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Old 7th March 2006, 07:25 AM   #1
AdamB is offline AdamB  United Kingdom
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Default laney DP150 mods

OK,

I just got (for free, muwahaha) a laney DP150 4x12 bass amp, fully working. Now, I've had a bit of experience with pedals, but don't feel confident about messing with high voltages yet. So, my plan is to keep the 150W mosfet power stage and replace the preamp (they are in seperate modules inside the chassis, handy...).

Now, I was just gonna stick in a marsha tube preamp, as that looks nice and simple to start with, but I'm gonna stick with using the connectors that go between the poweramp and preamp at the moment and socket all connections to the board, so that I can change the preamp to a better one in the future. Now, the problem is I'm having a hard time understanding the schematic from the DP150....

I can build the marsha valve easily, as I have a perf layout (and as un-professional as that is, I'm happy with doing that for now, it is my first amp project after all). Just, can someone tell me from the lettering on the schematics what each pin of the connector between the pre and power stages does? Just so that I know where to connect each pin to on the marsha valve perfboard, if you see what I mean.

Here's the schematics for the DP150, pre-amp (pdf) and poweramp (jpeg):
http://tremolo.elektroda.net/Firmowe...assPreamp2.pdf
http://tremolo.elektroda.net/Firmowe...P100-DP150.jpg

Here's a link to the topic where the verolayout for the marsha valve is (the second post on this thread):
http://www.elixant.com/~stompbox/smf...?topic=41895.0

Thanks for your interest and any help that can be given,
-Adam
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Old 7th March 2006, 11:31 AM   #2
AdamB is offline AdamB  United Kingdom
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right,

I've worked out some stuff, not sure that it's right tho...

The poweramp is outputting +/-24 volts to the preamp stage. The preamp stage then has a power supply that drops this further to +/-15V.

The pins are wired like this:
0 +LIM (no idea what this is)
0 +24V (voltage fed from power amp)
0 Pull Bass1 (an added feature on the amp I think that can be ignored)
0 LIM/S (no idea what this is)
0 Pull Bass2 (an added feature on the amp I think that can be ignored)
0 Ground
0 o/p (no idea what this is)
0 Ground
0 -24V (voltage fed from power amp)
0 -LIM (no idea what this is)

Now, what I don't understand is which of those pins is the output from the preamp? Could a preamp like the marsha even be made to work with this?

EDIT:
Ah, think I understand it now. O/P is the output, LIM is from the limiter circuit that is also an added feature of the amp, so I'm guessing I can just ignore that.

So, then I'd build the power supply marked on the schematic and then all I'd do is wire the pins like this:
o/p -> output of marhsa
+24V -> power supply (drops to +15 V) -> +12V on marsha (running at 15V on the marsha should be ok)
-24V can be ignored, yes?
both grounds -> ground of marsha
input jack -> input of marhsa

Is that right, please someone let me know coz I am just guessing my way around this stuff.

-Adam
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Old 7th March 2006, 01:28 PM   #3
sreten is offline sreten  United Kingdom
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Hi,

IMO removing the limiter from a bass amplifier is not a good idea.

The sound of a transistor power amplifier in hard clipping is not pleasant.

As a bass player with experience of several amplifiers I'm not sure what
you are trying to achieve by fitting a marshall based valve preamp circuit,
and in the process removing all the preamplifiers facilities.

If anything IMO you should fit a valve input stage, make the
input switchable between valve and op-amp, and thats it.
(The valve circuit instead of IC1A and IC1B)

/sreten.
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Old 7th March 2006, 02:52 PM   #4
AdamB is offline AdamB  United Kingdom
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I'm converting it into a guitar amp, I don't play bass.

-Adam
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Old 7th March 2006, 02:52 PM   #5
AdamB is offline AdamB  United Kingdom
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Also I should mention the description above is a simplified explanation of what I'm doing, I'm also adding 4 way mixable inputs, guitar tone stack (bass,mid,treble), reverb tank and digital reverb (selectable) and a tonebender fuzz (selectable) in front of the valve preamp, FX loop, line out and line in and a noise gate. Eventually I want to have several tube preamps that are selectable via remote, but that's not gonna be added in this build.
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Old 7th March 2006, 04:46 PM   #6
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by AdamB
I'm converting it into a guitar amp, I don't play bass.
-Adam

Hi,

fair enough but I think your wasting your time.

Instead of chucking half of the amp away i suggest you sell/swap
it for something that has a power amplifier with half a chance of
sounding decent with a guitar.

I've got no arguement with guitarists converting valve bass amplifiers,
but as far as I'm concerned a tranny bass amp is no good for guitars.

The 4x10 though is probably better on guitar than bass.

You could keep the 10's and fit a 15" to the combo before you move it on.

/sreten.
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Old 7th March 2006, 09:47 PM   #7
AdamB is offline AdamB  United Kingdom
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Please explain why a bass transistor power amp sound bad with a guitar?
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Old 7th March 2006, 09:47 PM   #8
AdamB is offline AdamB  United Kingdom
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also, eventually I'm gonna replace the poweramp with a valve one, I'm just not at the moment as I don't feel confident enougth to mess with the higher voltages.

Is there a reason why tranny bass power stages don't sound good with guitars tho?

-Adam
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Old 8th March 2006, 08:21 AM   #9
sreten is offline sreten  United Kingdom
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Quote:
Originally posted by AdamB
Please explain why a bass transistor power amp sound bad with a guitar?

Quote:
Originally posted by AdamB
also, eventually I'm gonna replace the poweramp with a valve one, I'm just not at the moment as I don't feel confident enougth to mess with the higher voltages.

Is there a reason why tranny bass power stages don't sound good with guitars tho?
-Adam
Hi,

So your eventually going to junk the complete working bass amplifier ?
Doesn't make much sense to me.

For bass amps I've already mentioned limiters to prevent hard
clipping, without limiters the amplifier starts struggling rather
than gracefully moving into a compressed mode of sound.

This is for a decent/good tranny bass amp. The effect doesn't sound
particular nice on guitar - but is better than allowing hard clipping.

The arrangements for tranny guitar amps can be much more complex
or much simpler - depending on the effort expended by the designers
on controlling what happens when the amplifier hits its end stops.

Most decent tranny guitar power amps try to implement a gradual
overload characteristic similar to the effect you get with valve power
amplifiers - usually involving arrays of diodes (+ possibly resistors +
capacitors) at the input and/or the feedback loop and/or multiple
feedback loops.

Comparatively speaking a Bass power amp is more like a Keyboard
power amp, relatively hi-fi with added compression and limiting.

I'd rebox the bass amplifier section and sell it (if you want the 4x10).

Then perhaps say get a second hand valve amp that sounds nice but
with limited facilities or gain and add the extra facilities/gain you need.

/sreten.
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Old 8th March 2006, 03:19 PM   #10
AdamB is offline AdamB  United Kingdom
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I'm not 'junking' it. It's not like I'm gonna throw the PCBs away, all I'd have to do is once I replace the mosfet stage with a valve stage, just rehouse the original preamp and the power amp in a new 19" rack. If you saw the amplifier, you'd also realize it's not worth selling as it is, as it's about 25 years old and rusted heavily, some of the knobs are missing and a couple of switches no longer work etc. etc. I mean I'd have to rehouse it and do it up to get rid of it, and if that's whats gonna happen eventually anyway, I might as well just do what I'm planning and eventually end up with a decent guitar amp a useable bass amp.

-Adam
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