Marshall 9005 stereo power amp - nice sound, low volume

[Michael m and m]

hey there,
thanks for checking in.

first of all a disclaimer: i know how to handle the life threatening voltages inside the tube amp, and know how to measure voltage and resistors, without risking my life. ; )

my great sounding 9005 stereo power amp, that i bouht used, unfortunately has very low volume. in HIGH mode i run the gain at 12 o'clock, and the volume is room level. not loud.
both channels the exact way. LOW mode also works fine, but low as well.

the amp sounds absolutely fine ... no hum, almost no noise and no crackling, etc.

as the channels both are the same sounding ... is it possible that someone before me has kind of severely reduced the output to speakers, with resistors, etc.?
maybe even for hi--fi use. dont know how many owners this power amp has seen already ... ; )

the big power supply in the middle is for both channels. is it common thst these lose power after 35 years? as it feeds both, channel a and b simultanously.

valve plate voltage and bias is fine ... all tubes are new.

thanks for help
maybe somebody had a similar experience. maybe with a jcm800 in mono! great sound but very low volume.

 

[Dogs of Doom]

to the forum...

what's the tube array?

In my EL34 50/50, there's a single pre-amp tube, the PI & a pair pf power tubes, for each channel.

mine takes:

ECC83 pre-amp
ECC83 PI
EL34 x's 2 (50 watt) power tubes

per channel.

I'm not sure what yours takes, by design, but, maybe they installed lower strength pre-amp tubes?

On my amp, there's only a gain volume & a presence knob (as well as voicing switches). The amp is basically a non-master volume amp. The pre/gain is the volume... If you put a low value signal tube in the circuit, say an ECC82, in place of an ECC83, that's going to give you 20% of the signal +/-... that's an 80% drop in signal

 

[Michael m and m]

hey there,

thanks for the reply, and thanks for the welcome!

well, there are two separate sides ... channel A and B. each having two ECC83s ... one for gain and one for phase inverter. I have changed them all myself before. to new ecc83s, 12ax7s. so this cannot be the reason.

my 9005 seems to been have changed to operate with 5881 power tubes. and I have redone all these changes, as I am using el34s now ...

 

[Raymondo]

Hi there, in a similar position to you, recently purchased a used Marshall el34 100/100 stereo monobloc, and experienced clear but relatively low volume. After some research, pulling every valve, voltage checks etc, I learnt these rack amps are designed for ‘line level’ gain, not instrument level. I was running my pedal board into it hence not enough input signal.

Solution was to add a 20db boost using a Harley Benton mini stomp magnum di at the end of my pedal chan prior to power amp….may work for you

 

[Michael m and m]

hello there,

well, guys. I'm getting more and more the feeling that the 9005 simply doesn't get enough input volume from my "preamp-pedal-board"

I'm using an effectrode blackbird tube-preamp (that even has a special output with more volume than to a guitar preamp) into a boss stereo delay and the mxr-reverb. stereo from there into the 9005.

this setup works flawlessly with my mesa boogie fifty/fifty power amp, but obviously the 9005 needs much higher levels.

is there a big difference in "db" or volts coming from a pedal-board setup like mine, and a rack-mounted preamp like the marshall jmp-1? for example.

thanks for help. I think the reason for the low volume could be as simple as that.

 

[Michael m and m]

thanks for moving to the workbench. sorry ...

 

[Michael m and m]

well, problem solved.

the 9005 marshall power amp simply needs a rack-amp-like volume at the input. I got myself a rack-preamp ... and now everything works fine. the 9005 has enough input volume and sounds amazing, and loud, and pants shaking power...

the volume from the pedalboard, though played with a "pedal-board-preamp" only seems to be classic "line-level" max +5db and a rack-mount preamp gives more than that. like a preamp stage in a complete marshall head. f.e.

 

[Raymondo]

Out of interest what preamp did you go with in the end?

Very little info out there on preamp output voltages/db etc. I thought my new to me second hand amp was broken until I looked into the input sensitivity etc

 

[Michael m and m]

hey there.

funnily, i got an old pcl "vintage amp" mk iii rack preamp.

I guess every rack preamp should work, as they are meant for line level and not this kind of pedal board ... instrument<>line level.

the mesa fifty/fifty I have doesnt need this preamp stage level ... as it has a real dedicated "preamping-amplifying 12ax7" tube for the input signal.

 

[Pete Farrington]

Wow, that schematic takes the biscuit for Marshall's least helpful ever https://el34world.com/charts/Schematics/files/Marshall/Marshall_9100_2x50w.pdf

 

[Michael m and m]

that is the 9100
not the 9005

 

[johan.b]

This is the one you want

https://www.drtube.com/schematics/marshall/9005.gif

 

[Michael m and m]

thanks. I got that already ... long ago.

but still good for the thread.

thanks.