Ampeg Portaflex PF115HE Mods

[grimreaper]

Hello from Germany, thanx to this threat I just ported my pf-115he, with two 3” tubes. I still use the stock speaker and ask myself, if it’s good or could I improve the cabinet with a “better” speaker. Unfortunately I can’t find the fact sheet with specs of the stock speaker. Does anybody knows more?
Cheers, Thomas

 

[grimreaper]

Ah….and I made another inputjack in the back from that I go directly into the speaker. That sounds better to me, than with the tweeter on.

 

[flatwound62p]

This is the schematic for the PF115he crossover network and tweeter. After going to all the trouble of pulling out my original jack plate with the crossover PCB attached to it and replacing with a direct to speaker input socket it occured to me that if you just turn the tweeter dial up to full and pull the wires off the tweeter, there is almost no path to earth for the high signal to be dumped.
Which is maybe close to the same result as pulling the whole thing out, i.e. full range signal gets sent to the 15" speaker. Or am I wrong?
Also, there would still be a path to earth via the lamp > 1uf capacitor and L1 inductor. What effect would that have?

 

[abarson]

From the manual:
The 3-position HF Horn switch allows for:
• Full high frequency output (0 setting, no attenuation) - CW on the schematic
• High frequencies reduced by 6 dB (–6 setting)
• Horn shutoff (off setting) - CCW on the schematic.

Full range is always sent to the woofer.
The lamp acts as a fuse and is removed from the circuit when the horn switch is in the off setting.

Instead of going through all the work and potential damage installing a direct jack, just turn the horn off with the switch.

https://ampeg.com/data/6/0a020a40c6175e0b812473074/application/pdf/Owner%E2%80%99s%20Manual%20-%20English%20.pdf

 

[flatwound62p]

Zero position on the tweeter knob definitely bleeeds top end off and dumps it to earth and doesn't feed full range to the speaker. I believed the manual until I swapped a JBL K140 in from another cab and wondered where all the top vanished to.

 

[keyofnight]

This is the schematic for the PF115he crossover network and tweeter. After going to all the trouble of pulling out my original jack plate with the crossover PCB attached to it and replacing with a direct to speaker input socket it occured to me that if you just turn the tweeter dial up to full and pull the wires off the tweeter, there is almost no path to earth for the high signal to be dumped.
Which is maybe close to the same result as pulling the whole thing out, i.e. full range signal gets sent to the 15" speaker. Or am I wrong?
Also, there would still be a path to earth via the lamp > 1uf capacitor and L1 inductor. What effect would that have?

Have you made any progress on this? I might try to mod this thing over the holidays.

 

[flatwound62p]

I recently picked up a second PF115HE which is completely stock standard unmodified. I'll pull the tweeter wires off and turn the tweeter knob up to full to confirm or smash my theory, using a bright amp and a guitar so it should be plainly obvious what the result is. Might take a day or two to get a chance.

 

[96tbird]

I just snipped the bulb lead. First in line. I nipped it without removing the board. Done.

 

[flatwound62p]

Great way to do it, I wish I'd thought of that before I replaced the rear panel. Do you have an opinion on your mod VS just turning the tweeter off?
I had a quick run through mine this morning switching between tweeter settings with the tweeter disconnected (via pulling the wires of the tweeter) and couldn't hear any difference.

So I believe the tweeter circuit still dumps some top end to earth even with the tweeter disconnected, based on what I heard pulling out the circuit completely and going straight to speaker in the other cab.

 

[keyofnight]

I just snipped the bulb lead. First in line. I nipped it without removing the board. Done.

I might just do this, as I'll don't think I'll ever use the tweeter. It would be nicer for me to put in a switch that lifts the first lead of the bulb from the circuit so I would at least have the option to use the tweeter later.

 

[96tbird]

I might just do this, as I'll don't think I'll ever use the tweeter. It would be nicer for me to put in a switch that lifts the first lead of the bulb from the circuit so I would at least have the option to use the tweeter later.

I was too lazy to remove the board, so I just reached in with the snippers. lol.

 

[96tbird]

Great way to do it, I wish I'd thought of that before I replaced the rear panel. Do you have an opinion on your mod VS just turning the tweeter off?
I had a quick run through mine this morning switching between tweeter settings with the tweeter disconnected (via pulling the wires of the tweeter) and couldn't hear any difference.

So I believe the tweeter circuit still dumps some top end to earth even with the tweeter disconnected, based on what I heard pulling out the circuit completely and going straight to speaker in the other cab.

I don’t really notice much difference, I just don’t like the idea of my signal going into a crossover that I had no use for after reading that it was still sucking up signal juice with the switch off.

 

[agedhorse]

Just beware that some crossovers, when unloaded, can present a damaging load to some class D amp topologies. It depends on the crossover design as well as the amp design. Some amps are protected against this but those that aren’t will typically fail in an expensive way.

 

[keyofnight]

I don’t really notice much difference, I just don’t like the idea of my signal going into a crossover that I had no use for after reading that it was still sucking up signal juice with the switch off.

I ended up getting cold feet about the mod. I'm not entirely convinced it'll change anything audible.

Can anyone tell me what the crossover frequency is on this circuit? Like, if it's sufficiently high, then I'm not gonna bother.

 

[96tbird]

I ended up getting cold feet about the mod. I'm not entirely convinced it'll change anything audible.

Can anyone tell me what the crossover frequency is on this circuit? Like, if it's sufficiently high, then I'm not gonna bother.

It shouldn’t matter what the xover freq is, the big driver is getting full range. The issue is that power is being bled off when the tweet is switched off. I just don’t like that idea, so I snipped it. Probably doesn’t make much difference, but it’s your decision; all good.

 

[agedhorse]

It shouldn’t matter what the xover freq is, the big driver is getting full range. The issue is that power is being bled off when the tweet is switched off. I just don’t like that idea, so I snipped it. Probably doesn’t make much difference, but it’s your decision; all good.

Re-read my post #93 so that you are aware of the possible pitfalls of doing this.

 

[96tbird]

Re-read my post #93 so that you are aware of the possible pitfalls of doing this.

Yes, the fuse-bulb is first in line on the Xover board. I snipped the lead on the bulb. Is that any different than physically removing the board and straight wiring the drivers?

I did it like that so it’s an easy fix to the next owner of the cab if they want the tweet back.

 

[agedhorse]

Yes, the fuse-bulb is first in line on the Xover board. I snipped the lead on the bulb. Is that any different than physically removing the board and straight wiring the drivers?

I did it like that so it’s an easy fix to the next owner of the cab if they want the tweet back.

That’s fine if it’s on the input side of the HPF. This is not often the case.

 

[dfp]

Piggybacking a little bit on this old thread. I just got new PF 115 and PF 210 cabinets. I think they are new old stock, probably sat around for a few years on the stores’ showroom floors. Anyway, they both sound great except the tweeter makes no sound in either cabinet. I understand some would consider that a feature not a bug, but I at least want to hear what they sound like before I decide whether or not to use them lol.

Because it’s so easy to open the top I disconnected the woofers to try to hear the tweeters, and there’s just nothing coming through the tweeters at all.

I’ve seen mention of a fuse bulb in this thread. Could a fuse or a bulb need replacing in each one? Hard to believe brand new tweeters would already be blown just from being used on a showroom floor a little bit. These cabs being new old stock, does that seem any more likely to affect the lifecycle of the fuse bulb?

 

[dfp]

Update to my above comment: I tested sending the woofer signal to the tweeter (with all the bass eq cut to prevent sending damaging low frequency to the tweeter) and DID get sound from the tweeter. So, tweeter is not blown. Then I disengaged the tweeter, and connected the tweeter signal to a woofer, and got no sound in any setting of the tweeter attenuator. It appears that some part of the crossover is the fail point for the tweeter, just don’t know yet exactly what. I’ll pull the crossover when I get a chance and see if there’s anything obvious like a burnt looking fuse or bulb.