Could use a little vintage tube amp help here...

[pasmithy]

I recently purchased a Oliver Powerflex 500 w/extension cab. As you can see by the pic, there's two inputs per channel. I've Googled extensively and haven't been able to find out what the difference between the "MID-RANGE" and the "FULL-RANGE" inputs are. Any insight or information would be greatly appreciated.

 

[Vintage-Blue]

I'm not smart enough to interpret what the differences mean in the schematic but perhaps you or someone else can. If you don't have a copy of the schematic I have a copy posted on my web site: Schematics

Look at the schematic for the P502, as it also covers the P500.

 

[rufus.K]

http://vintage-blue.com/assets/p502_schematic.jpg

looks like the classic Fender voltage divider setup (with different values).

full gain and attenuated gain may be better labels.

 

[rufus.K]

 

[SAlcott]

Do the two differently labeled inputs sound different?

 

[Wasnex]

It looks like one of the inputs for each channel is padded down a bit. That is what I see on the schematic. On other amps you might see the labels "active" and "passive" or "high" and "low" gain. Also note one of the resistor values is different between channel one and channel two...1.5M vs 3.3M

 

[rufus.K]

the lower gain (mid range) of each pair *may have a bit of treble roll off.
ch.1 will have more gain overall (because of the 1.5m and 3.3m resistors), so may be inherently brighter than ch.2. (and distort sooner, a long with possibly being noisier (source dependant))
you should be able to confirm these for us.
other than that, they seem to be voiced similarly, at least at the 1st gain stage.

there is (if you believe the schematic) 5 more volts on the plate of the 1st stage of ch.2 (and thusly .02v more on the cathode). I doubt you'd ever notice... ch.2 by nature of the above may have a more stable nature when driven hard than ch.1.
again, just speculation... the character of something is a subjective mofo.

 

[agedhorse]

The only real difference between the INPUTS on each channel is sensitivity. The grid leak resistor difference isn't going to make much difference because the first stage has a lot of local feedback, and is relatively low gain so it will be just about impossible to overdrive.

The CHANNELS are different, each is voiced differently, with different eq.

 

[rufus.K]

after the 1st stage of each channel, they're different.

ch.1. nextly has a volume pot , then feeds another amplification stage , and then drives a James tone stack.
ch.2. otoh , nextly drives a BMT fender style tone stack, then a volume pot, and lastly another a.plification stage.

so, they will sound quite different on the way out of the 2nd stage

 

[rufus.K]

the 2nd gain stage of each channel also has a few differences. the plate voltage on ch2 is higher.
that likely makes up for the BMT tone stack
(240 and 175, making a difference of 65 volts at the plate)

 

[agedhorse]

He was asking about inputs, not channels.

 

[rufus.K]

yes. I agree

 

[rufus.K]

@agedhorse , what's happening with the areas I've circled?

 

[Wasnex]

The bottom of the full schematic has a note that explains T as tremolo with the P. 502 model

 

[rufus.K]

doh!
so it does...

 

[Wasnex]

doh!
so it does...

IMHO, the JMI era Vox AC30 schematics are way worse .

 

[JimmyM]

How about some pics of the whole thing? Don't hold out on us!

 

[pasmithy]

The only real difference between the INPUTS on each channel is sensitivity. The grid leak resistor difference isn't going to make much difference because the first stage has a lot of local feedback, and is relatively low gain so it will be just about impossible to overdrive.

The CHANNELS are different, each is voiced differently, with different eq.

The two Channels definitely sound different.

How about some pics of the whole thing? Don't hold out on us!

I will get on it when I get home from work.

It looks like one of the inputs for each channel is padded down a bit. That is what I see on the schematic. On other amps you might see the labels "active" and "passive" or "high" and "low" gain. Also note one of the resistor values is different between channel one and channel two...1.5M vs 3.3M

the lower gain (mid range) of each pair *may have a bit of treble roll off.
ch.1 will have more gain overall (because of the 1.5m and 3.3m resistors), so may be inherently brighter than ch.2. (and distort sooner, a long with possibly being noisier (source dependant))
you should be able to confirm these for us.
other than that, they seem to be voiced similarly, at least at the 1st gain stage.

there is (if you believe the schematic) 5 more volts on the plate of the 1st stage of ch.2 (and thusly .02v more on the cathode). I doubt you'd ever notice... ch.2 by nature of the above may have a more stable nature when driven hard than ch.1.
again, just speculation... the character of something is a subjective mofo.

Do the two differently labeled inputs sound different?

I've only used the two channels on "full-range" so far. I'm still making my way around the differences in the EQ for each of them. But my next thing to play with is the difference in inputs.

I really want to thank all you guys! I honestly didn't expect to wake up this morning and see this much help!

 

[SirMjac28]

Very cool amps

 

[beans-on-toast]

It was common at the time to offer different input impedances depending on the pickup used or the sound that you wanted. Accordion pickups were not the same as guitar ones. Depending on which of the four inputs chosen the pickup may sound a bit different.

The second input of channel 2 is the closest to many modern amps. Channel 1 uses a James tone stage like that found in most Ampeg amps. Channel 2 is more like a Fender tone stack with some twists to the design. The inputs and the tone stages are intended to provide you with some tonal options.


This is a quote from an early Ampeg model, same designer.

Now plug your instrument into an appropriate input on the panel. All Portaflex Bassamp models are two channel amplifiers, each having its own set of volume and tone controls. While more than one instrument can be played through an amplifier at the same time, lets consider its use with a single instrument for the present. The illustration of input designations should help you select the proper input for your particular instrument. Electronically, these inputs are designed to favor certain instruments, i.e., some, such as the accordion, require a stronger bass response, especially on the left hand, where a mellowing, organ-like sound is desired. Many guitarists desire a crisper sound. The diagram is merely a guide. Experimentation will determine your preference.

They were trying to market the amp for different instruments with different requirements.