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Old 1st October 2002, 08:37 PM   #1
Kram is offline Kram  United Kingdom
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Question Help with Tortello's headphone amp.

Hello everyone,

I am in the process of finding parts to build Tortello's headphone amp ZEN-like headphones amp and have a few questions I hope some one can help me with. (By the way i have never built an amp before so be gentile with me ).

1. The transformer. what VA and secondary voltage is recommended for this design?
I found an 80VA 2x25 toroidal at www.maplin.co.uk stock No.vs24b, would this be suitable?

2. I have not been able to find anywhere (maplins, farnell and RS) the zener diodes that are on the schematic which Tortello sent me, could some one recommend suitable a replacement?

3. even more basic question now, sorry.
On the schematic some of the caps have one straight side with a + next to it and the other plate is curved, while some (actually only 1, C2) have both plates straight. what is the difference?
I know that there are many different types of caps all made from different materials, what type would you recommend for sound quality (However i am on a budget, sadly )

4. The Bias and Bal pots, are these trim pots?

OK I think that will do for now, I hope someone can help

Thankyou,
Kram
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Old 1st October 2002, 10:44 PM   #2
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A transformer at 80va rating is very good .I build mine with the same amount.
But use the secondaries in parallel for 0-25 volt.
At the results you will get around 35 volts on the unregulated supply.Just fine.

If you want to trim R15 (180k) - I refer to the schematic at page 1 of the thread- do it ! With a voltmeter measure set the drain of Q2 at half of the supply vaule.

On the schematic I see 5 polarized caps, they are:
C1,C2 power supply filtering;
C3,C4, current source;
C5 output cap.

It is not necessary go for exotic parts .

Ah, the diodes.Sure they are there back to back for input protection.The voltage rating of these zeners are from ,say 9 volts to 18 volts .

Cheers
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Old 2nd October 2002, 12:07 AM   #3
paulb is offline paulb  Canada
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Default Re: Help with Tortello's headphone amp.

Quote:
Originally posted by Kram

On the schematic some of the caps have one straight side with a + next to it and the other plate is curved, while some (actually only 1, C2) have both plates straight. what is the difference?
The ones with the + signs are polarized, or electrolytic, types. In order to cram more energy storage into a small package it becomes necessary that the capacitor voltage be applied only one way. There are some nonpolarized electrolytics but they are quite rare. Use aluminum electrolytics, not tantalum.
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Old 2nd October 2002, 07:06 PM   #4
Kram is offline Kram  United Kingdom
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Thanks for the swift replies.

stefanobilliani, so any zener with a voltage rating of between 9v and 18v would be good?

I am wanting to build this amp in a similar way to the one Tortello has done in the pictures he posted of one he completed, by that i mean with a preamp in the same box.
Would anyone know where i could get a schematic of the other parts of the amp he built or something similar? Well I could always ask Tortello anyway.

Thanks
Kram.
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Old 3rd October 2002, 10:40 AM   #5
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Yes, good!
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Old 4th October 2002, 12:10 PM   #6
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Hello,
I've just seen this thread, and all the replies seem to me correct.
The definitive schematic is slightly different from that was published in this forum, mainly in the power supply stage, and if you post here a request, I can email the main PCB stuff immediately, in case you haven't ever done.
As soon as possible Cmoy, from Headwize.com, will publish the whole project, included the power supply and the timer/h.f. equalizer (heresy!? Not for me, I have a Grado SR325...) stages.
The transformer should be at least 30VA rated, I use an high quality Talema 2x18V/50VA with good results.
If you build a dual mono power supply, you may join the GND rails (one for each channel) in only one point - the common ground of the headphone connector. This point can be wired to the metal chassis.
C5 and C4 should be good quality capacitors, an yes, no tantalum: the difference is quite notable.
Hope this helps.
Marcello
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Old 4th October 2002, 03:35 PM   #7
Kram is offline Kram  United Kingdom
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Hi Tortello, you did send me a schematic a while ago, it can be seen below.

there is one question i forgot to ask about the caps, what voltage rating should they be?

Thank you Tortello for sending me the schematic in the first place and i hope mine turns out at least half as good as yours.

Thanks
Attached Images
File Type: jpg pcb schematic.jpg (36.3 KB, 1273 views)
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Old 4th October 2002, 06:52 PM   #8
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Hi Kram,
it depends on the transformer voltage rating, since the circuit is not critical towards power supply values.
If you decide to follow the values recommended -18Vac for the P.T.- the power supply capacitors voltage ratings should be at least 35WV. C1, C3, C4 and C5 breakout voltage could be lower, but my advise is to put there 35V capacitors too, given that the price difference is marginal.
Let's consider that C4 and C5 resolve the B+/2 component (about +12Vdc) from your headphone coils.
I hope you'll enjoy with this circuit.
Best Regards
Marcello
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Old 5th October 2002, 08:47 AM   #9
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... and if you use a 25V transformer, the capacitor rating must be 50WV.
As Stefano wrote, in this case you need to trim the +B/2 at Q2 drain, to achieve the maximum voltage modulation.
Cheers
Marcello
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Old 26th November 2002, 03:07 PM   #10
Kram is offline Kram  United Kingdom
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Default IRF610

How many IRF610's would you recomend I buy to get some that match, i am planning on building 2 amps.
Do you think 25 will be enough?? or is that too many??

any help appreciated

Thanks Kram.
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