Revising Cambridge Soundworks DTT2500 amplifier, adding a TOSLINK? - Page 1
Forum section: electronics / projects

author: Dutchguy
author_rank: Newbie
timestamp: September 10, 2016, 05:35:05 pm
content: Hi everyone! I'm new to this forum so I will introduce myself first.I am 41 years old and was born and raised in a small town near Amsterdam.I discovered electricity at a very young age by fooling around with the 'child proofing adapter' my parents had placed in the wall outletthat powered my night lamp. I managed to pull it out of the socket just far enough so that I could touch both poles with my fingers.Although it was a painful experience I ended up in the field of electronics working as a security technician for almost 20 years.Currently I am looking to reinvent myself because I cannot do that kind of field-work anymore due to lower back issues.I discovered EEVBlog by watching YouTube videos. Both thumbs up for Dave!I recently decided to revise my 16 year old 'Desktop Theater' instead of buying something new.Although 'made in China' it is a great 5.1 channel amp build around pretty decent components.(Zoran 38601 processor and PCM1716 DACs on the decoder and 3x TDA7360 with TL072CP op-amps on the amplifier board)The build quality is also OK. for its price range but could have been better.Although it has 5.1 channels for AC3 decoding it only supports 4 channels on both analog and digital DIN inputs.To keep the costs down even further, they've also skimped on the quality of the electrolytic capacitors.But its worst 'feature' is the linear potentiometer used to control the sub-woofer level instead of using a logarithmic version (that it desperately needs).It has been in active service all those years and it was really starting to show;Noise coming from the speakers.Crackling potentiometers.A randomly resetting audio processor (causing all channels to briefly mute).No sound from the left surround speaker in analog 'four point' mode.The problems with the dirty pots was an easy fix and the constantly resetting audio-processor turned out to be a common issue withthis device. The capacitor buffering the processor power-supply was defective (high ESR).Since all the electrolytic caps are at least 16 years old I decided to replace all of them with high quality audio ones.A friend recommended I use Elna Silmic II capacitors and my ears are very happy I followed his advice.The Elna caps become quite a bit larger then the existing ones as the capacitance rises, so I also ordered some Panasonic NHG caps not being sure the Elna's would fit.(I ended up using just 5 Panasonics and almost 100 Elnas)Replacing the electrolytic caps has solved the other issues, except for the missing left surround channel when using analog 'four point' mode.It does produce a lot of (white/pink) noise on the left surround in this mode (and also on the right surround but a lot softer) when I turn the volume to 50% or higher.I do not care to much about it, my intended use for the device is SPDIF/AC3 decoding only.Nevertheless, I think I have traced the fault (through deductive reasoning) to the op-amp (NJM2123) directly behind the analog input jack of the rear speakers.Is there a method to verify this using a cheap multimeter?The main reason I made this forum thread is because I would like to add an optical input to the existing coaxial input.There are plenty of optical to coaxial circuits to be found on-line, or I could build the opto/coax-converter of Elektor 4/97 page 40.But I would like to build it into the device itself.I already have a TORX173 and the power and ground pins are easy enough to figure outbut I am unsure how to connect the output of the TORX173 to the existing circuit and could use a little help with that.Is it OK. to connect it in parallel to the output of the existing SN75179B differential driver/receiver pair that (as far as I can tell) directly connects to the SPDIF input of the audio processor?I've added a gschem screen shot to clarify what I mean.I would have liked to be able to post some higher detail screen shots but I do not think that would be wise since it is a copyrighted board.I did however add some screen shots with a little less detail to show off my new Elna caps

author: Dutchguy
author_rank: Newbie
timestamp: September 12, 2016, 08:06:45 pm
content: The circuit below should work just fine and requires very minimal modifications on the existing circuitboard. With a little bit of luck it will all fit inside the case.

author: Phantom8
author_rank: Newbie
timestamp: November 02, 2020, 02:20:34 pm
content: I understand this post is old, but I've a similar problem with the audio processor resetting resulting in all channels muted intermittently when using coaxial input.@Dutchguy, you mentioned that "The capacitor buffering the processor power-supply was defective (high ESR)." Can you tell me which capacitor is it? Is it under the shield? I'll like fix it if possible. Thanks!.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 02, 2020, 02:57:46 pm
content: Most straightforward way is to put in a switching circuit to select between the two.Quote from: Dutchguy on September 10, 2016, 05:35:05 pmIf it's a product available to the general public, you can post as much detail of the teardown as you like. ROM dumps, however, are indeed covered by copyright.

author: Dutchguy
author_rank: Newbie
timestamp: November 02, 2020, 10:48:21 pm
content: @Phantom8 It is under the shield. Next to the Zoran chip there is a LE33 voltage regulator (for the Zoron chip). The capacitor in question is right next to the voltage regulator (C224).I did manage to add the TOSLINK and it's still working today, connected to my Kodi box that encodes/upmixes all audio to 5.1 channel Dolby Digital.

author: Phantom8
author_rank: Newbie
timestamp: November 03, 2020, 03:03:17 pm
content: @Dutchguy, thank you so much for your help. I managed to fix the problem by replacing the two capacitors around the LE33 that you mentioned. First, I replaced the 100uF 16V (C224) with a 220uF 25V cap. Since I didn't have a 100uF cap, so I used a 220uF cap instead. However, this didn't solved the problem. Then, I proceeded to replace the 22uF 16V (C218) with a 22uF 25V cap and this finally fixed it. I measured the capacitance of the 2 unsoldered cap with a multi-meter and can confirm that the culprit is the 22uF 16V cap and the meter could't read any capacitance from it. The 100uF 16V cap seemed to be fine in my case.Your help is highly appreciated. Without your assistance, I don't think I can fix the Amp. Thanks again.BY THE WAY, I hope it's okay to use a 220uF cap instead of a 100uF for the C224.

author: Dutchguy
author_rank: Newbie
timestamp: November 03, 2020, 05:09:06 pm
content: It should be okey to have a larger value for C224. Replacing that was my original fix for the constantly resetting audio processor. I ended up replacing all electrolytic capacitors because I had nothing better to do at the timeI'm glad I could be of help.

author: Phantom8
author_rank: Newbie
timestamp: November 04, 2020, 12:51:00 pm
content: If I were to replace all capacitors, it will possibly take days, if not weeks for me to finish. The shield alone took me 2 hours to desolder. lolIt's really good to have a working AC3 amplifier for my PC again.

author: mrmuzzio
author_rank: Contributor
timestamp: October 06, 2021, 11:44:20 am
content: Hi everyone, I also have one of these amplifiers and I really like it.Some days ago, it suddenly powered off, and I took it apart, cleaned the volume pots and didn't find anything wrong, except a bit rusty fuse holder. Then it powered up and worked for a few days, now it doesn’t power up againI've started a new post, since this was inactive for quite some time... but nobody replied:https://www.eevblog.com/forum/projects/creative-soundworks-dtt2500-wont-power-up-(possible-solution)/msg3714295/#msg3714295The power brick seems to be OK and I only have a multimeter to test, but the output voltage its fine.The led inside the power button lights up very very dim so I believe that the problem seems to be in the power board.I’ve read that changing some capacitors near the sound processor may be of help, so I may try that also.Any help on how to diagnose the problem is really appreciated.Thanks a lot !!!

author: aytekdorken
author_rank: Newbie
timestamp: August 15, 2023, 07:22:38 pm
content: Hi, I am also an old DTT2500 owner and I have been keeping it in a box for almost 20 years.I would like to reuse it as 4.1 music speaker. My home ecosystem is build on Apple. (Apple TV, iPhone, iPad, Mac etc.) What I would like to achieve is to have 4.1 upmixed sound maybe by connecting a raspberry pi with kodi.1- Is it possible to have 4.1 upmixed sound by airplaying sound from an apple device to kodi?2- Do I need to make the modifications here that @dutchguy applied amazingly to his DTT2500 in order to achieve my goal?

author: tooki
author_rank: Super Contributor
timestamp: August 16, 2023, 02:38:54 pm
content: I wouldn’t invest the time to modify something like this, since you can buy real AV receivers for peanuts now: since everyone upgraded to models with HDMI, AV receivers with only analog video jacks sell for nothing on the used market.

author: 2N3055
author_rank: Super Contributor
timestamp: August 16, 2023, 02:45:28 pm
content: Quote from: tooki on August 16, 2023, 02:38:54 pmI kept the speakers and use them with a Yamaha receiver, I was given by the friend.... Sounds really, really good...