Donna Rocket gets a 2x12 speaker cab...speaker???

[Greg]

I have decided to get some scumbacks. Jim has suggested an H75 M75 mix in my LOPO 2x12 convertible dovetail cabinet. Is it ok to use a 25 and 30 watt in same cab? If I need to match wattage then I have to get two 65 watt speakers. I don't think the Rocket needs that much. Also I have impedance options to consider. Two at 8 ohms each would result in a 4 ohm cab. Or two at 16 ohm yields an 8 ohm cab...any preferences out there? Any benefits to different impedance...4 or 8?

[selloutrr]

No issue with mixing wattage. The 25 will break up before the 30 is all. It's common to see 4x12 with 75 / 30 so you get a clean / crunch popular in modern cabs.

If you have options for ohm load I suggest you make it which ever one matches other amplifiers you own so you can mix it up if you choose.

[Greg]

Excellent advice...thank you sir.

[gearhead]

I'd go with the 8 ohmers in series, making a 16 ohm cab. Gets all the windings.

Am not as familiar with the Rocket output, but ask yourself if you want to hear the amp as it is, or with speaker breakup. With the Scumback lower ratings, you might get some of the later.

[Greg]

Can you expand on "get's all the windings". Not sure what that means. From the OT? That doesn't happen in parallel?...also hear all the amp or get speaker breakup?

The more question I ask the more I realize I am in over my head. I did have success in "assembling" a Rocket.

[selloutrr]

I believe is refering to the construction of the output transformer meaning it uses all of the coils or taps to produce that load.

As for the voice of the amp it's completely subjective but the amp has it's own breakup in the preamplifier tubes then when the volume is turned up past a certain point you begin to get output tube distortion ( one of the benifits of low wattage tube amps). Then you have speaker distortion, caused by exceeding the wattage of a given speaker. Exceeding a speakers rating can be both musical and hazardous to the speaker and output transformer and output tubes.

The scumbacks combined offer 55watts of rms power handling. ( steady power ). The TW is going to put out 30 or so watts when maxed it's perfectly safe to run your tw and the scumbacks together. I would refrain from using any amp over 50 watts until you get comfortable with the speakers and can tell when you are driving then to hard.

8 ohms would be the most versital allowing you to raise or lower the load by running in series or parralel as well a single speakers / stereo

[selloutrr]

If you distort a speaker to far it gets farty or woofy detracting from the amps voicing. If you over power it it can blow. It's not a bad thing to give a speaker more power then it is spec'd with in reason it offers headroom but if you push it to hard it will fail. If you starve a speaker for power it can be just as stressful on the speaker. I hope I'm not confussing you more. What you are trying to do will work great!

As for the ot. It offers 4 8 and 16 ohm taps. Basically the addition of the 4 ohm tap and the 8 ohm tap become the 16 ohm tap. So when you run at 16 ohms you are using the OT to the fullest. There is no right or wrong ohm load just as long as the ohm loads are the same on the speaker cab and amplifier. There are exceptions to mismatching but let's not go down that road right now.

[gearhead]

Sorry about being obtuse.

What selloutr said on the OT.

AFA speakers are concerned, you don't actually have to exceed the stated rating to get speaker breakup. Some are designed to do so under less than max ratings. Don't remember if the Scumback M/H75s are are the early breakup type, but believe so. Have some H75s, but in the higher wattage config, cause -I- didn't want a lot of speaker breakup. Ask Jim S. (Scumback owner) and he'd be able to tell you.

[Greg]

Thanks guys. I did order the 8 ohm versions. I thought I could do more with those...option wise. Plus they will work with my Deluxe Reverb. Now I understand how the OT impedance taps work. Is 4, 8, 16 a mathematical necessity or could you have custom OT impedance...say 6 0r 5.7? I am still not sure why using the full impedance tap (16 ohm) could offer a tone advantage over the 4 ohm tap.

[selloutrr]

It's industry standard for the windings to terminate at 2,4,8, or 16 ohms. (with in a few tenths of an ohm) rule of thumb is go up... so if it's really 3.7ohms run it on 4 ohms.. 14.9 it's 16ohms... etc.

You can have custom wound transformers made to any spec you want. It's just how many winds equals that ohm load.

Tonally it's not that you aren't getting the voice of the amp it just spreads the work load over more area evenly... in theory less strain on any one given part or section. in some cases it may give some notes a better chance to mature.

[Greg]

I received my Lopoline 2x12 dovetail in a convertable configuration the other day. The 8 ohm Scumbacks are on back order so they will will be a bit longer till delivery. So I am sitting here looking at this great cab...empty! Well that just won't work...4x12 now has two huge holes and 2x12 has temp Celestion Vintage 30's.

I am playing the Donna Rocket with back off of the cab and it sounds much different...Duh right? Well I am surprised. Much more open sound, softer maybe. Notes seem less defined but smother. For same perceived volume level...I need to turn amp up...that's good.

2 16's in parallel, amp turned to 8 ohms...I am wondering if the sound difference I am hearing can be partly attributed to the switch from 16 ohms to 8 ohms.

I have tried to turn the Donna Rocket up and do not like the sound. Amp set at 1 o:clock and guitar volume maxed but sound is not creamy at all. When I turn down it is beautiful...I never really play at loud volume so this isn't really a big deal but I am wondering if these Vintage 30's are really just not a very good speaker and this may change significantly with the Scumbacks?

[M Fowler]

You want your Rocket to really sound good try a 212 open back loaded with Celestion blues. Nice!

[Greg]

I may just do that...I hope the Scummies sound good too.

[Greg]

Holy crap those Blues are not cheap...

[M Fowler]

Good tone doesn't come cheap.