Expressions of interest for buying transformers for diy amp ref Linuxguru's thread

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Re: Expressions of interest for buying transformers for diy amp ref Linuxguru's threa

linuxguru said:
24-0-24 is Mauro's recommended secondary voltage, and can be considered to be the best balance between sonics and power. There is some anecdotal evidence that lower voltages like 22-0-22, 20-0-20 or 18-0-18 are better for sonics on the MyRef, but I haven't tried them. Lower voltage secondaries will constrain the audio output power, naturally.
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Hi Shiva

What would be the best voltage for best sonics, never mind the wattage. We can use higher efficiency speakers or even use a pre for additional gain. what is your take on this?

Rgds


Rajesh
 
Re: Expressions of interest for buying transformers for diy amp ref Linuxguru's threa

captrajesh said:
Hi Shiva

What would be the best voltage for best sonics, never mind the wattage. We can use higher efficiency speakers or even use a pre for additional gain. what is your take on this?

Rgds


Rajesh
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Captain

How many folks are going to buy new speakers for this amp?

Just a reality check :)
 
Re: Expressions of interest for buying transformers for diy amp ref Linuxguru's threa

captrajesh said:
.
What would be the best voltage for best sonics, never mind the wattage. We can use higher efficiency speakers or even use a pre for additional gain. what is your take on this?
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+/- 28V rails are about the best for sonics with a traditional LM3886 gainclone. The MyRef is however a different topology, so it's hard to say without extensive auditioning, but it's reasonable to say that +/- 28V may also be optimal for sonics here. That would imply a 22-0-22 secondary.

Gain is probably not an issue - the MyRef has a gain of ~32, so even a 1 V amplitude signal at the input will drive it into clipping. It's not advisable to alter the MyRef gain significantly, though of course you can use a preamp.
 
Re: Expressions of interest for buying transformers for diy amp ref Linuxguru's threa

linuxguru said:
+/- 28V may also be optimal for sonics here. That would imply a 22-0-22 secondary.
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According to my calculation to arrive at DC Voltage out of the Power supply, (Volts @ secondary x 1.41) 22-0-22 volts at secondary of the transformer means 31.02 V. To get =/- 28 V, the voltage at secondary must be 20-0-20 (19.86V to be precise) Is my calculation wrong?

linuxguru said:
1 V amplitude signal at the input will drive it into clipping.
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I was under an impression that an average CDP output is 2V and an average Pre-Amp would give the signal about 14db gain. Is this assumption also wrong?:confused:

All my calculations & assumptions are going for a toss here??:sad:

linuxguru said:
It's not advisable to alter the MyRef gain significantly, though of course you can use a preamp.
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Shiva, what would be the difference between using a Pre to control gain compared to a Pot? Will there be any degradation of sonics?
 
Re: Expressions of interest for buying transformers for diy amp ref Linuxguru's threa

gobble said:
Captain

How many folks are going to buy new speakers for this amp?

Just a reality check :)
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Rahul,

Not everyone has nice speakers already. You ofcourse, don't need to, as your speakers are already of that category.:)
 
Re: Expressions of interest for buying transformers for diy amp ref Linuxguru's threa

captrajesh said:
Rahul,

Not everyone has nice speakers already. You ofcourse, don't need to, as your speakers are already of that category.:)
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Aaaha! So we are going to see a "What speakers shall I buy" thread soon :eek:hyeah: :clapping:
 
Re: Expressions of interest for buying transformers for diy amp ref Linuxguru's threa

captrajesh said:
According to my calculation to arrive at DC Voltage out of the Power supply, (Volts @ secondary x 1.41) 22-0-22 volts at secondary of the transformer means 31.02 V. To get =/- 28 V, the voltage at secondary must be 20-0-20 (19.86V to be precise) Is my calculation wrong?
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Pass gives an example using this formula to decide the trafo specs

VA rating (watts) = 2.5 * 2 * (regulated voltage + 8) * bias current per channel.

Assuming 1.4A is bais current with a 28V regulated DC rail we get a Trafo requirement of 224VA per channel.

"A simple way to calculate the secondary voltages required is to start with the regulated rail voltage, add the 8 volts, add another 3 volts for Bridge and Thermistor losses, and divide by 1.4, which will give you the AC voltage rating of each secondary winding... We want the unregulated supply coming off bridge rectifiers B1 and B2 to be about 8 volts higher than the desired regulated supply, and that is why you see the number 8 added to the regulated voltage in the above calculation."

Using this equation for secondaries we get (28 + 8 + 3) / 1.4 = 27.

But this is for his PSU design that requires 8V extra. Not sure how it fits in with the different GC PSU design. But can we use the same formula with different constants to approximate calculations for any amp?

HTH
 
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Re: Expressions of interest for buying transformers for diy amp ref Linuxguru's threa

gobble said:
Aaaha! So we are going to see a "What speakers shall I buy" thread soon :eek:hyeah: :clapping:
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Na Rahul. I already have 3 sets of speakers.:p

Regarding voltage calculations, hope Shiva also chips in.
 
Re: Expressions of interest for buying transformers for diy amp ref Linuxguru's threa

captrajesh said:
According to my calculation to arrive at DC Voltage out of the Power supply, (Volts @ secondary x 1.41) 22-0-22 volts at secondary of the transformer means 31.02 V. To get =/- 28 V, the voltage at secondary must be 20-0-20 (19.86V to be precise) Is my calculation wrong?
Click to expand...

The calculation is fine, but you also need to take into account the voltage drop across the bridge rectifier. This drop happens during high, pulsed currents of up to 10s of amps peak, so the drop will be around 1 to 1.5V per rectifier, bringing the rail voltages to 28 to 29V with a 22-0-22 secondary.

I was under an impression that an average CDP output is 2V and an average Pre-Amp would give the signal about 14db gain. Is this assumption also wrong?
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The numbers are about right - with a volume control (attenuator) somewhere in the signal path, signal levels can be adjusted to well below clipping.

Shiva, what would be the difference between using a Pre to control gain compared to a Pot? Will there be any degradation of sonics?
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It depends on the quality of the signal path in the pre-. There are certainly very good preamps around with minimal signal degradation. However, the most linear alternatives are purely passive - stepped attenuators, and LDR-based attenuators like the LightSpeed.
 
Re: Expressions of interest for buying transformers for diy amp ref Linuxguru's threa

captrajesh said:
what would be the difference between using a Pre to control gain compared to a Pot? Will there be any degradation of sonics?
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linuxguru said:
It depends on the quality of the signal path in the pre-. There are certainly very good preamps around with minimal signal degradation. However, the most linear alternatives are purely passive - stepped attenuators, and LDR-based attenuators like the LightSpeed.
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Hi Shiva

I asked that question to clarify my doubt with regard to usage of Class D Amp that I have.

It is an IR chip based Stereo Power Amp from Class D Audio. I'm routing the output of CDP through a Potentiometer to the Power Amp only to control the volume. Sounds very good to me.

Recently I carried out a test by routing the CDP signal through Nakamichi Pre-Amp, the SQ has gone down considerably.

I had also done the same by routing the CDP output through a Grounded Grid clone Pre-Amp assembled by a forum member where we didn't see any degradation of SQ.

But one thing is, in both cases, gain has improved considerably.

I do not know the reason. Hope you can chip in with your comments.

Rgds


Rajesh
 
Re: Expressions of interest for buying transformers for diy amp ref Linuxguru's threa

Captain

I think Siva already clarified earlier that this GC (Gone Case :D) amp has a very high inbuilt gain. Hence a preamp may provide too loud a volume even at minimal setting. However my understanding is that 14Db or whereabouts is max gain by a standard preamp where volume is at max. Usually the gain is eaten up by the volume pot - which is the rationale for using a unity gain buffer. Why add loads of gain then cap it with a volume pot, in the process adding its own coloration to the SQ?

Of course I use mine for the tube smoothness and their coloration. If my pot adds its own coloration its not audible - rather in my specific pre, I suspect the reverse - the coloration specifically from the volume pot (maybe if not the whole cloned circuit) makes a certain excitement and "lifting veils" effect that came through from the original GG inaudible hence this cloned pre does not deliver the same sound as the original GG. But is still very good in terms of a smoothness, providing a black background to the musical canvas, with speed pace and quietness and a much improved frequency extension (due to better impedance matching between CDP and power amp). hence I still enjoy the tremendous improvement over the earlier solid state.

I hope mine will sync well with the GC.

Cheers
 
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Re: Expressions of interest for buying transformers for diy amp ref Linuxguru's threa

Hi Rahul

Actually I was mentioning that my amp paired very well with your Pre-amp but not so with Nakamichi.

Since you've also heard it, what was your opinion?

Rgds


Rajesh
 
Re: Expressions of interest for buying transformers for diy amp ref Linuxguru's threa

captrajesh said:
Hi Rahul

Actually I was mentioning that my amp paired very well with your Pre-amp but not so with Nakamichi.

Since you've also heard it, what was your opinion?

Rgds


Rajesh
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Yes. For a kuteer Udhyog (Cottage Industry) finish the amp sounded pretty neat, SQ was on par with market gear for 3x the price you paid in setting it up. :) :eek:hyeah:

Like I mentioned macro dynamics did not scale compared to my poor NAD (which by itself is quiet poor compared to hi-end type sound in this regard) due to weak power supply and I would say its a great amp for background listening. This SQ was clean and good no issues with the chipamp, only the PSU and Trafo need an upgrade (and so does mine) - if you want grip scale and dynamics.

Cheers
 
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Re: Expressions of interest for buying transformers for diy amp ref Linuxguru's threa

Question about R-Core vs. toroid in myRef here

Answer 2 posts below the question.
 
Re: Expressions of interest for buying transformers for diy amp ref Linuxguru's threa

captrajesh said:
I assume this would be the case if it is mounted vertically. I have a 400VA 35-0-35 V Trafo which I'm using for my Class D Amp. If mounted horizantally, can even fit into 1U casing.
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Whats the weight of the trafo like ?

captrajesh said:
George, the SV Tronics guy is significantly cheaper. He had given me a quote for my class D Trafo for Rs. 2100/- all inclusive whereas Miracle had given me a quote for 3850/-:eek:
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What are the specs for this trafo ?
 
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