn't make sense.

My guess, Part II:
Page had echoplex's and other effects, and may have had something onstage that used an XLR cable and didn't need the gain of the whole preamp. Maybe his guitar signal was split before the amp, with 1 line to the amp and another to these effects. The balance control then is a dry/wet control.

The 1/4" jacks feed the 1st stage and the cathode follower, then hit the Balance control on one side. The XLR jack feeds the other side of the Balance pot.

The XLR input gets less gain as a result of not being boosted by V1. The Balance control selects guitar input or XLR input or any blend of both. If the XLR input is from effects, or perhaps studio outboard gear with a relatively high signal level and an XLR output, then the Balance control makes sense as well as the placement for less preamp gain.

[TIMBO]

Thanks HBP, If i was to build it i would probley delete the balance if it is not a useable thing.Thanks

[sluckey]

Just a thought... The onboard preamp on my Taylor 614CE uses a balanced output. The cable has a stereo 1/4" connector on the guitar end and an XLR on the other end. That amp with the XLR (even though it's wired for unbalanced input) would be useful to me because it would allow me to connect the acoustic to the XLR bypassing a couple gain stages since I don't need those with the onboard preamp, and also connect my Strat to the amp's hot input. Then just dial the 'balance' control one way or the other to select which instrument is active.

[SILVERGUN]

Thanks for posting that Sluckey (and HBP)....it made me go back and look harder at the XLR jack labeled "switch" (just one more reason why I shouldn't post before thinking)

Maybe Page used that to amplify his acoustic guitars onstage....(?)

And just in case you didn't think to try this: (just removed the specific file path from K's post)
http://hiwatt.org/Schematics/

[sluckey]

XLR jack labeled "switch"

I totally overlooked the word 'switch'! After seeing that and also seeing a similar schematic, I no longer think the XLR was used for an input signal. It was just a footswitch that changes the signal level. The only amp inputs are the 1/4" phone jacks.

[SILVERGUN]

Welllllll,,,,
Thanks for posting THAT......clears it all up a bit 

Just one more reason why I shouldn't post stupid replies too quickly 

Maybe next time I'll just map it out,, so I'll be able to see what it does and not just assume

Learn something new everyday....

[SILVERGUN]

So, would this be a crazy way to utilize that control for a lead solo boost?.....

Kinda like having a built in switchable LPB,,,,,only it's a "Tubular" Power Booster, on the frontend

[sluckey]

I think so.

[SILVERGUN]

I think so.

Now we're cooking 

So much for it being a useless control Timbo  ....I'm trying to draw it into my schematic now,,,and it's not that tough
I was trying to figure out how to put an interesting solo boost on my single channel........this might do it

[kagliostro]

I think the most part of the confusion is related with the kind of input female jack are used

I don't know the effect on you, but I become cross-eyed looking to it and trying to follow the signal 

K

[SILVERGUN]

I become cross-eyed looking to it and trying to follow the signal 

Yeah, thats why it beat me up a little at first....once I realized there was only one wire coming (ground) from the input jacks, it free'd up a couple brain cells  .......

It's just there to select how much signal gets sent to ground , and it's adjustable thanks to that Balance control 

Cool "trick", and I'm glad I joined in on this thread to be exposed to it 

[TIMBO]

OK, Sluckey you have twaeked my thoughts in that i don't have an amp for my acoustic so could a mod be done to do what you were saying

Silvergun, Go for it buddy, i'll be interested in what you find.Thanks

[HotBluePlates]

XLR jack labeled "switch"

I totally overlooked the word 'switch'! ... It was just a footswitch that changes the signal level. The only amp inputs are the 1/4" phone jacks.

I struggled with that one, too.

This is the thinking behind my guess:
If the "switch" label is truly a footswitch, then with the 1MΩ at the XLR in the circuit the signal level presented to the input volume is higher than when it is shorted out.

Now the "Balance" control has a confusing label. It alters the volume level of both switch settings, but doesn't exactly "balance" one against the other (unless, I guess, you think of "relative" in place of "balance"). The "Input Volume" control is now redundant, unless it was intended as a "preamp master volume" ahead of the master master volume. 

If the XLR is a second input instead, it might be for a relatively high-level signal with a ~100k or lower source impedance. Now the 1MΩ is a bridging resistance for the source impedance, the cathode follower has a ~100k output impedance, the "Balance" control forms a ~100k resistor string between the two sources. This lets the Balance control balance the two signal sources.

Hell, it might even be both... It wouldn't be the first time an amp company used an effects loop as a volume/distortion boost when effects aren't being used. It just this "loop" requires splitting of the signal before the amp's circuitry.

So maybe a two-fer? 

[TIMBO]

Here is some insite to what is going on http://forum.metroamp.com/viewtopic.php?f=10&t=22849 sounds neat

A bit more http://www.reevesamps.com/customJimmy.htm

[HotBluePlates]

Well, I guess I had that one wrong.

I'm digging the idea though... I may steal some version of my wrong guess to make a non-loop effects loop on a future build.

[Willabe]

Here is some insite to what is going on http://forum.metroamp.com/viewtopic.php?f=10&t=22849 sounds neat

I just got attacked at that site link above. Norton saved me.


              Brad     

[DummyLoad]

a variance of the same ckt.

[SILVERGUN]

I found this to be an easier way to see it: (don't see why it would be necessary to tie it in with the input jack grounds)

Just like the hand drawn 'detail' pic Sluckey posted above

[Willabe]

(don't see why it would be necessary to tie it in with the input jack grounds)

That's the shield connection. Look at how it's drawn. See the circle with the dots/dashes around the input grid wire.


          Brad      

[SILVERGUN]

That's the shield connection. Look at how it's drawn. See the circle with the dots/dashes around the input grid wire.

Yes,,,I saw that.....
I was referring to the way it was drawn that threw some of us off at first..........( my adjustment was meant to make it easier to "see")

BUT,,,I was considering putting the jack on the back panel,,,BUT I imagine there may be a noise issue, which would explain why Hiwatt would put that switch jack on the front ......

Maybe that's why it was drawn that way on the schematic 

[SILVERGUN]

Here's an OK demo:

Hiwatt SAP Balance control Demo DR 201 1969 KT88

For me it might be cool because I've got a single channel with a ton of OD built in and I was coming to a point where I was going to have to figure out how to tame the front end a little....

It also might make a good "SBC" (soundman bypass control)

[SILVERGUN]

One other thing.....

Wont the signal ground be traveling through the entire length of your footswitch cable?....noisy,,,right??

Makes me wonder if it might be a good canidate for a Hoffman relay board......hmmmmm

[sluckey]

Wont the signal ground be traveling through the entire length of your footswitch cable?....noisy,,,right??

Yes. It's very important to use shielded cable for the footswitch, just like a typical Fender reverb footswitch.

[SILVERGUN]

Sorry Sluckey,,,I was editing while you were posting....

Maybe I'll start mapping it out as a relayed switch for my application,,,cause I've already got enough noise

[Willabe]

Yes,,,I saw that.....
I was referring to the way it was drawn

On a shielded wire you only ground the shield at 1 end. So where should it be grounded? At the input jack ground or the tubes ground, ie, grid/cathode?

That's why it's drawn that way. Their telling/showing you ground it here and not just anywhere.


             Brad    

[SILVERGUN]

Cool.......I'm gonna try it, while this thing still has it's guts hangin' out, and nothings permanent

I guess the tricky part is going to be,,, where it sounds best in my circuit

I picture it as a sort of a fancy adjustable / switchable  grid leak resistor  

[SILVERGUN]

TIMBO,
Would you like me to continue my rants about experimentation here,,,,,or should I start a new thread?? 

I may need help, incorporating this into my circuit, and this may distract from your original intent...

Just figured I'd be polite and ask 

I'm going to separate my paralleled V1 and run the cathode follower route (like the print) into the balance control mod,,,and it's gonna involve moving my tonestack,,,but luckily I have an unused AU7 triode in the next stage ,,,,so this should be fun!!

[TIMBO]

You go for it SG, This is why i like these amps, there is something a bit different in them.

This is why i built the TBO (BTO) with the FUZZ and OD in it, But with the problems that it had, it was a pita to trouble shoot, so if someone is willing to do some of the hard work, in working out these circuits this can only help when doing the build. 

I have a pair of 6v6s and an OT to suit and the PT is from one of my scores, so if you are willing the do some leg work it might save me from drilling some unwanted holes in the chassis Thanks

[SILVERGUN]

I'm on it right now.....just the smell of flux has got me going 

I'm in a barely heated shop with 3 layers of clothes and foot warmers in my shoes,,,,with an ice cold beer,,,and I couldn't be happier 

I needed a good reason to really start moving wires around!

Wife's gone all night,,,,so if I can just get this done in time to catch the Flyers game (and a couple more beers),,,it'll be a great day!!!

[TIMBO]

Hey Willabe, Maybe the XLR would be better to use that a phono jack cause the outer ring of the XLR is connected to the shield and this leaves the ground as a separate connection.

[TIMBO]

SG, the weather here is 30Deg c sun shining and have a box of cronars to demolish, so i feel for you (not) so heat up that iron and get warm. Thanks

[Willabe]

Hey Willabe, Maybe the XLR would be better to use that a phono jack cause the outer ring of the XLR is connected to the shield and this leaves the ground as a separate connection.

Maybe. I guess it would depend on how you wire up your grounds?

The last 3 builds I've done had only 2 ground connections to the chassis. 1 for the safety ground and the other for the ac ground. All jacks are isolated/insulated from the chassis. It's a wired galactic ground from KOC TUT books. It's very quite.


            Brad     

[SILVERGUN]

Alright, it's in.....it aint pretty, but it's in  ....used double sided tape to secure pots and switch

So far I can control input vol. and balance,,,,,but switch doesn't do anything.....just taking a break to get ready to go back at it with a clear head...

I'll report back later, and hopefully be able to post a schematic,,,once i figure out what i did here 

I must be having fun if I'm missing the Flyers 

[Willabe]

Alcohol and high voltage don't mix!!!!!

No if's and's or but's!!!!    

Go watch the hockey game.


              Brad      

[SILVERGUN]

That's my one beer.....saving the rest for the couch 

Don't worry about me and electricity....I work around 600 AMP welding machines all day 

If I'm gonna get zapped, it'll be between 8am-5pm mon.-fri. 

[Willabe]

You drink at work? I don't think so.

Do what you want but it not wise.


   Brad     

[SILVERGUN]

OK, I ran out of time to troubleshoot,,,,but this is what I tried to accomplish....
Input Vol. works, balance control works, switch does not have any effect......for now,,,,until I figure out how I might have miswired it  


 

[SILVERGUN]

Here's how I wired it......
Please tell me if you see something wrong:

Found the problem and adjusted pic

[HotBluePlates]

Both pots are shown in your drawing with the pot shaft pointed towards you and lugs up? If so, they look right.

If your switch truly has only the 2 terminals, put the 1MΩ between the terminals, the 4.7k to one of the terminals, the ground connection on the other terminal. That should work.

[SILVERGUN]

Both pots are shown in your drawing with the pot shaft pointed towards you and lugs up? If so, they look right.

HBP, thanks AGAIN for your help, unfortunately no, they are bottom side facing us.....(but they did seem to work properly that way)

If your switch truly has only the 2 terminals, put the 1MΩ between the terminals, the 4.7k to one of the terminals, the ground connection on the other terminal. That should work.

Yes, I used a spst toggle with 2 posts, standard on/off
I won't get back to the amp until Mon. night,,,,but I can't wrap my head around what difference will be made by putting the 1M between the tabs (doesn't that accomplish the same result as whats pictured, just in a simpler fashion?)

Respectfully questioning, 
Dave

[HotBluePlates]

... I can't wrap my head around what difference will be made by putting the 1M between the tabs (doesn't that accomplish the same result as whats pictured, just in a simpler fashion?) ...

Yes, it should be exactly like what's in the drawing.

Here's the problem: your implementation of the drawing isn't working, and all I can tell from your picture is that the 1MΩ is not across the switch contacts. So, since both approaches are supposed to do the exact same thing, there is some wiring error in the your implementation.

My recommended wiring makes it very hard to make a mistake that's not visually-obvious. So if you do it that way and it doesn't work, you should be able to see pretty quickly why it didn't work.

I'd bet that in the Hiwatt, the 1MΩ resistor is right on the inside of the XLR jack, bridging pins 2 and 3. The pedal's cable just has a wire to each of those (with or without using an actual 2 conductor plus shield cable), and at the pedal those two wires go to either contact on a SPST footswitch.


Anyway, the lesson is tricky wiring yields faults that are tricky to find. Simple wiring yields faults that are simple to find.

It's not always clear why the standard way of physically hooking things up in an amp became the standard way, until you try to troubleshoot a build problem in someone's amp with a "creative approach" to making the connections...