Building a DIY amp with NVA amplifier boards

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Geoff.R.G
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Re: Building a DIY amp with NVA amplifier boards

Unread post by Geoff.R.G »

savvypaul wrote: Mon Mar 01, 2021 10:45 am The set-up instruction is to turn the amp on before connecting inputs, then lastly connect the speaker outputs - that avoids the bump. I forget that you don't leave your amp powered on 24/7.

Putting The System Together For The First Time
1. Lower the volume control(s) to minimum on pre-amplifier / integrated amplifier (do not connect any cables, yet)
2. Power on power amplifier(s) / integrated amplifier from the switch on the rear panel
3. Connect source interconnects to pre-amplifier / integrated amplifier input(s)
4. Connect pre-amp output interconnects to power amp(s) - ignore this step if using integrated amp
5. Connect speaker cables to speakers FIRST
6. Connect speaker cables to the amplifier starting with black
7. Check the selector switch is in the right position for your intended source, play some music and turn up the volume

Not sure why you wouldn't get it with your DIY amp, though.
Interesting Paul, almost the exact opposite of what I tell live sound volunteers. Switch on and mute all the inputs, connect the inputs then un-mute and start setting gain, equalisation and, gentle, compression.

With almost every electrical system I have ever worked on connections are made power off.

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Re: Building a DIY amp with NVA amplifier boards

Unread post by antonio66 »

I must have missed Savvypau'ls post regarding switching on and connecting wires, I've always had my amps turned off when doing that task as well.

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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

Daniel Quinn wrote: Sat Jul 03, 2021 7:22 pm Correct me if I'm wrong but if he makes his speakers active , how will he use other amps with them?
J don't think coach wants to turn his speakers active. I thought he only wanted to learn about what effect changing a toroid for a frame transformer would bring.

My set up isn't active anyway. There's just nothing between the amps and any of the drivers (including tweeters) except wire.
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CycleCoach (Sun Jul 04, 2021 9:00 am)
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Re: Building a DIY amp with NVA amplifier boards

Unread post by CN211276 »

antonio66 wrote: Sun Jul 04, 2021 12:45 am I must have missed Savvypau'ls post regarding switching on and connecting wires, I've always had my amps turned off when doing that task as well.
Same here.
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Re: Building a DIY amp with NVA amplifier boards

Unread post by CycleCoach »

karatestu wrote: Sun Jul 04, 2021 7:42 am
Daniel Quinn wrote: Sat Jul 03, 2021 7:22 pm Correct me if I'm wrong but if he makes his speakers active , how will he use other amps with them?
J don't think coach wants to turn his speakers active. I thought he only wanted to learn about what effect changing a toroid for a frame transformer would bring.

My set up isn't active anyway. There's just nothing between the amps and any of the drivers (including tweeters) except wire.
I didn't even know what an EI was, or looked like. Now I do. Ta Stu.
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karatestu (Sun Jul 04, 2021 9:09 am)
I think I might be in the HiFi trade.
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Re: Building a DIY amp with NVA amplifier boards

Unread post by savvypaul »

Geoff.R.G wrote: Sat Jul 03, 2021 8:28 pm
savvypaul wrote: Mon Mar 01, 2021 10:45 am The set-up instruction is to turn the amp on before connecting inputs, then lastly connect the speaker outputs - that avoids the bump. I forget that you don't leave your amp powered on 24/7.

Putting The System Together For The First Time
1. Lower the volume control(s) to minimum on pre-amplifier / integrated amplifier (do not connect any cables, yet)
2. Power on power amplifier(s) / integrated amplifier from the switch on the rear panel
3. Connect source interconnects to pre-amplifier / integrated amplifier input(s)
4. Connect pre-amp output interconnects to power amp(s) - ignore this step if using integrated amp
5. Connect speaker cables to speakers FIRST
6. Connect speaker cables to the amplifier starting with black
7. Check the selector switch is in the right position for your intended source, play some music and turn up the volume

Not sure why you wouldn't get it with your DIY amp, though.
Interesting Paul, almost the exact opposite of what I tell live sound volunteers. Switch on and mute all the inputs, connect the inputs then un-mute and start setting gain, equalisation and, gentle, compression.

With almost every electrical system I have ever worked on connections are made power off.
It's the way Richard taught me to do it. Don't try it with valve amps, though! Switching it on after all the connections are done is fine, but you will get a switch on thump. Either way, always take care not to short the speaker cables.
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CN211276 (Sun Jul 04, 2021 10:03 am) • CycleCoach (Sun Jul 04, 2021 12:29 pm)
I am in the hi-fi trade
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Company Name: NVA Hi-Fi
https://nvahifi.co.uk/

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karatestu
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Re: Building a DIY amp with NVA amplifier boards

Unread post by karatestu »

Copied from an article on transformers. Graph doesn't show here but the page is found at https://www.audialonline.com/blog/psu ... d-more/
As usual, believe which bits of it you want.

PSU TRANSFORMERS: EI VS. TOROIDAL, AND MORE
Jun 10, 2013, by Pedja

Back in 2010, when we were working at Gramofone GF01/GF02, we were determined to try as many power supply options as possible, and of course to check each particular option and its sonic effects in a controlled way. So we tried both switching and linear supplies, going there both passive and actively regulated routes, and combining conceptions changes with parts changes.

Once we definitely settled in linear campus, some of the most interesting points were about transformers. And here are the most important ones.

1. EI transformers sounded better than toroidals, for their better dynamics, more quiet background, and more natural tone.

2. Lower power transformers sounded better than higher power ones. This finding was totally opposite to what audiophile common sense would predict or recommend by the usual over-sizing recipe – higher power units sounded more thin and bright, whereas lower power units sounded more smooth and dynamic.

3. EI transformers positioning was critical, as one might expect, due to their higher external electromagnetic dissipation; interestingly, Gramofone units have external supply units, physically well separated from active electronics, so supply couldn’t upset it, yet this issue with positioning also appeared when we dealt with mutual positioning of two transformers (we had one isolation unit, and another one “main” unit). We did found this setup sounding best when two transformers were placed at 90° one with respect to the other.

Now, all this was extremely interesting, and it hugely counteracted to the common audiophile wisdom. Several checks hence took the place, in an effort to possibly find technical reasons behind, and frequency response measurement was the most revealing one. I took several samples here, all 1:1 (isolation) units, made of the same material, and put them into the measurement setup loop. Also, all these EI transformers were the same split bobbin construction – primary and secondary were completely separate coils sitting side by side, and not one on top of another, which excludes capacitive coupling between the windings. So, all else being the same, it was obvious that the higher power transformers had a higher bandwidth and, as we want mains transformers to act also as filters, passing by only 50/60 Hz, and stopping all above that as much as possible, this is unwanted performance. If we also consider that the higher power transformers dissipate more around, we are able to understand previously said sonic disadvantages of higher power transformers.

Time to look at the graph. (Click on it to see it the full resolution, please.)





Isolation Transformers Frequency Response
PSU transformers frequency response





This same measurement also pointed out that the bandwidth of the toroidal unit, even if it had an electrostatic shield between primary and secondary, was higher than the bandwidth of any of these EI units. In addition, it apparently had some reactive components at the upper end, peaking just before its “natural” roll off, and apparently suffering of capacitive coupling, which continued its frequency response above 70 kHz.

There is a stream among audio transformers designers that prefer toroidals above EI units for signal applications, due to their tight coupling and hence a higher frequency response – and this approach might have its time here. Still, it would be really interesting to see a toroidal transformer with controlled (and low) frequency response, for power supply purposes.

Now, we could sum up some things about EI vs. toroidal.

EI advantage:
1. Lower bandwidth (i.e. better mains filtering).

Toroidal advantages:
1. Lower external dissipation.
2. Lower mechanical hum – EIs are not always dead quiet, as toroidals usually are.
3. Less in size for the same power rating.

Obviously we may want all these advantages at once, and there is no reason to claim them impossible to get, but remember: improvements can come only from actual research, and in reality designing work is a set of compromises. Low external field and low interwinding capacitance don’t come together. Or to rephrase: do you want your windings tightly coupled or fully separated?

Practically speaking, the final choice should be based on particular requirements. The transformer’s power does have its limits, so it is not recommended to go beyond its power specifications. Also, you should consider that in our applications transformer could not work right at its specified power rating, as if the current flew constantly. Its output is rectified and it must fill capacitors by 100 Hz (or 120 Hz) spikes, and these spikes must be adequate high current pulses. But once you take this into account (circuit simulators can be of help here), and fulfill these power rating criteria, you better start thinking “less is more”, and stay at that power. Going with a higher power transformer you only increase the transformer’s bandwidth and its external electromagnetic field. In other words: yes, there is a right power for every transformer used in the audio.

So, as said, some of these things probably counteract to what you have learned about mains transformers’ sonic properties. But, as one fellow audio enthusiast wrote in the early days of the internet (when the internet was young and pure), “most of the things we could learn about hi-fi were simply wrong anyway”.
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Re: Building a DIY amp with NVA amplifier boards

Unread post by Daniel Quinn »

Isn't saying the type of transformer effects the sound on the same level as saying fuses do?

Geoff.R.G
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Re: Building a DIY amp with NVA amplifier boards

Unread post by Geoff.R.G »

Daniel Quinn wrote: Mon Jul 12, 2021 10:49 am Isn't saying the type of transformer effects the sound on the same level as saying fuses do?
No, because the differenced between EI transformers and toroidal transformers can be heard and, controversially, measured. The hum from an EI transformer can be obtrusive and, in a domestic setting, that can be important especially if equipment is left powered when not in use.

I have yet to hear anyone measuring any difference between fuses.

I know this is a subjectivist forum but it would be inappropriate to ignore the fact that some differences can be measured. That doesn't mean that we can draw any firm conclusions from those measurements but an absolute absence of measured difference, as is the case with fuses, does leave me wondering whether there might be a placebo effect involved.

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Re: Building a DIY amp with NVA amplifier boards

Unread post by r3xj0hn570n »

I know it's not my thread, but i thought Stu and others might be interested in a slight diversion...
delme.jpg
delme.jpg (469.12 KiB) Viewed 3345 times
These boards have been sitting in a box for the last 20 years. I think they were old then as they are much larger than the others. The enormous transformer is from a dead onyko AV amp, an old grundig receiver has donated it's heatsink and output transistors. I'll be playing with the circuitry on this one, because, why not.

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