Off topic. I wonder how many good audio amplifiers are let down by their power supply. It is an issue in amateur radio transmitters too as the signal goes from almost nothing to full power with audio. It is possible to dynamically test a power supply with a programmable DC load and an oscilloscope measuring current and voltage. The DC load can be programmed for a low frequency, say 100 Hz and a 10 to 90 per cent duty cycle square wave. This stresses the supply and allows its response to be measured.
Excellent information to used analog discovery in audio application, testing. Especially about the grounds, being connected and making your own board . This is the information I’ve been looking for .
I just started using the same setup to test a 300B amp. I’m mainly measuring THD vs. power. If I set the volume control on the amp to maximum, the distortion plot shows high distortion. If I set the volume to 1/2, the plot shows much lower distortion for the same power output. His do I know which is correct?
This is a great step by step - thank you. I assume you connect the Discovery 3 to a laptop running on battery. Or maybe you use a 1:1 isolation transformer. I wonder if the Discovery has the same issue as standard scopes having a grounded neutral. Thanks again for sharing.
I noticed the GPO header box you showed contained 2x20 pin headers, but the header on your breadboard is 2x15 which matches the pins on the discovery. I am having trouble locating a 2x15 right angle connector, did you cut yours or will a 2x20 fit.
Gaby, Would you be willing to hook up an Android cell phone on airplane mode running out of its USB connection to see how clean that is? Reason I'm asking is I use such a phone with USB Audio Pro Player to a USB dongle DAC amps or a chord mojo 2 (which are running off of battery or taking power from the phone). I think it sounds pretty good ! I'm wondering if I'm inherently avoiding some of the pitfalls in not having to use a switching power supply (or buy a expensive linear...) etc ... etc .. as everything is running off of battery ? Do you think a USB cleaner of some kind should be in the chain between the phone and the DAC in my scenario. The only downside to this is there are cables to deal with and you're dealing with the battery charge of the phone which is usually only a few hours but so far it's been working great in my opinion. I have 5 DACs And I run a different one every night which is a lot of fun
Your phone on battery will beat any computer Much lower noise so you are doing a good thing. But you still have some computing noise The better your dongle Dac is the better the sound
I don't understand the need for the extra board. As mentioned, when plugged in, all 'ground' connections from the i/o connectors are connected together. That would not change with the new board, would it?
Hi Jan I was away I had to double check When plugged in, all 'ground' connections from the i/o connectors are actually NOT connected together. they are all independent. Unless you use the I/O board that comes with it that connects all grounds together. So the extra board is critical for certain amps like Class D amps and certain Tube Amps, where you want the grounds separate
The Stuff made Video is in my description. Just go to the Video then the Description of The Stuff made video you will find a drobox link to the software and PDF. Leave him a nice comment for his efforts and contributions to the DIY community.
Hi thank you for the very valuable video Lately i have been a little shocked by reviews of amps judged quite good and sometimes very good for sound and then performing quite badly at the Lab bench I am talking about differences between channels bad square wave response and pretty high distortion even at low power Speaking of vintage i guess this means the need of maintenance But this fact that even bad measuring amps sound leaves me puzzled But what scares me is when amps with impeccable measurements sound bad How is this possible? Or said better Is this really possible? Thanks again and kind regards Gino
Generally, amplifiers that measure well tend to sound good, but since our ears and tastes vary, a bit of distortion in tube amps, typically less than 1%, is often appreciated. A completely flat response can sometimes be unexciting. When dealing with poorly measuring amps, it's wise to steer clear. They usually don't sound good, especially when the measurements are particularly bad. However, some people enjoy exaggerated bass, for instance. Additionally, not all reviewed units sound as good as the average sold unit, and some reviewers avoid being overly critical. I believe that if an amp measures really poorly, it will likely sound bad, at least to a well-trained ear.
@@Gabster1 hi thank you very much for your very kind and valuable reply There is one aspect in measurements that it could be overlooked Usually to perform distortion measurements a purely resistive load is used You're very right Tubes can sound so musical I don't like them for bass but for mid and high range could be a great option Congratulations for your speakers I like the concept very much indeed and I believe the sound must be excellent Kind regards Gino
Another great and usefull video for audio diy. Thanks a lot Gabster, this is priceless. I have a quick question concerning the 100 ohms load connected to your amplifiers. I understand that it reduces a lot the current compared to an 8 ohms resistor. But do you think this has negligible effect on THD mesurements (and others important parameters) compared to a mesurement with 8 ohms ..? Thanks a lot
Thanks G, great stuff. What wattage 15k resistors would you use in the jig, if you were to add attenuation? I also noticed that only yourself and @TheStuffMade are using the jig. Other RU-vidrs are just using the unrecommended bnc adapter. What’s up with that?
You can get away without a jig on simple Tube amps But I had a lot of issues with some amps so best is to follow The Stuffmade recommendations he knows his stuff :) So far I had not used any attenuation with Ver3 up to 90W. I would ask Jake about Wattage I am guessing 1W may be more then enough.
