Bass amp idea

[M Fowler]

Building a bass amp for my brother-in-law great guy. He already bought my Marshall 2550 build and now asked for custom bass amp.

I'm going to use 120w Hammond transformers and run four KT88's. What I'm thinking to do is not re-invent the bass circuit so was wondering about just following the schematic for the preamp of the Bassman 100 bass channel but add mid pot and will have gain, MV, T, M, B, and presence. The faceplate I'm using is a white JCM800 style I already have.

Does this circuit work well for most bass players, he doesn't gig at this time but still wants it plenty powerfull. Was thinking about just adding push/pull pots for treble-bright pull; mid-mid boost; and bass-deep pull.

Let me have it full force people I need some learning here about bass circuits especially amplifying lower frequencies and about the V1a/b bias resistor values and bypass cap choices.

I'll be the first to admit I'm not an amp designer, engineer, or tech just a dumb shit that likes to throw amps together and see what I get.

Mark

[Jana]

Mark,

I'm not sure that 120W is enough power for bass. I used to play with a very good bass player. He always said that the minimum power he needed was 300 to 400 watts. (We're not talking stadium gigs here--just the average club sized venues). It takes a lot of power to keep those low frequencies clean but still be at a suitable volume to keep up with the rest of the band.

Before you get too far into this, maybe ask him what he uses for a bass amp now and how much power he uses. If you have a 100 watt Marshall or similar head, maybe see if that is enough amp for him. If it is, then the 120W amp optimized for bass will probably work (there isn't going to be much difference between 100W and 120W). If he says it breaks up way too soon or gets mushy way too fast, then the 120W probably won't be enough.

[Gibsonman63]

I have a Bassman 100 in my studio that we use for practice. Most of my bass playing friends like it a lot, but we aren't super loud (anymore). I use a Tech 21 Bass Driver DI with it for more tonal posibilities and to get a DI for recording. I haven't tried it with different speakers, but the inverted pyramid 4x12 Fender speaker works well with it. I have learned that I cannot screw the head to the box because it literally rattles the amp apart. The Bias capacitor came completely off of the board and the second time a couple of wires broke off of the eyelet board. Now, I have foam between the head and the box and things are fine.

Interesting side note, I picked this up in a trade from a country guitar player. The normal channel was already wired to blackface Showman specs. Not bad for clean guitar, but I can understand how he was tired of lugging this beast around.

[gui_tarzan]

I've played in different size bars and other indoor & outdoor venues pretty frequently for the last ten years and on & off since the late '70s and I wouldn't to play with that few watts unless it was going into the mains via direct box (or mic I suppose). The outdoor events I've played at all had DI boxes fed into the PA so we were basically using my amp for myself and our drummer to hear/feel.

However my Ampeg SVTIII is only tube on the preamp side so I guess I'd have to hear the all-tube amp to say for sure but 120W just seems very low for bass unless you're going through the PA like I said. Mine is rated at 200w @ 8ohm which is how I typically use it indoors and 350w @ 4ohm and I use a pair of cabinets in larger venues or outdoors.

[martin manning]

Four KT88's will make 200W... Marshall Major bass.

[mhartman]

Check this out:

http://www.diytube.com/phpBB2/viewtopic ... 36&start=0

If I was building a bass amp, I would probably try this one (4x6550 for 150W-160W or so).

[gui_tarzan]

Sounds like that Hammond 120W transformer will be a bit on the small side then.

[M Fowler]

Thanks everyone he is new to bass so most will be at home and with friends.

I told him he didn't have enough in his budget for 300w transformers
So he is getting the next available the Hammond 120w. I was looking at calling O-netic for their 280w iron but never did.

Just worked on a Ampeg SVT classic with six 6550 tube section and the way that thing is put together is crazy compared to how simple mine will be and serviceable.

I have looked at that BFA amp build before and have his schematics thanks.

Mark

[M Fowler]

I'm also working on putting together a 600w class D bass amp so if he really needs the power for gigging I'll help him out with the Class D amp.

[Milkmansound]

my bass amp was about 85W from 2 KT88. Plenty loud.

The jump from 85W to 200W is not extreme. Does he play in arenas?

[xtian]

Mark, I built a bass amp for a client who used to work for GK in the Bay Area. He wanted a low-wattaged SE amp with Fender tone stack, which for gigs, he would run a line out into a 300-watt solid state rackmount amp. It came out really well. I used the AX84 SEL as my model.

https://tubeamparchive.com/viewtopic.php?t=22434

[M Fowler]

I have a cheap SS 300w bass amp and cabinet for my jam room for people to use along with a drum set.

A couple of the local bands are using Fender Bass 100 heads but most are using SVT 300w or going SS amps for even more wattage.

But my brother-in-law is not a gigging bass player so I'm sure he can get by with what I going to build him using the Hammond iron.

[M Fowler]

I'm going to use the

1650TA OT 120w 1k9 4/8/16 easy hookup

378CX OT 535mA 800vct

[martin manning]

I don't see how 4x KT88 at 540V B+ isn't way over 120W.

[M Fowler]

I agree Martin the amp should be able to see 150w-180w right?