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Old 1st October 2004, 10:46 PM   #981
eLarson is offline eLarson  United States
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Tim,

Are you using the circuit of figure 3 on http://www.tcaas.btinternet.co.uk/jlhupdate.htm then? If so, did you return to using C4 (the 470uF feedback cap)?

Erik
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Old 2nd October 2004, 10:33 AM   #982
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Erik,

I am still using the circuit shown in fig. 2 at http://www.tcaas.btinternet.co.uk/jlhupdate.htm
As the Quad ESL-57 will arc with inputs over 36V the ‘limited’ JLH output using +/-17.5V rails provides useful protection and is more than adequate to drive my ESLs to ear-splitting levels. I should add that I have rebuilt my ESLs and they are up to spec. This cannot be said for many (perhaps the majority of) ESL-57s in original condition that are probably working well below their specified efficiency and therefore may benefit from a larger amplifier. Certainly those that I have encountered in original condition all sadly fit this description, being noticeably inefficient.

Due to its sonic colouration I would be most reluctant to refit the feedback capacitor (though the reduced offset variation would not be unwelcome). I have ‘problems’ with most capacitors and find that lower values of capacitance (where realisable) with lower rated voltages (hence a smaller capacitor with more closely spaced electrodes and less dielectric area) sound better. To this end I use a small 100nF polystyrene on the JLH input and a separate active subwoofer for the bottom octave.

Tim.
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Old 3rd October 2004, 06:08 AM   #983
AX816 is offline AX816  Romania
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The 3055 are as old as my grandma' ...but in all the 3055 based schematics i've used with great success Sanken bipolars as 2sc2922 2sc2837.For more suggestive info:
http://www.ampslab.com/components_power.htm
where u can find an entire list of posiible replacements for those old 3055.Though 2sc2922 is a 200w bip ..has the cutting frequency at about 40Mhz wich should provide for most of the audio applications the most desired 'transient response'.
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Old 3rd October 2004, 09:34 AM   #984
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Default 2SC2922 are my test transistors too

They are very good to dissipate heat, as they have a great metal contact surface and very good current, voltage and frequency capacities.

I use the complementary too to simetrical amplifiers.

Elected the 2N5401 as input differential when testing "standard" amplifiers.

But discover that some 2C2922 are fake, Rodd Elliot published some comparison pictures, and discover also that they have not a flat surface to touch the heathsinks.

I order a flat block of inox steel metal, guaranteed flat by machines.... over them i use a grain 500 metal sandpapper, the one you use with water.... when you start to sand the under chromium finished surface..you will see that some parts will appear copper collor and others will keept the chromium finishment.

As you already notice, the chromium parts are not touching the sand paper and the metal as consequence...this way, you have some bubble of air if not sanded, that air bubble can be filled by heat compound grease or not, depends of the ammount you use and if you go directly to the point.... if you move the transistor rigth, left, up or down.....material is removed and the air bubble appear immediattely..... this motion is sometimes needed to center the transistor holes, related the screw pieces made on heatsink surface. the grease must splash outside, and in every part of the contour.... around the perimeter.

You can remove the excess with cotton wab... or some papper, also can use soft cloth dampened with some petrol chemical solution used to clean paint brushes.

Mine 2SC2922 is considered "the one" to experiments, as he can support a very big base to emitter voltage without burn... and enormous current for small instances...i made some 35 amperes passing inside once.... very small time... the time fuse oppened...and the transistor survive.

It is very good to people alike myself, that always made mistakes when assembling, sending crazy voltages to the poor output transistors.

If we can say that transistor have their own sound.... i do not believe that, but as some people think that way, and i am not God to say if true or not true!....this transistor left pass to speaker a very good and clear hi frequency.

regards,

Carlos
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Old 4th October 2004, 07:27 AM   #985
ralf is offline ralf  Germany
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Default Re: For driving 2 ohms

[QUOTE]Originally posted by EUVL
[B]> best to design it with lower voltage rails and a higher current

I have done this (JLH latest upgrade from Geoff's website) without problems -- +/-12V, 2.5A bias. I was using two of these to drive a 8 ohm (nominal) speaker in bridged mode using balanced input from a phase splitter (see JLH letter 1970, Fig. 4, I think).

+/- 12 Volts?

what does the others think about this power supply?
Does this amp really work properly with such low power supply?
What are the postitve and negative viewpoints in low supply?
When i hear +/- 12 V i think of Battery supply...

greets,
Ralf
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Old 4th October 2004, 07:33 AM   #986
ralf is offline ralf  Germany
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Default JLH Power supply

Hi,

a question in Power supply:
i have build my JLH update with capacitance multiplier.
I have diferent speakers:
with speaker-sensitivity at 87db the speaker is dead quiet,
with speaker-sensitivity at 96db you can hear little noises in tweeter and little hum in midrange-speaker.
with speaker-sensitivity at 105db you can hear hum at the place, where i hear music.

How can i modify the PSU, that i can reduce the hum -further?
Does battery supply generate any noise?

thanks,
Ralf
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Old 4th October 2004, 09:26 AM   #987
AX816 is offline AX816  Romania
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.....Does battery supply generate any noise?
Depends...type of the battery...component associations ,and many other aspects.The upper side of this low voltage solution is an overall low el-mag field interferrence....though the frequency response will suffer.To reduce the power supply parasites interference u can use different types of filters based on the frequency range that is to be cut.Or as a last resort u may get it stabilised using an old fashioned pair of LM7812-LM7912 eachone enhanced with a correspondent bip transistor for high current usage.This solution should provide u with a healthy 12v differencial power supply at 2 to 4 amps per each arm....but this solution will cost u on the thermal side.As a last resort u can change the transformer to a better model....or u can manufacture it by yourself.If u're interrested i'll give u a range of PSU filters and the math to calculate them...Anyway ...some time ago a saw an article that offered the mathematical link between the S/N ratio Slew Rate and the PSU filtering capacity .....i'll ook over it and bring it about later.
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Old 4th October 2004, 09:34 AM   #988
EUVL is offline EUVL  Europe
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Default Cap Multiplier

> How can i modify the PSU, that i can reduce the hum -further?

Add a pi (CLCLC) filter after the multiplier for Hum (100Hz) reduction without additional voltage drop. Or use a voltage regulator, which will take care of low frequency noise, at the expense of 5V drop and more heat dissipation.

>Does battery supply generate any noise?

Battery is the quietest you can have (and I know I am inviting lots of comments with this statement), but you need special deep-discharge battery types as used in Car HiFi, but they cost 400 Euro a piece (12V, 75AH), and I guess you need at least 4 ??

(Ordinary car batteries can only be discharged repeatedly up to 50% or less, so I was informed. Otherwise 4 of those at say 50 Euros each is probably one of the cheapest PSU you can get.)

That is the cost of Class A -- heatsinks and power supplies cost much more then the circuit, even with Vishay S102's and what not.


Patrick
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Old 4th October 2004, 09:45 AM   #989
EUVL is offline EUVL  Europe
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Default +/- 12V

Ralf,

> +/- 12 Volts?

Why not ? Hundreds of people are building Aleph-X with 4A bias at +/-15V, and they lose at least +/-4V at the output for Vgs (Mosfet).

With BJT, you can run them quite happily with 2V Vbe, so you get effective output of +/- 10V. But since I was bridging, the speaker sees +/-20V. And that would be enough voltage even at 5A bias.

> Does this amp really work properly with such low power supply?

I have been listening to one for the last year -- firstly on its own with low bias (2A) and then in bridged mode with 4A bias. Don't trust me, try it for yourself.

> When i hear +/- 12 V i think of Battery supply...

Well, you get the point.

Kaufst Du doch ein paar von Autoteile Unger, und probier mal aus. Sollte es Dir nicht gefallen, hast Du immer 2 Batterien fuers Auto oder Vorstufe. : )


Patrick
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Old 4th October 2004, 09:37 PM   #990
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Hi Ralf,

Completely removing hum from a JLH class-A is not difficult.

A simple series 1 ohm resistance filter with additional 10,000uF power rail capacitor will reduce 100Hz power rail ripple by approx 16dB or a factor of 6.

With a single power rail version the induced hum arises as it comes through the bootstrap and into the output stage w.r.t. (limited) NFB loop generated output terminal impedance.

Another way of reducing this hum at much less cost than using an additional electrolytic, is to optimally minimise it by connecting a high value resistor directly between the +ve power rail and the emitter of the first transistor.
The value I used was 820k, but it could be anywhere between 220k and 2.2M ohms depeding on devices, input filter/impedance etc. There is nothing to lose by trying this; it does not upset the biasing in any way, nor feed other noise into the amplifier, simply try different values until the best quietening can be acheived. This might be hard to believe, but it can work, and even with a simple bridge plus single electrolytic psu.

A third way involves phase nulling and this can acheive perfect hum quietening. Try say 27k connected to the +ve power rail; 270k connected to the emitter of the first transistor; a 5 to 10% tolerance 22nF capacitor connected to signal ground. When all three component leads are brought together the hum should be tuned completely away, though slight component value adjustment might be necessary for perfect hum nulling.

If your JLH amplifier is additionally driven by a low impedance source or pre-amplifier, as was recommended by JLH himself, then your amplifier should be virtually silent, even with your 105dB sensitive loudspeaker.

This was one thing I loved about my early JLH's; - if there was any noise then it came from the source, not the amplifier !!!

If this challenges you enough to give it a try, do please let us know how you get on.

Cheers ............. Graham.
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