Amp Tech Thread / Ask a tech Q

[liquidsmoke]

Is it safe to send a 3V +10dBV preamp signal to a power amp with a 1.23V +4dBm input sensitivity?

These numbers are straight from SoundTech PS802 and Peavey Rock Master manuals. +10dBV just seems exceptionally hot.

The other possibly worthy Rock Master output is 1V 0dBV which I assume is fairly weak for 1.23V +4dBm.

Another question would be how to run the PS802 in stereo with only one +10dBV output jack but one of my cabs also has a through output so I'm assuming I could chain them together and run the amp in bridged mode however that would I think be 800 watts mono 4 ohms which isn't listed in the manual as being okay. Each cab is 8 ohms and the PS802 manual lists the following:

Stereo 4 ohm   400W+400W
Stereo 8 ohm   230W+230W
 Mono 8 ohm   800W

Will I be forced to run the cabs chained through only one channel? That would I believe be a 4 ohm 400 watt load which should be plenty of power.

I don't want to fry anything. I've read both manuals and Google searched but I'm still unsure.





I don't dig the binding post output connectors(edit: just heard about banana clips!) but the price was very right for so much power. Some bass players use this amp so I'm hoping it will sound okay for guitar.

[liquidsmoke]

ignore

[liquidsmoke]

^ got this business resolved I think. Going to use the 3V output into one channel and chain the cabs. It's still 400 watts which should be plenty.

[beerrhino]

I just picked up a Univox model 1236 amp.  It has one speaker out but no output impedance listed.  How do you determine the output impedance of an amp?

[Mr. Foxen]

I just picked up a Univox model 1236 amp.  It has one speaker out but no output impedance listed.  How do you determine the output impedance of an amp?

Its pretty much run it into a load and see how it behaves on a scope, learning how mismatches sound by ear is prob a bad plan. If its all working right, start at 4ohm and see if it sounds right, big of goggling suggests may well be 4ohm and too low load on a tap is tone compromise not valve damage.

[Pissy]

I just picked up a Univox model 1236 amp.  It has one speaker out but no output impedance listed.  How do you determine the output impedance of an amp?

If I were to run into an issue like this with a 70's tube amp, I'd assume 8 ohms and go on with life.

[jibberish]

hey liquid, don't freak over those I/O numbers on those amps. those are max values if you turn up all the way. and the input sens just says that is the value that maxxes the amp to full rated output.  

I would try all combos and see how the units work the best.    if you go high gain and hi input , you have a tiny range of useable input values before the amp max's out
the higher the gain, the higher the noise floor.  so if you aren't using it, may as well back off and back the noise floor off too

you wont know what gain ranges suit your uses the best until you try them all.

the only way you can fuck up is if you short the speaker outs

in fact a lot of amps have gain controls so you can turn to something less than max gain based on what the pre signal is going to be

also somehow sharply cutoff deepest bass frequencies if you can. rumble just wastes power and muddies your sound. that will leave a ton of extra power for the music content

***regarding loading that amp down. I would just wire that for stereo like it is set up. you will also be evenly using the circuit as it was really designed. a mono signal stays mono, even through stereo output. stack the 2 speakers to kill the stereo field to a mono speaker system.    I have adapters for anything audio. I would split my peavey output and feed both amp inputs with the split mono signal. I like symmetry. the freak in me demands symmetry




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can you see any part number on th eoutput transformer or have you found the mfr specs online yet.  the info is out there to determine exactly what the output impedance is for that transformer

nm , I looked. the op transformer has 8 ohm and 4 ohm taps on a univox 1236. be very careful with that amp, there are some seriously high voltages set up in there. I don't like it already.

[dreglife]

Hi everyone, first time poster here. Does anyone know a tech that's handy and will work on Beta Leads? I asked John McNeece if he'd look at it awhile ago and he said that he has officially retired from repairing them.

[VOLVO)))]

Yep. He fixed all mine and hates them so much. He was my local tech for years.

I own several. They suck to work on.

[liquidsmoke]

hey liquid, don't freak over those I/O numbers on those amps. those are max values if you turn up all the way. and the input sens just says that is the value that maxxes the amp to full rated output.  

I would try all combos and see how the units work the best.    if you go high gain and hi input , you have a tiny range of useable input values before the amp max's out
the higher the gain, the higher the noise floor.  so if you aren't using it, may as well back off and back the noise floor off too

you wont know what gain ranges suit your uses the best until you try them all.

the only way you can fuck up is if you short the speaker outs

in fact a lot of amps have gain controls so you can turn to something less than max gain based on what the pre signal is going to be

also somehow sharply cutoff deepest bass frequencies if you can. rumble just wastes power and muddies your sound. that will leave a ton of extra power for the music content

***regarding loading that amp down. I would just wire that for stereo like it is set up. you will also be evenly using the circuit as it was really designed. a mono signal stays mono, even through stereo output. stack the 2 speakers to kill the stereo field to a mono speaker system.    I have adapters for anything audio. I would split my peavey output and feed both amp inputs with the split mono signal. I like symmetry. the freak in me demands symmetry




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-----------------------------------------------------------------------------------
can you see any part number on th eoutput transformer or have you found the mfr specs online yet.  the info is out there to determine exactly what the output impedance is for that transformer

nm , I looked. the op transformer has 8 ohm and 4 ohm taps on a univox 1236. be very careful with that amp, there are some seriously high voltages set up in there. I don't like it already.

Just seeing this post now. I'm not currently using this amp but hope to in the future bridged into an 8 ohm high wattage handling bass cab with my baritone. Need to get the cab first and get off my ass and put some serious time in on the baritone.

[Pissy]

Yep. He fixed all mine and hates them so much. He was my local tech for years.

I own several. They suck to work on.

Talked to one of the Red Fang dudes one time and he said that every 3 months something broke in their Betas. Constant rotation through techs. No idea who they used though.

I can tell you that if their anything like this coliseum bass I have here, that A) it was ridden really hard for a long time - beer and smoke and club schmeg galore- and B) the circuit boards and ribbon traces have lots of small brittle opportunities to open. It IS a pain.

[VOLVO)))]

Coliseums are child's play compared to working on betas. You can actually trace the circuit in the Coliseum heads. The beta its like following a maze with pungee pits (the switching chip,) and an unfair amount of capacitors that can introduce wicked noise to the circuit. Im very lucky that mine have been pretty damn reliable.

[Lumpy]

I have a Washburn solidbody beater with S/S/SS pickups (so the humbucker is configured like 2 singles). I want to make this guitar into a noise machine (shrieks, screeches, etc). It barely feeds back unless I literally put the guitar right in front of the cabinet (and even then, results not guaranteed). What can I do to make this mild mannered entry level guitar into an uncontrollable ear-fucker? Un-ground the pickups?

On another forum (yes, I am dating other forums) they told me that swapping out pickups won't really do anything, and just put a couple of dirt pedals together in a row. That's what I'm doing (rat clone is last in line) and it's not that satisfying. For one thing, it makes the guitar sound muddy. I'm looking for "shrill and piercing". I'll try again this weekend with clean boosters, but I'm doubtful.

My old guitar player had an old Supro that would scream and howl in the most delicious ways. The guitar was on the verge of falling apart. He could get sounds from tapping on the pickups, etc. How can I disable my guitar to get results like that?

Pic of same (or similar) Supro model I'm referring to (I remember slider switches too, but not certain):



Similar if not exact model of Washburn ('rocker series'):



Please help me ruin my guitar.

[Lumpy]

The EHG feedback seems like humbuckers and loud tube amps, it's warm and howly. I'm looking for screechy single coils, more shrill and trebly.

Hey, where'd your post go?

[Lumpy]

Not that I'm picky... this guitar seems like a dud though, that's what I'm trying to say. Not very lively.

I'm gonna return it - "This guitar aint broken!"

Trying to make a recent model $60 budget guitar sound like a 60's vintage Japanese pawnshop score. Fool's errand, my specialty.  

[Danny G]

So on my SVT-II this solder trace from an electro cap burned thru. It connects to about 6 other things.

Can I solder a wire jumper to just one of the other traces to re-establish the connection, or do I need to do leads to all the parts?




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[MichaelZodiac]

Lumpy, what about treble boosters in combination with rat and a possible clean boost?

[RAGER]

Cheap humbucker and lots of gain should do it.

Edit*  An unpotted one.

[Lumpy]

Lumpy, what about treble boosters in combination with rat and a possible clean boost?

I already use a Screaming Bird (it's maybe not a true treble booster though, it may be more like an EQ). Gonna try the clean boost in the chain too...

Cheap humbucker and lots of gain should do it.

Edit*  An unpotted one.

A different pickup was what I was thinking too. But the 'unpotted' might be the key factor. Maybe I should pull the existing HB, and if there's any wax, scrape it off.

[Metal and Beer]

The EHG feedback seems like humbuckers and loud tube amps, it's warm and howly. I'm looking for screechy single coils, more shrill and trebly.

Hey, where'd your post go?

I realized I wasn't gonna offer you anything useful. I usually filter myself before submitting, but occasionally one gets by me.

[moose23]

So on my SVT-II this solder trace from an electro cap burned thru. It connects to about 6 other things.

Can I solder a wire jumper to just one of the other traces to re-establish the connection, or do I need to do leads to all the parts?




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Just one connection as the rest are all still connected together.



Lumpy a Super Hard On clone will help with the feedback.

[VOLVO)))]

Really, anything that will boost gain will give more feedback...

[Danny G]

Good deal. I can shore up that bum solder joint this afternoon.

However tracking down the value and location on schem of the burned out resistor is proving to be a problem, at least trying to Google search using my iPhone.

More like eyeStrain.


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[Pissy]

Lumpy, I suggest EMG active pickups. They're so damn hot and high end biased, that I've always thought of them as useless and couldn't fathom why Kerry King would endorse them.


Did you try messing with the coil split configuration on the humbucker?  Series counter, vs series same direction winding (completely negating and buck of hum)?  Hell even parallel together or parallel counter wound?   That all sounds like really fun stuff to try and see what happens.  Can't hurt anything. If nothing else you'll be able to hear what all of those different configurations sound like - for science.

[Pissy]

Try installing it upside down( which would look really funny) , or turned 180 Peter green style too. The magnetic field still exists on the bottom of the pickup. It should make sound anyways.