Sound City 120R: need some advice

[Jonny toetags]

I picked up what looks like a bone stock Sound City 120R Mk4 (w/ matching cab) based on the cleans at a local mom n' pop shop.
Once I got it into the studio, I noticed that at loud volumes, it 'lacks' something (character?) and it really doesn't take drive/dist/fuzz pedals well at all. Everything sounds compressed and boxy.
Here's my dilemma, I'm not sure if it's sounding like this because of needed maintenance OR if it's just the way these amps are with the active EQ.
I can't really find any info from people who use Mk4's on the net, but I have heard that a lot of stoner rock/doom bands used these with fuzz with great success.
I just don't know if it's worth my time and $ to fix her up only to find out that it's just the way the amp 'sounds'.
I've included a gutshot pic.
The only thing I did when i got it is install a proper grounded plug. One thing I did notice is that the Presence control does absolutely nothing and I find that the Brill channel sounds more like the Std channel and vice versa.
Insight?Advice?

[gearhead63]

I've never heard one in person, but if it were me, I'd start with the tubes. If you have any 12AX7's that you know are good, try swapping them. Maybe even swap positions of the tubes.

[Jonny toetags]

I've never heard one in person, but if it were me, I'd start with the tubes. If you have any 12AX7's that you know are good, try swapping them. Maybe even swap positions of the tubes.

This is my first experience with one as well, so I have no basis for comparison. I've never seen one locally.
I might sit down with a bunch of tubes and do that.

[nsubulysses]

These amps have a very touchy preamp which yields lots of bad sounds. You really gotta mess with the settings and find something good to unlock it. I didn't like mine at first either, and strangely enough I bought one because I worked on someone else's and thought it sounded so good. The presence function is minimal.

What I do now is use normal channel and put treble, mid, presence on 10. From there i just add in bass to the desired amount. This worked good for me. The amp breaks up a little and I run an overdrive and then it's oppressively loud and gnarly sounding.

Does yours have sensitivity switch? Mine did and when it was on one it had some sort of weird instability. Certain high notes had a fuzzy ring modulator type sound almost. When I put the sensitivity on 2 it sounds way better. SO much that I even just removed the sensitivity switch altogether. Maybe it was just hte switch. I never tried another one.

[nsubulysses]

ALso its hard to tell but looks like yours has the phase inverter in the V4 position. If you take voltage readings don't be confused by this. Some 120s have the phase inverter in V4 and some have it in V5 position.

If you have a scope you should make sure it puts out 120W. It will only put out 120W with all tone knobs on 10.

[drewl]

I had a 120L halfstack, pretty much the same active preamp with teverb.
It may take a while to find the sweet spot but when you do it can sound great.

Mine needed filter caps and a couple noisy resistors replaced.
I added a post phase inverter master volume and made the boost switch on the rear footswitchable like the reverb.

It sounded great, used it for a few years then sold it for more than I paid for it.

[Jonny toetags]

Thanks guys.
To the guys that own(ed) one, did it take fuzz pedals well?

[patlaw]

Mine needed filter caps and a couple noisy resistors replaced.

How did you determine that there was a problem with noisy resistors?

[drewl]

Due to the active preamp the amp had alot of hissing and popping which was caused by the plate resistors and those 1 meg resistors all over the place.

Of course if you find you can't dial in any good sounds or just don't like the amp, they are easy to convert to a regular bon active preamp or make excellent Hiwatt clones.

[nsubulysses]

I run it loud enough til it starts to break up then I use either a menatone king of the britains or a fulltone full drive. It sounds pretty awesome.

I agree with drewl also. I always figured if I couldn't get a sound I liked I would just make a new preamp and use the huge power section. A friend has a 200 Plus with a gutted preamp. Has 1 pre tube and a phase inverter only. Starts to clip at 216W

[Jonny toetags]

So I took your advice nsubulysses and put Mid/Treble at 10 and worked the Bass/Presence accordingly.
It sounds much better! What an odd EQ section. I'm still trying to wrap my head around it.

[Jonny toetags]

Out of curiosity, how hard would it be to covert this active preamp version to Hiwatt spec, theoretically?