Thanks, so it's a soundcard loop test not DCG3 measurements.
I have a DCG3 new measurement, the best(lower THD) up to now.
I will post latter.
Was to show what just a bit loose contact between cheap RCA cables and the back of a jack adapter can do. Obvious 50Hz hum appears. Crosstalk curve also substantially worsens most probably due to capacitive coupling between low quality bonded together thin stereo cables.
My own DCG3 measurements are in post #1 from when I was prototyping it in an aluminum makeshift "open L chassis" on the bench. The audio interface was running on its native drivers with a Win XP notebook then.
I can't go better as my soundcard is a PCI one.
OK a PCI card has harmonic noise spikes but your DCG3's THD looks fine. It would have registered better without the spikes but we get the picture. Especially nice looking is the THD VS Frequency sweep being flat all the way to 20kHz and dominated by second H at 200 OHM load.
Not bad for a home studio interface box. Scarlett 2ndGen has flat 1/F to 20Hz is a nice thing I have seen in your and other's posts. My old EMU tracker box starts rising from 80Hz down which surely registers in THD+N numbers although it is still very competent in other areas.
If 3rd Gen proves any better for helping in measurements do let us know.
Another Pre- / Headphone Amp singing
Having joined already the Group-Buy organized by Tea end of 2016 I finally managed to get the build into a stage where I can actually listen to it (see attached pictures)...
Yes this took a while (the main obstacle in the end was buying a sink and the necessary tools for cutting it to size and drilling and tapping the holes for the transistors). What also helped to motivate me was buying a beyerdynamic T1.2 without having any proper headphone out in the house.
Went with 3X gain and the high bias (7.5R) simply because the sink is more than big enough. Everything worked just fine after firing it up and it was easy to adjust the offset before putting the opamp in place.
This is used as kind of a digital pre-amp / network streamer:
Next up: Putting it into a proper case (currently drawing the necessary front and back panel cut-outs) and more listening. Additionally trying the alternative relay wiring (I have turn-off pops so I usually remove headphones before powering down) as well as the Q1 / Q2 mod. Will post an update of the final stage hopefully soon.
Thank you, Salas and Tea-Bag!
Having joined already the Group-Buy organized by Tea end of 2016 I finally managed to get the build into a stage where I can actually listen to it (see attached pictures)...
Yes this took a while (the main obstacle in the end was buying a sink and the necessary tools for cutting it to size and drilling and tapping the holes for the transistors). What also helped to motivate me was buying a beyerdynamic T1.2 without having any proper headphone out in the house.
Went with 3X gain and the high bias (7.5R) simply because the sink is more than big enough. Everything worked just fine after firing it up and it was easy to adjust the offset before putting the opamp in place.
This is used as kind of a digital pre-amp / network streamer:
- Beaglebone Black Wireless with TPA Cronus re-clocker is used as a streaming device (see Support for Botic Linux driver).
- DAC is a diyinhk ES9018 (Build thread for Diyinhk ES9018 DAC on Ebay) that is also used (via isolated I2C control from BBBW) as digital volume control. This DAC was actually my first DIY project.
- DAC single ended output is directly connected to DCG3 input (R2 replaced with 33K to lower the input impedance since no pot is connected)
- Line out feeds a Pass M2 clone (Official M2 schematic) where boards, transformers and output transistors have been again supplied by Tea-Bag
Next up: Putting it into a proper case (currently drawing the necessary front and back panel cut-outs) and more listening. Additionally trying the alternative relay wiring (I have turn-off pops so I usually remove headphones before powering down) as well as the Q1 / Q2 mod. Will post an update of the final stage hopefully soon.
Thank you, Salas and Tea-Bag!
Attachments
Last edited:
Not just proper, Beyerdynamic T1.2 is way cool.
What I meant is that I did not have any proper headphone amp in the house and bought the T1.2 as motivational tool to make sure I finish the DCG3 at some point.
They are very nice indeed! I bought them and built the DCG3 in order to be able to enjoy listening without disturbing the wife and kids. Now I actually believe that I could even live without power amp and speakers.
I do not hear any noise at all having the phones plugged in and nothing playing. I did not perform any measurements but the build seems completely quiet.
This is without any connection between signal GND and mains earth.
I have some noise when playing through the power amp as the speakers are higher than 90dB sensitivity and there seems to be some grounding issue. This noise however was there even before the DCG3 arrived and when the DAC was playing directly into the power amp. I will need to resolve this in the power amp.
This is without any connection between signal GND and mains earth.
I have some noise when playing through the power amp as the speakers are higher than 90dB sensitivity and there seems to be some grounding issue. This noise however was there even before the DCG3 arrived and when the DAC was playing directly into the power amp. I will need to resolve this in the power amp.
A DIY Pass M2 clone. It had a very low level buzzing right from the start and so far I was simply too lazy to work on it. Probably needs shielding of the input transformers or further measures. Since the noise was not really harming the listening pleasure I did not really bother to try fix it. In addition it is nice sometimes to have a reminder that your power amp is still switched on
There are also phones sockets that can switch a contact and you may get creative with them. Audio Jack Switches and Configurations | DigiKey
Need some suggestion. I am using Firstwatt M2 (DIY) with a DIY tube preamp. My speakers are DIY Finalist that is of 86 db sensitivity. One of friends made the preamp (Tube) for me that has enough gain to drive this low sensitive speaker with M2, probably around 30 db. I am planning to make Salas DGC3 preamp. As I went through the forum, DGC3 has 10/15 db gain, will it be able to support 86 db speaker with 25 watt class A amp? is there any scope of increasing the gain of the preamp? I am a novice, need your kind suggestions.
Yes there is much scope because the preamp has much internal spare amplification to adjust.
Pass M2 is a 14dB gain power amp. Coroner21 already uses 89dB SPL/W/M speakers* with that amp and a DCG3 as he mentioned.
M2 is a 25W 8Ω amp. Thus it takes 12.65VRMS output to produce 20W (-1dBW from max) if not to risk clip.
14dB voltage gain is 5X. Input needed is 12.65V/5=2.53V. It goes without saying that on 2V full scale (0dBFS) digital sources the 3X DCG3 can deliver tons of spare peak voltage to M2 if set at high pot positions (above 2 o clock).
Even when assuming a worst case level source of 300mV phono stage at nominal 5cm/sec velocity we should also count that vinyl is made to can peak above zero. A 9dB record peak from that phono gives 2.53V line output on a 3X (9.54dB) DCG3. Depends on the average dynamics of cuts in a record collection. LPs from the 80s or 45RPM wide groove original analog masters heavy vinyl from 2010-2019? Even when produced from the same digital master as used for a file or CD release, it still many times results different if unintentionally**
In case of quiet peak results with a lower than average output cartridge and phono stage you may consider changing R6 for extra gain. 1500Ω will give 2.5dB more line gain (X4/12dB). 2200Ω will give 5 dB more (X5.4/14.65dB).
*Canton Karat 300 review
**Measuring Vinyl Dynamic Range
Pass M2 is a 14dB gain power amp. Coroner21 already uses 89dB SPL/W/M speakers* with that amp and a DCG3 as he mentioned.
M2 is a 25W 8Ω amp. Thus it takes 12.65VRMS output to produce 20W (-1dBW from max) if not to risk clip.
14dB voltage gain is 5X. Input needed is 12.65V/5=2.53V. It goes without saying that on 2V full scale (0dBFS) digital sources the 3X DCG3 can deliver tons of spare peak voltage to M2 if set at high pot positions (above 2 o clock).
Even when assuming a worst case level source of 300mV phono stage at nominal 5cm/sec velocity we should also count that vinyl is made to can peak above zero. A 9dB record peak from that phono gives 2.53V line output on a 3X (9.54dB) DCG3. Depends on the average dynamics of cuts in a record collection. LPs from the 80s or 45RPM wide groove original analog masters heavy vinyl from 2010-2019? Even when produced from the same digital master as used for a file or CD release, it still many times results different if unintentionally**
In case of quiet peak results with a lower than average output cartridge and phono stage you may consider changing R6 for extra gain. 1500Ω will give 2.5dB more line gain (X4/12dB). 2200Ω will give 5 dB more (X5.4/14.65dB).
*Canton Karat 300 review
**Measuring Vinyl Dynamic Range
Salas,
Can the DCG3 be pushed to drive a BA1 Pass Amp with no gain? If so what R6 value would work?
Rush
Last edited: