![]() |
![]() |
#61 |
Registered User
Join Date: Jan 2004
Location: Yorkshire
Posts: 744
|
I'm going to remove the op amp and regulator board anyway, I was just interested to see if there would be any difference but I don't think Commodore skimped at all really. I'll see if I can lower the volume and if so will record from the beginning to get an idea of noise.
BTW Stedy, do you have an A600 shielding with those boards you received? I plan to sell my A600 to make back some money but mine seems to have gone AWOL. |
![]() |
![]() |
#62 |
Registered User
Join Date: Jan 2004
Location: Yorkshire
Posts: 744
|
Capture volume is set at 100% so the clipping must be down to Commodore? unless there's something I'm doing wrong.
I've remove the bodge board and replaced the op amp back to TL084. https://ufile.io/f/b9ga0 https://postimg.cc/5HrKPzF2 ![]() I'm not really sure why they drift out of alignment over time? the time between powering on which is the spike at the very beginning and the intro sound is the same but then it drifts out after... |
![]() |
![]() |
#63 | |
Registered User
Join Date: Jun 2010
Location: PL?
Posts: 2,886
|
Quote:
That's why lot of audio DAC's use or passive I/V network or fast OPAMP's. To get "14" bit you need address this. |
|
![]() |
![]() |
#64 |
Registered User
Join Date: Jan 2004
Location: Yorkshire
Posts: 744
|
It might be worth someone who knows what they're doing looking into reducing the gain some more? I have A1200 2B spec and it was almost constantly in the red zone slamming 0dB and probably beyond, I think Audacity recommend input levels to be between -3 and -6dB.
The problem is if I change the feedback resistor value it might change what's needed as the feedback capacitor as from what I've read it is a stabiliser and it's beyond me to measure what's best, or maybe I can just tweak the voltage divider near to the RCA's? Also, I'm going to guess the alignment issue was down to slight difference in floppy drive reading time. |
![]() |
![]() |
#65 |
Registered User
Join Date: Jun 2010
Location: PL?
Posts: 2,886
|
Perhaps you can adjust input mixer level on your capture board?
|
![]() |
![]() |
#66 | |
Registered User
Join Date: Jan 2008
Location: United Kingdom
Age: 46
Posts: 735
|
Quote:
Mine's packed for storage so can't check it but they should be 390R-510R, not 2K as shown on schematics at AmigaWiki. This will give a true line level output. To truly answer the output levels from Oaula, I'd need the spec of the chip, it's one of the few custom chips I don't have the spec for. I assumed 8mA, a common value for the I/V converter and it worked in simulations which matched reality. ![]() I don't think I have A600 metalwork, like I said, all my Amiga gear is packed away for a few months, whilst building a new workshop @pandy71, do you have any idea how filter and op-amps work? You're spouting a lot of rubbish. A filter at the I/V converter, will attenuate higher frequencies above 27KHz, the slew rate will easily handle the required changes in output over a 20KHz range, any talk of 3.58MHz is irrelevant, the circuit works at ~20 KHz due to the filter. I've spent the last 18 years specialising in precision analogue and power electronics, kinda know what I'm doing (mostly). |
|
![]() |
![]() |
#67 | |
Registered User
Join Date: Jun 2010
Location: PL?
Posts: 2,886
|
Quote:
Good for you Steady - don't get me wrong but I/V converter in Paula is active not passive - PWM volume control is not 20kHz sinewave for sure. If you do passive I/V and low pass before OPAMP then i agree with all you wrote. |
|
![]() |
![]() |
#68 |
Registered User
Join Date: Jan 2004
Location: Yorkshire
Posts: 744
|
I just used line in on the sound card so I would assume it doesn't amplify the input signal?
360 ohms. I built the whole sound stage the same as the A1200 2B schematics and also checked with motherboard photos to make sure that's what Commodore actually used. Last edited by Mick; 27 June 2024 at 13:19. |
![]() |
![]() |
#69 |
Registered User
Join Date: Jun 2010
Location: PL?
Posts: 2,886
|
Amplify - probably not, but attenuate probably yes so you can reduce level by 50% (-6dB from 0dBFS) or more to prevent clipping if Amiga level is so high (usually supported maximum input level in consumer devices is around 2.504 Vrms)
Last edited by pandy71; 27 June 2024 at 22:05. |
![]() |
![]() |
#70 | |
Registered User
Join Date: Jan 2004
Location: Yorkshire
Posts: 744
|
Quote:
![]() |
|
![]() |
![]() |
#71 |
Registered User
Join Date: Jun 2010
Location: PL?
Posts: 2,886
|
It looks like clipped - but perhaps everything is fine (source dependent) - best test will be some sinewave with level for example -6.0206dBFS so easily maximum output level can be calculated (basic multimeter can be used to measure level if your sinewave frequency will be like 50 or 60Hz - depends on country).
|
![]() |
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests) | |
Thread Tools | |
![]() |
||||
Thread | Thread Starter | Forum | Replies | Last Post |
Modified Audio Filter | CHRIS-F | support.Hardware | 11 | 29 January 2017 23:42 |
Tools for set FILTER OFF audio | jhonny82 | support.Games | 14 | 22 July 2015 16:06 |
A600 Audio Filter Always On! | h0ffman | support.Hardware | 15 | 08 September 2013 22:29 |
Feature request (Audio Filter) | DaveMB | support.FS-UAE | 16 | 20 August 2013 21:53 |
Audio filter force on/off switch | TomCrazy | Hardware mods | 12 | 02 November 2012 14:18 |
|
|