Output Tube Saturation BOX

[zikaj]

First post. I was going to use the user name "I'mShocked", but then again...

I've been thinking about things to do with my $99 Valve Jr, and one of them was to use it as an Overdrive/Distortion "pedal" in my signal chain before a SS PowerAmp. Figured hook up a dummy load with a line out (from Weber).

The bottom line goal is to either play the thing CRANKED at a quieter level, or even play it CLEANER at a LOUDER level by using a secondary power amp and a dummy load. I already have a 300w SS amp to drive a guitar speaker cabinet (2x12 or 1x12 depending). (I needed the tone of 12 o'clock at a gig last week, but the volume of 5 o'clock)

Then I came across an article at Amptone which lead me here. FANTASTIC information, btw.

So here is the Q:

I'm thinking of making an Output Tube "Effect Box" to get true output saturation, with a built in Dummy Load and a line out (with level controller). The reference is here: http://www.amptone.com/g235.htm . What kind (and cost) of transformers am I looking at to drive an EL84? Power transformer needs for one tube?

In the end, I'd like to build a custom / tweakable preamp for 'modeling' different preamps, saturate it with the 5w "effect box", and send a nice line level to a power amp. This seems like tone and volume control nirvana- which is why I'm wondering if its doable.

This idea had really got me excited. Heck, even loading down my Valve Junior with a dummy load and an output to my power amp seems fantastic.
Signal chain:
Gtr-Doobtone-MicroBuffer-OD-Dist-FX-FX-Valve Junior-Dummy Load-Line Out-EQ-TC Electronics FX-SS Power Amp-Massive wall of speaker cabinets or one small 1x12.

THANKS.

All input is GREATLY appreciated.

Jeff

[steve]

I've thought of doing the same thing.

I scratch built a Valve Junior a while back that has a post OT line out:

http://www.diycustomamps.com/valvejunior.htm

The line out should drive an SS power amp to full power. Although I doubt it would sound that great as there is no speaker to color the sound.

I've recorded before with an AX84 P1, Rev. 10 that I built a few years ago. It is similar to the VJ but has a three-band EQ where the VJ has none.

I plugged the output of the P1 amp into a Behringer GI100 direct box/cabinet simulator:

http://www.behringer.com/GI100/index.cfm?lang=ENG

The GI100 doesn't have a dummy load, so I plugged it into an old Rockman Power Soak I've had for years. I don't see why the line out of the GI100 couldn't be plugged into an FX processor and then into an SS power amp. Adjust the tube amp for breakup and tone, then control the overall loudness with the SS power amp. The combo sounded really good recorded directly to my hard drive. The 4x12" cab speaker simulator provides convincing coloration of the sound. The speaker sim can be switched in and out of the circuit.

Hughes and Kettner makes a similar product called the Red Box:

http://www.hughes-and-kettner.com/pr...de=prod&id=110


steve

[zikaj]

Thanks Steve. Making my way thru your site. Had this question/comment-

The line out should drive an SS power amp to full power. Although I doubt it would sound that great as there is no speaker to color the sound.

As I envision it, I'm driving the speaker cabinets with the power amp (which, ideally, is duplicating a great, full, dynamic, harmonically rich sound) output, , so aren't I coloring the sound with a speaker? I know that Ted Weber makes attenuators with an actual speaker component to interact with the OP transformer, is this what you mean? Otherwise, I fully intended on (when needed) hitting multiple speakers hard with the signal, or (when needed) just hitting one. Am I not connecting something in my head? (probably!).

EDIT (Adding this). Ok. Was going thru this more in my head- much with the goal of understanding things. Going with this 'power tube saturation pedal' idea (although I'd probably rackmount it for safekeeping...). In a tube amp, the signal being put out of the preamp (before the power tube or inverter) is ?line level?. Thats the function of the recovery phase after the tone stack or pot, right? So the input to the power tube is just a line level signal? (possibley knocked down a bit by the resistor in front of it). And, since we're not going for power here, a smaller quality OP transformer (3w) would be just fine. It SOUNDS so simple, outside of the cost of a power transformer and an OP Transformer. It looks like the power section is significantly more complex than the output section, actually.
Or is my house filling with carbon monoxide....

Thanks.
Jeff

[Richard]

The speakers have an interaction with the power amp as well as how they color the sound. I'm not sure how much of the tone comes from the interaction and how much comes from the effect of the speaker itself.

[zikaj]

I have to be up in 5 hrs. what am I doing online....

As long as I'm hitting the speakers with a good signal, I'm going to bebefit from those effects, right? Or is there some mojo of driving the speaker directly from the ouput transformer of the tube instead of via the amp? Ideally, the SS amp is sending tube saturated tone and dynamic to the speaker, right? So, thats one in the 'plus' column. (correct?).

I recognize that you'll lose some of the depth, but in the world of +/- I think the balance is in favor of getting fat output tube saturation (then EQ'd before the power amp) as loud, or quiet, as you want.

jz

[Steve Conner]

Theoretically, there is a little extra mojo that comes from having a speaker connected directly to a tube amp, rather than sticking a dummy load and SS power amp in between. It comes from:

1) the fact that the output impedance of the tube amp is higher than any SS amp, so the speakers are damped less. This typically causes a bass hump and rise in the presence band, which is one of the things that makes tube amps sound more "fat" and "lively". Rocktron, Marshall etc. have made special SS power amps that use current feedback to present a more tube-like output impedance.

2) the fact that a speaker doesn't present a constant 8 (say) ohm load to an amp: it varies with frequency, volume etc: and the tone of a tube amp is affected by the load impedance, whereas the tone of a SS amp is not. (In fact, solid-state power amps don't even have a tone of their own- that's the point of them) Korg/Vox's Valve Reactor circuit tries to capture this too, by chaining a tube and SS amp together such that the tube section "sees" the speaker load through the SS output stage.

To some extent, 1) and 2) are both just descriptions of the same effect, I guess. But in 1) I'm thinking of changes in the frequency response, and in 2) of subtle changes in the distortion behaviour that are caused by the changed frequency response.

However, I did some A/B tests once with an SE EL84 amp without NFB, driving a speaker directly, vs, driving the same speaker through a power soak with line output and a SS power amp. The difference was hardly noticeable.

[zikaj]

I just googled "output tube saturation" and this forum topic is #1. I suppose we should now be responsible and put some meat and potatoes here...
I've got more questions than answers for now, but I'm working on it. Anyone have $0.02 on the merits of this idea?

And, since I guess I'm stuck now and HAVE TO do it, what power transformer recommendations? Do I have to get the same type I'd use for an full homebrew amp (a Hammond with minimal power (enough, of course, for my needs) )?

Project needs are so minimal. The big chink of $ is having to buy two transformers. Anything on top of the basics is icing on the cake (EQ).

[Steve Conner]

I've been a member of Ampage since about 2000 and have seen dozens of discussions on the subject of amp chaining.

First of all, several amp simulator boxes like this exist, the most famous one being the Hughes & Kettner Cream Machine. It's actually a complete 2 watt tube amp in a giant stomp box. I know someone who bought one off Ebay and modded it extensively to get the sound to his liking.

I believe Guyatone also made an amp that was actually a small amp driving a dummy load and a larger amp.

Eddie Van Halen is famous for using a Marshall driving a dummy load, with a tap from the dummy load going into the input of another Marshall. (Besides all his naughty tricks with variacs, and playing in front of a wall of 5150s while his real sound was coming from a couple of Marshalls off stage, but I digress.)

One really cool variation I saw was the "Dogzilla", a 200W tube guitar amp with a built-in small amp emulator to get power amp saturation without blowing your head off: http://www.dogstar.dantimax.dk/tubestuf/dzindex.htm

When Googling, remember that people don't always use the same words to describe the same concept, and search engines aren't (yet?) smart enough to take account of this for you. For instance, output and power, tube and valve, saturation and distortion, dummy load, power soak, speaker simulator, DI box, etc. So:

output tube saturation
power tube saturation
power tube distortion
output valve saturation
guitar amp chain
hughes kettner cream machine

etc. etc. should all have been part of your searching session. You could have tried searching the Ampage archives too. I'll leave you to Google for more details of the gear I mentioned above if you're interested ;-)

[zikaj]

Steve, was that a scolding?
I've decided to just give up guitar and music in general....

Ok. Seriously. I gotcha. And I understand where you're coming from. I really DID do a ton of searching on this. I'm usually the one (at work) who can google anything and find what we need. Just wasn't getting what I needed. I'm at about 4 hours of just searching and reading on this specific thing.

I could slap this thing together, I know for sure. But I am digging for the 'why's' more than the hows. I learn thru the 'why' much better. Hence my miles and miles of questions.

For now, I've decided to get the tone I want out of my Valve Jr (set at 1 o'clock) and the volume I want (see below) by implementing some of the stuff I've come across. My only question is on taking the line level off the speaker. I could just drop $70 and and get the Weber MiniMASS, but I wouldn't have learned anything (I know, nerdy).

If I used the 1x12, I'd still need some type of voltage divider apparatus and a pot for adjusting the level, correct? Although I really wouldn't need the speaker if I'm hitting the 2x12. Guess I'm just looking for some input and confirmation. And yes, I'm google-ing the line out deal (without as much success as I'd like).

Jeff
Searcher of all things google.

[Steve Conner]

Hi Jeff,

Sorry, I'm a moderator on a science and technology forum where the house policy is to stomp on people who ask questions without exhaustive Google searching. I forgot that I'm not a moderator here and guitar tone isn't as easy to find with a search engine as IC datasheets

Anyway, the classic way to get line out off a speaker is with one of those cheap Behringer DI boxes. The instruction booklet boasts that they can handle the speaker voltage from a 3,000 watt amp with both the 20dB pad buttons pressed in.

You don't even need the speaker: I have got some nice bass tones in the studio, playing my bass through a 50 watt tube guitar head, hooked up to a big dummy load resistor and a Behringer DI. We couldn't use a speaker because I was playing alongside our drummer who had his kit mic'd for recording. I used a giant (about 8" long) wirewound resistor with loads of inductance, which probably helped it sound brighter and more lively.

[zikaj]

Thanks Steve.
I took your advice and used differnet methods of searching, and went to AX84 too. I found a bunch of great stuff down those paths. I now understand voltage dividers and the simple tone control (shelving) circuits. Kinda did before, but now its all tying together. Even found one idea that uses a balancing transformer for the output.
It seems like a subject that comes up again and again like you said, but there isn't a place with a clear cut answer that says do this, this, and this. If you want more, do this...
I know, I know, that would defeat the purpose of DIY Learning and Doing. I get it.

I'm going to look into the products and ideas you mentioned, Steve. Again, thanks.

Any input on what power tranny to use if I build a EL84 power amp/output? 15w power tranny for sure. I guess I'd still need to get something like the 269EX (190-0-190), and then I'll have it for future use too.

JZ

[steve]

Any input on what power tranny to use if I build a EL84 power amp/output? 15w power tranny for sure. I guess I'd still need to get something like the 269EX (190-0-190), and then I'll have it for future use too.
JZ

I've built a couple of amps using an SE EL84 output.

I built the AX84 P1 Rev. 10 a few years ago. I used a Triad R6-A NOS PT. it is rated for 115v primary and 240-0-240v@50mA. At first, I used a 5Y3 rectifier to knock down the B+ voltage. I didn't like tone at 270v, so I put in SS rectifiers and rebiased the amp. The plate voltage is now 310v plate to cathode. The amp now sounds great. The OT was a Fender Champ 12 replacement OT. This is a 12W SE OT that has a 5K primary.

A few months ago I built a copy of the Epiphone Valve Junior amp. I tweaked some of the values as the stock circuit sounds pretty marginal. I used the same PT: Triad R6-A. For the OT I used a Hammond 125ESE, which is overkill but the amp sounds very good. This was the one that I described in my first post in this thread.

Hammond makes a similar PT, 270AX:

http://www.hammondmfg.com/263.htm

It doesn't have a 5v rectifier filament, but you don't really need it.

So my advice: keep your plate to cathode voltage down around 300v. Bias your EL84 right up to 12W dissipation (the maximum) and use one of the Hammond 125SE series, CSE, DSE, or ESE.

HTH,

steve

[zikaj]

Steve-
Regarding the Valve JR, you pointed out that:
# the preamp circuit had odd values
# the anode voltage was way too high
# the output transformer was mismatched to the EL84 tube

Can you elaborate on these. I get #1 and #2 pretty much, but can you address #3 a little more?

Modding my JR this weekend. Drive switch, Bright switch, Master Volume. Oh, and adding a tube driven reverb tank I'll pull from my original 59 Bassman

[steve]

Steve-
Regarding the Valve JR, you pointed out that:
# the preamp circuit had odd values
# the anode voltage was way too high
# the output transformer was mismatched to the EL84 tube

Can you elaborate on these. I get #1 and #2 pretty much, but can you address #3 a little more?

From what I understand from the 175 *pages* of threads discussing the Valve Junior over at 18watt.com, at 300v on the anode, an SE EL84 wants to see about 5K on the primary of the transformer. The stock OT in the VJ is 7.5k. The stock OT works in the circuit, but many people report improved sound using a Hammond 125CSE running at 5K. I tried a 125CSE in my VJ, and it sounded good but the 125ESE sounded even better.

HTH,
steve

[zikaj]

I'm here taking a break from the 40th page of reading over at 18watt. The summary page is a God send at this point. Referenced somewhere here. I put it in my favs.
Now I get it. I have my VJ apart ready for tomorrows procedures and the OT is clearly marked 7.5K. I'm going to order the 125ESE in the next week or so once some other stuff comes thru. Maybe two.
Believe it or not, I'm moving in leaps & bounds in getting the big picture with this stuff.
THe current mind bender- calculating the voltage drop across the resistors in the power supply. One Q- The OT puts out 190-0-190. So before any resistors in the power section, the voltage is 380? I'm going to start picking at that scab next...

Jeff