Amp Mod for some More Gain?

[monto]

Hi all, hope all are doing well and having fun

I'm enjoying using an award session sessionette 75 (SG75) mid-eighties guitar amplifier, but on Channel A (gain/crunch), i'm wanting if possible some more gain available on that channel.

I know i could use an effects pedal to obtain more gain but im trying to avoid effects pedals if possible.

if you see this schematic, here:

http://s3.postimg.org/9v8l54x2r/SG75.png

you can see the "Channel A" section in the top-right of the picture; the 'GAIN 1' potentiometer is the amount of gain, and the 'GAIN 2' potentiometer is the volume of the gain channel.

does anybody have any ideas as to some components to change/add/remove so as to get some more gain on "Channel A" ?

[J M Fahey]

Use an external pedal, seriously.

Being SS, the internal distortion is already "an Op Amp driving clipping diodes"
Maybe you can give it * a little* more gain ... it will still clip the same way, will have the same EQ, basically the same dated early 80's distortion.
Not *horrible* but uninspiring, by today's taste.

You are much better into buying or building a modern, killer pedal.

You are not more of a Purist by "avoiding pedals" because that preamp distortion IS what you find in a pedal, so replace it with a better one

Your choice, of course.

Even an old Marshall Guv'nor is way better than it, go figure.

And you can build it for peanuts ... you even have the iron on layout transfer available at some of the Pedal sites . (was it GGG???).

[monto]

hi Juan thanks for fast response
i agree about the distortion, im not overly keen on it.. i wouldnt say i hate it, im kind of neutral i think with it
pedals aside for a moment, hmm about what u said about maybe i can give it a *little* more gain.. that would actually be ok with me, i dont suppose you could provide some clues as to how to achieve that?

[pdf64]

A boost pedal would be a much better way forward than tinkering with an old fragile PCB.
To get much more gain without screwing up the frequency response (ie making it muffled / thin), quite a few parts may need swapping; and with a PCB, it's a whole lot easier if replacement capacitors are a good physical match for the originals.

But if you're still determined, try bringing R8 and R9 down to 100k and C11 to 22nF; that should give ~15dB boost.
And / or R11 to 3k3 and C18 to 330nF (or 220nF for less bass, 470nF for more bass) for ~10dB boost.

The PCB traces and pads are likely fragile and liable to lift off; unless you're very skilled and have good equipment, you risk screwing up a nice amp.

If you're in the EU, consider sending it to Stuart to upgrade it to a mixed feedback topology (Retrotoned) Award Session Sessionette Amplifiers. Welcome to award-session.com [AwardSession Sessionette Amplifiers]
It should be a big improvement.

[monto]

hey pdf64 thank you for the reply, i will attempt this modding and report back how it goes i will be very careful (i have already changed all of the electrolytic capacitors and some other bits, and it all went fine, no problems (i took the switches and pots apart also to properly service them (i had to adjust (re-aim/reposition) the wipers in the pots as they had worn tracks into the conductive material, making the pots crackly/unreliable)
ps. i do live in the UK and had seen about the retrotone service that award session provide but did not go down that route (i only really play at home at very quiet levels.. i have been experimenting with a passive attenuator through the effects loop to try to help with keeping the volume very low..)

[pdf64]

If still crackly, you should be able to swap the pot tracks with the regular (OMEG) ones from Maplins.

[monto]

hey pdf64, i did the mods
holy ... hey it went really well so thanks a million
with the amp gain cranked full it's nice to finally hear my guitar/amplifier feed-backing even at low volumes, which the amp didn't do before the mods (incase that sounded like sarcasm, trust me it's not, i actually do want high gain/feedback) - so now i can get a very hot/touch sensitive tone on the gain channel, it really screams overdriven now and i can do pull-offs and they sound lively with attack, rather than dull and soft/lifeless sounding like they sounded before doing the mods.
... and of course if i just want to go back to regular sounding sensible distortion i can turn down the gain knob on the amp.

so it really has been quite a success, so again thanks very much!