Sound Quality Vs. Measurements

Status
Not open for further replies.
For now 7 A is enough. The speaker is 4R pure resisitve. I will measure it one day. For now I believe it. I will use +/- 33.5V for now. If I made this for a friend I would go more on volts and current. For my needs this should be 4 times more powerful on transients than I have.

The transitors you listed for once give a realistic i max at 3 amps ( 15 amps standard statement ). As I run at a much lower voltage I might optimistically say 5 amps. 7 amps peak is 3.5 amps per device. With real music I supect this could be made 16 amps for double devices if peak. A LED would hit about that point if my maths OK for the simple protection circuit? Circa 8 A if to the original recipe when LED. 3 x 1N4148 = 8.5 amps. Take the difference to be 0.2V. Re Quad is 0R33, mine 0R15 and 0R15 to each device.

One thing that has come from this. FT might be higher if double devices at nomal loud levels ( 2 amps peak ). The Ft of the device I have bought is 6 MHz typical. 2.5 MHz minimum and 18 MHz at 1 amp. Something like the old BDY56. Cob is stated and is slightly lower if voltage is higher. A risky game that one. Maybe Dejan that's the magic of the multiple and not the exit current ? The Naim of old was very sweet. It was BDY56.

BTW. MJ115003 looks fantastic for the price asked. If wanting a truely 1967 sound it should be excellent. Ft > 2.5 MHz and 20 amps .
 
....On the other side of the scale, we have the Otala/Lohstroh amp, modestly powered at 25/50W into 8/4 Ohms, ultra wide bandwdith, and with an unusually high bias current of 300 mA per output device, or 600 mA for the whole. The argument there is that with such a high qiescent current (2.9/5.8 W into 4/8 Ohms), the listener will in fact spend around 98% of his listening time in pure class A, leaving it only for the worst of transients. Their emitter resistors were 1 Ohm/5W. VAS current was 20 mA, also rather high.
Have you heard/spent time with one of these ?.

Dan.
 
Have you heard/spent time with one of these ?.

Dan.

Worse, Dan, I had built one and lived happily with it for around 6 years. Then something possessed me to sell it off, easily the most stupid thing I have ever done. No other amp I have ever heard came as near to the ideal of a wire with gain as that one.

So I must atone for my stupidity then ny making a new one. I hope to have the boards ready in about a month's time or so, including the greber files. Whne I do, build it and make sure it works, I will send then to anyone interseted.

That is the ONE to be used as THE yardstick, trust me on this.
 
Have you heard/spent time with one of these ?.

Dan.

Worse, Dan, I had built one and lived happily with it for around 6 years. Then something possessed me to sell it off, easily the most stupid thing I have ever done. No other amp I have ever heard came as near to the ideal of a wire with gain as that one.

So I must atone for my stupidity then ny making a new one. I hope to have the boards ready in about a month's time or so, including the greber files. Whne I do, build it and make sure it works, I will send then to anyone interseted.

That is the ONE to be used as THE yardstick, trust me on this.
 
Have you heard/spent time with one of these ?.

Dan.

Worse, Dan, I had built one and lived happily with it for around 6 years. Then something possessed me to sell it off, easily the most stupid thing I have ever done. No other amp I have ever heard came as near to the ideal of a wire with gain as that one.

So I must atone for my stupidity then ny making a new one. I hope to have the boards ready in about a month's time or so, including the greber files. When I do, build it and make sure it works, I will send then to anyone interseted.

That is the ONE to be used as THE yardstick, trust me on this.
 
Nige, you are being pig headed about this. For some incomprehensible reason, you have locked on to Quad 33 amp, as if it was some great achievement. It was not, might have been different from the majority of its time, but really no better. Do as you please, but I cannot understnd why you insist on doing one job twice, I do not understsnd why are you locked to the measily +/-33V of psu lines, I do not understnd why you don't use at least two pairs of power devices per channel, nor anything else. To me, it seems like a damn waste of time, I'd do it once and for all, never below +/- 52V, to obtain a decent 100W/8 Ohm amp. What is the point of using low supply voltage? Are you trying to prove something?
 
o as you please, but I cannot understnd why you insist on doing one job twice, I do not understsnd why are you locked to the measily +/-33V of psu lines, I do not understnd why you don't use at least two pairs of power devices per channel, nor anything else. To me, it seems like a damn waste of time, I'd do it once and for all, never below +/- 52V, to obtain a decent 100W/8 Ohm amp. What is the point of using low supply voltage? Are you trying to prove something?
This will amuse, and horrify, some people - when I did my LM38xx gainclone I ran them on 40.5V rails - I think it was that - just a volt and a two under the absolute max. How did I get away with it? By using very stringent regulation, the rails were locked to that voltage, no matter what the games the mains were playing.

I wanted to get maximum grunt for my money, and that's what it delivered - no trouble doing a full blast drum solo, that sort of thing; the only issues were thermal overload, when extreme, sine wave like music moments came along, at full volume ... ;)
 
Jay, I am unaware of any assymetrically fed amps, by Otala or anybody else.The one I refer to is the original Otala/Lohstroh amp as publushed in 1973 in IEEE.

AES, perhaps, for Otala Lohstroh amp.

The asymmetrical one was like a printed image, so maybe AES, I think it is the original. What I have built is I think an implementation by Electrocompaniet. But I can't check it right now.
 
Nige, you are being pig headed about this. For some incomprehensible reason, you have locked on to Quad 33 amp, as if it was some great achievement. It was not, might have been different from the majority of its time, but really no better. Do as you please, but I cannot understnd why you insist on doing one job twice, I do not understsnd why are you locked to the measily +/-33V of psu lines, I do not understnd why you don't use at least two pairs of power devices per channel, nor anything else. To me, it seems like a damn waste of time, I'd do it once and for all, never below +/- 52V, to obtain a decent 100W/8 Ohm amp. What is the point of using low supply voltage? Are you trying to prove something?

Nigel is apparently on a mission to repay a favour to John Ellis. They have a mutual interest in the Quad 303.
 
At first, I was delighted to hear that Nige is about to make his own amp, I think it was about time, too. Now, we all know that increasing power rarely boils down to just increasing PSU line voltage, other things almost always need to be reconsidered and reworked, which I see as additionl work for which there is simply no need. Also, right or wrong, I believe an ideal power level for a home power amp is 100W/8 Ohms, usually more than enough to do the job well. So I fail to understnd why first make a low power model, and then have to rework it all over again, and if the power goes up, then the outut stage will need, at the very least, two pairs of those 250W devices, a different driver, so a whole set of different olution. Why? What's the point?
 
At first, I was delighted to hear that Nige is about to make his own amp, I think it was about time, too. Now, we all know that increasing power rarely boils down to just increasing PSU line voltage, other things almost always need to be reconsidered and reworked, which I see as additionl work for which there is simply no need. Also, right or wrong, I believe an ideal power level for a home power amp is 100W/8 Ohms, usually more than enough to do the job well. So I fail to understnd why first make a low power model, and then have to rework it all over again, and if the power goes up, then the outut stage will need, at the very least, two pairs of those 250W devices, a different driver, so a whole set of different olution. Why? What's the point?

That is a question for Nigel to answer however he mentioned in an early episode in the continuing story that he had been given a transformer which he is using for this project - we know the rating is 500 V.A. but not the secondary winding voltages, probably enough to power a 303 from a regulated power supply - also that he was given some 0.2 degree C per watt heat sinks. He also planned to use bits he already had and had only spent 40 pounds.

Nigel's friend John Ellis has an Amcron amplifier and wants something less powerful for his children's entertainment needs.
 
Last edited:
The asymmetrical one was like a printed image, so maybe AES, I think it is the original. What I have built is I think an implementation by Electrocompaniet. But I can't check it right now.

Ooops I mixed things up. The Electrocompaniet version is the one with asymmetrical supply rail (+/-26 for output, +19/-44 for front end).
 

Attachments

  • Otala_EC25.png
    Otala_EC25.png
    78.8 KB · Views: 131
Dejan. I totally agree. There is a plan B. That is to buy or better still be given a 1000 VA 0-35 0-35. I am 90% sure Loricraft Audio have one I can have made by Carnhill years ago. We called it the Dundee cake. It was for a PSU we called Magnox ( 400VA pure 50 Hz ). Like the Isotek Genisis. So funny you said Hinkley Point as it was a Magnox type reactor like Sizewell A. You may not realise electrical power is my employment although not power stations, very boring stuff. The Magnox was about -52 dB distortion full load. My experiance says that's as good as you need and anthing better is silly money for a regenerator. I did not have the voltage regulation of that other design although I did perfect a JFET circuit to do it. Adding it required going to a 12 pole filter as the JFET hurt the distortion badly just to keep the ill imformed happy over voltage. None were sold.

I also feel very guilty over how Quad were treated years ago. Out of a need to be noted I tended to be as bad as anyone to knock them. This amplifer project is a fantasy that I could have made a difference. Worst of it is I do have many ideas for a designs and I should not be doing this. As you know I did draw up a 1000 watt version for parts I have that is DC coupled. It resembles your desings as I can not get transitors that do what I want at the voltages that I want to use ( 0- 55 0 - 55 V 2000VA ). Thus I must use a cascode ( BC337-40 and MPSA42 or better x 2 ). I will take everything out that I can, that is understood. If the longtail pair with resistor tail do not be surprised. I will use a current mirror ( I have no choice as it will need to slew very hard ), double VAS with second current mirror. DC offset < 50 mV with no servo. Fetlington output using 250 V FET and Bipolar. I suspect the MJ's you recomend. The Fetlington needs some thinking to be sure it wouldn't be better as all FET. The problem is I don't need this power. My boss said he would like one so perhaps.

Some very good news. The 500 VA 0- 25 0 -25 for the Quad clone is 76V off load. That should be OK to give 67V. It might need to go down a notch. The good news is I will have a good 400 VA to use. Assuming 50 % for a class AB that is bang on target. In transient terms the 200 VA is possible. The transformer already blows 5 A mains fuses, that's typical of many ( early saturation I guess due to my 243V ). I am lucky to have between 238 and 243V as without that the voltage is too low. Finger crossed I am right. The Quad did not hum too badly when the regulator failed hard on ( very rare ). There is scope to not use the regulator.

I can not afford posh capacitors. I have 6 x 4700 uF of about 5 amps ripple current. If a +/- supply that would be 12 x 10 000 uF. That is > 6 greater than the 303. I have bought some 100 uF 100 V high grade for the 303 bootstrap. I have bought some spares for the PSU. My dilema is do I tie them to -ve or nominal 0V. There are arguments both ways. Nominal zero I guess. I have some 4.7 uF 250 V polyester also to use.

The original 303 used Iskra resistor. I have bought some Iskra pots in rememberance of that. They will be replace by fixed reistors once settings known.
 
Last edited:
Status
Not open for further replies.