Hi pliedtka,
Sorry to hear about your 'puter problems. Load Fedora or some other flavour you like. Open Office is a no charge office suite.
XP is not too bad, but it's caused me a great deal of grief as well. This due to u$oft "updates", not virus activity. Windows 7 looks much better as well.
The IT-18 is available on Eeekbay and local estate sales. There are other meters from Heathkit that require more setup, but will furnish the same answers. The Beta reading will be more accurate with an IT-121 for example. I think I'll drag mine out and try to use it more. It's just not quite as fast to use as the IT-18.
Bridging an amp is not something I recommend doing. I feel they don't sound as good in that mode. You aren't buying a great deal more volume either.
-Chris
Sorry to hear about your 'puter problems. Load Fedora or some other flavour you like. Open Office is a no charge office suite.
XP is not too bad, but it's caused me a great deal of grief as well. This due to u$oft "updates", not virus activity. Windows 7 looks much better as well.
The IT-18 is available on Eeekbay and local estate sales. There are other meters from Heathkit that require more setup, but will furnish the same answers. The Beta reading will be more accurate with an IT-121 for example. I think I'll drag mine out and try to use it more. It's just not quite as fast to use as the IT-18.
Bridging an amp is not something I recommend doing. I feel they don't sound as good in that mode. You aren't buying a great deal more volume either.
-Chris
I quoted from D. Self's third addition, but I see this included in the fifth addition.
David.
Subtle difference between channels
Fred:
You mention room placement..and vintage ears. I hear that! (...or don't)
I may have missed this, but some channel swapping will help narrow the field of possibilites. A simple change of inputs on the back of the Adcom is something that may tell you a lot.
Do bleed the amp all the way down, shut down your pre/integrated amp before you change any inputs..always a good idea...and not always remembered (by me, I'm sayin').
For anyone that's a 'thumber'...you prolly don't have to worry about it.
Re: 'This was a monumentally bad idea on my part...'
I think it was a great idea! Well, now that it works, anyway. It was a great learning experience...and someone else got to do the work!
Fred:
You mention room placement..and vintage ears. I hear that! (...or don't)
I may have missed this, but some channel swapping will help narrow the field of possibilites. A simple change of inputs on the back of the Adcom is something that may tell you a lot.
Do bleed the amp all the way down, shut down your pre/integrated amp before you change any inputs..always a good idea...and not always remembered (by me, I'm sayin').
For anyone that's a 'thumber'...you prolly don't have to worry about it.
Re: 'This was a monumentally bad idea on my part...'
I think it was a great idea! Well, now that it works, anyway. It was a great learning experience...and someone else got to do the work!
Last edited:
Hi Dave,
That's okay, I'm sure that future editions will include even more material.
BTW, I wasn't trying to prove you wrong. The intent was for amusement really. The other point I wanted made was that a choice in relays can affect what an amplifier does sound like.
I've heard positive reports on bridging the relay contacts with a low value, high quality capacitor. It's was supposed to reduce low level audio rectification. Hey!, I'm just paraphrasing what I read elsewhere. I may give this a try at some point in time. I imagine the capacitor may have to be a foil type and film types may not withstand the current when the contacts are open.
-Chris
That's okay, I'm sure that future editions will include even more material.
BTW, I wasn't trying to prove you wrong. The intent was for amusement really. The other point I wanted made was that a choice in relays can affect what an amplifier does sound like.
I've heard positive reports on bridging the relay contacts with a low value, high quality capacitor. It's was supposed to reduce low level audio rectification. Hey!, I'm just paraphrasing what I read elsewhere. I may give this a try at some point in time. I imagine the capacitor may have to be a foil type and film types may not withstand the current when the contacts are open.
-Chris
Hi Chris,
I don't like to bridge the amps unless the amp is really up to it, I'm aware of the trade offs. For some people, eg. some car audio installers, it's like some magic since the specs may list some 3,4 times the power increase, without realizing that it's only some 4.5dB more and the transistors are stressed to the max when they drive the inefficient woofers, say 85dB/1w, 1000W, 2X2Ohm.
I like your comment on the relay contacts. Capacitor and relay, same idea like power ON/OFF switch with the cap in parallel, right? I did us it for house light switches when I had regular house TV antenna instead of cable and got flicking on the screen every time the light was turned ON.
Also some idea about measuring dist., freq. resp - might work for Fred, I haven't try it yet but I know many people use MarkRight Analyzer with voltage divider. I love my ancient win 98, ISA Clio card: measures loudspkrs and since it allows up to 20 kHz, 70Vp-p on inputs, I can do other things as well within it's limited capabilities.
I don't like to bridge the amps unless the amp is really up to it, I'm aware of the trade offs. For some people, eg. some car audio installers, it's like some magic since the specs may list some 3,4 times the power increase, without realizing that it's only some 4.5dB more and the transistors are stressed to the max when they drive the inefficient woofers, say 85dB/1w, 1000W, 2X2Ohm
.I like your comment on the relay contacts. Capacitor and relay, same idea like power ON/OFF switch with the cap in parallel, right? I did us it for house light switches when I had regular house TV antenna instead of cable and got flicking on the screen every time the light was turned ON.
Also some idea about measuring dist., freq. resp - might work for Fred, I haven't try it yet but I know many people use MarkRight Analyzer with voltage divider. I love my ancient win 98, ISA Clio card: measures loudspkrs and since it allows up to 20 kHz, 70Vp-p on inputs, I can do other things as well within it's limited capabilities.
Hi, everyone
well since Chris wrote about relays, how about the never ending audible differences in cables debate. Cool article, with some measurements.
Loudspeakers: Effects of amplifiers and cables - Part 5 | Audio DesignLine
And just for good laugh , the effect of Focal 6.5"/10 ohm midwfr. on Rear and Centre channels in JVC A/V 5x100W ProLogic receiver - bootstrapping in their amplifiers clearly stinks
Paul
well since Chris wrote about relays, how about the never ending audible differences in cables debate. Cool article, with some measurements.
Loudspeakers: Effects of amplifiers and cables - Part 5 | Audio DesignLine
And just for good laugh
, the effect of Focal 6.5"/10 ohm midwfr. on Rear and Centre channels in JVC A/V 5x100W ProLogic receiver - bootstrapping in their amplifiers clearly stinks Paul
Hi pliedtka,
You've hit on some of the more popular reasons why bridging an amplifier isn't a great idea. There are a couple others too.
Bridging doubles the resistance as seen by the speaker system (damping is divided by a factor of 2). The speaker is seen as being 1/2 of it's true impedance. So an 8 ohm speaker "looks" like a 4 ohm speaker to the amp. Finally, the feedback doesn't seem to work as it did in normal mode. The speaker system is normally returned and referenced to ground (or common), but in bridged mode the other end is connected to a dynamic point that is free to do it's own thing. It can sound ... well ... odd sometimes. Certainly not accurate.
You are also not assured of a 4.5 dB increase in power. In the perfect world, it's a 6 dB increase, so 4.5 dB is more realistic. In truth, due to power supply sag and protection networks, plus series resistances, you may only actually see a 3 dB increase. That is just audible when comparing A-B quickly. Not worth while since you are also running more current through the VC in the speaker. That increases the coil DCR (DC resistance) and may further cause another 2 dB loss in power - realistically speaking. So you may not actually gain anything over what you had without bridging the system. Want to increase the bass wallop? Add another bass driver and power that from the other channel. That will reduce distortion, increase efficiency (lower VC temps) and a host of other good things.
One last point for the "car people". When it says on an amp that it's "2 ohm stable", it means the amp is rated for 4 ohms, but will handle brief transitions to 2 ohms due to the impedance curve of the speaker system. We had to service many amps that died when run into a 2 ohm load because people were too lazy to read the information. Guess what? No warranty.
-Chris
You've hit on some of the more popular reasons why bridging an amplifier isn't a great idea. There are a couple others too.
Bridging doubles the resistance as seen by the speaker system (damping is divided by a factor of 2). The speaker is seen as being 1/2 of it's true impedance. So an 8 ohm speaker "looks" like a 4 ohm speaker to the amp. Finally, the feedback doesn't seem to work as it did in normal mode. The speaker system is normally returned and referenced to ground (or common), but in bridged mode the other end is connected to a dynamic point that is free to do it's own thing. It can sound ... well ... odd sometimes. Certainly not accurate.
You are also not assured of a 4.5 dB increase in power. In the perfect world, it's a 6 dB increase, so 4.5 dB is more realistic. In truth, due to power supply sag and protection networks, plus series resistances, you may only actually see a 3 dB increase. That is just audible when comparing A-B quickly. Not worth while since you are also running more current through the VC in the speaker. That increases the coil DCR (DC resistance) and may further cause another 2 dB loss in power - realistically speaking. So you may not actually gain anything over what you had without bridging the system. Want to increase the bass wallop? Add another bass driver and power that from the other channel. That will reduce distortion, increase efficiency (lower VC temps) and a host of other good things.
One last point for the "car people". When it says on an amp that it's "2 ohm stable", it means the amp is rated for 4 ohms, but will handle brief transitions to 2 ohms due to the impedance curve of the speaker system. We had to service many amps that died when run into a 2 ohm load because people were too lazy to read the information. Guess what? No warranty.
-Chris
I get little embarrassed if I misquote or say something utterly wrong on a public forum.
No big deal.
I was referring to Self's comment about relay contacts not being a problem.
He also mentioned in the fifth addition a problem with cheapo binding posts made from plated iron or steel causing distortion.
Relay contacts act as rectifiers for low level audio, I didn't know that. Did you know that you can use a pickle as a rectifier? lol. The engineers at Linear Technology demonstrated this and wrote a paper on it. Although the pickle did begin to smoke after a minute or so. Perhaps we need to put capacitors across our pickles.
There is a type of distortion in RF transmission systems called common path distortion. It's caused from a small rectification between the contact points of two dissimilar metals. The oxides that form on the metals create a rectifier which acts like a detector and causes the signals to mix. The problem can become so severe that it can wipe out all the other signals by raising the noise floor as much as 30dB.
I've wondered if this same or similar problem has been sighted in audio.
David.
Hi pliedtka,
We had to service many amps that died when run into a 2 ohm load because people were too lazy to read the information. Guess what? No warranty.
-Chris
Yes but more money for you.
Hi Chris,
You said:
While that would seem to be the logical case, it does fail to address one other change in the output impedance. You have removed the ground return from the signal path. This ground return can easily have a greater impedance than the output of an amp using feedback, so in some cases at least, the output impedance will actually be lower, not twice as much.
Nothing should change in the feedback behavior. If it does, I would have to consider the design unacceptable for use bridged, or just a poor design.
You said:
While that would seem to be the logical case, it does fail to address one other change in the output impedance. You have removed the ground return from the signal path. This ground return can easily have a greater impedance than the output of an amp using feedback, so in some cases at least, the output impedance will actually be lower, not twice as much.
Nothing should change in the feedback behavior. If it does, I would have to consider the design unacceptable for use bridged, or just a poor design.
Hi Dave,
There was no end to that. It really helped having the reputation that we could fix anything. Of course, that also meant we got stuff that had been around to more than one shop. I figure that helped keep me sharper, since cause and effect didn't apply any more for many units. Believe me though, figuring out the first fixes cost me dearly in time.
Hi Steve,
Well, the ground return was often better than the output wiring in many amps. So the effect was still to increase the impedance powering the speaker system. The output impedance of most amplifiers goes up with frequency as I'm sure you know, so the effects might be heard in bass (depending on many things), but what goes on in the midrange and higher can be very un-musical. Again, depending on the amplifier involved.
Just observations from over the years.
-Chris
There was no end to that. It really helped having the reputation that we could fix anything. Of course, that also meant we got stuff that had been around to more than one shop. I figure that helped keep me sharper, since cause and effect didn't apply any more for many units. Believe me though, figuring out the first fixes cost me dearly in time.
Hi Steve,
Well, the ground return was often better than the output wiring in many amps. So the effect was still to increase the impedance powering the speaker system. The output impedance of most amplifiers goes up with frequency as I'm sure you know, so the effects might be heard in bass (depending on many things), but what goes on in the midrange and higher can be very un-musical. Again, depending on the amplifier involved.
Completely agree with you. Still, this is in theory and I have never actually spent the time to try to figure this out. It may simply be a current thing to be honest with you. Also, as the aberrations become larger, the feedback circuit - amplifier combination may not be able to keep up with several different problems that can be traced back to current flow in the outputs and wiring.
Let me see now. An amplifier suffering from poor design .... can't be! Most amplifiers that are prone to be connected in bridge mode are the less expensive models, in home. In car audio, everything goes and all bets are off. The other market subject to running in bridge mode would be "pro sound" and DJ work. Those amplifiers are not designed with sound quality as a primary goal. No surprises there. They are designed to hang together through abuse. It takes much more money to arrive at professional amplifiers with good audio design that are suitable for the pro market. DJs will use anything that turns on.
Just observations from over the years.
-Chris
The problem with gear having been in a shop or an attempt to fix it by the owner means it is often in bits or parts missing !
I suppose it least it has worked once.
With own designs and first power up it has never worked !
Hi Nigel,
Hi Steve,
You would know from looking at competing products. You get so you can perform a mental inventory very quickly just by looking at a piece. It's a sickness I tell you!
-Chris
So true! Refused estimate from other shops can be quite a lot of fun too. Missing parts are common with the "bottom feeder" shops. Dishonest people! Owners looking inside are normally okay. Friends helping out are another thing again. Some are okay, but they are in the minority.
Not something you can bet on always. I've seen units that were designed to fail.
So true, but those can be pretty funny. At least you know what to expect in that case. Having one presented to you is another thing, but those I enjoy, believe it or not.
Hi Steve,
Well, ain't that the truth! I have to agree with you there.
You would know from looking at competing products. You get so you can perform a mental inventory very quickly just by looking at a piece. It's a sickness I tell you!
-Chris
Hi Nigel,
So true! Refused estimate from other shops can be quite a lot of fun too.
-Chris
Chris it got so I could tell which shop the stuff had been in.
"I've seen units that were designed to fail."
This is so true. There were certain products I would refuse to service. Or if I got talked into it, I would do it without warranty and this was made very clear to the customer.
Another funny thing, or not so funny, is the car audio installers who sandwiched power amplifiers behind back seats. The customer can't figure out why their amp keeps blowing up. This was worse than the DJs.
David.
Hi David,
Yes, some we could tell as well. Pretty sad when they have a trademarked way of screwing up. Do these people get points for consistency?
One amp brand called "Proximity" was prone to fire. These were designed and built in Quebec. The typical fire involved any speaker cabinets, plus the amp. I got one in from an insurance company. They wouldn't listen to reason and I was directed to repair it. I did after they agreed to my two conditions. The amp was never to be installed in any system again, and I would not provide any sort of warranty with the repair. I even asked them why they were willing to underwrite the risk from this piece of equipment. You see, this one caused five fires with no shortage of collateral damage! Four speakers went up, and the amp plus the rack. The fire fighting powder filled the chassis, it was pretty funny. So, it was repaired and tested (with a strong positive bias tempco). The insurance sompany paid and I made sure my conditions were not only on the invoice, but also taped to the side of the amp, and inside the amp folded up near the power transformer.
Car audio installers can be a completely weird bunch of people. I've seen car amps installed just about everywhere (including one in an engine compartment). I've seen amps screwed into the transmission casing, inside door panels and any number of otehr places. The ones I saw on the headliner in the passenger's cabin takes the cake. Screws pointing out everywhere (not really) on the roof top. I'll bet it was hard on car washes! Those two amps failed due to water damage. Go figure.
-Chris
Yes, some we could tell as well. Pretty sad when they have a trademarked way of screwing up. Do these people get points for consistency?
One amp brand called "Proximity" was prone to fire. These were designed and built in Quebec. The typical fire involved any speaker cabinets, plus the amp. I got one in from an insurance company. They wouldn't listen to reason and I was directed to repair it. I did after they agreed to my two conditions. The amp was never to be installed in any system again, and I would not provide any sort of warranty with the repair. I even asked them why they were willing to underwrite the risk from this piece of equipment. You see, this one caused five fires with no shortage of collateral damage! Four speakers went up, and the amp plus the rack. The fire fighting powder filled the chassis, it was pretty funny. So, it was repaired and tested (with a strong positive bias tempco). The insurance sompany paid and I made sure my conditions were not only on the invoice, but also taped to the side of the amp, and inside the amp folded up near the power transformer.
Car audio installers can be a completely weird bunch of people. I've seen car amps installed just about everywhere (including one in an engine compartment). I've seen amps screwed into the transmission casing, inside door panels and any number of otehr places. The ones I saw on the headliner in the passenger's cabin takes the cake. Screws pointing out everywhere (not really) on the roof top. I'll bet it was hard on car washes! Those two amps failed due to water damage. Go figure.
-Chris
Greetings, DIY community! 
I would like to say hey and comment that I've just finished reading through this thread, and found it very educational and entertaining! I have a 555 II that one channel quit working on the other day, and although I really didn't want to join another forum I don't have time to keep up with, I did here in order to get some schematics. Turned out, luckily, it was only Q4 (or, Q107 on my board) that shorted B-E, and replacing it with an MJE15030 put it back in service. I do appreciate the forum, this thread, and the contributors here for helping me get my head in the game.
And Fred, I'm very pleased that you persisted and got yours back in service. So, congrats! What was that Coolidge quote about persistance being king? Great job! 
As for bridging, I've never operated my 555 II in bridge mode. But I wouldn't be reluctant to try it if I had a suitable application. Since Adcom built the function in, I'd expect it to do okay with an 8 ohm load. I designed an amp, and built a pair, where each only operates bridged - that was some 20 years ago and they still provide sweet sounds daily. And they've been pushing electrons through nominal 4 ohm loads with dips below 2 ohms at certain frequencies, at six drivers per side, which is precisely what I designed the amps to drive. I'm a firm believer in bridged outputs which serve to double the output voltage swing over a single-ended output using the same rail voltages, not to mention driving speakers with a "balanced" signal, for what that may be worth. Works for me, anyway!
I would like to say hey and comment that I've just finished reading through this thread, and found it very educational and entertaining! I have a 555 II that one channel quit working on the other day, and although I really didn't want to join another forum I don't have time to keep up with, I did here in order to get some schematics. Turned out, luckily, it was only Q4 (or, Q107 on my board) that shorted B-E, and replacing it with an MJE15030 put it back in service. I do appreciate the forum, this thread, and the contributors here for helping me get my head in the game. An externally hosted image should be here but it was not working when we last tested it.
And Fred, I'm very pleased that you persisted and got yours back in service. So, congrats!
What was that Coolidge quote about persistance being king? Great job! As for bridging, I've never operated my 555 II in bridge mode. But I wouldn't be reluctant to try it if I had a suitable application. Since Adcom built the function in, I'd expect it to do okay with an 8 ohm load. I designed an amp, and built a pair, where each only operates bridged - that was some 20 years ago and they still provide sweet sounds daily. And they've been pushing electrons through nominal 4 ohm loads with dips below 2 ohms at certain frequencies, at six drivers per side, which is precisely what I designed the amps to drive. I'm a firm believer in bridged outputs which serve to double the output voltage swing over a single-ended output using the same rail voltages, not to mention driving speakers with a "balanced" signal, for what that may be worth. Works for me, anyway! - Status
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