Studio 350

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Hi All, I'm new to these forums here, but am a big DIY enthusiast.
One thing i'm dying to find out, after reading about the Studio 350- Would it be possible to increase the output power so it would run around 500 watts into 4ohms? If so... what would I need to do to achieve this? Merely add more output transistors and up the supply voltage? Or would other parts need changing?

I also have 2 ETI480 modules- same question as above for them as well... How can I soup them up a bit?

Thanks in anticipation!
 
500 watt Studio 350

Assuming you do not want to run them in bridge mode then you will need to;

- Increase the supply rails to +/- 80v
- Transistors Q4,Q5 & Q6 will run hotter so I would change them to MJE340/350. Don't skimp on the heatsinks for these.
- I would add 2 MJL21194 and 2 MJL21193 to each amp module to keep within the output stage SOAR. Extending connections to these with links and emmitter resistors should be straightforward.
- Changing the 1k feedback resistor to 820 ohm will give you slightly more gain (might be needed).
- All other components should be ok as is.

Build a big power supply. For a stereo pair you will need at least a 1.5kva transformer (or 2 800va) with at least 40,000uF per rail per amp. Your AC voltages will need to be about 58 0 58 volts at 1.5kva.

Don't bother with the ETI480's. You would need to change every transistor (and most other components) to achieve significant power (single ended).

Cheers
 
studio 350

Biggest transformer i can find is 1kva with 55-0-55. Thats through Farnell. Costs a fortune though. Would give approx +-77V DC.
How would this affect desired power increase? I don't know how likely a toroid that gives 58-0-58 will be.
Might just be simpler to make them as 350w models and make more of them as +-70Vdc is easier to make than 80v. (Due to the availability of 50-0-50v toroids.

These amps are intended for use in PA style applications so headroom is of the utmost importance.

So... a 350watt model, with a 500VA toroid per amp plus say 20000 microfarads per rail? Would that be suitable?

I'm currently working on a large PA system, the plan is to make a 3 way tri amplified system. It'll have 4 x sub cabinets (size of driver undecided), 4 x mid boxes (probably 12") and 4 x high boxes (a combination of 8", 4" and piezo horns).

I already have 2 amps, 1 is 2 x 400 watt 4ohms, the other is 2 x 350 watt 4 ohms. The plan is to use these for mids and tops, what i'd like to do is build some of these studio 350 modules to run the subs and to run any further additions to this system (like foldbacks, more mid high speakers etc).
If I made sub boxes that were 4ohms each, and made 1 amp for each of these then I figure that the amps only being 350 watts will be irrelevant because there'll be 4 of them.
Any thoughts? I think i'm leaning towards the 4 smaller amps rather than the 2 really big ones, but i'm curious to hear other opinions on this. What do people think? Should i go for 1 big lot of grunt or several smaller lots...

I'm liking the look and what i've heard about the studio 350's. Can pick em up as a kit on ebay for $150, I guess what I really want to find out from people who've used them is, will they do what I want them to do?
Thanks
 
The good news is that in terms of loudness the difference between 350 watts and 500 watts is only about 2 dB. Given also that the floating voltage will be higher, the dynamic (instantaneous) power of the amp is likely to be greater than 350 watts anyway.

You should be able to buy transformers directly from here;

http://www.users.bigpond.com/harbuch/harbuch/toroids1.htm
and
http://www.tortech.com.au/

If you can find 55 0 55 volt 500va toroids go for it. This will give you more dynamic power when you need it i.e; PA punch.

20,000 uF would be the bare minimum per rail per amp.

The Studio 350 will in my view handle your job without any problems, but note the design does not have any short cct protection so extra care will be needed in PA applications. I would still add the extra power transistors if you intend running the amp loud for a long time and add fan cooling.

Have you though about a MOSFET design? While the Studio 350 is an excellent design, a MOSFET amp might be better suited for PA work because MOSFETs are far more robust than a similararly rated transistor.

Cheers
 
studio 350

Thanks everyone for the hints.
What i'm planning on doing is building a heap of these 350's as mono amps so i can customize the PA system.
So i'm intending on having the central basis of the system as the 4 mid and 4 high boxes with the 2 power amps i've got.
And having the studio 350 amps setup as mono amps, 1 for each speaker box (probably double 15" into 4ohms boxes.) So the number of subs (or other boxes) can be altered and changed to suit the type of gig.

One thing i noticed on the schematic was that there are 4 220nF 100v capacitors going from the +70 and -70v rails to ground right near the output devices. If i'm adding more transistors do I need to add more of these capacitors?

The ESP 101 does look like an interesting avenue to venture into. I might consider it sometime soon. I think i'll start off with the 1 studio 350 to start. There'd be a way to insert some sort of relay protection across the outputs wouldn't there? Because of the nature of the work they'll be doing I'd like to have some sort of protection. Is there a simple relay protection circuit i could build up on veroboard or similar? How do they work exactly? Do they cut off if the amplifier goes DC? or do they cut off when the output reaches a certain limit?

Thanks again for the quick responses!
 
Reliability

I'm not familiar with the Studio 350 so my comments may not make any sense. But just in case...

500W average into 4 ohms requires 63V peak. I don't know what the circuit is you are intending to use but I'd have thought 70V rails would be ample...ie a 50-0-50 transformer.

The MJL21194/5 are 200W devices in TO-247 cases. You'll need to check the SOA curves to see how many of them you'll need. Otherwise you may have problems. Remember that the SOA curves in the datasheets are specified at a case temperature of 25C. This will almost certainly not be true when you are running the amp at high power in a studio. The power must be reduced by 1.43W per C above 25 for this case. I'd recommend you use transistors in a TO-3 case instead as these have better thermal handling and you should find a 250W device with less derating with Tc. If you are driving 4 ohm speakers then design for reliability into 2 ohm resistive load to be safe. You may well find you need 4 or more of each device.

If you choose mosfets you have to be careful of the Vgs drop, especially at high currents. This may cause you to have to use extra high voltage rails...thus expending more power...or to design a more complicated output stage circuit.

In any case, make sure the transistors don't get killed by a sudden short circuit of the output. Putting current limiters in place is vital. As you say it is a good idea to have a relay to disconnect the speaker in case of a transistor failure. This failure can be a dead short so a simple dc offset detector would be a good precaution.
 
bmurray86 said:
Hi All, I'm new to these forums here, but am a big DIY enthusiast.
One thing i'm dying to find out, after reading about the Studio 350- Would it be possible to increase the output power so it would run around 500 watts into 4ohms? If so... what would I need to do to achieve this? Merely add more output transistors and up the supply voltage? Or would other parts need changing?

I also have 2 ETI480 modules- same question as above for them as well... How can I soup them up a bit?

Thanks in anticipation!


Wouldnt it be easier, at the end of the day, to just build SCs 500w amp? It doesnt come as a kit anymore, but all the parts are still available, boards can be bought from RCS Radio http://www.rcsradio.com.au/ I think the articles are in August and September 1997 of Silicon Chip magazine.

Actually, a search for the SC 500w amp on here returns a nice example of a 1KW amp built for PA use, you might be interested to have a look if you havent done so already.

Attatched is a pic of one of my Studio 350 'monoblocks' might give you some ideas should you choose to go with the 350. For hard PA use, I expect forced air cooling will be needed, It wouldnt be hard to manufacture a mounting arrangement for some 60mm fans on the external heatsink. Rear of the toroid and left of the amp board is a speaker protector, it detects DC and has turn on delay, also controls fans.
 

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Hi Dilby,


"Rear of the toroid and left of the amp board is a speaker protector, it detects DC and has turn on delay, also controls fans."

Are you saying that the fans are turned on only above a certain temp. or the fan is turned on all the time but the speed varies as the temp.?

Tony
 
Re: Re: Studio 350

Dilby© said:



Wouldnt it be easier, at the end of the day, to just build SCs 500w amp? It doesnt come as a kit anymore, but all the parts are still available, boards can be bought from RCS Radio http://www.rcsradio.com.au/ I think the articles are in August and September 1997 of Silicon Chip magazine.

Actually, a search for the SC 500w amp on here returns a nice example of a 1KW amp built for PA use, you might be interested to have a look if you havent done so already.

Attatched is a pic of one of my Studio 350 'monoblocks' might give you some ideas should you choose to go with the 350. For hard PA use, I expect forced air cooling will be needed, It wouldnt be hard to manufacture a mounting arrangement for some 60mm fans on the external heatsink. Rear of the toroid and left of the amp board is a speaker protector, it detects DC and has turn on delay, also controls fans.

It would be easier to do that... I didn't know they were once available as a kit... i'll have to do some research on that. I did see that 1kw PA amp, but i thought it was a modified version of the 350.
I like the look of your monoblock amps. The cooling arrangement i was thinking of would be to use the fan assisted heatsink tunnels from jaycar that have 2 lengths of heatsink that fit together to form a tunnel and have screw holes in the end to mount 80mm fans on. This should have a good result i'm hoping.

RE: the speaker protection circuit... is this available as a kit from anywhere? Do you have a circuit diagram and maybe a PCB layout that you could post for me?

Going from your experience building them, what would be your honest opinion of them?
Thanks
 
Well with that particular amp, there are no fans so that function isnt used.

There are 3 thermal protection systems with that board. First is 60° thermal switch that turns the fan on, second is a 80° thermal switch that disconnects the load, and thirdly there is provision for a thermistor input with comparator switching to control fans at any temp required.

Normally, thats how it works, the fan switches on at 60°

There is no reason that the fans cant be running all the time through a limiting resistor, then switch on full when temp reaches 60° for example.

With that amp in the pic, the load is simply disconnected at 80° I havent had a need to add fans yet. With normal program material and the output just under clipping level, heat hasnt been an issue.
 
Re: Re: Re: Studio 350

bmurray86 said:


It would be easier to do that... I didn't know they were once available as a kit... i'll have to do some research on that. I did see that 1kw PA amp, but i thought it was a modified version of the 350.
I like the look of your monoblock amps. The cooling arrangement i was thinking of would be to use the fan assisted heatsink tunnels from jaycar that have 2 lengths of heatsink that fit together to form a tunnel and have screw holes in the end to mount 80mm fans on. This should have a good result i'm hoping.

RE: the speaker protection circuit... is this available as a kit from anywhere? Do you have a circuit diagram and maybe a PCB layout that you could post for me?

Going from your experience building them, what would be your honest opinion of them?
Thanks

I believe Altronics had the module as a kit once, not a complete amp. The 1KW amp on here is based on the SC 500w one, but I think it uses a different PCB.

Your cooling idea would likely mean that the amp will be stereo, and also likely mean that it'll need a custom case. That or you use one half of the tunnel and fit a blank plate and use 2 40mm fans.

The speaker protector is available from both Jaycar and Altronics, but for use on the Studio 350, modifications are required. I dont have any schematic or PCB information available, only paper copy that I cant easily scan. There is however a similar design published about the same time the 500w amp was that obviously is more suited, it may even be in the second issue of the 500w amp that I dont have.

My opinion.. I built the Altronics kit modules, very nice boards, silkscreen component layout makes it easy to build, infact I rarely referred to the schematic and PCB layout during construction. Some parts were missing, but that was fixed easily. I went with Altronics for a few reasons, but mostly because the heatsink was included and suited the case that I had planned to use. The only issue I have is that the board is actually cut to suit vertical transistor mounting, but supplied with the shelf heatsink, so the only rear support for the board is the transistor leads, might cause dry joints over a period of time. All important transistors supplied are genuine ON Semiconductor devices.

The rest of the design was left up to me, so I cant comment on that.

The performance meets SC specifications as far as I can test with my simple equipment and knowledge. I did however measure output into 8R slightly better than quoted, about 220W. As for quality, I havent had a chance for any critical listening, as I havent completed the rest of the system. Distortion, damping and frequency response figures are all very good, so I'd expect very good performance. I've read comments about the idea that they dont have enough 'sonic impact' and all this talk about not sounding like a valve amp. Isnt that what we want? These comments can be disregarded IMO.

I have inadvertently let the smell out of some 12" 150W drivers on a few occasions now, so theyre up to the task as far as power output is concerned. I've built some SC480 modules too, which are essentially the same amp, but use different output and driver devices. They are very good, sound better and are quieter than my Marantz commercial amp. The Studio 350 is an improvement on the SC480 design, so its got to be good, right? I certainly dont have golden ears, I'd probably never hear the difference.

For Hifi use, theyre excellent. For PA use, youd never need such a refined design, and if you're looking for increased power output then I think the 500w design is the way to go. The 500W design has SOA protection, the Studio 350 doesnt. The 500W amp has been designed with PA use in mind. The operation of the SOA protection circuit induces high frequency noise into the output, we dont want this in hifi applications, hence its omission in the 350.

Edit: Last paragraph. Spelling.
 
Re: Re: Re: Re: Studio 350

Dilby© said:


I believe Altronics had the module as a kit once, not a complete amp. The 1KW amp on here is based on the SC 500w one, but I think it uses a different PCB.

Your cooling idea would likely mean that the amp will be stereo, and also likely mean that it'll need a custom case. That or you use one half of the tunnel and fit a blank plate and use 2 40mm fans.

The speaker protector is available from both Jaycar and Altronics, but for use on the Studio 350, modifications are required. I dont have any schematic or PCB information available, only paper copy that I cant easily scan. There is however a similar design published about the same time the 500w amp was that obviously is more suited, it may even be in the second issue of the 500w amp that I dont have.

My opinion.. I built the Altronics kit modules, very nice boards, silkscreen component layout makes it easy to build, infact I rarely referred to the schematic and PCB layout during construction. Some parts were missing, but that was fixed easily. I went with Altronics for a few reasons, but mostly because the heatsink was included and suited the case that I had planned to use. The only issue I have is that the board is actually cut to suit vertical transistor mounting, but supplied with the shelf heatsink, so the only rear support for the board is the transistor leads, might cause dry joints over a period of time. All important transistors supplied are genuine ON Semiconductor devices.

The rest of the design was left up to me, so I cant comment on that.

The performance meets SC specifications as far as I can test with my simple equipment and knowledge. I did however measure output into 8R slightly better than quoted, about 220W. As for quality, I havent had a chance for any critical listening, as I havent completed the rest of the system. Distortion, damping and frequency response figures are all very good, so I'd expect very good performance. I've read comments about the idea that they dont have enough 'sonic impact' and all this talk about not sounding like a valve amp. Isnt that what we want? These comments can be disregarded IMO.

I have inadvertently let the smell out of some 12" 150W drivers on a few occasions now, so theyre up to the task as far as power output is concerned. I've built some SC480 modules too, which are essentially the same amp, but use different output and driver devices. They are very good, sound better and are quieter than my Marantz commercial amp. The Studio 350 is an improvement on the SC480 design, so its got to be good, right? I certainly dont have golden ears, I'd probably never hear the difference.

For Hifi use, theyre excellent. For PA use, youd never need such a refined design, and if you're looking for increased power output then I think the 500w design is the way to go. The 500W design has SOA protection, the Studio 350 doesnt. The 500W amp has been designed with PA use in mind. The operation of the SOA protection circuit induces high frequency noise into the output, we dont want this in hifi applications, hence its omission in the 350.

Edit: Last paragraph. Spelling.


sounds like a good way to go... would anyone have a circuit diagram of this? or a copy of the silicon chip article by any chance? I can get the boards from rcsradio for about $36 each. a circuit diagram would be good so i can do a costing for how much this thing would cost to put together.
500 watt mono amps would need a considerable sized toroidal. at least 800VA from what i've been told before... i think i'll weigh up the options. if, as has been mentioned... 150 watts isn't a sizable noticable difference... then perhaps i'll just go with the 350 watt modules prepackaged for the sake of ease. although i would still like to have a go at a 500 watter one day... i'll see how the figures add up...
 
Re: Re: Re: Re: Re: Studio 350

bmurray86 said:



sounds like a good way to go... would anyone have a circuit diagram of this? or a copy of the silicon chip article by any chance? I can get the boards from rcsradio for about $36 each. a circuit diagram would be good so i can do a costing for how much this thing would cost to put together.
500 watt mono amps would need a considerable sized toroidal. at least 800VA from what i've been told before... i think i'll weigh up the options. if, as has been mentioned... 150 watts isn't a sizable noticable difference... then perhaps i'll just go with the 350 watt modules prepackaged for the sake of ease. although i would still like to have a go at a 500 watter one day... i'll see how the figures add up...


The back issues can be ordered from Silicon Chip, via their website.

The difference is 1.5dB, you wouldnt hear the difference with the ear, but the extra headroom cant be a bad thing.

800VA will suffice.

One of my 350s cost a bit over $500 to build I think.
If you work out the cost per watt, youll probably find that they arent that much different.

If youre inexperienced, then start with something smaller and easier. Having said that, the 350 was my first amp project.

You might be interested to know that the 350 pair will be combined with a 100w and 50w stereo amp as a tri-amped hifi system that will deliver when reqired, and take punishment at high level, prolonged use at parties.
 
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