Little Wing/Vixen ECL84 in a cash box

[TIMBO]

Hi guy's, Found an aluminium cash box at work and thought it would make a great chassis for a small build.Wanting to use the ECL84s for the low output and great sound and found the Little Wing and Little Vixen to be perfect for the parts that i have and some tweaking i have wanted to try out.

First i wanted to try Darryls back-to-back transformers cause their cheap and i can also run the heaters off them as well (if i have calculated right)

Please check my schem for any goofs or component values that may not be right/suitable as i have joined a few builds together.

This is what i have so far. Thanks

[DummyLoad]

nice!   

--DL

[tubenit]

On my SoLow Watt, I kept overdriving the ECL84 tubes more than I liked.  I finally used a PPIMV that essentially had about 110k to ground.  AND I got rid of the MV after the tone stack. Ironically, the MV would cause squeal when I would crank it all the way up, but withOUT the MV, I had no squeal. Probably was a layout issue, I'd guess?

So, ............ IF you find the tubes too overdriven, maybe try that. I still get tons of sustain and it's still a pretty loud 3-4 watt volume.

I also played with the tone stack values ALOT and eventually settled on these. As I mentioned in several posts, the amp still has amazing bass for a small tube.

With respect, Tubenit

[Fresh_Start]

TIMBO - thanks very much for posting that schematic.  Looking at it got two ideas to come together into a probable solution for a circuit I've been trying to figure out for a long time.

Cheers,

Chip

[TIMBO]

Hi guys, Fired the little lady up and after having to rewire the heaters cause i'm a dope have had some success. With no guitar plugged in and all dials on "0" i have no hums or buzzes. The only buzz i get when i turn the master vol i get a hum at about "4" and it gets louder to about "11" but when i get to "12" it disappears. When on "11" the presence adds some static when turned to "11-12".

This maybe a similar problem to what Tubenit was having when the MV was dimed, so i'll will give the PPIMV a go.
I haven't had a thrash with the guitar as it is early morning.

The back-to-back transformers worked well and aren't getting hot so i have been able to keep the current under 1A  BUT when hooked up as per schem i was only getting 168v @ node "A" maybe a little low, so i connected to the 15v tap on the second transformer and have bumped the volts @ node "A" to 187v maybe still a little low but i think thats the best i'll well get as 15v is the lowest tap on the second transformer.
SO, what could be the lowest values i could use as dropping resistors in the PSU chain and plate resistors to give me a few more volts (first i well play a bit before changing)

VOLTAGES

                     1      2     3      4       5       6       7       8       9

V1-12AX7       103          0.7                    107           0.78
V2-ECL84       13.8  130  39.3                   187     3              170
V3-ECL84        13    126  39.3                   185     3              170

I think these volts are OK just a little LOW.Thanks

[jojokeo]

Timbo, temporarily disconnect the pi's NFB loop and see if this is affecting the humm/buzzing? Also, what you're describing sounds like it could be oscillating (unaudible) through a range. Take a test lead w/ sm value capacitor and test w/ it at the usual points across the plate/cath r, etc...

[TIMBO]

Hi. guy's, Not familiar With that type of probing Jojokeo, but disconnecting the NF only makes it worse with added oscillation, with the NF connected it buzzes and only really gets out of control at higher levels. Buzz is present with V1 removed and buzz gone with ECL84s removed. Tapped all components to see if any present noise, all good. Will add PPIMV next.

As Tubenit said the ECL84s are very bass responsive so some tweaking of the TS is required,I have changed the TS slightly and it helped a little. I tried the TS Calculator but not real sure of what i was doing, so if anyone who knows how to work the TS calculator and could give me some possible values to increase the treble.

I also increased the B+ voltage by another 30v by connecting the 15v tap on the first transformer to the 15v tap on the second. Still having the heaters connected to the 12v tap on the first transformer.  Thanks

[TIMBO]

Hi guy's, I did some more poking around and added the PPIMV. Adding the PPIMV helped a lot and reduced some of the buzz and distortion. The buzz i have tracked down to V1. The buzz appears (without guitar not plugged in) when the gain is turned to "10" and gets louder when turned to "12" and with V1 removed, no buzz. The buzz stays the same with guitar plugged in. With tone controls at "0" buzz is low but increases when turned up.

So i 'm thinking it may be the MOSFET.

I think my new voltages are good and if my calcs are right i am pumping out a massive 3W

NEW VOLTAGES

                      1           2           3          6           7            8            9
V1-12AX7       125                    .79        130                      .9
V2-ECL84       15.5        152      44.7       225         3.68                     205
V3-ECL84       16.4        155      44.7       225         3.68                     203

NODE A-228
        B-208
        C-202
        D-197

Plate-Cathode - 221v

[TIMBO]

Hi guy's,I disconnected the mosfet and don't think thats the problem BUT this is what i found. When a note is plucked hard the buzz (again the buzz is only present with gain at "10" plus) almost disappears and slowly returns as the note decays.Tapped components and solder joints for loose connections but nothing presented itself as bad. Thanks

[tubenit]

Timbo,

I did not think it would be the mosfet.  

Here is what I would first try.

1)  get rid of the NFB 1st   Nevermind, I see you already did this

2)  lower the .02 to .01 after the V1b going into V1a

3)  definitely lower the .02 coupling caps to .01 after the LTPI.    I don't think it's going to sound right with .02

4)  add the smoothing caps that I indicate in yellow.

5)  if the above does not fix it, I'd try lowering the .01 into the LTPI to .0047

6)  Try a 12AY7 or 12AV7 in V1

Jojokeo stated something that he thought there might be oscillation issues.  I agree with that as a best guess.  I had an amp that I built that had a weird buzz on decaying notes and it turned out that when I reversed the OT wires, ................ it went away.   In other words, instead of the terrible squeal usually associated with oscillation from the OT being hooked up "backwards", ....... the amp would play without a squeal and had sort of a oscillation/buzz instead.

With respect, Tubenit

[zendragon63]

Cool little build Timbo. I have built a couple of amps using those pentode-triode combo valves and I had the worse time trying to keep the triode section from oscillating at any level. (I found the problem by frustrating stage by stage elimination) I ended up running 2 conductor shielded cable into the triode LTP and it eliminated my issues; your layout is a bit different but if you find this stage to be the offender, you might consider getting a little more distance on the components into and around the LTP portion rather than just adding snubbing caps.

FWIW I am increasingly convinced that layout and wire routing plays a much larger role in the real amp 'magic' than is generally given credit (i.e. Dumbles and Trainwrecks). Not that I any expert. Good luck man. Regards

dennis

[tubenit]

I have built a couple of amps using those pentode-triode combo valves and I had the worse time trying to keep the triode section from oscillating at any level.

I sort of came to the same conclusion with the 56T (my version of Geezer's HoSo56)  using 6BM8 tubes.  I ended up just using the pentode of the 6BM8 & a 12A_7 for the LTPI.

Having said that,  I find the SoLow Watt to have a very transparent tone that is quite smooth. I can not tell that the smoothing caps took away anything from the tone except fizziness. 

I can dime everything on the amp with NO oscillation issues at all.

with respect, Tubenit

[TIMBO]

Thanks for the help Tubenit, I have some good news and some bad news. First the good news, i changed the coupling caps as directed and this made a nice changed to the voice and made the amp more stable, so thanks for those ideas. This is the really good news i have almost eliminated the buzz that i was getting at high volume. I was using an inline rectifier and i replaced it with 4x1N4007 diodes and it reduced the buzz to only a small amount between "11.5 - 12" on the gain pot. This good as i feel that some of the buzz could layout related and now that i have worked out some of the kinks a different layout could be done.

TONE, the TS does need some work but i am finding that when the treble and bass are turned up the buzz tone changes and gets louder from "10 -12" 

The bad news is that this amp suffers the same ground buzz that my other amps suffer, it gets a fizzy buzz and when the strings are touched its disappears.

So i am able to turn the gain and PPIMV to max and only get a small buzz (while the strings are touched).

I am also thinking of running the heaters on DC.Thanks

PS. More addons to come 

[tubenit]

TONE, the TS does need some work but i am finding that when the treble and bass are turned up the buzz tone changes and gets louder from "10 -12" 

A couple of comments.  Try the tone stack that I used in my SoLow Watt. The ECL84 tubes are so bass oriented (for a small tube) that I had to change from typical values that I use.

If the amp is for yourself and not a build for someone else, then don't turn the tone stack up all the way.  I don't think I've ever played an amp with the tone stack dimed.   


With respect, Tubenit

[jojokeo]

Timbo,

Although I'm not a fan of your grounding method, I'm not sure that this is an issue here with you're remaining issue(s)? I can't really see what you've done regarding wiring to & from the send/return jacks but this is grid wiring to your pi section and sensitive. How long are the wires, are they shielded, and do they get very close the OT's wiring? A quick thing to try is temporarily bypass the send/return jacks and make a short run to the pi directly from the preamp treble or vol out (sorry, I can't see the schem at the moment). I agree with dennis/zendragon on lead dress being very important especially when the preamp gets a little "too creative" with too many switches & controls or the amp as a whole like that. Remember the higher the designed gain of an amp the more you're going to hear that hissing when volume and treble is added in together. This is normal...to a point. Experience tells you what is normal/allowable in this regard. Another thing, it's also normal for a slight hiss when not touching the strings of your guitar...especially considering what pickups, shielding, etc. it has. Lastly, when you're sitting right in front of the amp you're dialing in it's common to have your guitar "too close" to the amp which gives wierd hissing noises and the like. Step away from the amp a bit and turn 90º one way and then 90º the other way. See how your movement and proximity changes any sounds you're hearing and if this is causing "percieved" issues you are confusing with your build?

On my Cherrybomb amp wich is similar to the Little Wing amp using 6bm8s, it had a very slight (but aggrevating) oscillation on certain settings of the gain & master vol controls together. Oddly enough what fixed it was putting a treble bleed circuit on the MV control. It only showed itself the worst when the control was on "8". Oscillations are like that sometimes, meaning they can go away when dimed or lowered and they usually get better and worse as the controls/gain is moved around. They are frequency dependant in this way. Not all are like this but the frustrating ones that are hard to pin down can be. So after all this is said, do you think you're dealing with oscillation or ground humm issue currently?

HTH, Keo

[TIMBO]

Hi jojokeo, The amp is a lot better after changing a few components under Tubenits direction and the original buzz and oscillation was being cause by the SS rectifier. Now that that i changed it to 4X1N4007 diodes it reduced it to a small amount that is only present when controls are turn to max, this small amount of buzz i could blame on layout and lead dress.

I tried another type of build with this one as i had the tag strips and after seeing Darryls Impact build (he doesn't seem to have many problems with Buzz/Oscillation) plus being a simple circuit i didn't bank on having too many problems.

As for grounding this has been a PAIN. I used the tag strips mounting lugs as my grounding points, thinking that multiple grounds could be a good thing and i think it work well for the general grounding of the amp.
BUT when touching the strings made the amp almost dead quiet it,this amp too has suffered the same fate as all my other amps and is something i have to live with whilst living in this house.(this is the only thing i can see that is the common problem)

My captive audience (wife,neighbours) have never complained about the ANNOYING buzz, but........
Thanks

[jojokeo]

Learning grounding points & schemes are not nearly as easy as some may think. By keeping at it with each successive build you will get better each time. Good to hear the issues are minimized.

[TIMBO]

Hi guy's, The first attempt had some success and was happy with the result, but having another look at my layout i was concerned with some components too close to each other and too clustered around the valve sockets. Fearing that this could part of the buzz problem i took to the amp and GUTTED it  and adding more tag strips gave me a better layout, also the schem i used was not one that someone had built so there was no way to know if it would work anyway.
So sticking with another of Tubenits ideas and having the parts i went with the 12A_7 version of the SoLow Watt. I able to use the IRF820 again having the limited mAs, this was a good challenge.

So when all was put back together the same BUZZ/FIZZ remained  so i was thinking that it may not be the layout  next some poking and proding and still no change.Then  this buuzz was similar to a another build and elevating the heaters did the trick but no ct on heaters, Thankfully darryl had posted some info on one of his builds and had a humdinger circuit on his 12v heater circuit. This worked a treat and now the hum is more like a fizz and this is only at max levels, and some also disappears when touching the strings.I can live with this. More to come. Thanks

[DummyLoad]

cash box huh?


Money - Pink Floyd HD (Studio Version)


good work finding the issue(s).

--DL

[tubenit]

Timbo,

I am impressed!  Your perseverance is absolutely remarkable!

Congrats on making progress on the amp. Very cool.

With respect, Tubenit

[TIMBO]

Hi guy's, I put my 2c worth in on this topic http://www.el34world.com/Forum/index.php?topic=13926.0 and thought it worth a try on this build now that i had some of the main buzz under control. I think i have tried about every combo of grounding and i am still plagued with this fizzy/buzz i get that disappears when the strings are touched.
This build is quite straight forward so with the grounding i didn't think i could go too wrong.

GROUNDING IS AS FOLLOWS:-
The IEC socket earth connection is grounded next to it via bolt and star washer.
Node "A" cap is grounded with the SS rect. on one of the PT bolts.
Nodes "B & C" are grounded with the PPIMV, ECL84s cathode and PI grounds on other PT bolt.
Node "D" has preamp grounds grounded at the input socket outer sleeve (switchcraft type)
Speaker ground also grounded at the jacks outer sleeve.
Main buss bar soldered to back of pots and preamp grounds soldered to it.
I think that this is an OK grounding for this amp and yet it suffers from a the same buzz/fizz as my other amps ( for the moment i can live with it as it only kicks in when the amp is turned up, still investigating other causes )
V1 is a 12ay7 which sounds the best so far as it does not overdrive the ECL84s too much and you can get a smooth overdrive sound with he gain turned up (nice) 
With the voltages on V1 as they are it sounds great, would increasing the plate voltages make much difference and how could i do this as there is not much volts anyway or are they OK?????
The tone controls do not respond much but as Tubenit said this may need to be tweaked anyway, any ideas??
This amp does not have a NF circuit.What effect would one have and would an adjustable NF be of use and would adding one help to remove some of the FIZZ??
The amp has a passive FX loop and they work well and i have not tried an active fx so i hoped that this could be a good one to try it on.
Does adding one increase gain (i don't think it needs any more gain) clarity, boost  and it would have to be SS (not much mAs left) I thinking of Tubenits mosfet FX 
And while i think of it how about a mosfet reverb Will adding these SS circuits push my mAs too much 
Last but not THE last, there has been talk about SS rectifier HASH noise . Has anyone a circuit that might help me reduce some noise i have in my amp where this could be a possibe cause as i would like to try it. New schem with voltages.  Thanks

[tubenit]

i am still plagued with this fizzy/buzz i get that disappears when the strings are touched.

My SoLow Watt has NO buzz.  I used Hoffman's grounding scheme  (which may or may not make any difference on your amp).

My phase invertor and PPIMV are grounded along with the preamp section on the buss wire.  (this included preamp and phase invertor filter caps).

All B+ rail going to power section is grounded on one PT bolt.

Can you answer these specific questions please?

1) Is the buzz there withOUT the guitar plugged in?  And does it stop when you touch the input jack?

2) IF it is just there with the guitar plugged in, is the buzz lessened with the guitar volume on "10" or below "7"?

Sure wish I was there to trouble shoot this with you.  I greatly admire your stick-with-it-ness.  Bravo.

The tone stack on mine does work & I can hear the treble, mid and bass all changing the tone.  However, it is not as dramatic as a typical Fender tone stack.

With respect, Tubenit

[jojokeo]

Hi Timbo,

I'd like to try to help and attempt to clear up a few things the way I see them addressing humm or hiss, grounding, lead dress, and the like. These things can be excruciatingly frustrating BUT in going through these very difficult experiences, it's what it takes sometimes to help to ultimately get the understanding and learning needed to get to the bottom of these things.

!. An amp is never absolutely dead quiet at full volume but if you connect only an unsoldered jack plug only into the input, it should be close. Then there's no guitar grounding or chord's influence on listening for hum levels. The control settings do and should influence what you will hear.
2. It's been seen where after everything that's been done and being "correct" no matter the gounding/layout/lead dress - certain components like trannies or tubes can be responsible, and aluminum chassis being better than steel (for what we're discussing here w/ not inducing humm, eddy currents, magnetic fields, etc. as easily)
3. Then one must consider the placement & proximity of the trannies to each other and to other components. Are they brand new w/ isolation washers or old NOS types, recycled/re-used, etc.?
4. You are using switchcraft jacks but it's been long suggested that "good practice" is to use isolating types for BOTH input and output jacks and on effects loops if applicable. It may or may not be an issue on your build but it's always suggested to use isolating types.

[jojokeo]

(Okay new window that doesn't bounce around as I type)
One of the hardest things is to properly identify what it is that is causing this kind of issue. Is it a humm, buzz, rattle or hiss? Does it do it when playing, not playing, playing only certain notes, or bass or treble strings, only on a certain guitar or chord or when plugged into an effect or board or computer, etc.?

I don't mean to sound excessive in description nor question your experience but this may help you or others at some point at getting basics of troubleshooting out of the way.

Your specific issue:
I said those other things first because if any of them are of issue, then nothing else you may try short of rebuilding the entire thing will likely not help and be an exercise in futility.

In your preamp grounding descriiptions: you are both gounding to the input jack and you say you are grounding points to the buss at the back of the pots. This is a ground loop situation by definition (but likely not your issue IMHO). Star grounding by Aiken and Blencowe both suggest that each stage's grounds go directly to that stage's filter capacitor. Then the filter cap ground goes back to the star ground lug or point. The buss bar method should be okay but choose one or the other, not both.

[sluckey]

(Okay new window that doesn't bounce around as I type)

Choose "Compatability View" if using IE.

[jojokeo]

Thanks Steve. I'm on a laptop, how or where do I choose that?

[sluckey]

Look just to the right of the address bar. First icon. Click it. IE will remember to use compatability view for Hoffman's website. I've had to do it for several sites that use similar type text entry boxes.

[jojokeo]

Continuing:
After you've shielded all applicable low leve high impedance wiring, check any signal wires that might be running near plate & cathode wires and keep a physical distance. If possible have them crossing at 90º angles to each other. This causes more issues dealing with oscillations/parasitics and not likely humming/hissing (but is still good practice).

Keep your heater wires twisted tightly and away from any other wires as much as possible. This is a very easy "humm causer".

OT & wiring: you don't want your OT wiring near any preamp sensitive wiring if at all possible. In your pic you have your primary tranny wires running right next to some components. Route these wires up and away from everything else. This is especially important with the OT secondary wiring as very large currents flow in these wires. This is why it's so important for the output jack to be isolated and for the ground wire to go directly to the tranny or star lug. Keep these wires away from everything possible. If using NFB then run the output ground wire to the p.i.'s ground.

I recently helped someone with a high gain amp have a similar humm as yours and only relocating the OT wiring is what was needed and cured this very type of issue. Maybe you will see a benefit and maybe not? Like tubenit says, it's very hard doing this stuff on-line when having something in your hands and it may be something completely obvious that was overlooked. I hope you find your "bug" Timbo.

jojo-

ps - THANK YOU STEVE!!! You've "fixed" my irritation with that screen bouncing thing

[Willabe]

I'd also twist the 2 OT secondary wires going to the speaker jack, cap/tape off the white OT wire (if that's a tap, 8 ohm?, 16 ohm? it's got the full OT's output voltage and current on it) and add/twist the white with the other 2 and shorten the green OT wire, is that an OT shield?


                              Brad      

[fdesalvo]

I bet it's your guitar - as tubenit mentioned.  If you have nothing plugged into the input and the buzz is absent, it it likely your guitar.  I'd verify the string ground is intact!

[TIMBO]

Thanks guy's,I do believe that there is a common party at fault and i'm thinking that it could be my guitar leads (not overly expensive) because :-
All guitars (LP, Strat, LP Jr, EP Swingstar) have similar problem.
This is what i have.
No guitar plugged in :-
No buzz with all controls @ 0
No buzz with Gain @ 0 and PPIMV @ 10 (10 being max)
No buzz with Gain @ 10 and PPIMV @ 0
Buzz present from 8 to 10 on gain and PPIMV @ 10
Buzz present from 8 to 10 on PPIMV and Gain on 10
With Gain and PPIMV @ 10 Treble control increases the fizz/Hash
I find that it is more of a Fizz/hash with a slight buzz 
Fizz does not go away when touching jack or any part of the amp

Guitar plugged in:-
With Gain and PPIMV @ 5, amp is playable and fizz is bearly noticeable Guitar Vol @ 10
No fizz, guitar vol @ 0 but kicks in @ 2 and gets louder to 10
Fizz disappears when touching string and amp chassis and has minor buzz Gain and PPIMV @ 7 and gets worse with FEEDBACK @ 10
Here is another finding when guitar is held against body the Fizz can be reduced by touching the strings but when guitar is on stand the fizz does not go away when touching strings or amp 
I do believe that there IS some small amount of BUZZ/FIZZ that is part of valve amps and is cause by many factors and i am OK with this as alot of the BUZZ/FIZZ only kicks is at high volumes(my other amps suffer the same) and these levels are way too loud for my use.

I look at the big picture and it goes like this, I have no electrical training and never built a working valve amp before joining this forum and i have my own ideas as how they are constructed (A never ending lesson being learn't) and i have five working amps,three under construction, one on the drawing board, four guitars and a very understanding wife. My goal in life , to master them all 

There is a common factor to this on going problem and one day it will present itself. Thanks to all