Genz Benz Neo Pak 3.5

[birdxofxprey]

The reason why a tube power amp should not be operated unloaded is because of ringing and back EMF spikes due to the inductive nature of the output transformer. This ringing can cause voltages greater than the designed breakdown voltages inside the transformer and break down the insulating system of the transformer. This can also carry back to the power tubes due to reflected signal being stepped up back through the transformer. This mechanism just doesn't exist with solid state amps.

This is very interesting, and it raises a couple other questions.

First, what do you mean by "ringing?"

Second, if by "ringing" you mean an actual ringing sound, I did in fact hear a very slight ringing (in the headphones) when I ran my 3.5 with no speaker load. It was slight enough that once I added music and bass it was no longer audible. Probably something else?

Third, why would the ringing and EMF spikes happen in a tube power amp but not in a tube pre amp? is it because there's no output transformer in the preamp?

Thanks again!

Chris

 

[agedhorse]

This is very interesting, and it raises a couple other questions.

First, what do you mean by "ringing?"

Ringing is an oscillation on the waveform due to an underdamped inductive load on the power amp from the output transformer, and also from it's interaction with the power amp's global feedback. this doesn't happen on a solid state amp because there's no transformer.

Second, if by "ringing" you mean an actual ringing sound, I did in fact hear a very slight ringing (in the headphones) when I ran my 3.5 with no speaker load. It was slight enough that once I added music and bass it was no longer audible. Probably something else?

Definately something else. How did you get the headphone signal? There's no headphone output on that model.

Third, why would the ringing and EMF spikes happen in a tube power amp but not in a tube pre amp? is it because there's no output transformer in the preamp?

Correct, the preamp tube stages are all resistively and capacitively coupled, and without global feedback so there's plenty of stability margin and no chance of ringing. Ringing with a POWER amp is worse when the signal is clipped because the rapid change in voltage or current (step input) can cause a response that's not linear (called the impulse response). With an inductor (transformers look like inductors) hanging on the output, energy is stored and released in the transformer's iron/steel core and the current is phase shifted form the voltage by 90 degrees in a pure inductive load. Once a speaker is added to the output, everything changes and it's no longer a "pure" inductance, so this problem goes away.

 

[birdxofxprey]

How did you get the headphone signal? There's no headphone output on that model.

i ran a direct line out from the back of the amp into a mixer that has a headphone jack. used a balanced cable too.

thanks for your detailed explanation, i won't sweat what must certainly be background noise of some kind. i'm using wireless headphones, perhaps that's where my extraneous noise is coming from.

 

[realdeal]

Indulge me in a break from some of the more technical discussion here-

I'm a big fan of all-tube heads, as well as the classic "phat" vintage Ampeg sound.
I also have Genz-Benz owner's experience having used a 112T cab as an extension for years with much satisfaction. I like what they do.

I decided to jump on the "small rig" bandwagon that's going on- you know, starting with WW, AI, of course MarkBass, and now EA and Eden, etc.
NOT going to stop using my tube heads or my beloved 3-Pro, but-
I'm involved in a creative project locally, the studio used has poor backline, and I dislike load-in (spoiled, having toured with a road crew, I admit it!)
So- I took the plunge 'cause I liked the buzz, rep, and specs of this head.
WOW. I repeat:
WOW.
There's already been more eloquent reviews, so other than to add my props- It's punchy, plenty Loud, very warm and balanced, well-made, nice eq, I could go on.
THEN I put it in the gigbag, and...
I repeat...
I think I'm ging to need to put a brick inside to justify the tone and headroom this amp gets- It's not that tiny, small, yes, but HOLY
*&*&^%^! It sounds real good-
And I'm comparing it to a V4BH, a Mesa Buster, and a 3-PRO.
Amazing work, Genz-Benz, great design engineering, thanks!
It will not replace my road gear, but it will see LOTS of action both in the rehearsal studio and at the local week-end gigs. I'm loving it.

To all players looking into adding a "mighty-mite' rig to their gear-
Give this one some careful consideration. I personally found it warmer than the LMII (just an opinion) and it performs.
I could say I'll see what happens on-stage, etc. but I've played enough and have enough ears to know what's gonna happen:
It's gonna ROCK!
It really does.
Good work, Scottsdale! Thanks!

 

[Michael Vee]

But what if the light flashes for my whole set ?

Hey, Ian- I'd either run an outboard power amp for gigs, or better yet, give it up, sell the Neo-Pak and go for the big iron - the GBE 1200. Run that horse out of power.. bet you couldn't!!

 

[Eublet]

THEN I put it in the gigbag, and...
I repeat...
I think I'm ging to need to put a brick inside to justify the tone and headroom this amp gets- It's not that tiny, small, yes, but HOLY
*&*&^%^! It sounds real good-

That's one of the things I like about it. It's not tiny. The knobs are easy to see and tweak on stage. Some of the AI stuff and the new wtx are too small for my taste. Plus, the Neo-pak also looks more authentic sitting on top of a larger setup. If I sat a little matchbox head on top of my 212/112 rig, it would look very strange to me. The Neo-pak fits right in, looks very sexy, and has plenty of room in the case to keep things running cool. Best of all it has a tube in the pre! Can't beat that.

 

[realdeal]

The "footprint" of the Neo Pak was one of the selling points for me, as was the 12AX7.
My first move away from all- tube was the 3-PRO, which utilizes 3 pre- amp and 2 driver tubes in the signal path.

Genz-Benz was very smart in the design and utilization of the (1) 12AX7- It has a seperate gain for tube drive (as does the 3-Pro) and that does a LOT for "coloring" the tones you can get- from adding warmth and roundness to a nice growl.
I also like the very solid detents in the eq knobs-It's a very responsive Active eq, and even small sweeps color the overall tone.

I did a lot of spec comparing as well as A/B listening between the other new "little giants' on the market, and this is what I chose for a lot of reasons.

I'm sure I would find quality and reason to like most of the other heads of this type- But for me, GB comes out in front.

And damn! That must be how it feels being weightless in space when I pick this unit up!
I repeat- WOW!

 

[Ian774]

Hey, Ian- I'd either run an outboard power amp for gigs, or better yet, give it up, sell the Neo-Pak and go for the big iron - the GBE 1200. Run that horse out of power.. bet you couldn't!!

Dude, I'm almost skint these days and you want me to go for a GBE 1200 ? LOL !

I'd rather go for the 750 if I could... but I don't need that much power !!!

I think that the solution will be running the Neo Pak in 4 ohms and then I'll have more power than I'll ever need.

Man I'm an amateur, I don't need a 1200w head... The Neo Pak sounds awesome to my ears, dont need another head for now. Just a 4 ohm cab or another 8 ohm one...

 

[birdxofxprey]

there's an ongoing debate in another thread about running an amp on 2 ohms. of course, some say it's fine and some say it will ultimately facilitate the beginning of the apocalypse...

just curious what you guys have to say about this concerning the neopack 3.5. not just to settle the debate (with regard to the neopak 3.5, anyway), but more because I'd love to be able to pick up another GB cab and run it off my current rig.

how about it?

thanks!

chris

 

[Freddels]

there's an ongoing debate in another thread about running an amp on 2 ohms. of course, some say it's fine and some say it will ultimately facilitate the beginning of the apocalypse...

just curious what you guys have to say about this concerning the neopack 3.5. not just to settle the debate (with regard to the neopak 3.5, anyway), but more because I'd love to be able to pick up another GB cab and run it off my current rig.

how about it?

thanks!

chris

I think this has been answered many times. If the amp is only rated for 4 ohms then it will get damaged if you try to run it below that. The NeoPak 3.5 is rated at 4 ohms (unless you get the newer version or upgrade the original version). The new ones coming out are rated to 2 ohms.

All 2 ohm capable NeoPak 3.5's are labeled as such on the back panel in the ratings section.

Please allow me to clarify the 2 ohm operation on the NeoPak.

The NeoPak 3.5 was introduced with a 4 ohm minimum load capability. All 4 ohm capable NeoPaks are noted as such on the back panel.

With the availability of some improved components that were not available (in production) when I originally designed the amp, we upgraded the NeoPak to 500 watts at 2 ohms once we were confident that the parts would perform as excpected. All 2 ohm capable NeoPak 3.5's are identified as such on the back panel. The new owner's manuals reflect this change as well. The duty cycle of 2 ohm operation is similar to that of the GBE series.

Hope this helps clarify.

Looks like Roger just beat me to it!

 

[Eublet]

I think he's asking about choosing to run at 2 ohms or avoiding it, regardless of what the amp is spec'ed to handle. There is some truth behind the idea that 2 ohm operation is undesirable with some designs. It becomes progressively harder for an amp to maintain control over the drivers as resistance is lowered, and the ability to handle dynamics are often reduced with some amps. There's also the added heat which can create problems.

Having said that, I've noticed none of the those things using my Neo-pak at 2.66 ohms. Still very responsive, powerful, and seems to run very cool. The same goes for my GBE 1200, which just sounds stellar at 2 ohms to me. Very responsive and musical. A well designed amp that hasn't cut corners under the hood should run quite well at 2ohms if it was truly designed and built to do so. I suspect that many people don't like 2 ohm operation because some heads, even though they are advertised for it, can only handle 2 ohm operation under specific pristine conditions, otherwise they shut off from over-heating, or they exhibit lots of farting and such from classic damping issues, or they sound lifeless from the lack of headroom to handle the dynamics of one's playing. This is not the case with the Neo-pak or the GBE's for that matter.

 

[Freddels]

The 1200 and 750 are designed to do 2 ohms without breaking a sweat. The original version of the neopak wasn't. I wouldn't run mine at 2 ohms without getting the upgrade.

 

[Eublet]

The 1200 and 750 are designed to do 2 ohms without breaking a sweat. The original version of the neopak wasn't. I wouldn't run mine at 2 ohms without getting the upgrade.

Definitely not. The upgrade, if I understand this correctly, involves a whole new power supply. There may be other items involved as well.

 

[birdxofxprey]

I think he's asking about choosing to run at 2 ohms or avoiding it, regardless of what the amp is spec'ed to handle.

yes, this is what I'm asking about. However, I rechecked my amp and it is not one of the 2 ohm rated amps. I had assumed that it was because I only bought it a month ago. Maybe it was an older model that was still in stock - how long has it been since the non 2ohm rated versions were produced?

 

[Eublet]

yes, this is what I'm asking about. However, I rechecked my amp and it is not one of the 2 ohm rated amps. I had assumed that it was because I only bought it a month ago. Maybe it was an older model that was still in stock - how long has it been since the non 2ohm rated versions were produced?

I think I remember it being said that they might not even be available in the US yet. I doubt it was "old". I haven't seen a 2ohm Neo-pak advertised anywhere. Even the website specs and such list 4 ohm minimum only. I'm sure it will take a little bit of time for the current reserves to thin out before they confuse people by changing all their advertising.

 

[agedhorse]

There is no difficulty to design an amp that will run just fine all day at 2 ohms. In fact, knowing the load impedance will be that low allows the designer to optimize parameters and produce an even better amp for 2 ohm operation. It's not rocket science, but does take an understanding of the basic mechanics of load lines and VI protection limiting curves and probably even more importantly the characteristics of reactive and sub-nominal impedance speaker loads. This is probably the most mis-understood and most important parameter of any low impedance amp design. (IMO of course).

As far as the Neopak 3.5, the 4 ohm versions will work ok at 2 ohms, but under high output the power supply will shut down to protect itself. The power amp portion itself is already overdesigned to accomodate 2 ohm operation, it's the power supply that get's the upgrade. It won't hurt the amp, but not a great way to play bass either. If you have the older version, PM Roger (hasbeen) as we have been modifying TB'er's units for 2 ohm operation. Roger has all the details.

 

[birdxofxprey]

hard to believe no one has posted about this great amp in almost two weeks

anyway -

when i got my neopak, i declined to buy the rackears that the dealer showed me - big mistake. now the dealer tells me that they have none and don't know how long it will take to get them.

MF doesn't sell them either (btw, MF has permanently backordered the fitted carrying bag for the neopak).

so where can i get a set of rackears for my amp?

love my GB gear

chris

 

[Eublet]

hard to believe no one has posted about this great amp in almost two weeks

anyway -

when i got my neopak, i declined to buy the rackears that the dealer showed me - big mistake. now the dealer tells me that they have none and don't know how long it will take to get them.

MF doesn't sell them either (btw, MF has permanently backordered the fitted carrying bag for the neopak).

so where can i get a set of rackears for my amp?

love my GB gear

chris

haha, business must be good!

Out of curiosity, why do you want to rack mount it? Do you have other gear going in with it.

I've been thinking lately about racking mine in a shallow 2 space SKB. It would still be really light, and it would offer it some protection when it was setup.

 

[birdxofxprey]

haha, business must be good!

Out of curiosity, why do you want to rack mount it? Do you have other gear going in with it.

I've been thinking lately about racking mine in a shallow 2 space SKB. It would still be really light, and it would offer it some protection when it was setup.

yeah, i want to rack it with a bass pod. separately, the pod and the 3.5 are very different in size and weight, and i'm thinking that they will sit, travel, and look better in a common 4 space rack.

ears for the 3.5 appear to be a bit of a rare item...

 

[fenderjazz68]

Kinda like this? I got the rack ears from Link Removed, you may want to see if he has any or can get more. I am debating on what to put in the last rack, I may put an Aphex 204 in there...

yeah, i want to rack it with a bass pod. separately, the pod and the 3.5 are very different in size and weight, and i'm thinking that they will sit, travel, and look better in a common 4 space rack.

ears for the 3.5 appear to be a bit of a rare item...