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Q & A / Re: Coliseum 880 Questions
« Last post by S_wood on December 13, 2020, 12:35:07 pm »
Thanks so much!  That?s really helpful!
Q & A / Re: Coliseum 880 Questions
« Last post by Isaac on December 11, 2020, 10:15:07 am »
No, it's not adding a gain stage.

Took me a while to figure it out; I'm out of practice reading schematics.

What's going on is this: R150 provides negative feedback for Q108. As the Sustain control is turned up, the amount of negative feedback through R150 is decreased, and feedback is supplied through the CR103/CR104 leg. This decreases the total amount of negative feedback, increasing the gain of the Q108 stage. Above a certain voltage, the diodes provide more feedback, reducing the gain, effectively clipping the signal.

So, not another gain stage, but more gain to a certain point, then distortion.

I haven't looked at the Distortion circuit, but the waveforms on the schematic indicate that it adds asymmetrical, odd-order harmonics, while the Sustain circuit adds symmetrical, even-order harmonics.
Q & A / Re: Coliseum 880 Questions
« Last post by S_wood on December 09, 2020, 09:19:07 am »
Thanks so very much!  That is what my ears were telling me.  Given the volume increases that the sustain control causes, do you think it's adding a gain stage somewhere?
Q & A / Re: Coliseum 880 Questions
« Last post by loudthud on December 07, 2020, 02:16:59 am »
A quick look at the schematic leads me to think the Sustain control is active all the time. The Distort control is controlled by the switch under the pot on the front panel. The two RCA Footswitch jacks are in parallel with the front panel switch, it must be in the off position to enable the footswitch.

The Distort function is active on two parts of the preamp. The first part is before the EQ section, the second is after the EQ section. The front panel switch turns both sections on and off simultaneously. The footswitch allows independent control of each section.  I don't know if the factory footswitch allowed independent control, or if both sides were simply connected to a double pole switch.
Q & A / Coliseum 880 Questions
« Last post by S_wood on December 06, 2020, 07:00:07 pm »
I just picked up an early 70?s Coliseum 880. Like many before me I am confused about the distortion and sustain controls. The sustain knob seems to affect the sound with or without my jury-rigged footswitch. Both knobs work with the footswitch but neither footswitch button seems to turn either knob on or off

Does anybody know how these things are supposed to work?  Does anybody have an owner?s manual or scan for the 880 that might clear this up?

Classified / Re: Oct 2016 - New Rogan Plastics Sunn & Music Man Knobs 0-10 with screw
« Last post by Watson on December 05, 2020, 09:46:01 am »
Hi George,

I am still wondering about the Rogan knobs you said were available.  I've heard nothing since early October when you mentioned you would be back "next week".

If you can't or aren't going to follow through, please at least let me know that things have changed.

Many thanks,
Q & A / Re: New Sunn Coliseum Slave Amplifier- what speaker cabs can I use ?
« Last post by loudthud on December 05, 2020, 12:05:37 am »
The Coliseum power amps can drive a 2 Ohm load. That's four 8 Ohm or two 4 Ohm cabinets. The coil and resistor combo is a standard part of the power amp. It prevents oscillation with a capacitive load like a piezo tweeter or long coax speaker cables.
Q & A / New Sunn Coliseum Slave Amplifier- what speaker cabs can I use ?
« Last post by BASSPLAYER on December 04, 2020, 11:20:34 am »
Hello fellow forum members. I am a new member, that just took ownership of a Coliseum Slave amplifier. It was given away free, and nothing known of working condition.I know it is a power amp that can be used to power more speakers, but I want to use it with a pre-amp to play my bass guitar. I tried out the amp after bringing it  home. I powered it up on a dim bulb tester, and everything was good. Then plugged my bass into a Sansamp pre and plugged  a 1x10- 8 ohm speaker cabinet into one of the 1/4" jacks on the back. It played fine, but had a scratchy pot. It didn't seem very loud to me, but I thought it was because of the 8 ohm cab. I didn't want to plug into a 4 ohm cab without knowing the speaker output layout. As it looked like there was a extra jack that was added. And the last time I plugged a 4 ohm cab into a new to me solid state amplifier, I let out the magic smoke. I took the case cover off, cleaned the pot and jacks and took a few pictures of the speaker output jacks. It looks like all the speaker outputs are wired in parallel. But the one jack that looks like it was added, looks to have a coil and resistor /cap ??? I have enclosed pictures, and hope somebody will set me straight on what size cabs I can safely use with this amplifier.
Q & A / Re: Sun Solarus volume and eq
« Last post by Isaac on November 28, 2020, 09:53:04 am »
It is also possible that Messers Fletcher and Munson may have some useful input on this.

Human hearing is not linear. Usually, that means that something with twice the acoustic power is perceived as only a little louder, while something with ten times the acoustic power is perceived as only twice as loud. In this case, it's a different kind of non-linearity I'm going for. We don't hear all frequencies the same. Specifically, when all are at the same acoustic power, we hear midrange best, treble less well, and bass not nearly as well. To complicate matters further, those relationships change with volume. At low levels, we don't hear bass well at all, but, as levels increase, the bass increases faster. Fletcher and Munson demonstrated this back in the 1930s. So, if we adjust our tone controls to get a good sound at low volume, then turn it up, we are necessarily changing the perceived EQ. Essentialy, we're turning up the bass more than anything else. This can be the reason a setup can sound anemic at low volume, then really bloom when turned up.

I don't know if that's what's happening here, but it's likely part of it.

Q & A / Re: First gen model T with orange Sunn logo ?
« Last post by Isaac on November 27, 2020, 09:13:15 am »
For what it's worth, my Model T has the silver logo, silver knob centers and the mid selector switch. It's definitely a 2G. So why not a 1G with a red logo?
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