DC blocking capacitor
"the problem is capacitors in parallel with the output". Cool, experts immediately ready with straight answers. I'm putting a series capacitor on the output of my my CS800 before I use it on the $600 (new) SP2 speakers. It already has triac-diac clamping on the outputs. Since the ST120 has 3300 uf I'll try 10000 uf on the CS800 amp. The ST120 uses a plain electrolytic with the plus to the quasi-complementary output, minus to the plus output terminal. I'll try that on the Peavey. Rails are +_81V.
"the problem is capacitors in parallel with the output". Cool, experts immediately ready with straight answers. I'm putting a series capacitor on the output of my my CS800 before I use it on the $600 (new) SP2 speakers. It already has triac-diac clamping on the outputs. Since the ST120 has 3300 uf I'll try 10000 uf on the CS800 amp. The ST120 uses a plain electrolytic with the plus to the quasi-complementary output, minus to the plus output terminal. I'll try that on the Peavey. Rails are +_81V.
back to back electrolytics
Thanks, I forgot the ST120 is so weird because the transformer has no center tap and the quasi-comp output transistors make their own phantom ground with the 3300 uf output caps. Pretty stupid proof way to balance the output transistors, I thought. I looked at output with scope, waveform is symmetrical alright. I don't have any amp manuals, I know zilch about "balancing" output transistors, one reason I parked the package deal '98 model CS800 until I understand it. 10 output transistors, whew-I'll never have it turned all the way up. The CS800 has +- rail supplies, I'll have to make non-polarized capacitors. I have 1 9600 uf @ 150 WVDC cap in the junk box, and 6 or 8 boards of 10 gang PCB's of 400 uf 400 WVDC Nichicons from motor drives. Will be heavy, but cheap. Might install some speaker fuses while I'm at it. 8 ohm speakers, real old school design sort of copy of VOT's.
Thanks, I forgot the ST120 is so weird because the transformer has no center tap and the quasi-comp output transistors make their own phantom ground with the 3300 uf output caps. Pretty stupid proof way to balance the output transistors, I thought. I looked at output with scope, waveform is symmetrical alright. I don't have any amp manuals, I know zilch about "balancing" output transistors, one reason I parked the package deal '98 model CS800 until I understand it. 10 output transistors, whew-I'll never have it turned all the way up. The CS800 has +- rail supplies, I'll have to make non-polarized capacitors. I have 1 9600 uf @ 150 WVDC cap in the junk box, and 6 or 8 boards of 10 gang PCB's of 400 uf 400 WVDC Nichicons from motor drives. Will be heavy, but cheap. Might install some speaker fuses while I'm at it. 8 ohm speakers, real old school design sort of copy of VOT's.
DC Protection?
WHAT? I have to make the DC protection myself? I was just gonna make a box with two of (see below link) in cos I'd rather just assemble this kit and mount it into a box with some speaker clamps and 1/4 jack outputs. I'm not a big fan of SpeakON or XLR.
DC Protection link
Rapid Electronics - Electrical & Power
This kit'll withstand a nasty 90 volts DC at 10 amps.
WHAT? I have to make the DC protection myself? I was just gonna make a box with two of (see below link) in cos I'd rather just assemble this kit and mount it into a box with some speaker clamps and 1/4 jack outputs. I'm not a big fan of SpeakON or XLR.
DC Protection link
Rapid Electronics - Electrical & Power
This kit'll withstand a nasty 90 volts DC at 10 amps.
I blew up an ST120 when it was powered off and I was changing speaker wiring. The output coupling caps hold a lot of DC, there's no bleeder resistor on them, so if you short the speaker leads with the amp OFF it blows the output transistors.
DC Protection
Someone7272, Your Capacitor box is fine for DC protection on cheap amps, as Mooly said it is cheaper to build non-polarized capacitors with two electrolytics back to back per speaker than buying them non-polarized from the distributor. If you can find a used Crown amp for cheap (there is one locally on Craigslist for $300, might need repair) it might have DC speaker protection and other protections included. Most crowns for sure have speaker disconnect relays. My Peavey has diac-triac clamping of the output included, which "usually" protects against shorted output transistors. Another risk to speakers are temporary oscillation at turn-on, protected by speaker disconnect relays and a 555 timer circuit (or delay-on-power-on relay or microprocessor timer). Another risk is speaker wire hookup shorting the amp and blowing the transistors, the Crown speaker disconnect relays are part of the solution for that but I haven't seen on this forum how this problem is detected to deenergize the speaker relays- the Crown schematic had a white box showing this sensor. Another risk is lightning blowing through the amp, probably not a problem in the UK but a serious problem in the US midwest. To protect against this the entire sound system can be plugged in a SOLA isolation-voltage stabilization transformer. Metal Oxide Varistors on the input from hots (and western hemisphere supply neutral) to safety ground can also help against this. It is a scary world out there, the charity resale shops are full of speaker boxes with blown drivers. 99% of this forum is about DIY good sound, but I'm more interested in the protection end since used band amps are $200 a kilowatt but protection circuits are scarcer than gold. Prariemystic thanks on the tip about ST120 blowing output transistors with the power off if you short the speaker output. If the TIP-mod (a famous Mod to the ST120) resistor on the output doesn't bleed down the speaker blocking cap, I'll add a bleed down resistor. Someone7272, you should also put a 1k-2k-5k or 10k 1/2 watt bleeddown resistor across each pair of blocking caps in your outboard box if for no other reason than to prevent arcing if you disconnect the speaker.
Someone7272, Your Capacitor box is fine for DC protection on cheap amps, as Mooly said it is cheaper to build non-polarized capacitors with two electrolytics back to back per speaker than buying them non-polarized from the distributor. If you can find a used Crown amp for cheap (there is one locally on Craigslist for $300, might need repair) it might have DC speaker protection and other protections included. Most crowns for sure have speaker disconnect relays. My Peavey has diac-triac clamping of the output included, which "usually" protects against shorted output transistors. Another risk to speakers are temporary oscillation at turn-on, protected by speaker disconnect relays and a 555 timer circuit (or delay-on-power-on relay or microprocessor timer). Another risk is speaker wire hookup shorting the amp and blowing the transistors, the Crown speaker disconnect relays are part of the solution for that but I haven't seen on this forum how this problem is detected to deenergize the speaker relays- the Crown schematic had a white box showing this sensor. Another risk is lightning blowing through the amp, probably not a problem in the UK but a serious problem in the US midwest. To protect against this the entire sound system can be plugged in a SOLA isolation-voltage stabilization transformer. Metal Oxide Varistors on the input from hots (and western hemisphere supply neutral) to safety ground can also help against this. It is a scary world out there, the charity resale shops are full of speaker boxes with blown drivers. 99% of this forum is about DIY good sound, but I'm more interested in the protection end since used band amps are $200 a kilowatt but protection circuits are scarcer than gold. Prariemystic thanks on the tip about ST120 blowing output transistors with the power off if you short the speaker output. If the TIP-mod (a famous Mod to the ST120) resistor on the output doesn't bleed down the speaker blocking cap, I'll add a bleed down resistor. Someone7272, you should also put a 1k-2k-5k or 10k 1/2 watt bleeddown resistor across each pair of blocking caps in your outboard box if for no other reason than to prevent arcing if you disconnect the speaker.
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You shouldn't have to use caps if the amp is designed properly. Crown makes good amps with protection. But its those amps you don't know about that need protection. I wouldn't use speakons, xlr or 1/4 phoneplugs. I'd use binding posts for my protection box. But ideally you should test it with a switchable on-off load and a scope until you are SURE its OK.
I know Crown would have been a better choice, but they're just out of reach. Amps of that league are too expensive (£337.15), and I know you get what you pay for but at the moment, I only needed to keep it under the 150 mark. I know cheappy things can turn ugly, that's why I'm using cheappy Skytronic drivers rather than the Emience expensive monsters. But in all honesty, although they're only about 15 quid, I've been pretty impressed by the Skytronic drivers. Probably cos I havn't heard an Emience before.
I was planning to use both speaker binding posts and 1/4 jack for the DC protection box in a way that if a 1/4 is plugged, it'll bypass the binding posts. Any reason why you think it's better to use binding posts?
No you can't... If you mean for the most foul smelling electrical thing I've ever smelled in my life.
But in reality, what I've been told is that an amplifier is an amplifier. Doesn't matter which make or model, if it's got a volume control, VU meter, jack outputs and switch on delay, I'm happy. Oh, and a warrenty which is longer than a year 😀
1/4 phono plugs
1/4 phone plugs short out the device they are connecting nearly every time. This means on an amplifier with direct connected transistors, a very dangerous condition for the output transistors when connecting which you must counterbalance by keeping the amp off every time before you connect it or disconnect it. Binding posts with crimp on spade connectors on the wires, you only short out the output sometimes. However, crimping on terminals is an art usually done best with an ideal or klein brand tool, professional grade tool that are very difficult to find, as 99% of crimp tools sold have handles that are too short for proper crimp force. If you use 16 gauge speaker wire you can insert them through the hole in the binding terminal, but I find 10 ga. speaker wire ever so much accurate at carrying the high currents of speakers. The guy that sold me my CS800 amp instructed me to use the volume control to turn up the amp after everything had stabilized. This accomplishes the same thing as speaker disconnect relays and timers, but manually. Someone7272 I realized after discussing your package solution that your response was an internet link to a packaged protection PCB, and looked at it. Nice looking little package with relays and a couple of electrolytic caps. The specification link did not come up, so I have no idea what size the capacitors are or how the relays determine the amp has been turned on, or whether there is a diac-triac clamp and how do you set the trip voltage to the amp you have? On DIYaudio you may find that many of us responders either would rather buy a used blown high quality amp that we could repair, like a 1000W $300 Crown, or a 260 W $100 Peavey, than a new amp with a great warrentee but questionable reliability Or other DIY responders would build an amp theirselves out of parts, though not me. I abandoned consumer products in 1972 when all the consumer choices available had volume and tone controls that would wear out in two years, besides output stages that frequently blew up. I've used an archaic PAS2 & ST70 tube amps until very recently, which are fine without protection, by design. I didn't find out that "PA" equipment had reasonably good controls and reasonably good protection circuits until the invention of craigslist and diyaudio recently.
1/4 phone plugs short out the device they are connecting nearly every time. This means on an amplifier with direct connected transistors, a very dangerous condition for the output transistors when connecting which you must counterbalance by keeping the amp off every time before you connect it or disconnect it. Binding posts with crimp on spade connectors on the wires, you only short out the output sometimes. However, crimping on terminals is an art usually done best with an ideal or klein brand tool, professional grade tool that are very difficult to find, as 99% of crimp tools sold have handles that are too short for proper crimp force. If you use 16 gauge speaker wire you can insert them through the hole in the binding terminal, but I find 10 ga. speaker wire ever so much accurate at carrying the high currents of speakers. The guy that sold me my CS800 amp instructed me to use the volume control to turn up the amp after everything had stabilized. This accomplishes the same thing as speaker disconnect relays and timers, but manually. Someone7272 I realized after discussing your package solution that your response was an internet link to a packaged protection PCB, and looked at it. Nice looking little package with relays and a couple of electrolytic caps. The specification link did not come up, so I have no idea what size the capacitors are or how the relays determine the amp has been turned on, or whether there is a diac-triac clamp and how do you set the trip voltage to the amp you have? On DIYaudio you may find that many of us responders either would rather buy a used blown high quality amp that we could repair, like a 1000W $300 Crown, or a 260 W $100 Peavey, than a new amp with a great warrentee but questionable reliability Or other DIY responders would build an amp theirselves out of parts, though not me. I abandoned consumer products in 1972 when all the consumer choices available had volume and tone controls that would wear out in two years, besides output stages that frequently blew up. I've used an archaic PAS2 & ST70 tube amps until very recently, which are fine without protection, by design. I didn't find out that "PA" equipment had reasonably good controls and reasonably good protection circuits until the invention of craigslist and diyaudio recently.
I havent had a problem with jack plugs shorting out the amplifier.
The only I time I had a problem with jack socets is when I once used a stereo jack with a mono signal and that shorted out the signal every time due to the contacts being very close to each other.
The only I time I had a problem with jack socets is when I once used a stereo jack with a mono signal and that shorted out the signal every time due to the contacts being very close to each other.
I think when plugging the 1/4 jacks, the can short. Which is why I only plug/unplug them with the amp off. Now as I have no idea on how to repair an amplifier, it's not a good idea for me to delve into the chasis cos I'd probably kill my self with electrocution or cause the amp to explode.
repair basics
"Now as I have no idea on how to repair an amplifier, it's not a good idea for me to delve into the chasis cos I'd probably kill my self with electrocution or cause the amp to explode." Uh, it is wise to get a little education. The internet offers cheap education, although the lab projects are unsupervised. Rule 1 - don't work alone, or away from a phone with 911 service (999 in UK) Rule 2 - no jewelry on hands or head or neck. Rule 3- Keep one hand in pocket. For more rules of working safely, see aikenamps.com the technical resources button, the technician safety button. For a lot on practical repair of guitar amps ((that are blown up a lot by plugging/unplugging, too much etc) , see Tube Amplifier Debugging Page . I found a practical book on transistor circuits obsoleted by the local trade school at the charity resale shop for $2: Thomas L. Floyd, Electronic Devices Electron-Flow Version, pub Prentice Hall. The resale shops near any trade school might have obsolete texts as good abandoned by your local schools. However, when I was in college I didn't have time to pat my head and rub my tummy simultaneously. I carried 20-24 hours at a time because the draft deferment I had from Viet Nam required me to finish school in 4 years. If you're focused on something else, enjoy your consumer product for now and look forward to a more capable and exciting life later (repairmen defying DEATH in their own back rooms) when you have time.
"Now as I have no idea on how to repair an amplifier, it's not a good idea for me to delve into the chasis cos I'd probably kill my self with electrocution or cause the amp to explode." Uh, it is wise to get a little education. The internet offers cheap education, although the lab projects are unsupervised. Rule 1 - don't work alone, or away from a phone with 911 service (999 in UK) Rule 2 - no jewelry on hands or head or neck. Rule 3- Keep one hand in pocket. For more rules of working safely, see aikenamps.com the technical resources button, the technician safety button. For a lot on practical repair of guitar amps ((that are blown up a lot by plugging/unplugging, too much etc) , see Tube Amplifier Debugging Page . I found a practical book on transistor circuits obsoleted by the local trade school at the charity resale shop for $2: Thomas L. Floyd, Electronic Devices Electron-Flow Version, pub Prentice Hall. The resale shops near any trade school might have obsolete texts as good abandoned by your local schools. However, when I was in college I didn't have time to pat my head and rub my tummy simultaneously. I carried 20-24 hours at a time because the draft deferment I had from Viet Nam required me to finish school in 4 years. If you're focused on something else, enjoy your consumer product for now and look forward to a more capable and exciting life later (repairmen defying DEATH in their own back rooms) when you have time.
repair?
Well... it's not a good idea to try this till after my exams. It looks like repair will be my only choice because the company won't refund or replace the amp. Very pissed off. I recently read on the Skytronic website (SkyTronic product: SKYTEC PA AMPLIFIERS BLACK) earlier, this amplifier has protection circuits. Why didn't they work?!
Would probably repair this when I get some time on my hands and the right equipment. But I don't expect it to work after I repair it. But I do happen to know an electronics specialist I know in person nearby. Might get help from him to repair the amp.
Well... it's not a good idea to try this till after my exams. It looks like repair will be my only choice because the company won't refund or replace the amp. Very pissed off. I recently read on the Skytronic website (SkyTronic product: SKYTEC PA AMPLIFIERS BLACK) earlier, this amplifier has protection circuits. Why didn't they work?!
Would probably repair this when I get some time on my hands and the right equipment. But I don't expect it to work after I repair it. But I do happen to know an electronics specialist I know in person nearby. Might get help from him to repair the amp.
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I can't get no satisfaction
ya I'd be mad too.
Is this their return policy in general? Consumer rights in GB?
I would def not accept the 1st answer and persist in a firm but polite tone. Going up the chain until satisfaction for a full price refund, maybe more because of damage to your speakers. Make written detailed notes of your interactions, there s/b other avenues even when the top manager is reluctant I'm sure.
EDIT>You didn't do anything wrong. They are guilty of passing off rubbish as PRO GEAR.
ya I'd be mad too.
Is this their return policy in general? Consumer rights in GB?
I would def not accept the 1st answer and persist in a firm but polite tone. Going up the chain until satisfaction for a full price refund, maybe more because of damage to your speakers. Make written detailed notes of your interactions, there s/b other avenues even when the top manager is reluctant I'm sure.
EDIT>You didn't do anything wrong. They are guilty of passing off rubbish as PRO GEAR.
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If you're thinking about repairing the amp, Skytronic will normally provide you with a service manual or a schematic. Just contact their parent company (AVSL Group) and hopefully they will send it to you. They did it for me but sometimes it just depends on who receives and reads your email! BTW: when it asks you for what department to email, send it to the technical department.
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