Bugera V22 : 12A_7 and FX Send

[stevewf]

Two questions about my Bugera V22 Infinium:

1) Mixed pre-amp tubes. In the preamp section, could damage be caused by mixing a 12AX7 with a 12AT7 in sockets #1 and #2?

In fact, that's what's in there now, and I prefer the resulting range on the Gain knob. But am I asking for trouble?

The amp arrived with twin Bugera 12AX7a tubes in #1 and #2, and a Bugera 12AX7b in the inverter position. It sounded pretty muffled. So I replaced the power tubes. Maybe slightly better. So on a grasp, I replaced all three preamp tubes with new JJ 12AX7s, and surprise, it brightened up, and I was happy, end of story.

End of story, but beginning of this question. The Gain knob was not ranged right for my taste; turn it up to 3 and it's darn hairy already. That's the sound I'd like it to make at 10. So, I got me a 12AT7 and put it in socket#2. It behaves much better in the gain department now. But am I gonna regret that?

There's a schematic of the Bugera V22 found at music-electronics-forum.com. That is not the same as my amp, which has the Infinium (supposedly auto-bias), but I thought it might aid pondering of the literate among us. More able to read amp schematics than me, anyway.

And so, I suppose my real question should be: Aside from what I've already done, is there a simple way for me to adjust the Gain knob's range?

2) Cheap cable ok? Is there risk of tone-suck over the cable that connects this amp's "FX Send" jack to my pedals? Should I consider investing in a low-capacitance cable for that job?

To my understanding, long instrument cables can apply capacitance, and in high-impedance circuits, this can result in loss of highs; buffers can overcome this. So I guess I'm making a stab at narrowing down the question to "is the FX Send jack buffered?" but since I'm a novice...

Thanks for any advice!!!

[thetragichero]

for preamp usage in almost all cases (can't think of an exception but that doesn't mean there isn't one) 12a_7 can be used interchangeably (although you may or may not like the resulting sound of a swap). no damage should result

the effects send *should* be buffered so that wouldn't result in tone suck with "crappy" cables (what's a crappy cable? i like the proco stuff because they're dirt cheap and i don't have to feel bad throwing em out when they become problematic... maybe it's the years of playing in front of 100w guitar stacks but i don't really notice a difference between cables anyway. maybe i'm a luddite)

[gckelloch]

From what I've read, a 12AT7 draws more current and puts out more power than a 12AX7. Just one shouldn't tax the PSU. I imagine that "smart" PSU would start cutting out if it was too much for it, but who knows? Technically, it should be filtered differently. I think it might pass more high-end than a 12AX7. You might notice it when the power tubes are driven hard, depending on the speaker.

If going with JJ tubes, you could buy an ECC832 - 12DW7 or 5751 and an ECC83MG. Ditch the 12AT7 and try the ECC832 - 12DW7 or 5751 in V1 or V2 and the ECC83MG as the PI tube. I'd recomend an ECC803S for the PI, but there are mixed reviews. I doubt it's any better than the ECC83MG and spiral filaments can rattle in combo amps. You could also try the 12AT7 as the PI if you want more power tube than PI tube distortion, but the high-end might be a bit brittle. Those are all fairly inexpensive and easy solutions.

I'd bet the FX loop is buffered, but here is some excellent affordable low capacitance cable with connector suggestions:

store.haveinc.com/p-62046-sommer-cable-300-0091-sc-spirit-llx-low-loss-instrument-cable-per-foot.aspx

You could try 10-15' as your guitar cable to smooth off and extend the high end. I use 10' with the Hi-CON noisefree connectors. They are smaller than the Neutrix, which puts less stress when hanging from jacks, and the shorting mechanism eliminates the boom/pop when pluggin in and out.

[sumgai]

steve,


Not necessarily in order:

The 12A?7 series of tubes all have different characteristics, to be sure. The 12AT7 is often used to drive current to the next device in line, but it has a lower gain factor than the 12AX7. (Gain: About 60 versus 100. Current capability: 10ma versus 1.2, respectively)  This means that in your amp, the gain stage won't be quite as productive (read: quite as loud), hence you turn up the Gain control.  (Because the following stage expects to be fed some voltage, it doesn't care so much about current.)  Long story short, no harm, no foul, every body has a good time.  (Until the usual end-of-life for most tubes of this type.)

Bugera certainly does not make their own tubes, they re-brand them from wherever they got a good deal.  Could be almost any tube maker on the planet, and that tube maker may change over time. I have no preferences, so your choice of JJ is as good as any I could possibly recommend.

Regarding the Gain control..... It appears to me that you might try inserting a 1MΩ resistor in series with the upper terminal of the control.  This means, of course, that you're never get a "full out" gain setting, but you could season it to taste with no fear of harming anything.  Tune to your personal preference.  Actually changing the control for another taper is also possible, the schematic calls out an 'A' taper, you might consider using a reverse of that ('C'). But that's more effort, and cost, than my first suggestion.

The linked schematic does not appear to have any buffering on the Send/Return lines.  Of course, this might change once the 'Effects Module' schematic is revealed.  More concerning to me is that this version of the amp does not use a pair of standard jacks, it uses a proprietary connector.  What's mounted on your chassis?

As to cables, right now it's a toss-up.  Depending on whether you have jacks instead of that special connector for the effects loop (and if so, are the buffered), you need to decide what's cheaper in the long run.... do you modify your amp to suit, or do you buy good quality cables.  Up to you, my friend, up to you.

And finally, the amp's power stage.  The linked schematic shows a self-bias (auto-adjusting) circuit on the power tubes.  Usually considered (for no good reason) to present a more "singing" quality to the output signal, and adds a bit of "sag" as well.  From an engineering standpoint, it's good enough, and shown in the field to last as long as a fixed-bias circuit.  But I do prefer the latter, I like that last bit of control over what my amp sounds like. For reference, nearly all of the big amp makers have used both types over the years.

'Nuff said.

HTH






sumgai

[gckelloch]

I may misunderstand the data on the JJ ECC81 (12AT7). It lists 2.5W under "Limiting Values". The ECC83's list 1W, and the ECC803S lists 1.2W:
www.jj-electronic.com/en/preamplifying-tubes

That's why I assumed the ECC81 output is higher, but I could well be mistaken.

My recommendation for the other JJ tubes is to be able to change the gain response of different stages to your liking. The stock 12AX7a and 12AX7b tubes in the amp indicate Chinese tubes. The "b" grade is higher gain. They are generally well-liked, if not a bit mushy. I'm surprised the ECC83S sounds brighter. Many think they sound darker. That could have to do with the relative lack of higher harmonics, yet more crunchy breakup, that splits opinions. From the lowest to highest gain 12AX7 variants it goes: 5751, ECC82 - 12DW7, ECC803S, ECC83MG, ECC83S. The longer plate tubes tend to have a smoother sound, but higher noise. You might not want to use the ECC82 - 12DW7 in V1. I don't know which triode would be for which channel. It might make the clean channel lower gain than you want, or not affect the gain channel gain at all, depending on how it's configured.

[thetragichero]

on thing to keep in mind wrt 12at7 higher current is that it's not generally being asking to swing a lot of current with a 100k resistor on the anode along with a coupling capacitor, but rather essentially connected to b+ (through a single-ended output transformer like in the standard fender reverb driver). when specing out a power transformer one might assume a couple ma ht current per little bottle and focus mainly on the output tubes drawing several tens of ma ht current apiece

[stevewf]

Aug 10, 2022 23:23:13 GMT -5 sumgai said:

Long story short, no harm, no foul, every body has a good time.

Thanks, sumgai, for the invaluable reassurance that I don't need to increase my fire insurance coverage 

More concerning to me is that this version of the amp does not use a pair of standard jacks, it uses a proprietary connector. What's mounted on your chassis?

There are three 1/4 inch jacks back there; one's for the included foot switch (which has a TRS plug) and the others are FX Send and Receive. As far as I can tell by looking, they're not proprietary, thank goodness, so I can use standard instrument cables.

As to cables, right now it's a toss-up. Depending on whether you have jacks instead of that special connector for the effects loop (and if so, are the buffered), you need to decide what's cheaper in the long run.... do you modify your amp to suit, or do you buy good quality cables. Up to you, my friend, up to you.

...and also factoring in what's in my range of capability. I know how to buy good cables, and I don't know (yet) how to mod the amp. To me, the latter would make more sense in the long run, because the result would be that I can use whatever cable happens to be around, any time... rather than having to make sure there's a special cable for that job. I'm not bothered by potentially lowering the amp's sale value with simple mods that would be more or less viewed by all as improvements.

But I do prefer the latter, I like that last bit of control over what my amp sounds like.

That approach also appeals to me, but I'm guessing that altering the biasing mechanism in this amp might be a bit involved, plus might not universally be viewed as an improvement.

Thanks for taking the time, sumgai!

[stevewf]

Aug 10, 2022 21:10:52 GMT -5 thetragichero said:

no damage should result

Whew, thanks.

the effects send *should* be buffered so that wouldn't result in tone suck with "crappy" cables (what's a crappy cable? i like the proco stuff because they're dirt cheap and i don't have to feel bad throwing em out when they become problematic... maybe it's the years of playing in front of 100w guitar stacks but i don't really notice a difference between cables anyway. maybe i'm a luddite)

There won't be 100W amps in this setting! The two Vol knobs, added together, never go higher than 12 or so (IOW, if the Master's up high, the other one is low and vice-versa). I do genuinely respect the neighbors. So maybe I'll be able to hear tome suck. Or maybe simply believing that it's OK will make me happy, even if there's actually no difference .

[stevewf]

Aug 10, 2022 23:12:43 GMT -5 gckelloch said:

If going with JJ tubes, you could buy an ECC832 - 12DW7 or 5751 and an ECC83MG. Ditch the 12AT7 and try the ECC832 - 12DW7 or 5751 in V1 or V2 and the ECC83MG as the PI tube. I'd recomend an ECC803S for the PI, but there are mixed reviews. I doubt it's any better than the ECC83MG and spiral filaments can rattle in combo amps. You could also try the 12AT7 as the PI if you want more power tube than PI tube distortion, but the high-end might be a bit brittle. Those are all fairly inexpensive and easy solutions.

Thanks. I haven't been aware of how the tube models you've mentioned compare with the 12AX7 and 12AT7 tubes in there now... time to read up in order to better understand your suggestions!

here is some excellent affordable low capacitance cable with connector suggestions:
store.haveinc.com/p-62046-sommer-cable-300-0091-sc-spirit-llx-low-loss-instrument-cable-per-foot.aspx

Yes, those Sommers do appear to impart very low capacitance, and at a decent price. When I figure out if it maters with this amp's FX loop, I'll decide about buying cables. No-pop is always nice for the guitar, but I think I could get by with normal plugs for the pedals.

[stevewf]

Aug 11, 2022 9:45:58 GMT -5 thetragichero said:

on thing to keep in mind wrt 12at7 higher current is that it's not generally being asking to swing a lot of current with a 100k resistor on the anode along with a coupling capacitor, but rather essentially connected to b+ (through a single-ended output transformer like in the standard fender reverb driver). when specing out a power transformer one might assume a couple ma ht current per little bottle and focus mainly on the output tubes drawing several tens of ma ht current apiece

Zoom! It mussed my hair when it went right over my head.   I knew I had a lot to learn... and that thetragichero among others would already know it!

[stevewf]

Aug 11, 2022 4:45:48 GMT -5 gckelloch said:

I may misunderstand the data on the JJ ECC81 (12AT7). It lists 2.5W under "Limiting Values". The ECC83's list 1W, and the ECC803S lists 1.2W:
www.jj-electronic.com/en/preamplifying-tubes

That's why I assumed the ECC81 output is higher, but I could well be mistaken.

My recommendation for the other JJ tubes is to be able to change the gain response of different stages to your liking. The stock 12AX7a and 12AX7b tubes in the amp indicate Chinese tubes. The "b" grade is higher gain. They are generally well-liked, if not a bit mushy. I'm surprised the ECC83S sounds brighter. Many think they sound darker. That could have to do with the relative lack of higher harmonics, yet more crunchy breakup, that splits opinions. From the lowest to highest gain 12AX7 variants it goes: 5751, ECC82 - 12DW7, ECC803S, ECC83MG, ECC83S. The longer plate tubes tend to have a smoother sound, but higher noise. You might not want to use the ECC82 - 12DW7 in V1. 

I can't know for sure why the tube swap brightened things up. The amp was used when I bought it, and it was shipped with all the tubes in the sockets. Maybe some jostling rectum wrecked 'em in transit? in any case, I *think* I want lower gain, but aside from knowing that 12AT7 being lower output than its 12AX7 counterpart, I don't know:
- which tube(s) to choose
- which socket(s) to put 'em in.

In addition to the low-to-high list you've provided, you've also given me some research material, thanks.

I don't know which triode would be for which channel. It might make the clean channel lower gain than you want, or not affect the gain channel gain at all, depending on how it's configured.

While I don't fully understand the schematic, I've read (and it looks like) the Clean channel goes V1a-V2b, whereas the OD channel goes V1a-V1b-V2a-V2b. This has complicated my (already-uninformed) decision making on where to put that 12AT7 I got.

[sumgai]

steve,


To amplify trag's statement:

Aug 11, 2022 9:45:58 GMT -5 thetragichero said:

on thing to keep in mind wrt 12at7 higher current is that it's not generally being asking to swing a lot of current with a 100k resistor on the anode along with a coupling capacitor, but rather essentially connected to b+ (through a single-ended output transformer like in the standard fender reverb driver). when specing out a power transformer one might assume a couple ma ht current per little bottle and focus mainly on the output tubes drawing several tens of ma ht current apiece

Generally speaking, voltage is "forced" into a following device, and current is "drawn as needed" from a preceding device. If the device (for this thread, an amplifier tube) needs X amount of current, it will ask for it, regardless of the voltage available to "push" that current into the requesting device (our tube). Whereas the output of a tube (or transistor, etc.) will have some voltage available to "push" the signal along to the next stage. That output will be, necessarily, limited in how much current it can provide.

And how do we know that? Simple, Herr Georg Ohm gave us a magic formula: E = I x R.  (And at that, he formulated it in 1827, nearly 200 years ago!)  Changing around that formula, we can determine any one of the values when given the other two. Meaning, if a load (trag's anode resistor) remains constant, then as voltage goes up, current goes down. Easy arithmetic.

Thus, for your purposes, changing tubes, while expensive, is an easy mod to see if you can get what you're looking for - no soldering, no using screwdrivers to remove the chassis, no accidentally dropping the chassis because it's heavier than you thought, no anything else.... just R & R some little glass bottles. (Shorthand for remove and replace.)  The values of current versus voltage will change, and thus affect the various devices/tubes/stages of amplification.  Sometimes you'll come up a winner, other times you'll kick yourself for wasting the money.  What can I say, life's a crapshoot.  But the answer to your original question remains the same - the amp won't be harmed in any way for doing all these experiments.  It was designed to be rugged in this regard, it will shrug off your choices with aplomb.  (After all, it is a near-direct descendant of the venerable Williamson circuit, the one that Leo copied in 1946 for his first amplifier sold to the public.)

Next....
Good to hear that standard jacks are mounted on the FX loop, but I still fear that they are unbuffered.  Can you possibly find a proper schematic for this unit?  Lacking that, you'll have to do the same thing as for your tubes - experiment with different cables to see if there is a noticeable change in tonal quality.  And depending on the effects pedals' physical placement juxtaposed with the amp, your cables may have to be longer than 10 feet.  Keep that in mind when you go shopping.

HTH




sumgai

[gckelloch]

I don't know which triode would be for which channel. It might make the clean channel lower gain than you want, or not affect the gain channel gain at all, depending on how it's configured.

While I don't fully understand the schematic, I've read (and it looks like) the Clean channel goes V1a-V2b, whereas the OD channel goes V1a-V1b-V2a-V2b. This has complicated my (already-uninformed) decision making on where to put that 12AT7 I got.

[/quote]

In that case, any lower gain tube will lower the Clean channel gain as well. I'd get at least one ECC83MG and a 5751 and/or a 12DW7. I'd definitely want the ECC83MG because it's a sweeter and more "dynamic" sounding tube. Although it won't substantially lower gain, I'd prefer it in any slot over the ECC83S -- definitely the PI slot. Hard to say about the other two. They are both essentially lower gain versions of the ECC83S, although the 5751 appears to have an even shorter plate. It should be very low noise and is a common V1 replacement. Either one should affect the gain knob range a good bit. So, that's at least ~$60 for three tubes vs 20 cents for a resistor on the gain knob, but no overdrive character change with the smooth ECC83MG. TheTubeStore.com looks like a good tube source. They also have the new Mil-spec EHx 7025EH. It's like a harmonically richer ECC83MG for $10 more.

[MattB]

It looks to me like everything after the "effect send" and "effect return" labels on your schematic is for the internal reverb. There is another section at the top with "loop send" and "loop return" jacks, and it does appear to have a buffer.

[sumgai]

Matt,


Well, that's a bit different. It's not intended for an effects loop, so to speak, it's more of a mis-labeled "pre-amp out" and "power-amp in" scenario.  Usually, plugging in an effects device here will play havoc with one's tone, mainly because this comes after all of the tone and volume controls within the amplifier.  In the great majority of cases, an effects device does not expect to see the greater voltage levels that are present at this point in the circuit.  And to my way of thinking, one does not (usually) attempt to control the tone of the signal going into an effects device, that's usually accomplished after the signal from the device has been mixed back into the main ("dry") signal.  As seen here, where the tone controls are placed just before the master volume, and well after the effects return signal path.

We now have to ask.... steve, are these the two jacks you see on the amp's backside?  Are they labeled with "loop", or with "effects", or not labeled at all?  If they aren't clearly labeled, then I'd suspect that they are most likely for the mis-labeled loop function, and not for the effects function.  The easy way to test that is to take a cable from your mp3 player and, via an adapter, plug it into the "Return" jack.  Power up the amp, and if you get sound out of the speaker, and you're not able to control the volume via the Master control, then this indeed as I said, a power-amp input, not an effects return jack.  By the other side of that coin, if you can control the volume and tone with the Master, then it is indeed a effects return jack.

EDIT: Do start that test with all volumes way down low - you don't wanna break anything, including your ear drums!
/edit


HTH





sumgai

[stevewf]

Aug 13, 2022 21:47:13 GMT -5 sumgai said:

We now have to ask.... steve, are these the two jacks you see on the amp's backside?  Are they labeled with "loop", or with "effects", or not labeled at all?  If they aren't clearly labeled, then I'd suspect that they are most likely for the mis-labeled loop function, and not for the effects function.  

The labeling of the two 1/4-inch jacks is like this:
There's a box painted on the chassis that surrounds both jacks, and also surrounds the words "FX LOOP"". Above one jack (the left one) - still inside the painted box - is the word "SEND". Above the right jack is "RETURN".

The easy way to test that is to take a cable from your mp3 player and, via an adapter, plug it into the "Return" jack. Power up the amp, and if you get sound out of the speaker, and you're not able to control the volume via the Master control, then this indeed as I said, a power-amp input, not an effects return jack. By the other side of that coin, if you can control the volume and tone with the Master, then it is indeed a effects return jack.

Test result is: NOT able to control via Master Volume.

Raises big questions in rookie's mind:
- Where should my pedals be? Between the Send and Return jacks, or before the amp's front input jack? Right now, I have fuzz and overdrive before the front input, but other pedals (chorus, delay, tremolo...) between Send and Return. More than a little reading led me to believe that's the typical setup, but perhaps it's not right for this amp.
- What things would a power-amp input be (best) used for? Just trying to imagine. And learn how to make best use of my only tube amp.

[gckelloch]

I always figured the amp tone stack should come b4 the FX loop and the master volume after, but I only owned one amp that had an FX loop. That was a Peavey Heritage back in the mid-80s. I think at least the tone stack b4 the loop is pretty standard, but some amps have FX loop send and return volumes. With the Bugera, you can get as much overdrive b4 the PI tube as you want and use the MV knob to set the level to your first loop effect, but you have to use the last loop effect to set the amp volume. I can see that you could overload your first effect if you set the MV too high. Maybe one of your pedals has an input level LED to let you know if that's the case? You could plug that first to set the MV level, and then move it to wherever you want in the chain. Then, set the loop chain for unity gain and control the amp volume with the last effect.

Modulation, delay, and reverb are generally used in the loop, but you can get more of a Hendrix sound with something like a Uni-vibe b4 the amp, and maybe after the Fuzz. Of course, EVH originally ran his Echoplex b4 the amp because he didn't have an FX loop.

[MattB]

Aug 13, 2022 21:47:13 GMT -5 sumgai said:

Matt,


Well, that's a bit different. It's not intended for an effects loop, so to speak, it's more of a mis-labeled "pre-amp out" and "power-amp in" scenario.



sumgai

Wow, they even mis-labeled it on the amp.

[thetragichero]

Aug 13, 2022 23:52:37 GMT -5 stevewf said:

- Where should my pedals be? Between the Send and Return jacks, or before the amp's front input jack? Right now, I have fuzz and overdrive before the front input, but other pedals (chorus, delay, tremolo...) between Send and Return. More than a little reading led me to believe that's the typical setup, but perhaps it's not right for this amp.

while not satisfying in the "tell me what to do" sense the answer to this question is: wherever you've determined they sound best in your setup to play what you're going to play. i have my chorus and reverb before any of my drive pedals because that gets the sound i want, even if it flies in the face of "conventional wisdom". spend a lazy weekend afternoon moving around pedals to see what works best for you

[stevewf]

Aug 14, 2022 7:45:31 GMT -5 MattB said:

Wow, they even mis-labeled it on the amp.

Those images are what my amp looks like, except the amp also has an "Infinium" logo directly beneath the "Vintage 22" text on the front of the chassis. Despite this difference, I believe that yes, it would appear that it's a mis-label.

Aha. The Quick Start Guide for my model is available here (that's via a link at bugera-amps.com). Regarding the "FX Loop" jacks (labeled as p.25), there's blurb that reads, "FX LOOP — Route an external effects processor into your signal chain or send the preamp tone to a power amplifer." They illustrate a couple other Bugera products that I do not own (a rack-mounted DSP and an accompanying control pedal, I think) being plugged into these jacks... not standard pedalboard-type pedals. In short, I don't know how to use these ports.

Later (p.36), there are some specs on the impedance, i.e "Effects Send:1.2 kΩ" and "Effects Return:53 kΩ". I note that these names don't match verbatim the labels on the chassis.

I haven't encountered any other manual-like documentation from the maker.

[stevewf]

Aug 14, 2022 9:40:54 GMT -5 thetragichero said:

while not satisfying in the "tell me what to do" sense the answer to this question is: wherever you've determined they sound best in your setup to play what you're going to play. i have my chorus and reverb before any of my drive pedals because that gets the sound i want, even if it flies in the face of "conventional wisdom". spend a lazy weekend afternoon moving around pedals to see what works best for you

Yep. Aside from hazard considerations, it always seems to boil down to "take time to test and find what you like." Alas, time seems to be a limiter for me. So why do I spend it typing instead of testing? Constraints... the neighbors can sleep no matter hard hard I hammer the computer keyboard, whereas with the guitar...

[sumgai]

steve,



trag nails it, in the final epoch, you are the one who says what sounds good, and what works best. For all I hammer on "normal" or "conventional", the fact is, you can put whatever you want wherever you want, and so long as it satisfies you, then it's all good - the rest of the world's thinking be damned. To that end, you should not actually damage anything, but you do want to listen closely for small amounts of undesired distortion in your tone. This coloration can make it difficult to "dial in" the tone you want.

HTH





sumgai