Outputs on audio amplifier - Page 1
Forum section: electronics / beginners

author: DefinitivVair0
author_rank: Contributor
timestamp: June 20, 2025, 05:15:28 am
content: Hi there,I recently bought a SABA PA-2065 alongside the matching set and now try to understand what is doing what and how to connect it.(Schematic:https://ibb.co/h6gbkMz)My Problem is, that I can't seem to completely figure out what the Tape 1 Record (MON out on schematic) and the Tape 2 Record (VIDEO out on schematic) is used for and when they activate/deactivate.What I figured out so far:The signal for both outputs originate at the same point except that the VIDEO one comes after an op amp and the MON before itThe input signals go through op amps which are probably all buffers maybe except for the PHONO one which acts as a pre-amp (?)The MON output always gets its signal from whatever input is selected except for when Tape 1 is selected; then it turns offTherefore I still have some questions:When is the VIDEO output active/inactive (I can't figure out what this weird 3 transistor contraption at the base of the JFETs is supposed to do)What is the op-amp after the source select doing? It looks like a pre-amp but every input except the PHONO one are supposed to be amplified already.(Bonus: For recording audio to tape, would I use the VIDEO or MON out?)Also, please take a look at the schematic before giving me the google answer since how it is normally does not apply here. I have had a lot of people over on Reddit trying to tell me that a tape monitor port is for listening what the tape output sounds like during recording which is simply not possible due to the way the source select is designed.Thanks in advance, every input is appreciated

author: tooki
author_rank: Super Contributor
timestamp: June 20, 2025, 11:54:17 am
content: Quote from: DefinitivVair0 on June 20, 2025, 05:15:28 am1. If I understand it correctly, when tape monitor is on, OR when any input except Video is selected, the Video outputs are enabled. As best I can tell, this is simply a workaround to add an extra set of tapemonitor functionalityinputs to a selector chip that only has one tape selector.2. Just a buffer, I think. Perhaps for impedance matching or increased power to support the Video outputs.3. Use the monitor output that matches whichever inputs you use for the deck. Functionally they are probably identical.Quote from: DefinitivVair0 on June 20, 2025, 05:15:28 amThey’re telling you that because it is correct. The circuit does just that: when Tape Monitor (DE: Hinterbandkontrolle) is selected, the selector chip IC111 disconnects the main output from the selected input, but the input remains connected to the Monitor Out output of the IC, and internally connects the main output to the Monitor In input so that the amp receives the tape monitor signal. I’m not sure why you think this circuit can’t do that; it absolutely can and does.See also:Sharper version of the schematic (attached)Datasheet of the input selector IC (attached)

author: DefinitivVair0
author_rank: Contributor
timestamp: June 20, 2025, 12:37:32 pm
content: Oh that makes sense thanks.Apperently my confusion came from the schematic. I misunderstood what the IC is doing there. Thanks

author: DefinitivVair0
author_rank: Contributor
timestamp: June 20, 2025, 01:17:13 pm
content: Ok I just came home and tested it and guess what, it turns out all were rightBoth Tape 1 and Tape 2 rec can monitor everything except themselves. This means (for tape 1 because you can toggle it) that there is allways the first selected input going to the record in/out on the tape deck while listening to the original input and if you toggle tape 1 mon, you get whats coming out of the tape deck while still sending the first selection signal to the record. That means that it allways can record but you can select if you want to hear the original signal or the monitor of the tape deck.

author: themadhippy
author_rank: Super Contributor
timestamp: June 20, 2025, 01:45:37 pm
content: QuoteNormally the tape monitor lets you hear whats being put onto the tape,but requires a 3 head machine,it can also be used to insert stuff like a graphic equaliser in the system

author: DefinitivVair0
author_rank: Contributor
timestamp: June 20, 2025, 01:49:06 pm
content: Quote from: themadhippy on June 20, 2025, 01:45:37 pmI just updated the last comment since I now know whats going on. This specific tape deck has no 3rd head but passes the post volume signal back to the output when recording

author: tooki
author_rank: Super Contributor
timestamp: June 20, 2025, 01:51:44 pm
content: Quote from: DefinitivVair0 on June 20, 2025, 01:17:13 pmThat’s exactly right, you got it now.P.S. In English we don’t say “boxes” for speakers. (“Boxes” simply means “Schachteln”.)

author: DefinitivVair0
author_rank: Contributor
timestamp: June 20, 2025, 02:28:34 pm
content: Quote from: tooki on June 20, 2025, 01:51:44 pmYea sorry, I allways get confused with german since I usually say "Boxen" instead of "Lautsprecher" xD

author: tooki
author_rank: Super Contributor
timestamp: June 20, 2025, 04:04:35 pm
content: Quote from: DefinitivVair0 on June 20, 2025, 02:28:34 pmYeah, it’s super common. If anything, what’s weird in German is the name for speaker drivers: Lautsprecherchassis. So I think people often end up saying “Lautsprecher” for the drivers and “Boxen” for the assembled speakers.