For the record, the odd linear audio electronics article does appear in EW. Presumably if they fit the criteria of current or emerging technology. Yet I'm surprised to find our sometime member Michael Kinwanuka, aka Mikeks and other nicknames, has just had a deep and scholarly article on 2-pole compensated audio amps published in this month's edition. How 'bout that? Full PDF file here: Double-pole compensation and the push-pull transimpedance stage in discrete audio frequency power amplifiers – Electronics World
You could conclude that Naim was aware of this effect when they fitted soft rubber mountings for the large PCBs in their later, all black models like NAP200. I listened to a recent clone build of this, where the builder just used standard brass pillars and it was not as good and clear as mine with home-made silicone rubber mouldings. Maybe I'm biased but I believe the owner when he said that he agreed with my assessment.
The condition is referred to as "microphony" which means there are some component(s) of the circuit or even the PCB, in which the signal can be modulated by mechanical vibration. This can be explored further by bringing the amplifier up to the loudspeaker and rechecking, prodding any suspect parts with a rubber pencil eraser etc. Apart from the tantalum caps, I didn't find any microphonic components but I now suspect it's the long PCB traces.
FWIW, I used to think that tanatalum caps (almost unique to Naim) were microphonic because they made a noise if you tapped them with a hard object like a screwdriver but that can occur with other caps too.
There was a very strange quality of Naim 32.5 preamps. If the feet were finger tight they sounded more dynamic. The latter versions had a large Allan bolts to hold it tight. As much as I found it irrational I always checked this. The smile on people's faces and saying it restored the sound. It was discovered in demonstrations where phono boards swapped. The salesman kept the feet finger tight.
The Sony research was Esprit range. They alegedly on my advice bought a Linn Naim Isobaric set up possibly from Graham's in London. The speakers obviously inspired by the Isobarics. I was working with video at the time. For some reason they preferred my view. The vibration caused small currents to flow in components due to magnetic fields. Effects from -120 to -126 dB. Sony were very cautious to admit that. My feeling is that the effect is harder to measure than hear.
Cyril Bateman caught out people who have no interest in subjective evaluation. He forced them to open their minds a little. The strange thing is the measurements almost prove the opposite of what he set out to do. He excellent abilities as an advocate won the day. -120 dB good -100 dB bad. How did he get away with that? I'm glad he did. My Quest is that given low cost choices listen to your choices. 70% of the time your choice might follow others. 30% very likely a personal choice.
The Sony research was Esprit range. They alegedly on my advice bought a Linn Naim Isobaric set up possibly from Graham's in London. The speakers obviously inspired by the Isobarics. I was working with video at the time. For some reason they preferred my view. The vibration caused small currents to flow in components due to magnetic fields. Effects from -120 to -126 dB. Sony were very cautious to admit that. My feeling is that the effect is harder to measure than hear.
Cyril Bateman caught out people who have no interest in subjective evaluation. He forced them to open their minds a little. The strange thing is the measurements almost prove the opposite of what he set out to do. He excellent abilities as an advocate won the day. -120 dB good -100 dB bad. How did he get away with that? I'm glad he did. My Quest is that given low cost choices listen to your choices. 70% of the time your choice might follow others. 30% very likely a personal choice.
Tubes are certainly microphonic to varying degrees and by tapping the glass, you can even see some of the tiny metal elements vibrating on big, old octal base types, such as those intended for the horizontal drive of B&W TVs. They made excellent, high power guitar audio amps too but the jingling, ringing effect of acoustic feedback completely wrecked the sound. Consequently, the actual power amplifier needed to be cushioned and shielded with polyurethane foam rubber material like sorbothane or acrylic wool on stage. Special miniature tubes with short, rigid elements were preferred for low level amplifiers but I haven't worked on tube gear much since....well, a very long time ago 
Self has a very interesting take on two pole compensation. Looks dreadful yet works. What is proves is negative feedback can work better than some believe. Two pole compensation becomes very interesting from output to VAS. Suddenly bags of current and correcting the whole local loop. MOSFETs suit this.
The JLH looks to be a transimpedance design, the 8K2 seems just to stabilise the circuit at DC no signal. I suspect if something is a I to V converter it has to be a drastic one. My attemps to rectify the usual set up were not conclusive. An arguement used is that transistors more ideally are current ampifiers. Making the VAS a TIS ( transimpedance stage ) which usually it is helps. That's where TIM might be caused. Not least most amps can not source and sink current equally ( Hitachi Mosfet can and is ultra simple ). Put an oscilloscope at the VAS base. Usually it looks very bad. Put a very small resistor in the VAS base and measure across it if your scope will. It will look OK. That's a transimpedance amplifier. That small resistor if optimum can be a cure in the old days rather than a capacitor base to collector.
DACs can use I to V converters. Some feel that part is the doubtful component. It can be a very simple circuit. Some valve circuits use them them like RH84.
The JLH looks to be a transimpedance design, the 8K2 seems just to stabilise the circuit at DC no signal. I suspect if something is a I to V converter it has to be a drastic one. My attemps to rectify the usual set up were not conclusive. An arguement used is that transistors more ideally are current ampifiers. Making the VAS a TIS ( transimpedance stage ) which usually it is helps. That's where TIM might be caused. Not least most amps can not source and sink current equally ( Hitachi Mosfet can and is ultra simple ). Put an oscilloscope at the VAS base. Usually it looks very bad. Put a very small resistor in the VAS base and measure across it if your scope will. It will look OK. That's a transimpedance amplifier. That small resistor if optimum can be a cure in the old days rather than a capacitor base to collector.
DACs can use I to V converters. Some feel that part is the doubtful component. It can be a very simple circuit. Some valve circuits use them them like RH84.
Some of what's said is very high flung. Vibration isn't. Also if sensible about low DCR keep the power supply separate as vibration might very truely be the Elephant in the room along with the waste product the magnetic field. Single PSUs like JLH tollerate this better. Usually a long cable sounds worse.
I used a 10 mH inductor on my oscilloscope to measure these fields. 5 mm can be a big difference. Cheap and easy. It's not like a volt meter where you can share readings. You can compare which is useful.
A bicycle inner tube is a cheap vibration isolator. An isolated amplifier can be worse. Sometimes a semi isolated one works better. The isolator can throw the vibration back into the case! This idea is called a vibration sink. Don't believe what you are told. Use your ears.
I used a 10 mH inductor on my oscilloscope to measure these fields. 5 mm can be a big difference. Cheap and easy. It's not like a volt meter where you can share readings. You can compare which is useful.
A bicycle inner tube is a cheap vibration isolator. An isolated amplifier can be worse. Sometimes a semi isolated one works better. The isolator can throw the vibration back into the case! This idea is called a vibration sink. Don't believe what you are told. Use your ears.
Member
Joined 2009
Paid Member
I think there are too many variables to have a definitive opinion on this point.
let's just take the example of cd players (I take this one because I have done a lot of tests on it)
it is almost impossible to predict the result before trying everything on a model.
and it has to be done for each reader.
some will like to be completely decoupled, others isolated, others weighted (above or below), others nothing at all.
and there, I have not yet entered the reader, some people like to decouple the motherboard, or to cushion the quartz, or even to decouple it from the card.
and that, just for cd players, we have not yet talked about vinyl turntables, amplifiers, preamps, transistors, tubes.
in short, I stopped taking the lead with all this, I reduce to "sorbothane or not sorbothane"...
let's just take the example of cd players (I take this one because I have done a lot of tests on it)
it is almost impossible to predict the result before trying everything on a model.
and it has to be done for each reader.
some will like to be completely decoupled, others isolated, others weighted (above or below), others nothing at all.
and there, I have not yet entered the reader, some people like to decouple the motherboard, or to cushion the quartz, or even to decouple it from the card.
and that, just for cd players, we have not yet talked about vinyl turntables, amplifiers, preamps, transistors, tubes.
in short, I stopped taking the lead with all this, I reduce to "sorbothane or not sorbothane"...
Hello everyone,
I'm sure all of this has been covered in this thread and I am trying to work my way through it but its a long thread so appologies in advance.
I've decided to build a class A amp or two, and I think I've settled on the JLH 1996 direct coupled design.
I've acquired some used hardware, 2 x approx 400VA toroids at 2x 22V secondaries each. I've also got 8 x (and more if needed) 22,000uF caps, so a lot of the expense is sorted. I've yet to acquire heatsinks so I am looking at inventive ways of possible making one with perhaps fan assistance. The amp will eventually be in an enclosed space (WAF) so fans will probably be needed.
I've got the Wireless World articles and I am aware of at least one error in the schematic, the one where the feedback cap is connected to -22V but should be 0V. Anything else I should be aware of?
Which transistors should I use, should I stick with the originals, assuming they are still available?
I've got 2 x 5mH crossover inductors not being used so was thinking of getting 2 more to build 2x +/- C-L-C PSU filters, is 5mH adequate?
Cheers!
I'm sure all of this has been covered in this thread and I am trying to work my way through it but its a long thread so appologies in advance.
I've decided to build a class A amp or two, and I think I've settled on the JLH 1996 direct coupled design.
I've acquired some used hardware, 2 x approx 400VA toroids at 2x 22V secondaries each. I've also got 8 x (and more if needed) 22,000uF caps, so a lot of the expense is sorted. I've yet to acquire heatsinks so I am looking at inventive ways of possible making one with perhaps fan assistance. The amp will eventually be in an enclosed space (WAF) so fans will probably be needed.
I've got the Wireless World articles and I am aware of at least one error in the schematic, the one where the feedback cap is connected to -22V but should be 0V. Anything else I should be aware of?
Which transistors should I use, should I stick with the originals, assuming they are still available?
I've got 2 x 5mH crossover inductors not being used so was thinking of getting 2 more to build 2x +/- C-L-C PSU filters, is 5mH adequate?
Cheers!
Being crossover chokes they might be usable. DC resistance or DCR will be part of it. 5 mH is exactly π ohms or circa 3 ohms at 100. Hz. The chokes are possibly more use at higher frequencies. XL= 2πfl.
The mistake in the Wireless World article isn't really a mistake. It's less good. Loudspeakers can be returned to the positive or 0 V connection if the polarity of the output capacitor is made suitable. One reason we do it the conventional way is it avoids the non capacitor terminal being shorted to chassis. As chassis is often connected to mains earth it often is quieter. Sometimes a 100 ohms resistor is placed between chassis and PSU 0V as a mild separation. The chassis hard to mains earth. There will be a number of times when the wrong way is better. As to feedback capacitors. To 0V. If using Cyril Batemans ideas we keep the signal or DC offset below 0.4 V . This favours the split rail version and using a non polar electrolytic. DC offset slightly matters for this reason alone if ≤ 100 mV.
If Kirchoff's laws are being respected either + or - is equal. This is especially true in power amplifiers where if a Linear regulator is used the PSU output impedance is very low . Almost 0 ohms compared with wiring of the usual type. The thing to note is we say + and 0v. 0 v denotes chassis earth is connected. LD1084 is a very nice Linear regulator. It might out class a capacitance multiplier. Being lower dropout it almost is as efficient. Have voltage adjust to reduce hum if using it's dropout to the full.
The mistake in the Wireless World article isn't really a mistake. It's less good. Loudspeakers can be returned to the positive or 0 V connection if the polarity of the output capacitor is made suitable. One reason we do it the conventional way is it avoids the non capacitor terminal being shorted to chassis. As chassis is often connected to mains earth it often is quieter. Sometimes a 100 ohms resistor is placed between chassis and PSU 0V as a mild separation. The chassis hard to mains earth. There will be a number of times when the wrong way is better. As to feedback capacitors. To 0V. If using Cyril Batemans ideas we keep the signal or DC offset below 0.4 V . This favours the split rail version and using a non polar electrolytic. DC offset slightly matters for this reason alone if ≤ 100 mV.
If Kirchoff's laws are being respected either + or - is equal. This is especially true in power amplifiers where if a Linear regulator is used the PSU output impedance is very low . Almost 0 ohms compared with wiring of the usual type. The thing to note is we say + and 0v. 0 v denotes chassis earth is connected. LD1084 is a very nice Linear regulator. It might out class a capacitance multiplier. Being lower dropout it almost is as efficient. Have voltage adjust to reduce hum if using it's dropout to the full.
That's a great idea. Some use a 100nF in parallel. That is debatable..
Feedback capacitor to 0V o a split rail design is logical and mostly the right way.
I've been watching French TV news. Congratulations France 24 for being professional. Our BBC could learn from that. BBC Wales better than BBC UK. I fool myself my French is improving. It's not so hard when the same news. I learned of Christophe a French singer who died recently as my non obvious listening. Huggy your English is very good.
Feedback capacitor to 0V o a split rail design is logical and mostly the right way.
I've been watching French TV news. Congratulations France 24 for being professional. Our BBC could learn from that. BBC Wales better than BBC UK. I fool myself my French is improving. It's not so hard when the same news. I learned of Christophe a French singer who died recently as my non obvious listening. Huggy your English is very good.
my english should be about as good as your french.
I still help myself with a translator to check if my sentences are well constructed and my partner from Dublin gives me private lessons and I give her French lessons in the same spirit
personally i don't watch tv anymore
and actually when I look at the news, it's france 24 or france inter or france info because there is no sensationalism, just fact and
they don't try to scare.
for christophe it's sad yes, I don't know if you know but it's been years that he only slept every other night to stay "connected" and keep this state of consciousness that we have at night.
I was not a fan, however when Michel Jonasz died, there I will be very sad
I still help myself with a translator to check if my sentences are well constructed and my partner from Dublin gives me private lessons and I give her French lessons in the same spirit
personally i don't watch tv anymore
and actually when I look at the news, it's france 24 or france inter or france info because there is no sensationalism, just fact and
they don't try to scare.
for christophe it's sad yes, I don't know if you know but it's been years that he only slept every other night to stay "connected" and keep this state of consciousness that we have at night.
I was not a fan, however when Michel Jonasz died, there I will be very sad
That will give you quite high DC supply to the amps. Have you checked the charts for load impedance/supply voltage and power dissipation?
If you use the 0-22 in parallel that would give you 30 VDC given that we mostly still get 240 V. That would suit the 1969 design quite well. Lose a couple of volts in the capacitance multiplier if used. My JLH was about that. 8 watts is fine. 100 watts is obviously more. 20 watts isn't. One winding per channel might not be best use of money. Might be interesting.
I get BBC Wales as Shaftesbury is high up. The transmitter is 52 miles away which theoretically is out of range. The Somerset levels help. I often watch BBC Wales. I feel better informed when I do.
A waste of such big transformers though. The standard JLH 10-watter needs only 120VA for a stereo amp driving 8 ohm speakers and there you have 400+400. Even a beefed-up version would have oodles of overkill capability with just a single transformer.
I like the idea of dual mono amplifiers though. It usually affords some emphasis to stereo effects and the extra care required to separate the grounds of each channel definitely improves the imaging, noise perception and low level sounds etc. I guess that's another topic and I haven't tried it with any JLH design myself but I would look around for a 120-160VA 18+18V transformer or 2 x 9+9V 80VA versions for a more appropriate build.
Sadly, some fool committee decided we don't need stock transformers with windings between 18 and 25VAC anymore. Well, that also means no unregulated DC power rails between 25 and 35V anymore. Ridiculous, I say
I like the idea of dual mono amplifiers though. It usually affords some emphasis to stereo effects and the extra care required to separate the grounds of each channel definitely improves the imaging, noise perception and low level sounds etc. I guess that's another topic and I haven't tried it with any JLH design myself but I would look around for a 120-160VA 18+18V transformer or 2 x 9+9V 80VA versions for a more appropriate build.
Sadly, some fool committee decided we don't need stock transformers with windings between 18 and 25VAC anymore. Well, that also means no unregulated DC power rails between 25 and 35V anymore. Ridiculous, I say
Last edited: