Hello,
I have a pair of Dynacord Mosquito S boxes for open air amplification. So far I have used my good old Marshall Leach power amplifiers (one of my first home hifi amp build, from about 1995, used for long time as main home power amp), but recently, one of the Leach amp module died.
It blows the fuses.
I do not want to go into debugging it, I know when it fails, a chain of transistors are dead and this includes carefully matched pairs.
I'm thinking of you guys would suggest a kit for me, what I can just put it.
Although it is for open air amplification, I want something musical. It is also for live acoustic instrument amplification and comparing to some modern (and not cheap) systems, it had a really musical sound amplification. So, I do not want to go for a class D (unless you really suggest) of cheapest amp kit.
What I found on Aliexpress so far are cheap ones, maybe I give it a try like this :
LJM L20 SE Audio Amplifier Board Toshiba A1943 C5200 Stereo Dual Channels 350W Amplifier Amp Board 4Ω 4ohm DIY kits 2pieces|Amplifier| - AliExpress
Can you guys suggest a kit for me for replacing the Leach amp modules?
Thanks,
JG
I have a pair of Dynacord Mosquito S boxes for open air amplification. So far I have used my good old Marshall Leach power amplifiers (one of my first home hifi amp build, from about 1995, used for long time as main home power amp), but recently, one of the Leach amp module died.
It blows the fuses.
I do not want to go into debugging it, I know when it fails, a chain of transistors are dead and this includes carefully matched pairs.
I'm thinking of you guys would suggest a kit for me, what I can just put it.
Although it is for open air amplification, I want something musical. It is also for live acoustic instrument amplification and comparing to some modern (and not cheap) systems, it had a really musical sound amplification. So, I do not want to go for a class D (unless you really suggest) of cheapest amp kit.
What I found on Aliexpress so far are cheap ones, maybe I give it a try like this :
LJM L20 SE Audio Amplifier Board Toshiba A1943 C5200 Stereo Dual Channels 350W Amplifier Amp Board 4Ω 4ohm DIY kits 2pieces|Amplifier| - AliExpress
Can you guys suggest a kit for me for replacing the Leach amp modules?
Thanks,
JG
The availability of matched input transistors for long tailed pair is low. It is something one has to do out of a batch of 100 from the same production run with instruments.
The modern substitute input stage is the op amp. Quite well balenced, and certain parts for <$1 are quiet and fast enough.
That alibaba amp has 2 pairs 2sa1943 2sc5200 so the 350 W rating is a figment of imagination. Honeybadger from diyaudio store uses three pairs for 150 W. The alibaba amp also uses TO92 transistors for the input stage, so the matching of an input pair is probably also imaginary at the price charged.
You don't state what your sensitivity of your speaker is, the impedance, the maximum watt rating, or the size of your audience. I could imagine 350 W is entirely adequate for most speakers and an audience of 500, however you might do okay at 150 for audiences of 100 with 100 db 1w1m speakers.
I don't recommend anything modern. Conarski on PA thread has stated even modern "reputable" QSC, the case gets quite hot after a couple of hours when used at the maximum rating. Recipe for a device that will require replacement in a couple of years, as is the goal of all modern sales organizations.
The best bargain stateside @ 150 W mono is a used Peavey MMA-8150t or MMA-81502. The downside is that the 8 ohm rating only applies above 50 hz. I picked up one allegedly working @ $35 + $30 freight, and the one I bought previously working cost $60. There are other brands of PA amp @150 w with <.2% HD sold overseas. These have a transformer for the 8 ohm rating, also 70 v or 100 v output for transformer speakers which you don't want.
With the high cost of cases heatsinks and switcher supplies, The best bargain @ 300-400 w is a used 80's 90's PA amp, possibly blown. I picked up a used working Peavey CS800s this year for $204 + $45 freight. Switcher supply, 400 w/ch 4 ohms, 240 w/ch 8 ohms, 23 lb. Will probably require new e-caps in the power supply to be reliable at this age but worked okay upon delivery at 5 watts. Old Peavey CS800x transformer models or earlier are even cheaper, but the freight tends to be higher because they weigh above 70 lb and can't be mailed. Revisions A, B, C, have a 741 op amp as the input stage and to hiss less at low power need updated to some op amp quieter like TL071 or OPA604. Crown has equivalent models but cost more on the used market so I don't know their model numbers.
Used working 80's 90's amps, require updating even if not bought blown up "for parts or repair". Pots, e-caps, and fans may need replaced, and some heat sink cleaning, but used you get back to the days when a watt rating from Peavey, Crown, QSC, or Yamaha, was something to be relied on 24 hours a day 7 days a week in a beach bar.
If you want to build, the only 350 W schematic I've downloaded was a destroyer x Blame MK3, and that had a long tailed pair input with discrete transistors that require matching. Op amps are much more the proper input since 1980 if one doesn't have an incoming inspection staff to do the LTP matching for you. Look at the repair threads for Crown, Peavey, QSC, Yamaha PA amps for schematics of op amp input 4 to 5 output pair class AB amps. But I don't know where one would buy a board for that. Perhaps someone on alibaba has cloned one of those as a pcb, without all the smoke & mirrors traditional on that website.
For decent speakers, don't forget the DC on speaker protection circuit, which @ 400 w/ch requires a better relay than the ones sold in $5 protection boards from ali or ebay either. Tiny AC rated relays weld their contacts closed when subjected to 1000 A capacitor dump through a shorted output stage. Again, Peavey, Crown, QSC have selected suitable relays for their high end products as CS800. Cheaper models like PV-1.3k short the output on DC detect with a triac, which blows all the output transistors, but may save your speaker.
Happy shopping.
The modern substitute input stage is the op amp. Quite well balenced, and certain parts for <$1 are quiet and fast enough.
That alibaba amp has 2 pairs 2sa1943 2sc5200 so the 350 W rating is a figment of imagination. Honeybadger from diyaudio store uses three pairs for 150 W. The alibaba amp also uses TO92 transistors for the input stage, so the matching of an input pair is probably also imaginary at the price charged.
You don't state what your sensitivity of your speaker is, the impedance, the maximum watt rating, or the size of your audience. I could imagine 350 W is entirely adequate for most speakers and an audience of 500, however you might do okay at 150 for audiences of 100 with 100 db 1w1m speakers.
I don't recommend anything modern. Conarski on PA thread has stated even modern "reputable" QSC, the case gets quite hot after a couple of hours when used at the maximum rating. Recipe for a device that will require replacement in a couple of years, as is the goal of all modern sales organizations.
The best bargain stateside @ 150 W mono is a used Peavey MMA-8150t or MMA-81502. The downside is that the 8 ohm rating only applies above 50 hz. I picked up one allegedly working @ $35 + $30 freight, and the one I bought previously working cost $60. There are other brands of PA amp @150 w with <.2% HD sold overseas. These have a transformer for the 8 ohm rating, also 70 v or 100 v output for transformer speakers which you don't want.
With the high cost of cases heatsinks and switcher supplies, The best bargain @ 300-400 w is a used 80's 90's PA amp, possibly blown. I picked up a used working Peavey CS800s this year for $204 + $45 freight. Switcher supply, 400 w/ch 4 ohms, 240 w/ch 8 ohms, 23 lb. Will probably require new e-caps in the power supply to be reliable at this age but worked okay upon delivery at 5 watts. Old Peavey CS800x transformer models or earlier are even cheaper, but the freight tends to be higher because they weigh above 70 lb and can't be mailed. Revisions A, B, C, have a 741 op amp as the input stage and to hiss less at low power need updated to some op amp quieter like TL071 or OPA604. Crown has equivalent models but cost more on the used market so I don't know their model numbers.
Used working 80's 90's amps, require updating even if not bought blown up "for parts or repair". Pots, e-caps, and fans may need replaced, and some heat sink cleaning, but used you get back to the days when a watt rating from Peavey, Crown, QSC, or Yamaha, was something to be relied on 24 hours a day 7 days a week in a beach bar.
If you want to build, the only 350 W schematic I've downloaded was a destroyer x Blame MK3, and that had a long tailed pair input with discrete transistors that require matching. Op amps are much more the proper input since 1980 if one doesn't have an incoming inspection staff to do the LTP matching for you. Look at the repair threads for Crown, Peavey, QSC, Yamaha PA amps for schematics of op amp input 4 to 5 output pair class AB amps. But I don't know where one would buy a board for that. Perhaps someone on alibaba has cloned one of those as a pcb, without all the smoke & mirrors traditional on that website.
For decent speakers, don't forget the DC on speaker protection circuit, which @ 400 w/ch requires a better relay than the ones sold in $5 protection boards from ali or ebay either. Tiny AC rated relays weld their contacts closed when subjected to 1000 A capacitor dump through a shorted output stage. Again, Peavey, Crown, QSC have selected suitable relays for their high end products as CS800. Cheaper models like PV-1.3k short the output on DC detect with a triac, which blows all the output transistors, but may save your speaker.
Happy shopping.
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Than You for your reply!
It is my fault, I did not mention any power rating and the ali link is misleading. With the Leach amp I had it running from +-50V and the speaker impedance is 8 Ohms. So, about 100W is more than enough for me, but let's say a normal 100W with high duty, low THD. I've picked the linked amp because I thought it should do 100W fine. On the other hand, what you write on input transistor pairs makes a lot of sense to me. At home I use built tube amps, did not make solid state for long time. I do remember I spent a lot of time matching the transistors, I just do not want it again :- )
The mosquito S is rated 150W for longer periods and 200W peak. I have no idea of the efficiency rating, also, below 50Hz it does not do much, so, it is fine.
I also thought about just buy a used professional PA, but, I like the case I built with large heatsinks (no fan needed), also, it has a 390W toroid transformer with plenty of buffer caps. ... but, I may end up just getting a PA. Even I do get, I know it will always annoying me to do something with the remainder of the Leach.
Thanks,
JG
It is my fault, I did not mention any power rating and the ali link is misleading. With the Leach amp I had it running from +-50V and the speaker impedance is 8 Ohms. So, about 100W is more than enough for me, but let's say a normal 100W with high duty, low THD. I've picked the linked amp because I thought it should do 100W fine. On the other hand, what you write on input transistor pairs makes a lot of sense to me. At home I use built tube amps, did not make solid state for long time. I do remember I spent a lot of time matching the transistors, I just do not want it again :- )
The mosquito S is rated 150W for longer periods and 200W peak. I have no idea of the efficiency rating, also, below 50Hz it does not do much, so, it is fine.
I also thought about just buy a used professional PA, but, I like the case I built with large heatsinks (no fan needed), also, it has a 390W toroid transformer with plenty of buffer caps. ... but, I may end up just getting a PA. Even I do get, I know it will always annoying me to do something with the remainder of the Leach.
Thanks,
JG
At 150 W mono, Peavey MMA-8150T has no fan. It does require free air flow from bottom to top with tall feet. There is one today on US ebay for $40, $35 freight to my location. Allegedly working but not tested. Of course that doesn't help you in Hungary. The MMA-81502 have a smaller heat sink and a fan. 2 pairs TO3 transistors in both models, 41 v rails with a step up transformer from 4 ohms to 8 ohms. Step up transformer provides inherent protection against DC on 8 ohm speaker without any relays or triac shorting. No matched transistors on input, they use NJM4560 op amps at start of power amp.
MMA amps also have a input mixer section and I've had some models develop bad connection between the mixer & the power amp. But there is a direct wired RCA jack feeding the power amp that doesn't have any such problem. I'm listening to streaming audio right now over a MMA-875t. sounds great except for the $2 salvage speaker I'm using in the computer room. Don't buy a MMA-800t, it is only a mixer with no power amp section.
Crown has a similar architectural model with an output tranformer. 1160MA is 160 watts mono, 4 inputs. 180MA is 80 watts 4 inputs. < .5% HD. Used 180MA are running $50 + $23 freight to my location. Another is $41 + $29 freight.
All the above much more industrial 24/7 service than some alibaba junk. Old ones may need volume pots and/or rail caps. They are 20-30 years old.
MMA amps also have a input mixer section and I've had some models develop bad connection between the mixer & the power amp. But there is a direct wired RCA jack feeding the power amp that doesn't have any such problem. I'm listening to streaming audio right now over a MMA-875t. sounds great except for the $2 salvage speaker I'm using in the computer room. Don't buy a MMA-800t, it is only a mixer with no power amp section.
Crown has a similar architectural model with an output tranformer. 1160MA is 160 watts mono, 4 inputs. 180MA is 80 watts 4 inputs. < .5% HD. Used 180MA are running $50 + $23 freight to my location. Another is $41 + $29 freight.
All the above much more industrial 24/7 service than some alibaba junk. Old ones may need volume pots and/or rail caps. They are 20-30 years old.
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I, personally, would not worry about matching input pairs. Once you've decoupled them thermally, they drift and do not stay matched, anyway. If there is plenty of emitter degeneration, more than 47 ohms for a 2 mA tail current, then the resistors and the feedback will even up your collector current.
Be sure to use transistors with a large beta, so beta mismatch doesn't matter.
Be sure to use transistors with a large beta, so beta mismatch doesn't matter.
That amp ??
They lie ... 2 pair 5200/1943 might get you 120W @ 60V rails 8R. 45-50V
rails possibly 150W 4R. There is no way around SOA.
At these levels it looks like it could work well , typical EF2 design.
But no 350w 😛😛 .
OS
None of those cheap-o kits will get the advertised power. You get what you pay for. If I wanted class D modules, I’d be looking at ICEPower - price to performance ratio. is pretty good. Those little Sure modules can’t compete. Indianajo’s suggestion of rebuilding a burnt up PA workhorse is a good one. One can be had for far less than you would pay for a transformer and heat sinks - stuff you will NOT get with one of those kits and have to buy anyway. You can then rebuild the original circuitry, or gut it and replace with one of the proven Apexaudio designs floating around here - if the PCBs have been torched which is often the case. PCB artwork is available and they’re no harder to get going than an E-bay kit.
Hello,
Thank, but no, you misunderstood the situation. I have a solid case with large heatsink and overkill psu. What I need is a good amp module. From size point of view it looks like any of these will fit easy because the Leach amp pcb I've used is much larger than any of these.
Also, as I stated above, of course the 350W is a lie. I need 100W of that, that is why I picked the 350W module.
Still, on the other hand, those Peavay amps are very impressive and cheap. I did tried to look at used market yesterday, but without success so far.
Even the new price is not bad.
I may do both. Play with the module and get a new PA.
Now my main question would be, do you guys have any suggestion for other concrete kit?
Thanks!
JG
Thank, but no, you misunderstood the situation. I have a solid case with large heatsink and overkill psu. What I need is a good amp module. From size point of view it looks like any of these will fit easy because the Leach amp pcb I've used is much larger than any of these.
Also, as I stated above, of course the 350W is a lie. I need 100W of that, that is why I picked the 350W module.
Still, on the other hand, those Peavay amps are very impressive and cheap. I did tried to look at used market yesterday, but without success so far.
Even the new price is not bad.
I may do both. Play with the module and get a new PA.
Now my main question would be, do you guys have any suggestion for other concrete kit?
Thanks!
JG
Try Salcon and Monty in India for ideas.
Depending on your supply, you can use multiple 3886, 7293,7294,498xx or Mosfet based circuits, there are versions for serious power, but you said 100 WRMS, 24 x 7 quality.
Then these chip and solid state amps will work well, as it is you need the modules only.
If you do buy from India, the Keltron capacitor kits are worth the extra cost.
Depending on your supply, you can use multiple 3886, 7293,7294,498xx or Mosfet based circuits, there are versions for serious power, but you said 100 WRMS, 24 x 7 quality.
Then these chip and solid state amps will work well, as it is you need the modules only.
If you do buy from India, the Keltron capacitor kits are worth the extra cost.
Do you mean LM3886? I did not really consider it for this project. I'm not against chip amps, but I'm afraid if those can handle the power.
On the other hand, in the last days I was also looking for used professional PAs. No luck. What I find, those are multiple hundreds of Watts output amps. It seems to me, this power range is rare. High for home hifi (and home hifi would not be reliable), low for professionals.
Regards,
JG
On the other hand, in the last days I was also looking for used professional PAs. No luck. What I find, those are multiple hundreds of Watts output amps. It seems to me, this power range is rare. High for home hifi (and home hifi would not be reliable), low for professionals.
Regards,
JG
Peavey made a CS400 and CS600. They are pretty cheap in working condition around here. Too small for most bands. 400 was 3 pairs MJ15024/25 instead of 4 in CS800.
PV-4c is 200 w/ch 4 ohm 120 w/ch 8 ohm, .1% hd. PV-8.5c is 400 w/ch 4 ohm 240 w/ch 8 ohms .1% hd. Advertised wattages are higher, at 1% HD. Check ohms of ratings of other brands, 4 ohm rating is usually a lot higher than 8 ohm. 1% HD rating a lot higher than .1% hd rating.
PV-4c is 200 w/ch 4 ohm 120 w/ch 8 ohm, .1% hd. PV-8.5c is 400 w/ch 4 ohm 240 w/ch 8 ohms .1% hd. Advertised wattages are higher, at 1% HD. Check ohms of ratings of other brands, 4 ohm rating is usually a lot higher than 8 ohm. 1% HD rating a lot higher than .1% hd rating.
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3886 will give up to 68 watts power, 7293 goes to about 100 watts, 49810 even more.
I did say check your voltages, so a suitable amp circuit can be selected.
@indianjo, he is in Hungary, I don't think there is as big a band scene there for used equipment to be available in the variety you have in the USA.
The population is less than 10 million, more than 15% are above 65.
The USA has about 30 times more people.
I did say check your voltages, so a suitable amp circuit can be selected.
@indianjo, he is in Hungary, I don't think there is as big a band scene there for used equipment to be available in the variety you have in the USA.
The population is less than 10 million, more than 15% are above 65.
The USA has about 30 times more people.
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As a European Giordana can buy from Germany, Italy, CZR, France, Poland, Sweden. Like me buying from Georgia, Florida, California. Shipping is too high from California, Georgia is about $40 away. I don't imagine he can buy profitably from Sweden.
Ebay calculates shipping to my location via the company the vendor has selected. I buy used amps $30-$40 shipping cost away, not $80 from California. For example, FedEx shipped amps cost more to ship my location than UPS or USPS, so I don't usually buy those.
There are other useful Class AB amps from Crown, QSC, with schematics & parts lists available. Repairable amps in his size range have 2 or 3 pairs of TO3 transistors.QSC-RMX85 has 3 pairs TO-247 On parts. The crown XLS-402 has 5 pairs TO3 OT, a little large. I don't see any IC amp being useful at 150 W into 8 ohms. 150 W 8 ohms would take 5 or 6 pairs 2SA1943 2SC5200 as are popular on aliexpress products.
Greece has a huge party scene, badly crimped by lockdowns. Check their scrap lists. Greece had a Peavey assembly factory during class AB era. Check the Croatia party zones, Italy party coast. Frankfurt is a huge air hub, many warehouses should be scrapping off 70 v MMA-8150t or MA-1160 with 8 ohm windings. Poland is close to Hun. Barrier in EU is checking product lists in various languages. That should be doable, product numbers don't change in different languages. There have been oriental warehouse amps show up with two pairs, I don't remember part numbers or brand but were serious bargains.
What is not useful is Behringer, proprietary schematic diagrams. I don't see Yamaha schematics showing up much on internet, either. I think the pro repair/resellers may buy all those up, fix them, and resell. No place for bargain hunters.
BTW the $35 MMA-81502 $68 with shipping+tax worked on delivery. No repair required. Has 8 useless telephone mixer cards, but the RCA jack to power amp works fine. Will be donated to a church for an organ replacement.
Happy shopping.
Ebay calculates shipping to my location via the company the vendor has selected. I buy used amps $30-$40 shipping cost away, not $80 from California. For example, FedEx shipped amps cost more to ship my location than UPS or USPS, so I don't usually buy those.
There are other useful Class AB amps from Crown, QSC, with schematics & parts lists available. Repairable amps in his size range have 2 or 3 pairs of TO3 transistors.QSC-RMX85 has 3 pairs TO-247 On parts. The crown XLS-402 has 5 pairs TO3 OT, a little large. I don't see any IC amp being useful at 150 W into 8 ohms. 150 W 8 ohms would take 5 or 6 pairs 2SA1943 2SC5200 as are popular on aliexpress products.
Greece has a huge party scene, badly crimped by lockdowns. Check their scrap lists. Greece had a Peavey assembly factory during class AB era. Check the Croatia party zones, Italy party coast. Frankfurt is a huge air hub, many warehouses should be scrapping off 70 v MMA-8150t or MA-1160 with 8 ohm windings. Poland is close to Hun. Barrier in EU is checking product lists in various languages. That should be doable, product numbers don't change in different languages. There have been oriental warehouse amps show up with two pairs, I don't remember part numbers or brand but were serious bargains.
What is not useful is Behringer, proprietary schematic diagrams. I don't see Yamaha schematics showing up much on internet, either. I think the pro repair/resellers may buy all those up, fix them, and resell. No place for bargain hunters.
BTW the $35 MMA-81502 $68 with shipping+tax worked on delivery. No repair required. Has 8 useless telephone mixer cards, but the RCA jack to power amp works fine. Will be donated to a church for an organ replacement.
Happy shopping.
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Have you thought about the LJM L12-2?
Lots of people are impressed. I'm sitting on a pair....
https://www.diyaudio.com/forums/solid-state/196089-l12-2-cfp-output-amp-120w-2-8r-4.html#post3440357
Lots of people are impressed. I'm sitting on a pair....
https://www.diyaudio.com/forums/solid-state/196089-l12-2-cfp-output-amp-120w-2-8r-4.html#post3440357