Hiraga 20W class A

[lineup]

copper bar
looks good daniel
.. a lot of work .. but very good quality (better than wire, for high currents)

 

[danieljw]

still going....

this is the results of building today.


-Dan

 

[danieljw]

Hi all,

Just got the hiraga amp working last night,

was a bit worried at switch on, but thats what variacs are for.

running approx 1.7A bias after all that, using a 500VA toroid.

have only heard one channel at a time on the test speaker so far.

PS check out the star earth..........

 

[lineup]

Star ground. Good!

Any problems with inrush currents?
To those big caps.
I see you have some resistors to second pair.
But for the first pair od capacitors?

Toroids have more peak inrush, than EI transformers,
I have been told.

 

[rmgvs]

one remark and a question to daniel

This remains a very fine amp indeed, even after 25 + years since first published. I made several of these amps in all kind of settings (from very close to the original text to cheap versions with standard transistors and modest power supply).

I would recommend two big power resistors of 25W (metal case) that can be fitted to the chassis. An idle current of 1,7 Amps will makes these white resistors hanging in the air very very hot.

If I see it right you use no proper cooling blocks, instead you attach the power transistors straight to the chassis. Is this going allright? I would guess the transfer of heat to the chassis is quite slow and might lead to warming up too much during the first half hour or so?

Finally the question: I have difficulty lately in getting these big electrolytic caps (let's say 60.000-100.000 mF, 25-40 V) (prefarably in can form with the right diameter for the Hiraga chassis) for reasonable prices. Does anyone know a good source for these things?

 

[danieljw]

Re: one remark and a question to daniel

Star ground. Good!

Any problems with inrush currents?
To those big caps.
I see you have some resistors to second pair.
But for the first pair od capacitors?

Toroids have more peak inrush, than EI transformers,
I have been told.

Hi Lineup,

Yes that star ground only just fits all the connectors

The amp has a very large inrush current, so i have a small NTC thermistor added (other side of EMC filter)
which reduces this problem significantly.

This remains a very fine amp indeed, even after 25 + years since first published. I made several of these amps in all kind of settings (from very close to the original text to cheap versions with standard transistors and modest power supply).

I would recommend two big power resistors of 25W (metal case) that can be fitted to the chassis. An idle current of 1,7 Amps will makes these white resistors hanging in the air very very hot.

I am running 1.77A / channel but the resistor value is 0.5 Ohms only
using I^2R thats approx 6.26W continuous yes they get hot but not significantly. I plan to change these for inductors once the amp is up and running properly.

If I see it right you use no proper cooling blocks, instead you attach the power transistors straight to the chassis. Is this going allright? I would guess the transfer of heat to the chassis is quite slow and might lead to warming up too much during the first half hour or so?
[/B]

there is heatsinking bolted on the other side of the chassis attached with thermal transfer compound.

Finally the question: I have difficulty lately in getting these big electrolytic caps (let's say 60.000-100.000 mF, 25-40 V) (prefarably in can form with the right diameter for the Hiraga chassis) for reasonable prices. Does anyone know a good source for these things? [/B]

I have used Ebay before, and also RS components and Farnell components.

I would not say the prices reasonable though !!!

-Dan

 

[lineup]

NTC thermistor

transient current limiting resistors
with very low resistance at higher normal working temperature
at first, when cold they have some ohms resistance
but later much less

I guess those are the ones you use,
for power on current inrush protection

 

[danieljw]

That is the one Lineup,

It is in series with the Active.

-Dan

 

[danieljw]

almost done

Hi all,
Just put the base of the case on........

listening to the amp running just over 1.7A bias current.
the heatsink(s) are at 49 deg C after about 1 hour run time.

in terms of the sound *VERY HAPPY*

been listening to it for a while tonight.

any way here are the pics.

note the transformer cover is not made yet, and the front panel is not painted or polished yet. (not in the pics)

the sound output is belies its modest power rating.....

-Dan

 

[danieljw]

a few more pics

 

[danieljw]

angle view

 

[danieljw]

running

 

[lineup]

and actually making wonderful sounds, i suppose
congrats!

 

[rmgvs]

please compare

Would you in due time like to compare your subjective results with some of your other amps? In the article on the Monstre the comparisons with the older 20 Watter were already made. But the proof is in the eating of the pudding and tastes might differ.

Very nice chassis, good looking too! Compliments are in order.

 

[danieljw]

Thanks Guys i am happy with the way it is turning out,

First impressions are very clean sound and the power available is
alot more than Le monstre.

6-8W versus approx 50W with this one......

there is a very big difference in power.

The soundstage seems to be very good on the Le class A

will have to do a blind A-B too see the real difference though !

-Dan

 

[danieljw]

Hi all,

some test results:

(1kHz)

 

[danieljw]

(10kHz)

 

[danieljw]

(100kHz)

 

[danieljw]

(161 kHz -3dB)

 

[danieljw]

(1MHz small signal - filter is doing its job here)