Trace Acoustic DC2 module

[retgaz]

Hi
I've had a Trace Acoustic TA100R brought to me for repair (schematic attached). The DC2 module has gone faulty giving random bursts of noise. The DC2 unit can be seen on the left hand side of the output stage schematic.. The amplifier was made in 1993 and Trace Elliot aren't responding to requests for a replacement module or information regarding what's inside the sealed unit. So my questions are:
1 Does anybody have a source for a replacement unit or a schematic to build a replacement?
2 If the answer to question 1 is no (as expected) can anybody see any problems with my plan B, which is to disconnect the DC2 module and either remove c5 or ground the open end of R4?
I realise the sound of the amp will change without the module, but at the moment it's just a very big paperweight and useless to my customer.
Thanks in advance

[Enzo]

We don;t really have any idea how much or if it would change the sound. But before we start worrying about removing parts or grounding anything, why not just remove it and see what happens. It only had 5 connections, two are power supplies and a third is ground. That 0.2 ohm resistor that provides its input would never miss it, and the output from it is cap isolated from the amplifier, so it wouldn;t upset the DC. So see what just ditching it gets you


You are in the UK, so if you are emailing Trace UK, try picking up the phone and calling them. it is easy to ignore emails, they have to work not to talk to you on the phone. Unless they just tell you they have nothing to tell you, at which point you have your answer

But then, Peavey has bought them, at least over here. And if you contacted - email OK - the repair techs there, not the parts department, you might ask if they have them or know what is inside.

But i also have this thought. It is a potted part. They are never repaired then. And while Trace engineers at some point designed a circuit for inside it, it would never be used for anyone in repairing it. The only repair would be replacing it - it is potted.

Then again, if you have a bad one and remove it, what is to lose by carefully excavating it out of the potting stuff and tracing out your own little schematic. And at that point we could see what it does, and if you wanted, duplicate the circuot.

[retgaz]

Hi Enzo.
Thanks for your reply.

I'd already removed the unit before posting to prove that the fault was coming from that module, having looked at the schematic and come to the same conclusions as you about removing it for testing. I haven't heard the sound of the amp with the unit in circuit to be able to compare sounds. With the unit in place the bursts of noise were like machine gun fire at the full output power of the amp, so to protect the speakers I had connected to a dummy load and chased the fault with a scope. After removing the module I was able to run the amp for several hours without any problems. The only problem occurred when I switched the amp off, at which point the amplifier oscillated until the capacitors discharged. I did not have the pre amp connected at this point, having disconnected it in the search for the source of the problem.

I haven't seen any contact details for Trace in the UK, but I will look again and try your suggestions for contacting them. I didn't know Peavey had bought them, that gives me some hope.

I had considered trying to excavate the circuit from the module, but it looks like they have immersed the circuit in a black epoxy resin, so I'm not hopeful about getting the board out and still being able to identify components.

Thanks again

[Enzo]

You don;t need to know what it sounded like with the DC2, all you need to know is what it sounds like now, and does it sound good or bad?


I don't know if there even are any good contacts in the UK, I just meant if you are emailing somewhere in the UK, they probably also have a phone. If all of them are in Malaysia, then forget the phone.


Ever watch then dig a dinosaur fossil out of solid rock? Pick pick pick, tiny flakes of not-dinosaur are removed slowly and with care. After a while all that is left is dinosaur. It won;t be like cracking the candy off a tootsie pop.

[retgaz]

Thanks Enzo

All good points.

I suppose eventually the question of how it sounds will be up to the customer, but I do take your point.

Before I connect it to a speaker to try out I want to eliminate the oscillation that occurred at switch off. I was also wanting to tie up any loose ends before refitting the output board into the amplifier and reconnecting the pre amp. Hence my question about R4 and C5.

If I can't replace the DC2 module and the amp's working I can ask the customer if he wants to pay for the faulty one to be cut into.

[Ted]

I've had exactly the same problem. I called EMS, who inherited a lot of Trace Elliot's spares stock when the company changed hands a few years back.

Electronic Music Services - repairs to all major makes of electronic instruments - Southend-on-Sea

The guy said that they used to remanufacture DC2s when they had enough orders, but that nobody had asked for one for years. He also said that if you disconnect the unit, the only audible result is a slight change in EQ which can be corrected by use of tone controls. I've done this on a couple of them, with no complaints.

I guess someone should take a Dremel to a DC2 some time to find out what lies under the epoxy. Not much would be my guess.

[retgaz]

Hi Ted.

You beat me to that bit of info.

I'd rung EMS yesterday after Enzos tip off about Peavey taking over Trace had sent me in their direction. They look after all pre 2005 Trace Elliot support. The guy I spoke to said they have the DC2 modules in kit form which they will make up if anybody wants one for about £50. Delivery taking about a week in the UK.

The rest of the conversation was pretty much the same as yours though.