Phase Inverter Coupling Cap Values

[Webby14]

Hi All!

Mainly loving my Split Cathode '68 Plexi Lead Spec Head, but since getting rid of my Marshall 1960AX 4 x 12" (Greenbacks) and downsizing to using a Marshall 1936V 2 x 12" (Vintage 30's) on a tilted amp stand, I am missing a bit of the low end thump.

I have tried jumping the channels, but it just sounds a a bit mushy to me!

I was just wondering whether or not, to try .047pf PI Coupling Caps instead of the stock .022pf's?

Tried a Bass Spec Amp once with .1pf's and that was more bottom end than I would ever use!

So what do you think?

Thanks in anticipation to all!

Webby

[RockinRocket]

I think it would help a tad although its probably the least bang for the buck. Low E at 82hz in standard tuning wont make a difference much, from a text book point of view. Don't know what real world experiences would yield though.

I think its more of the V30 comparied to the greenbacks regardless of it being a 2x12 or 4 x 12.

[neikeel]

You can use 0.047 or 0.056 PI output couplers but most of the low end gets skimmed off in the early part of the preamp.

Odd that Greenbacks to V30s and you lose low end, but I guess the size of the cab counts. I find T1221s can get mushy and V30s very beamy! If the cab is tilted back and not securely on the floor that can be an issue. I usually take my castors off and have the cab on my head flight case or preferably on the floor.

Personally I would not mid my amp for a problem I created by changing my cab............

[Webby14]

Hi Guys,

Thanks for the replies.

Forgot to say, the 2 x 12" V30 Cab was modified to open back, Maybe I'll try returning to closed back before messing with the amp specs.

V30's have a lower fundamental resonance than Greenbacks (70hz instead of 75hz), and in most Youtube Greenback vs V30 clips, the V30's always seem to have a bit more bottom end, so i was a little surprised.

I agree with Neil about the 'beaming', but I can live with that (tried 'Beam Blockers' once, but they totally killed the sound for me).

Cheers for now

Webby

[neikeel]

Hi Guys,

...............tried 'Beam Blockers' once, but they totally killed the sound for me..............

Webby

I use x3 beam blockers on my current gigging cab ('69 1935A with T1511s) on lower speakers and top left. The top right is my mic'd speaker and the one I can hear during a gig (cab is raised up on my head flightcase). So I have a monitor (I like the vocals and keys in my monitor) behind me and the sound of the other speakers are spread aaround the stage. I do not hink that it is perfect but I have the memory of someone at a gig saying that they could hear my attenuated cab ('69 1982B with G12Hs as I like the tone of these speakers better- they do cut through the mix ) 3 buildings away when I could hardly hear it on stage . So I use the T1511s now and stage volumes are kept lower.

[Webby14]

Hi Guys,

Thanks to you all for chiming in!

Sorry Neil, I ignored the advice about not modifying the amp to suit the speaker cab!

Well ... I had a free afternoon, some caps & resistors lying around, so I thought lets fire up the soldering iron and experiment!

Anyway, to cut a long story short, I converted the amp to shared cathode 1986 Bass Amp Specs, removed the bright cap completely, and hey presto! Les Paul Standard + 1986 Bass Plexi + 1936V 2 x 12" (with open back) = A match made in heaven!

More Bass response than you can shake a stick at, plenty of treble on tap (even without the bright cap), and with more responsive tone controls generally, you can even dial in a pretty reasonable sound at bedroom volume (with the PPIMV right down low).

Thanks again to everyone

Webby