martin manning wrote:Just got a chance to listen to the two clips- great tones and very nice pickin' too! What speakers do you have in it?
Thanks Martin.
They're Jensen C10Q. I might try some Alnico down the road if a good deal presents itself. But, I hear it takes a few weeks of steady playing to break them in so I may stick with all ceramic.
Reeltarded wrote:It sounds great though. It looks as good too!
vibratoking wrote:Congrats...you persevered and have a nice sounding amp. Pretty cool result. You came to the right place. Kudos to everyone on this one.
Thanks guys! Absolutely. This is a great community full of generous, knowledgable people. I couldn't have done it without help from the group.
I've been busy the last few days and when I've had time to play the amp, I've kept the tone controls in the same place, straight down 6 o-clock except for Presence at 2. Just trying different guitars and evaluating the differences.
Last night I was doing some tweaking of the controls with a Strat and I noticed that I'm not getting much response from the mid and bass. Presence is working quite well, and treble appears to make a difference though not substantial. Big difference between Norm and Bright inputs but the change appears to be only because of the bright cap on the Bright vol.
Are the tone controls in this circuit that minimal or should I hear a fair amount of difference thru their sweep? I've checked all the wiring many times and it's correct. I've checked solder joints and they all seem fine.
I have the chassis back on the bench adding the 1 ohm resistors for bias checks so I thought I would see what's up with the tone stack.
Any help or troubleshooting tips would be very helpful.
I've been busy the last few days and when I've had time to play the amp, I've kept the tone controls in the same place, straight down 6 o-clock except for Presence at 2. Just trying different guitars and evaluating the differences.
Last night I was doing some tweaking of the controls with a Strat and I noticed that I'm not getting much response from the mid and bass. Presence is working quite well, and treble appears to make a difference though not substantial. Big difference between Norm and Bright inputs but the change appears to be only because of the bright cap on the Bright vol.
Are the tone controls in this circuit that minimal or should I hear a fair amount of difference thru their sweep? I've checked all the wiring many times and it's correct. I've checked solder joints and they all seem fine.
I have the chassis back on the bench adding the 1 ohm resistors for bias checks so I thought I would see what's up with the tone stack.
Any help or troubleshooting tips would be very helpful.
Peace,
Mark
Make sure the CCW terminal of the MID pot is in-fact tied to ground.
Definitely verify that the tone stack ground is good, and good call, JGG!
The tone stack components shown in the schematic you posted are the original '57 values. Later production increased the slope resistor to 100k, and increased the bass cap to 0.1uF. In addition to those, the PI tail resistor was reduced to 6k8, and the non-scratchy presence pot circuit was adopted. You can see those changes on the '59 Bassman Reissue schematic. I would try the 100k slope and the 0.1uF bass cap to start. I like the older-type presence circuit since it spreads the action over more of the pot rotation. The 6k8 vs. 10k PI tail will be more about balance and headroom in the PI, and probably not a big deal. You can easily try that out by clipping a 22k across the 10k that you have in there now.
Thanks guys that was the issue. I think I may have soldered that ground with a 25W iron before I picked up the 150/230 gun.
I unsoldered and replaced the mids ground and the tone stack is much better now. Though it does seem more responsive with the presence at 6-oclock. Still not seeing much movement in the bass response but I'm guessing that's a component value at this point since both ends of the stack are working properly.
Would the slope resistor and cap value changes you mentioned from the later production increase or decrease bass response? Right now it's a little boomy.
Thanks for the link and info guys. I had the calc already loaded a few months back but had no idea what to do with it at the time.
I ran a few scenarios on the tone stack. The '57 and '59 differ just like Martin said. I like the drop at 100Hz since I play a fair amount of drop D pieces. And the mid seems to have a shallower, slightly wider dip.
I also ran the '59 specs with a 500K bass pot and it appears to be very similar except it rolls off the bass a bit more from the same 100Hz point and an even shallower dip on the mids. Plus the adjustment range would be a bit smoother over 500K vs 1M. Any downside to the lower bass pot value outside of the changes it makes in the tone stack?
Note that the Fender schematic in the TSC is not the same as the 5F6-A. In the Bassman the mid cap goes directly to the mid pot wiper, with no connection to the top of the mid pot. The TSC Marshall schematic is wired that way, however, so that will work nicely with the source impedance set to 38k and the load impedance set to 2Meg (since it's driving the LTP PI). I would keep the bass pot at 1M.
So, the Marshall model set up like you suggested looks like this for '57 and '59. There's no way my amp is cutting bass to that extent. I must still have an issue with that pot. It's just not responding like these plots would indicate. Both plots show a 12db range at 100Hz...that's something I would definitely hear.
Is there a known R for the entire circuit that I can test for from one end to the other? Or a voltage check?
Looks like there is a bug in the TSC. Here is a SPICE comparison. You can measure from the top of the treble pot to ground with the bass pot all the way up and look for 1275k, then turn the bass pot all the way down and look for 275k.
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768]http://www.crenshawweb.com/bassman/marshall_57.jpg[/img]
