Hi, how is everyone?
I am purchasing a 1980s Hitachi integrated amplifier, model HA-6. It is in fine condition and was checked out by a stereo tech.
Has anyone used an amp from this line? It has liquid cooled heatsinks and the front panel says something about being 'optimized for digital recordings'. There is not much info available about this piece, besides that it outputs 100WPC @ 8.
Any information you could provide regarding its design would be appreciated.
Thank you
I am purchasing a 1980s Hitachi integrated amplifier, model HA-6. It is in fine condition and was checked out by a stereo tech.
Has anyone used an amp from this line? It has liquid cooled heatsinks and the front panel says something about being 'optimized for digital recordings'. There is not much info available about this piece, besides that it outputs 100WPC @ 8.
Any information you could provide regarding its design would be appreciated.
Thank you
Does anyone know what Hitachi means by "Pure Drive"?
On the front bezel there is an illuminated Pure Drive emblem and it also states in text, " Pure Drive low impedance volume control circuit ensures optimal signal characteristics for use with digital audio components".
Is this a digital volume control, even though it uses a standard potentiometer?
On the front bezel there is an illuminated Pure Drive emblem and it also states in text, " Pure Drive low impedance volume control circuit ensures optimal signal characteristics for use with digital audio components".
Is this a digital volume control, even though it uses a standard potentiometer?
Probably marketing speak for compatible with standard red book CD player output levels, the older IHF line level standard at 700mVrms meant in some instances low level circuitry could be overloaded ahead of the volume control (tone amps, tape buffers) by the then new CD player.
I remember making a lot of pads for friends when they got their first cd players.
I remember making a lot of pads for friends when they got their first cd players.
Hi,
It almost certainly means a low impedance volume pot and
bypassing the linestage for the CD input, "source direct".
It is essentially a passive preamp for the CD input.
rgds, sreten.
Interesting information, thank you.
Having just replaced my speaker wiring to true 12awg bi-wires, and splurging for quality interconnects, this ampli sounds very pleasing to my ear.
It does run pretty warm, so I am careful about not covering the top and not running 4-ohm nominal loads with it. If you press an ear to the top of the case, the sound of the heatpipe cooling is apparent. Luckily it is silent at a distance of 2 feet away.
Wish there were affordable commercial amplifiers built to this level today.
A quick turn of the tone controls and loudness and the thing sounds like it has hundreds of watts available, even though it is 100w.
Having just replaced my speaker wiring to true 12awg bi-wires, and splurging for quality interconnects, this ampli sounds very pleasing to my ear.
It does run pretty warm, so I am careful about not covering the top and not running 4-ohm nominal loads with it. If you press an ear to the top of the case, the sound of the heatpipe cooling is apparent. Luckily it is silent at a distance of 2 feet away.
Wish there were affordable commercial amplifiers built to this level today.
A quick turn of the tone controls and loudness and the thing sounds like it has hundreds of watts available, even though it is 100w.
I have a SEARS labeled dual mono MOSFET power amp that satisfies that criterion.
dave
Hi, I have obtained the service manual for the HA-6 (also known as the "Lo-D HA-505") And there seems to be a misprint in the manual.
It says to set idle current at 6.6mV +/-2.2mV, on each channel's emitter resistors.
I have set it at 7.0mV each side, Does this seem correct? The output devices are complimentary 2SC3280 and 2SA1301 .
Amp sounds fine at the 7.0mV setting.
It says to set idle current at 6.6mV +/-2.2mV, on each channel's emitter resistors.
I have set it at 7.0mV each side, Does this seem correct? The output devices are complimentary 2SC3280 and 2SA1301 .
Amp sounds fine at the 7.0mV setting.
Considering the specification is 6.6 plus or minus 2.2mV, a setting which is +0.4 mV is just fine.
The problem with measuring the minute voltage with such precision, is in the accuracy capabilities of handheld DMMs and the precision of relevant components in the amp. At an implied resolution of 0.00005V, these determine whether such readings would even be meaningful.
The problem with measuring the minute voltage with such precision, is in the accuracy capabilities of handheld DMMs and the precision of relevant components in the amp. At an implied resolution of 0.00005V, these determine whether such readings would even be meaningful.
Hi, Mr. Finch, I have verified the readings with a VTVM made by Simpson and my DMM with fresh batteries. However, I meant, the 6.6mV seemed very light for an amplifier with such a large power supply and 100 WPC at 8 ohms. Someone earlier in the thread mentioned 50mA..not sure what voltage that would correlate to.
Bias may be low by today's standards but this was common in the 1980s when most Japanese amps ran quite cool and heatsinks and chassis vents were designed accordingly. 0.22R emitter resistors are apparent in wahab's pic, which indicates ~30mA is the bias or idle current. It would be uncertain what might happen to thermal stability and the temperature inside the case, if bias were raised to say 120 mA, the level for optimum class AB operation of EF design output stages.
I would emphasize keeping to original spec. conditions because the thermal compensation scheme looks unusual too. Hitachi used some odd thermistor arrangements for compensation in their amplifiers of all types, which were not simply controlled with a bias controller/sensor transistor. I don't have the schematic to support this, but in the pic, there do appear to be thermistors located immediately in front of each bias controller transistor on the heatsink mounting plate - that's a sign.
Whatever the popular opinion and desire is to raise bias as matter of principle, I'd consider the likely temperature problems first. Stay with the designed specification unless there is good reason and evidence it will remain thermally stable in use, since nobody needs a smoking amp. For interest, the voltage measured across an output transistor's emitter resistor would need to be increased to 50/30 x 6.6 = 11 mV for 50mA bias current.
I should have simply said earlier that it doesn't matter how good your measuring accuracy is if the emitter resistors plus other circuit resistances are only 5-10% precision. However, as you say, this wasn't your real concern.
I would emphasize keeping to original spec. conditions because the thermal compensation scheme looks unusual too. Hitachi used some odd thermistor arrangements for compensation in their amplifiers of all types, which were not simply controlled with a bias controller/sensor transistor. I don't have the schematic to support this, but in the pic, there do appear to be thermistors located immediately in front of each bias controller transistor on the heatsink mounting plate - that's a sign.
Whatever the popular opinion and desire is to raise bias as matter of principle, I'd consider the likely temperature problems first. Stay with the designed specification unless there is good reason and evidence it will remain thermally stable in use, since nobody needs a smoking amp. For interest, the voltage measured across an output transistor's emitter resistor would need to be increased to 50/30 x 6.6 = 11 mV for 50mA bias current.
I should have simply said earlier that it doesn't matter how good your measuring accuracy is if the emitter resistors plus other circuit resistances are only 5-10% precision. However, as you say, this wasn't your real concern.
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Had to repair a Sears integrated amplifier imported to Greece god knows where from ( presumably Canada ) and since the amp was pretty neat on the outside the costumer that got it from a scrap yard actually asked for a new toroid 230 wired, full refurbish caps and many more and at the time i thought it didn't worth.
When finished the amplifier kicked me out of my chair , together with scope , generator and spectrum analyzer ...awesome performance , astronomical bandwidth and speed , excellent figures on ch separation and crosstalk and plenty of kick and power ...
At the time i could only put it next to an Accuphase
Kind regards
Sakis
This is an essentially distortionless amplifier, and like I said good....
Quality parts are used throughout.
You asked for opinion.
Just set the bias precisely to factory value, and enjoy what you have as the maker intended.
By all means play with tweaks like cables and mountings/stands.
If you are keen to experiment, experiment with something else less valuable (sonically).
Dan.
Lowering the bias and injecting square wave 10K will show you what you are looking for .But ! as said from Ian and others elimination of small crossover distortion can and will happen with a bit of bias .
As an amplifier though there is a number of other issues that will effect overall performance far more a bit of crossover distortion ...
Increasing the bias can and will effect thermals so in long time run you will have stability issues ... Keep it as was !!!
A few better capacitors in the signal line and the power supply will make a better amplifier without any thermal issues ... thing about this first ...Work with caution and no extremities....
Kind regards
Sakis
As an amplifier though there is a number of other issues that will effect overall performance far more a bit of crossover distortion ...
Increasing the bias can and will effect thermals so in long time run you will have stability issues ... Keep it as was !!!
A few better capacitors in the signal line and the power supply will make a better amplifier without any thermal issues ... thing about this first ...Work with caution and no extremities....
Kind regards
Sakis
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