Bangs are fine when something's sitting on the bench, it's when it's in the rack playing music that I get annoyed! 🙂
ash_dac said:
Not sold it for several years. Maplin went the way of Radio Shack, more emphasis on toys and computer stuff, less on components and the electronics hobbyist.
Thanks for replys all, especially traderbam for your circuit diagram which i will be using, not sure on which drive transistors to use yet ill see what i have lying around.
I am going to go ahead with the regulator for this amp despite all the warnings you guys have given me about heat 🙂
If it doesnt work out practical in the end it will be a learning experience for me at least.
im gonna whack in a 50-55v zener in after the regulators so if they do pop my circuits will be protected and the HT fuses will pop first along with the zeners.
This seems like a safe idea.
Cheers
Craig
I am going to go ahead with the regulator for this amp despite all the warnings you guys have given me about heat 🙂
If it doesnt work out practical in the end it will be a learning experience for me at least.
im gonna whack in a 50-55v zener in after the regulators so if they do pop my circuits will be protected and the HT fuses will pop first along with the zeners.
This seems like a safe idea.
Cheers
Craig
Craig405 said:
The circuit (& kits I assume) was updated & bugfixed late '90 as some parts got scarce, is that what you have? Mosfets 2SK135 & 2SJ50 in the newer version. I have the Maplin Mag construction article if you need any info.
Connect you Zeners to a pair of large thyristors and turn it into a crow bar
I have used this myself many times with great success
regards
trev
I have used this myself many times with great success
regards
trev
cpemma, I do have an article from Maplin on the modules but it is dated 1987.
If you have a newer article i would be interested to see it. yes the MOSFET's are 2SK135/J50, Interestingly my article definatly specifies the max operating voltages of the module to be 50v not 55v, i wonder if the design had changed by 1990?
I am about to begin construction of my regulators, haha the weather in south england may be cruddy today but ill be warm 😉
Craig
If you have a newer article i would be interested to see it. yes the MOSFET's are 2SK135/J50, Interestingly my article definatly specifies the max operating voltages of the module to be 50v not 55v, i wonder if the design had changed by 1990?
I am about to begin construction of my regulators, haha the weather in south england may be cruddy today but ill be warm 😉
Craig
Just wear an asbestos body suit and welding visor before power-on. On reflection, you can afford to increase R1 and R3 to 2k to reduce the power dissipation of the zener a little. The hot air from the 3055s might make them sweat a little.
Cpemma thanks for the link they have only changed Tr3,4 and 5 to newer devices. The rest seems identical to my 1987 schematic.
Traderbam ill change my resistors over to 2k, I am using a string of 2x24v zeners each with 1 watt dissipation to achieve 50v, this should be fine with your circuit right?
Also can i use the 2N5551 transistors as drivers?
vce = 160v
ic = 600mA
hfe ranges between 30 and 250 depending on Ic.
either them or the Tip31A transistors i have which only have a Vce of 60v.
Thanks
Craig
Traderbam ill change my resistors over to 2k, I am using a string of 2x24v zeners each with 1 watt dissipation to achieve 50v, this should be fine with your circuit right?
Also can i use the 2N5551 transistors as drivers?
vce = 160v
ic = 600mA
hfe ranges between 30 and 250 depending on Ic.
either them or the Tip31A transistors i have which only have a Vce of 60v.
Thanks
Craig
Should be ok with the series zeners and 2N5551: you ought to get at least 30A before the drivers expire, which should be fine unless you short the amp outputs at full power. Don't use the TIP31A as they are too slow.
See also http://www.google.co.uk/url?sa=U&st...&pagenumber=1&e=14905&ei=3CF_RPmtEJLqQeX4paYP which has different MOSFETS and a slightly different inductor but otherwise looks very familiar. Note "The design is based on the Hitachi application note for their MOSFETs".
I take that back! 😱 It's been a long time since I've used a 2N3055...I just checked the datasheet and their hfe drop to below 10 at 10A which means a base current of over 1A. The 2N5551 will only do 600mA. Although it is arguable at normal listening levels with normal speakers that the duration will be ok I would use higher current drivers to be on the safe side. You want something with hfe about 100 and Ft above 10MHz.
You want something like an MJE15028, MJE243 or even a ZTX653. There are plenty of others if you look in catalogs. Failing that, a BD711 or a TIP31B or C will work but are a little slow and won't regulate as well.
You want something like an MJE15028, MJE243 or even a ZTX653. There are plenty of others if you look in catalogs. Failing that, a BD711 or a TIP31B or C will work but are a little slow and won't regulate as well.
Traderbam yea, i also saw that the gain of the 2N3055 was quite low.
So i am using the darlington configuration with the pass transistors to make life easier on the driver transistor.
If i were to run a negative regulator without using your supply stacking trick...
I would reverse the zener diode, replace the driver with a pnp, and would i also have to point the 2N3055's collector at the more negative end of the supply, i.e. the 63vdc input?
Just curious.
Construction has commenced! i will pot a few pics later today if i finish.
Regards
Craig
So i am using the darlington configuration with the pass transistors to make life easier on the driver transistor.
If i were to run a negative regulator without using your supply stacking trick...
I would reverse the zener diode, replace the driver with a pnp, and would i also have to point the 2N3055's collector at the more negative end of the supply, i.e. the 63vdc input?
Just curious.
Construction has commenced! i will pot a few pics later today if i finish.
Regards
Craig
Definitely not "cheap and nasty" - with the right mods. The topology is so simple - it should sound good.
Fit a large polyprop cap at the input, improve the PSRR and fit a massive PSU for best results.
Constant current sources need to be added to prevent voltage sag in the driver stage when the output stage is loaded.
The Maplin is descended from the Hitachi apps data, and the late Phase Linear (used by Pink Floyd on tour) amps were based around the topology.
Fit a large polypropylene cap at the input, parallel the OPS (I prefer the sound of the Exicon 16A to the Hitachi - sacrilege I know!) and run well into Class A for best results.
I've used ATC, Bryston etc etc in treated rooms; an up-rated Hitachi / Maplin will challenge all contenders - seriously!
A brief 'spec on mine:
Dual mono-block: 1.5Kva; 60,000u+ (44,000u @ 120v mil-spec) per rail + "capacitance multiplier" circuit; chokes in a Pi-network; +/- 75v rails.
Maplin fitted sk133 / 134 / 135 as well as sj48 / 49 / 50
Please excuse any vagueness in the post - it's late here!
Justin
Fit a large polyprop cap at the input, improve the PSRR and fit a massive PSU for best results.
Constant current sources need to be added to prevent voltage sag in the driver stage when the output stage is loaded.
The Maplin is descended from the Hitachi apps data, and the late Phase Linear (used by Pink Floyd on tour) amps were based around the topology.
Fit a large polypropylene cap at the input, parallel the OPS (I prefer the sound of the Exicon 16A to the Hitachi - sacrilege I know!) and run well into Class A for best results.
I've used ATC, Bryston etc etc in treated rooms; an up-rated Hitachi / Maplin will challenge all contenders - seriously!
A brief 'spec on mine:
Dual mono-block: 1.5Kva; 60,000u+ (44,000u @ 120v mil-spec) per rail + "capacitance multiplier" circuit; chokes in a Pi-network; +/- 75v rails.
Maplin fitted sk133 / 134 / 135 as well as sj48 / 49 / 50
Please excuse any vagueness in the post - it's late here!
Justin
Constant current sources will do nothing for rail sag, which is down to the lack of PSU capacity. However, if the design is so on the edge that a mere loading of the rails causes the VAS stage to not be able to supply enough current to drive the output devices, they might help but the design would be too flawed in other respects if that is the case!
Improving PSRR is the best thing to do. Adding a regulated supply as you are doing will negate most of the need for this. Using separate rectifier+caps for each side will also help.
They do sound good though even in fairly basic form. Many a British pro amp has used the basic topology.
Improving PSRR is the best thing to do. Adding a regulated supply as you are doing will negate most of the need for this. Using separate rectifier+caps for each side will also help.
They do sound good though even in fairly basic form. Many a British pro amp has used the basic topology.
Hi Justin, I saw your post in the other thread and thought I'd pop over. Are you using any particular CCS, or just a bog standard one?
From the bits I've got, I'll be building a dual mono, 30Kuf per side, on fifty five V rails, (rats, the number five key has just stopped working, time to clean my keyboard!), and I'm going to add DC protection from Randy Slone's design. I have some nice 4.7u polys I can pair up for the inputs. Anything else people can suggest?
From the bits I've got, I'll be building a dual mono, 30Kuf per side, on fifty five V rails, (rats, the number five key has just stopped working, time to clean my keyboard!), and I'm going to add DC protection from Randy Slone's design. I have some nice 4.7u polys I can pair up for the inputs. Anything else people can suggest?
Are you using the Maplin PCB Al or one of your own design? Also are you just using a single pair of output devices?
Adding CCS can be risky as the design already has pretty high gain. IMO the best way to approach the design unless you want to spend a lot of time on honing the stability (and lets face it these amps are not the most stable in the world) is to simply regulate the input and VAS stages about 5V higher than the high current rails. You can use the Pass A75 PSU scheme for this, or simply wrap some turns round the main toroid for an extra set of windings and use an emitter follower regulator.
Adding CCS can be risky as the design already has pretty high gain. IMO the best way to approach the design unless you want to spend a lot of time on honing the stability (and lets face it these amps are not the most stable in the world) is to simply regulate the input and VAS stages about 5V higher than the high current rails. You can use the Pass A75 PSU scheme for this, or simply wrap some turns round the main toroid for an extra set of windings and use an emitter follower regulator.
- Status
- Not open for further replies.