Rob Flinn
Well-known member
I think if you look at thecircuit you will notice that there is a connection to the centre tap of one of the transformers. This seems to be a potential stumbling block for your plans
IJR's 2254/33609!
- Thread starter ijr
- Start date
Help Support GroupDIY Audio Forum:
I'm looking at this schematic by the way:
http://voyager.celestial.com.au/~rosswood/data/33609c/33609_ca.jpg
Okko
http://voyager.celestial.com.au/~rosswood/data/33609c/33609_ca.jpg
In this schematic the T1 center tap is used for parallel connection of the secondaries or am I missing something?
Okko
Rob Flinn
Well-known member
I was looking at a different diagram, so no you`re not missing anything !! :wink:
Rob Flinn
Well-known member
I`m getting a bit closer to testing this project, & I`m still wondering about matching the diodes.
Nobody seems to give a succinct method for doing this. Can anyone say exactly what property it is that we`re trying to match?
I`m sure IJR`s method is good, but I`m not quite sure how he`s doing it from the description.
I put a post at Geoff Tanners site & he said just use a DMM to match the forward voltage drop, but that sounds a bit too simple.
I spoke with a friend who suggested the following:
Use a saw tooth wave generator & feed 2 diodes at once via current limiting resistors. Monitor the voltage drop/curve across each diode on separate channels of a scope. Theoretically one should be able to match the curves at break over. I would try this but I don`t have a saw tooth generator here !!
Can anyone shed a bit more light on this subject please?
Nobody seems to give a succinct method for doing this. Can anyone say exactly what property it is that we`re trying to match?
I`m sure IJR`s method is good, but I`m not quite sure how he`s doing it from the description.
I put a post at Geoff Tanners site & he said just use a DMM to match the forward voltage drop, but that sounds a bit too simple.
I spoke with a friend who suggested the following:
Use a saw tooth wave generator & feed 2 diodes at once via current limiting resistors. Monitor the voltage drop/curve across each diode on separate channels of a scope. Theoretically one should be able to match the curves at break over. I would try this but I don`t have a saw tooth generator here !!
Can anyone shed a bit more light on this subject please?
Rob Flinn
Well-known member
BUMP. Someone must know the answer to the above please help me.
Tekay
Well-known member
In one of the manual the diodes are listed as FW matched (Forward voltage)
1N4153 are easier to match as the FW from each diode are closer to each other than 1N4148's
1N4153 are easier to match as the FW from each diode are closer to each other than 1N4148's
Rob Flinn
Well-known member
Thanks again Tekay.
So this means that it is not essential to match the curves of the diodes ?
Rob Flinn
Well-known member
I`m quite close. Need to get some 24 way elmas, & I have some interwiring left to do.
One other question.
On IJR`s version he has 4 300pf caps across the diodes. Which there are only 2 100pf caps on the 33609 diagram. I`m having a bit of a problem getting 300pf caps & am wondering how critical the value is. I guess I can cobble together a pair of 150pf`s.
Tekay
Well-known member
The early 2252 that was rejected by BBC used 1000p across the diodes, the 2264 with BAX52 diodes didn't have these caps at all!
Greg
Well-known member
A mastering engineer here in New Orleans contacted me last week about building him a 33609. He has MANY Neve preamps so I'm thinking that we'll be using a couple for parts, if applicable. After skimming this thread, it appears that this isn't the easiest project. But I'd like to help out in any way I can. Do you think it would be worthwhile for me to start on a version IJRs boards, or just wait since there are several people already working on it?
Rob Flinn
Well-known member
The boards aren`t too difficult to build, but the interwiring is tricky. I`m quite far down the road on this one, but I`m waiting for some Elmas at the moment, & also some spare time !!!!!
Tekay, do you think that these diodes are necessary ?? Now you`ve told of a 3rd option (not using the caps at all) I`m even more puzzled !!
Tekay
Well-known member
I'm using FW voltage matched 1N4153 and the 100p caps but I don't think that the two 100p caps are needed when you run it with L31267 and L10468 around the bridge.
I remember this bridge attenuator since I was in highschool over 25 years ago! we did some passiv line limiters for ham radio use.
Think the idea of a balanced bridge came from the mixer stage in a radio?
I remember this bridge attenuator since I was in highschool over 25 years ago! we did some passiv line limiters for ham radio use.
Think the idea of a balanced bridge came from the mixer stage in a radio?
Rob Flinn
Well-known member
Thanks Tekay.
I also have some 1N4153 that I have to match. I have 2 maters & decided to check with both. Got a strange result in that both meters gave different results. The strangest thing of all was that the results for each diode were not out by the same amount, just randomly different ???????
I also have some 1N4153 that I have to match. I have 2 maters & decided to check with both. Got a strange result in that both meters gave different results. The strangest thing of all was that the results for each diode were not out by the same amount, just randomly different ???????
Tekay
Well-known member
I've tested with two different multimeters and I've also got different voltage readings but they're still mached but just at a different FW voltage. Make shure you have a fresh battery in your multimeter.
Someone suggested to run 5 volt through the diode with a 10k serieal resistor and then measure over the diode!
Someone suggested to run 5 volt through the diode with a 10k serieal resistor and then measure over the diode!
Rob Flinn
Well-known member
One method that someone suggested to me was to run a sawtooth waveform through separate dropper resistors to 2 diodes & monitoring on different channels of a scope to see forward voltage & the curve as it rolls over.
q2audio
Well-known member
Here is a diode matching setup that I managed to find. I suppose you want there to be "0mV" difference between the diodes if you are going to call them matched... but in reality there is some tolerance window I'm sure. Maybe a faster way would be to pick a few points along the curve and see how a few random diodes match to that. At least then you aren't spending all day trying to match to one diode that may be way out of spec. I have replaced a bad diode in a 2254 (the kind with the matched bridge, square black thing) with a 4148 and never could tell the difference, it still sounded poofy (in the best sense of the word)!
http://www.electronicpeasant.com/circuits/diodemch.gif
http://www.electronicpeasant.com/circuits/diodemch.gif
