Bridge rectifier vs diodes?
Post
by shakti » Mon Oct 19, 8:58 am
Hornby Electronic Product Page
I'm not very knowledgeable about rectifier circuits, so if this question is answered better by a reference to some online tutorial, feel free to guide me in that direction.
I was wondering if there's a technical difference between a bridge rectifier, like the one used in Metroamp's 50W kits, and a setup using diodes. Many early ('67-'68) 50W amps simply had diodes soldered directly to the power transformer HT leads. Probably not a very safe way of doing it, but I was wondering if there are any technical advantages or disadvantages with one method of (solid state) rectification over the other, and how that could translate to a difference in sound or feel. Would it be better to use diode rectification with FREDs, or is the bridge rectifier superior...? This is what I'm getting at...
JTM45 RS OT, 18W, JTM45/100, JTM50, JMP50 , JMP100 "West Coast", AC15, AC30, BF Super Reverb, Boogie Mk 1, Hiwatt CP103, DR103
Re: Bridge rectifier vs diodes?
Post
by jcmjmp » Mon Oct 19, 11:01 am
A bridge rectifier is a single package version of a 4 individual diode rectifier and is usually setup for a single tap (no center tap) voltage source from the PT (vs center tapped output).
http://hyperphysics.phy-astr.gsu.edu/Hb ... ectbr2.gif" onclick="window.open(this.href);return false;
A standard bridge rectifier cannot be used with a center tapped PT i.e.
http://hyperphysics.phy-astr.gsu.edu/Hb ... ectct2.gif" onclick="window.open(this.href);return false;
Well, you could use it but it would be a waste of space and money because you'd be using half of it. I've never done it but I guess it could be done.
Electronically, there is no difference. With individual diodes, you have more flexibility and as you say, you can experiment with fred or fast recovery diodes.
Re: Bridge rectifier vs diodes?
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by neikeel » Mon Oct 19, 11:35 am
My understanding is that the 100w amps use a bridge type rectifier with the voltage doubler type circuit.
Here you need the 4 diodes. The PT does have a centre tap but that is run to a point between the first two filter caps to even out the voltages across caps which are of variable (+/- 10% values).
Exception is the JTM45/100 which has 3 diodes pretty much as the 50watter arrangement:
In a 50 watt most amps use the 1A rated diodes but in series pairs for each half of the PT, the centre tap on this is to chassis earth.
On the amps with the diode block you are only actually using two of the diodes (the fourth terminal that is earthed on a 100watter is left unused see below).
http://amparchives.com/album/Marshall/5 ... 85a_3.html
I personally would use the 3A rated diodes in pairs on a new build 50watter for a safety margin.
There are probably more erudite opinions around and I sit back for them to pour forth
Neil
Re: Bridge rectifier vs diodes?
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by flemingmras » Mon Oct 19, 12:54 pm
IMHO, in the case of solid state rectifiers you're not gonna hear a tonal difference between different rectifier circuits. It's not even an area of the amp worth screwing with. Rectifiers either work or they don't, plain and simple.
In regards to the "voltage doubler" circuit...that as has been said before is a matter of semantics. If you look at it as if you're doubling the center tap voltage, then yeah you could say it's a voltage doubler. But hooking up across the full winding without the center tap connected will give you the same end result, but you'll have to install bleeder resistors across the first stage filter caps to keep the voltage on the caps balanced. This circuit is more of a full wave voltage balancer as it is used to allow each half of the HT secondary to charge the first filter caps instead of using bleeder resistors to do it. Since each half of the HT secondary is 1/2 the voltage of the full HT secondary, you get 1/2 the voltage on each cap and each cap on the first filtering stage sees the same voltage to prevent one from going overvoltage.
Now a note on voltage doubler circuits...all they are is a dual polarity rectifier with the negative supply output grounded instead of the 1/2 voltage point being the ground reference. This gives you the "peak to peak" value of the incoming AC (i.e. the voltage measured from the negative peak to the positive peak), which is double the "peak" value (the voltage measured from 0 volts to the positive peak on one side of the supply and the voltage measured from 0 volts to the negative peak on the other side), rather than just the "peak" value of both halves of the AC signal. This is how it "doubles" the voltage output. Since the filter caps are in series, just like with batteries you get double the voltage out since the positive peak charges 1 cap while the negative peak charges the other. Due to the way the cap is oriented in a positive fashion relative to ground, you get a positive voltage out of the cap that's charged by the negative peak.
Look in the MetroAmp Wiki in the Tube Amp Power Supplies section...I've written articles there covering the operation of each type of rectifier that you'll find in a tube amp. The link to the Rectifier Circuits section is posted below.
Rectifier Circuits
As was stated above, a bridge rectifier is a self contained unit with 4 diodes hooked up in a bridge configuration and will perform the same as hooking up 4 individual diodes in a bridge config, just like the 100 watt Marshalls.
There's just that fine line between stupid and clever - Nigel Tufnel
Re: Bridge rectifier vs diodes?
Post
by shakti » Mon Oct 19, 3:38 pm
Thanks guys! The answer is usually closer to home than you think...I should spend more time on the Wiki!
Just one thing; some of you say the rectifier isn't worth poring over, yet some people say that using FREDs will have an effect particularly on the high end. I'm ready to believe that changes in the power amp section will affect the overall sound and feel (witness the difference between different filter cap brands, let alone ratings), but as far as the rectifier, I've never done any experimentation. I did have a tech install FREDs in a '71 years ago. The amp came back sounding fantastic, but I changed tubes in the same operation, so that's not much to base any opinion on...
JTM45 RS OT, 18W, JTM45/100, JTM50, JMP50 , JMP100 "West Coast", AC15, AC30, BF Super Reverb, Boogie Mk 1, Hiwatt CP103, DR103
Re: Bridge rectifier vs diodes?
Post
by flemingmras » Mon Oct 19, 3:50 pm
Contact us to discuss your requirements of ultra fast bridge rectifier. Our experienced sales team can help you identify the options that best suit your needs.
shakti wrote:Thanks guys! The answer is usually closer to home than you think...I should spend more time on the Wiki!
Just one thing; some of you say the rectifier isn't worth poring over, yet some people say that using FREDs will have an effect particularly on the high end. I'm ready to believe that changes in the power amp section will affect the overall sound and feel (witness the difference between different filter cap brands, let alone ratings), but as far as the rectifier, I've never done any experimentation. I did have a tech install FREDs in a '71 years ago. The amp came back sounding fantastic, but I changed tubes in the same operation, so that's not much to base any opinion on...
And the same people who claim the FRED diodes make any difference are probably the same guys who claim that Monster brand speaker cable is the best sounding speaker cable on the market...the same people who came from the audiophile/hi-fi community (i.e. "audiophools") at one time too. And some people claim to hear things they THINK they hear that they really don't...because when people listen for subtle things, they hear what they wanna hear...especially if they spent a lot of money on what it was they had changed on something. Helps them justify spending the large amount of money they just spent.
I never did understand why people try hi-fi tricks on guitar amps that were never meant to be a hi-fi amp, and wouldn't sound nearly as good if they were. The fact that they're far from hi-fi is what makes them what they are. Leave them imperfect like they are...that's why they sound as good as they do.
Filtering will affect the dynamic feel and tone of the amp..to a point. It depends on how much filtering the amp started out with. If it was a low filtered power supply to begin with, then increasing the filtering will have a dramatic effect. However, if the amp already has decent filtering and you step it up beyond that, you won't have as drastic of an effect. Eventually you reach the point of diminishing returns, and no amount of filtering increase will make a difference.
The filter circuit is the "current reservoir" of the amp...when you run the amp hard that has a low filtered power supply, there's not as much current in reserve for the tubes to pull, so the filter caps discharge quicker, causing the power supply voltage to drop. Some refer to this as "sag". But when you do it on an amp that has high filtering, there's more current stored by the filter caps, so the power supply voltage doesn't drop near as much. This affects the tightness of the amp. But again, once you reach the point where the filter circuit has sufficient filtering, you won't hardly notice a difference.
Here's another article in the Wiki regarding filter circuits, their components and what they do.
Filter Circuit Components
There's just that fine line between stupid and clever - Nigel Tufnel
Re: Bridge rectifier vs diodes?
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by paulster » Tue Oct 20, 7:05 am
flemingmras wrote:IMHO, in the case of solid state rectifiers you're not gonna hear a tonal difference between different rectifier circuits. It's not even an area of the amp worth screwing with. Rectifiers either work or they don't, plain and simple.
There have actually been some comparisons and clips done here which, if you accept the comparison method, clearly show a difference between regular 1Ns and fast recovery diodes.
These threads give a lot of useful information on what you might expect:
http://forum.metroamp.com/viewtopic.php?f=4&t=" onclick="window.open(this.href);return false;
http://forum.metroamp.com/viewtopic.php?f=4&t=" onclick="window.open(this.href);return false;
http://forum.metroamp.com/viewtopic.php?f=4&t=" onclick="window.open(this.href);return false;
http://forum.metroamp.com/viewtopic.php?f=3&t=" onclick="window.open(this.href);return false;
I'll stick with my ultra-fast diodes, thanks.
Re: Bridge rectifier vs diodes?
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by jcmjmp » Tue Oct 20, 9:13 am
Regardless of the tonal benefits of having fast recovery diodes or FREDs, I believe that there are benefits in terms or spikes and switching noise going into the circuit and back into the PT.
Some say that snubber caps can have the same effect as a fast recovery diode.
Re: Bridge rectifier vs diodes?
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by Roe » Tue Oct 20, 1:09 pm
does the bridge rectifer george supplies in the 50w kit feature ultra fast diodes?
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Super 100 amps: -119 & -84
JTM45 RS OT JTM50 JMP50 //34/39
Re: Bridge rectifier vs diodes?
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by paulster » Tue Oct 20, 1:21 pm
Most bridge rectifier modules use generic 1N400x type specification diodes, but there are exceptions. You need to know the part number of the item in question and look up its specifications and/or data sheet to find out exactly what you're going to get.
I can't help you on the specifics of George's one, unfortunately.
Re: Bridge rectifier vs diodes?
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by flemingmras » Tue Oct 20, 1:28 pm
paulster wrote:Most bridge rectifier modules use generic 1N400x type specification diodes, but there are exceptions. You need to know the part number of the item in question and look up its specifications and/or data sheet to find out exactly what you're going to get.
I can't help you on the specifics of George's one, unfortunately.
Most self-contained rectifiers are 4 regular standard diodes on a common substrate.
There's just that fine line between stupid and clever - Nigel Tufnel
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lordvader88
What are good diodes to get?
«
on: May 27, , 07:27:41 pm »
What are the most recommended diodes to have on hand ? I'm nearly out of general purpose rectifiers, and signal diodes, and zeners, and LEDs too.
And how good/bad are cheap ebay diodes vs buying brand name, diodes ?
I have lots of 1N60 Germanium diodes, some varactor diodes.
What all precision diodes are there ?
my short list is some
1N
1N400x
1N54xx
higher wattage zeners than the 1/8 or 1/4W ones I have, but they are hard to find on ebay and expensive
What are some high current rectifiers for mains powered projects/repairs
I barely have any fast switching diodes, for SMPS.
Whats are some state of the art diodes ?? And RF diodes ?
« Last Edit: May 27, , 07:31:15 pm by lordvader88 »
bd139
Re: What are good diodes to get?
«
Reply #1 on: May 27, , 07:52:16 pm »
1n for 99% of stuff. 1n for RF bits, mostly power detection for me. 1N for low current rectifier
Everything else I buy when I need it. There's not a lot that can't be done with the above that isn't expensive to keep in stock.
mariush
Re: What are good diodes to get?
«
Reply #2 on: May 27, , 07:55:49 pm »
Go to a store like Digikey and sort by quantity in stock - chances are whatever's stocked in bigger quantity is more popular. ex see https://www.digikey.com/short/p4dwnz
Look into some fast/ultrafast rectifiers (UF**), schottky diodes, maybe stock some bridge rectifiers in DIP package or SIP (gbu family and others) instead of using 4 diodes to rectify ac voltage
look into max current and also forward voltage drop at some current... ex. 1n may be good for up to 1A as long as you're fine with 0.8v..1v voltage drop at even 200mA but maybe you'll also want a 1A diode that has only 0.3..0.5v drop at 100-300mA
May want to have some 3A..5A diodes in stock even if you're gonna use them in 0.5A..1A circuits, simply because at 0.5A..1A the voltage drop will be very small and the diode's properties won't change as much with heat (bigger package, thermal mass etc)
bob
Re: What are good diodes to get?
«
Reply #3 on: May 27, , 09:28:57 pm »
I have thousands of 1Ns so I will never have to buy any. I have a large stock of 1Ns so those are good.
Anything else, well I try to get germanium diodes like 1N270 to keep handy. And zener diodes are a different issue.
From salvaging parts of obsolete or broken stuff I have amassed lots of LEDs, and rectifiers of the two and three or four in a package, some capable of several amperes. There are some high voltage diodes too, many with high current ratings.
For varicaps I have found that ordinary diodes will behave well. I measure on my bridge while adjusting reverse bias. For temperature compensation of power amplifiers, again ordinary diodes do well, especially 1N. Sometimes I need a few in series and of course attached to the heat sink.
David Hess
Re: What are good diodes to get?
«
Reply #4 on: May 28, , 12:15:33 am »
These days I tend to use fast recovery rectifiers in place of standard recovery parts like the ubiquitous 1N series simply so that I can stock fewer parts. I also tend to only buy the highest voltage part of a given series for the same reason.
So for instance the 200 nanosecond 1N replaces the 1N through 1N standard recovery rectifiers.
lordvader88
Re: What are good diodes to get?
«
Reply #5 on: May 28, , 03:33:25 am »
For typical usage, is there any reason to buy rectifiers that have lower blocking rating lower like the 100V 1n, if the price is the same would u just buy 1kV 1n ?
IDK any diode or transistor model that add internal capacitance or inductance. Over the years I've collected lots of diodes from CRT TVs, I guess I'll need them to make a CRT TV.
Lately I made a little 17VAC Octopus tester , now I'm working on a curve tracer circuit, finally I made a way to test zener, but now to sort them out
« Last Edit: May 28, , 03:45:43 am by lordvader88 »
Re: What are good diodes to get?
«
Reply #6 on: May 28, , 04:18:06 am »
Quote from: lordvader88
For typical usage, is there any reason to buy rectifiers that have lower blocking rating lower like the 100V 1n, if the price is the same would u just buy 1kV 1n ? ...
There's be a bees dick in it - capacitance, leakage, IR loss etc but nothing that would concern any power app or general use. In those cases, you'd be looking
for something a lot more specialized anyway. 1N is most peoples "standard". Plus the 1N or similar for 3A
Hello
.. is this thing on?
David Hess
Re: What are good diodes to get?
« Reply #7 on: May 28, , 04:32:02 am »
For typical usage, is there any reason to buy rectifiers that have lower blocking rating lower like the 100V 1n, if the price is the same would u just buy 1kV 1n?
The higher voltage diodes may have slightly different specifications in other respects. For instance the 600 volt MUR160 is 50 nanoseconds and 27 picofarads but the 900 volt MUR190 is 75 nanoseconds and 15 picofarads.
Higher voltage parts usually have higher forward voltage drops but not always.
All of the members of the 1N series are the same except for voltage but the similar 1N series has longer recovery times for higher voltage parts.
« Last Edit: May 28, , 09:52:00 pm by David Hess »
T3sl4co1l
Re: What are good diodes to get?
« Reply #8 on: May 28, , 04:43:50 am »
General purpose switching diode, PN: 1N914/1N (THT), 1NW (SOT-123)
Signal schottky diode: BAT85 (THT), BAT54H (SOT-123), BAT54S (SOT-23) (or other variants, -C and -A are common cathode/anode, S is series, etc.)
General purpose rectifier: UF (THT), ES1J (SMA), don't bother with slow (1N400x), who cares
Schottky rectifier: B340 (SMA), etc.
Also UF540x for higher current, or anything MUR (ultrafast rectifier), MBR ([schottky] barrier rectifier), B or SB, PMEG, etc.
Zener: 1NB (5.1V 500mW), (12V), etc. 47xx is 1W series, etc.
TVS: P6KExx(C)A, 1.5KExx(C)A, SMAJxx(C)A, etc.
Probably if you need something more special than these, just buy them specific for the project.
Tim
Seven Transistor Labs, LLC
Electronic design, from concept to prototype.
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Brumby
Re: What are good diodes to get?
« Reply #9 on: May 28, , 05:15:17 am »
1n for 99% of stuff. 1n for RF bits, mostly power detection for me. 1N for low current rectifier
Everything else I buy when I need it. There's not a lot that can't be done with the above that isn't expensive to keep in stock.
I'm the same, but I have a fistful of 1N (3A) left over from a project that have been useful every now and then.
bd139
Re: What are good diodes to get?
« Reply #10 on: May 28, , 07:21:04 am »
I probably have some 54xx as well. I’ll probably just buy more rather than try and find them. Although up there I tend to go for Vishay SB series diodes.
A couple of things that are good about the 1N which is why I keep them around versus an UF diode:
1. They actually make a fairly reasonable and cheap PIN diode.
2. They are less noisy than UF400x.
I have some super fast diodes as well which were used to fix a Tek power supply (STTH2R06)