I recall a couple of friends constructing a pair John Linsley Hood integrated stereo amp kits in the early/mid 70s. They were solid state and somewhere in the region of 50-70w, and included (I think) a parametric tone control. I think the articles appeared in Wireless world, but I could be wrong. A search of the web came up with the "Direct-Coupled High Quality Stereo Amplifier" but I can't be sure if this was the one. At the time we thought they were the 'ants pants', but remember ....this was the 70's!
Anyway, my questions are....
Does anyone have more details?
Can anyone comment on the performance of the amp?
Cheers,
Kim
Anyway, my questions are....
Does anyone have more details?
Can anyone comment on the performance of the amp?
Cheers,
Kim
You will find an (almost) complete list of JLH articles on my website:
http://www.tcaas.btinternet.co.uk/jlharticles.htm
The 'Direct-Coupled High Quality Stereo Amplifier' was published in Hi-Fi News and Record Review between Nov '72 and Feb '73. I have a copy of the power amp schematic but unfortunately not the full article. This amp used a BJT output stage and was rated at 75W.
As you will see from the list of articles, there were later designs with a similar power rating but using a MOSFET output stage published in WW and ETI in the early '80s.
http://www.tcaas.btinternet.co.uk/jlharticles.htm
The 'Direct-Coupled High Quality Stereo Amplifier' was published in Hi-Fi News and Record Review between Nov '72 and Feb '73. I have a copy of the power amp schematic but unfortunately not the full article. This amp used a BJT output stage and was rated at 75W.
As you will see from the list of articles, there were later designs with a similar power rating but using a MOSFET output stage published in WW and ETI in the early '80s.
Yes, Geoff's right Re: reference. (A) it didn't have a parametric tone control. But it wasn't a completely conventional tone control either. The difference was that JLH included switched capacitors to allow the turn over frequencies to be varied. Other than that it was a classic Baxandall feedback type. (B) performance. JLH always placed a high premium on stability and square wave performance. It had low THD, good stability. The other feature is that he used a shunt feedback RIAA circuit that seems to get better response from listeners that the series type.
It would still sound good in the 21st Century!!!
Kimbo, I've just reviewed your post and notice that you live in Melb'. I see also that you are "incomunicado" via email. But as an ex-Melbournian (and Essendon fan) can I ask that you contact me via my email (bright@gil.com.au) and, as they say in the movies "you will learn something to your advantage". Just a hint. None of the Melb' libraries carry back copies of HFN/RR that go back that far (bitter experience)..........but "Brisvagas" does (deep joy)......
Jonathan Bright
It would still sound good in the 21st Century!!!
Kimbo, I've just reviewed your post and notice that you live in Melb'. I see also that you are "incomunicado" via email. But as an ex-Melbournian (and Essendon fan) can I ask that you contact me via my email (bright@gil.com.au) and, as they say in the movies "you will learn something to your advantage". Just a hint. None of the Melb' libraries carry back copies of HFN/RR that go back that far (bitter experience)..........but "Brisvagas" does (deep joy)......
Jonathan Bright
EUVL said:
Patrick
Done (plus one or two others
)http://www.tcaas.btinternet.co.uk/index-5.htm
Geoff
I am still doing it.... not entirelly ready
The medium power transistors are not the correct ones...they are soldered into the place were i will pick wires to solder the correct transistors into a heatsink's flat surface.
Some parts are missed and the circuit will receive double check before receive power...next week probable.
A friend told me that this amplifier sound very good.
regards,
Carlos
The medium power transistors are not the correct ones...they are soldered into the place were i will pick wires to solder the correct transistors into a heatsink's flat surface.
Some parts are missed and the circuit will receive double check before receive power...next week probable.
A friend told me that this amplifier sound very good.
regards,
Carlos
Wires will be soldered were you see medium power transistors
They will travel less than 2 inches to be soldered ...the medium and power transistors will be over a flat heatsink surface.
The board, as have nothing in the other side...no electrical connection, will be glued into the heatsink surface.
Fast way to do things...to listen as soon as possible.
regards,
Carlos
They will travel less than 2 inches to be soldered ...the medium and power transistors will be over a flat heatsink surface.
The board, as have nothing in the other side...no electrical connection, will be glued into the heatsink surface.
Fast way to do things...to listen as soon as possible.
regards,
Carlos
I was listening to it carefully..it is good..but not so good!
I have spent two hours listening carefully after a very easy
adjustment made…. the amplifier seems to be something
alike “plug and play”…very easy to remove offset (3 mV)
and to adjust current (130 mA my choice).
It has power, but do not goes very low in bass response, at
least nothing that I can compare with GEM designs, from
Graham Maynard… the input condenser was increased to
10 uF trying to obtain more bass…the feedback line
condenser was also changed in value….negative to obtain
really deep bass…it seems to have some loss around 35
Hertz.
Treble also did not show any special quality…a very standard
reproduction, remembering those systems we find everywhere,
not a top performer as Aksa 55 and others units for audiophiles.
Dinamics did not touch Symassym….. well, it seem to be a
little compressed…. diferences in volume from pianissimo
to fortissimo will make you angry.
Also power nothing special… with same voltage Holton amplifer
was a room shacking unit.
I switch to those amplifiers and I perceive that GEM and Aksa made me feel that I was more near the orchestra…more real reproduction, being GEM incredible with voices and Aksa Nirvana incredible with treble.
Also my P3A from Rodd have eated this one in the breakfast.
I am sorry guys..it is a JLH…and I also have enormous respect for
John hood….but….really….. only common, standard and good..
nothing special on it.
I have used the same supply, the same audio source and the same speakers to the audition.
Also transistors in the audio patch were the same used to Aksa, Symassym, Gem and P3A…. with Holton as exception using Lateral Fets.
Well…. Using same supply and some parts I can remove my suspections about influences of this or that…. also the same power level…and same audio source.
Vbes normal…no oscilation… easy to adjust…. run cool… good sensitivity…low noise and reduced distortion… the protection was disabled.
It is good…no doubts…but nothing very special.
Carlos
I have spent two hours listening carefully after a very easy
adjustment made…. the amplifier seems to be something
alike “plug and play”…very easy to remove offset (3 mV)
and to adjust current (130 mA my choice).
It has power, but do not goes very low in bass response, at
least nothing that I can compare with GEM designs, from
Graham Maynard… the input condenser was increased to
10 uF trying to obtain more bass…the feedback line
condenser was also changed in value….negative to obtain
really deep bass…it seems to have some loss around 35
Hertz.
Treble also did not show any special quality…a very standard
reproduction, remembering those systems we find everywhere,
not a top performer as Aksa 55 and others units for audiophiles.
Dinamics did not touch Symassym….. well, it seem to be a
little compressed…. diferences in volume from pianissimo
to fortissimo will make you angry.
Also power nothing special… with same voltage Holton amplifer
was a room shacking unit.
I switch to those amplifiers and I perceive that GEM and Aksa made me feel that I was more near the orchestra…more real reproduction, being GEM incredible with voices and Aksa Nirvana incredible with treble.
Also my P3A from Rodd have eated this one in the breakfast.
I am sorry guys..it is a JLH…and I also have enormous respect for
John hood….but….really….. only common, standard and good..
nothing special on it.
I have used the same supply, the same audio source and the same speakers to the audition.
Also transistors in the audio patch were the same used to Aksa, Symassym, Gem and P3A…. with Holton as exception using Lateral Fets.
Well…. Using same supply and some parts I can remove my suspections about influences of this or that…. also the same power level…and same audio source.
Vbes normal…no oscilation… easy to adjust…. run cool… good sensitivity…low noise and reduced distortion… the protection was disabled.
It is good…no doubts…but nothing very special.
Carlos
Hi Carlos
I'm sorry you were disappointed in your JLH. There are some ways to improve it. I hope we are talking about the one Geoff posted showing BDY56 outputs?
First, the compensation capacitor of 220 pF is too large for the feedback resistor. The combination with 22k gives a -3dB of 33 kHZ.
That is pretty ordinary 1970's for you.
Secondly the gain improvements by using a Darlington VAS are limited by the use of a 4.7k ohm, as Self explained.
I think that a few tweaks will significantly improve the performance.
If the resistors R3, R4 and C3, C4 are removed and a current mirror put in their place, the open loop gain will be much higher and distortion will become reduced as a result.
The input resistor of 330kohms unbalances the input. R1 should be 10k , R2 2kohms and to balance this, R10 (the feedback) should be 12 kohms. The feedback decoupling resistor can be 330 ohms (use this instead of 680 for R9).
C7 can be 470 uF to boost the bass. I'd use a 10 uF electrolytic on the input.
The feedback compensation capacitor should be around 33 pF with 12 kohm to give a 2000's standard 10 MHz closed loop response (not taking the input filter into account).
Finally, the bootstrap should be replaced by a CCS.
I've outlined the changes in this circuit below.
Some notes: with a current mirror, the absolute current in the input CCS is no longer critical. You can keep JLH's FET if you prefer, but I've shown my preferred CCS.
I've not shown any protection circuits. I would recommend adding a couple of diodes or a transistor at the base of the VAS (BD139), and keeping JHL's protection transistors, but add series diodes in the collectors and remove R22, R25 series resistors.
I'm not sure, but in an overload these may actually allow one half to reverse bias the other and exceed Vebo limits. I need to check this.
Of all the suggestions I've made, the most important would be to change the feedback compensation capacitor to give a better frequency response.
CIrcuit shown below simulated OK, but I can't guarantee that it won't oscillate!
The additional capacitor 680 pF is in keeping with JLH's design approach. I hope he would approve.
cheers
John
I'm sorry you were disappointed in your JLH. There are some ways to improve it. I hope we are talking about the one Geoff posted showing BDY56 outputs?
First, the compensation capacitor of 220 pF is too large for the feedback resistor. The combination with 22k gives a -3dB of 33 kHZ.
That is pretty ordinary 1970's for you.
Secondly the gain improvements by using a Darlington VAS are limited by the use of a 4.7k ohm, as Self explained.
I think that a few tweaks will significantly improve the performance.
If the resistors R3, R4 and C3, C4 are removed and a current mirror put in their place, the open loop gain will be much higher and distortion will become reduced as a result.
The input resistor of 330kohms unbalances the input. R1 should be 10k , R2 2kohms and to balance this, R10 (the feedback) should be 12 kohms. The feedback decoupling resistor can be 330 ohms (use this instead of 680 for R9).
C7 can be 470 uF to boost the bass. I'd use a 10 uF electrolytic on the input.
The feedback compensation capacitor should be around 33 pF with 12 kohm to give a 2000's standard 10 MHz closed loop response (not taking the input filter into account).
Finally, the bootstrap should be replaced by a CCS.
I've outlined the changes in this circuit below.
Some notes: with a current mirror, the absolute current in the input CCS is no longer critical. You can keep JLH's FET if you prefer, but I've shown my preferred CCS.
I've not shown any protection circuits. I would recommend adding a couple of diodes or a transistor at the base of the VAS (BD139), and keeping JHL's protection transistors, but add series diodes in the collectors and remove R22, R25 series resistors.
I'm not sure, but in an overload these may actually allow one half to reverse bias the other and exceed Vebo limits. I need to check this.
Of all the suggestions I've made, the most important would be to change the feedback compensation capacitor to give a better frequency response.
CIrcuit shown below simulated OK, but I can't guarantee that it won't oscillate!
The additional capacitor 680 pF is in keeping with JLH's design approach. I hope he would approve.
cheers
John
John Ellis.....your amplifier is much better...what a difference.
This one you are showing will beat the original design very easy.
I made modifications trying to increase...i could not.
Please, Graham Maynard wants to have your personal mail adress...can you please contact me to give you his adress and to capture yours.
nanabrother@yahoo.com
regards,
Carlos
This one you are showing will beat the original design very easy.
I made modifications trying to increase...i could not.
Please, Graham Maynard wants to have your personal mail adress...can you please contact me to give you his adress and to capture yours.
nanabrother@yahoo.com
regards,
Carlos
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