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Help?!?!?! Pignose 7-100 Mod???

Started by Bucky, December 12, 2006, 01:26:38 PM

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Bucky

Does anyone have any ideas as to how to modify the classic pignose (7-100) so that a clean tone can be obtained at full volume?

Specifically, my goal is to use the amp to accentuate the volume (without distortion) of a washtub bass in live settings. I have already ordered a "replacement" speaker that can handle tones as low as 20hz, but am wondering if I need to replace the volume pot and/or capaciters as well.

Your help or advice would be greatly appreciated.


Thanks!

Buckster

p.s. I'm really dead set on using the 7-100 model rather than the Hog30, due to portability issues.

joecool85

The speaker is the first real good mod to get better clean volume out of the amp, after that I'm not 100% sure.  One thing you might be able to do is raise the voltage to the opamps, we'd need to see a schematic to see if that's possible.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

teemuk

#2
A portable battery amp powered by six AA batteries and you want clean output at loud volume - for BASS! Sounds like a nearly impossible equation: 6 x 1,5 V means a maximum supply voltage of 9V... Doesn't seem like much headroom to me. The specs indicate 5 watts of output power but thats likely the peak power rating - RMS is only half of that. I don't believe this amp has a step-up DC-DC converter to boost up the 9V supply...

I would leave circuit modding aside; your best bet is to invest into a speaker(s) with insane efficiency rating (SPL). That is basically pretty much ALL you can do.

Though I guess that the amplifier is set up to attenuate frequencies that are lower than, say, 100 Hz quite heavily. I think that this device was never really intented to be a bass amplifier. If you know what "decoupling capacitors" between gain stages are, you'd might want to focus on incresing their value. This is just a guess that I make without a schematic. I, however, do believe that decreasing the attenuation of bass frequencies will increase the distortion as well.

An efficienct speaker is way more "efficient" way to boost up amplifiers than trying to mod their circuitry for more output power: Using a speaker that is 3 dB more efficient than the original one has the same effect as doubling up your amplifier's output power. However, 3 dB increase will mean only a slightly perceivable change in loudness. To double the loudness you'd need ten times more output power - your "5W" amp would have to be a 50 watter! This is 10 dB increase. Now, which do you think is easier: To buy a speaker that is 10 dB more efficient or mod your 5W circuit to 50W. Buy efficient speaker and/or try connecting more speakers/hooking up to big cabinets. Be careful not to go below minimum load impedance though.

Joecool85, I believe that (at least the original) 7-100 is a discrete design - over thirty years old too. I have never seen the schematic, though. The Pignose company seems to want to make some profit out of selling it. For circuit mods, icreasing the rail voltage was what I thought about too but it might prove to be an extensive mod because the voltage ratings of some parts might get exceeded, bias points drifted etc. Adding more output devices in parallel could help as well. When comparing to benefits of just changing the speaker to another one all those efforts seem pretty worthless. I guess it would be easier to build a higher power amp and just house it inside the 7-100's case.

This is one of the amps that get praised a lot. I'm quite curious to see it's schematic to find out what all the fuzz is about. That could prove to be a similar dissapointment as the "Smokey" amplifier, though. Wish I could try one too - if I could just get my hands on one it shouldn't be a problem to trace out the schematic either: For 5 watts of output power there's hardly anything astounding or complex inside.

joecool85

#3
I didn't know it was battery powered lol.  I don't know a ton about pignose amps, but I did know some where battery and some are not.  Well, there is a good chance you could run it at 12volts with no problem, I wouldn't do it without looking at a schematic first and making sure it would work.  The other thing would be to run it on some size C or D batteries, keep the same voltage but up the mAH at your dispossal, not only should this help clean it up a bit, but also it will play longer on the same set of batteries.  Not sure if they'd fit though.  Also you might consider putting in larger power supply caps, or if it has none, put some in lol.  I would say something like a 1,000uF cap would do the trick, should help keep it clean when you're hitting the low notes.

**edit**
Just noticed this is a one knob amp, there is a good chance that you could mod your gain stages to keep it clean better.  It is SUPPOSE to get dirty when loud the way it comes out of the box.  Regardless of messing with gain stages or not, the mods I mentioned (caps, possible raising of voltage, and larger batteries) along with the speaker you are getting, WILL help.  It's hard to tell how much though.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

teemuk

Good point about those capacitors. Make sure you have some good, low ESR reservoir capacitors in your amplifier if you plan to mess with batteries: A typical AA battery has an internal resistance of around one ohm. When you connect six batteries in series you also connect their internal resistances in series, thus your supply has a series resistance of six ohms. Now, let's think what happens when your amp's output swings to it's ideally highest potential, which with a 9V supply is 4,5 volts. The current over 4 ohm load is U/R = 4,5V / 4R = 1,125 A. The current must come from the supply but the internal resistance of batteries causes a voltage drop, which is I*R = 1,125A * 6R = 6,75V. So, under highest theoretical loading your batteries are capable of providing only 2,25 V. Quite depressing figure right?
During this voltage "sag" the required current (and thus also the voltage) is supplied mainly by the reservoir capacitors. I sure hope the guys at Pignose put some into this amplifier.

joecool85

Regardless of what they put in (if any) you can always change them out for larger ones/add some.  Like I said, something in the order of a 1000uF cap should do it.
Life is what you make it.
Still rockin' the Dean Markley K-20X
thatraymond.com

azrael

Saw this a while ago...But I didn't know anything about the schematic of the Pignose, so I didn't bother trying to change anything.
I'm looking into speaker replacements...So far I've found that Jensen and Weber make 6 inch speakers, but I fear those might be too big for the Pignose.
Any ideas?

rad-sound

I have a copy of the schematic for the post 1986 model Pignose 7-100.  PM me for a copy or I can post it in the schematics section.
Rich

teemuk


baviaan69

Why mod a pignose?
It might loose that brilliant valvelike overdrive sound.

When playing Jazz chords, or, when clean sounds matter, I just turn the Pignose all the way up, and roll back the volume pot on the guitar.

Les Paul, neckhumbucker, volume around 4. very usable clean sound.

rikhi

I wish pignose had made a 7-100 version for the bass.

I have a couple of old schematics, would it be hard to adapt it to suit a bass? And if so what type of speaker would you guys recommend to capture the fuzz and character of the guitar version.

Sorry if I sound like a dick, i'm noob and learning electronics.

J M Fahey

Short answer, the Pignose 7-100 is unusable for bass.
Yea, I know, if you play at 3AM with it 5 inches from your head you can have clean bass sound ... if that's enough for you I can't complain.
The least you can use is, say, 15W RMS and a good  8" or 10" speaker, plus a 12V battery for any reasonable playing time, which leads you straight to the Hog 30 the original poster didn't want to use ... but nothing smaller will do.
Sorry.
PS: I have made 60W and 100W Bass battery powered combos successfully, they are quite portable but not exactly pocket size.