Salas DCG3 preamp (line & headphone)

Connection between i-select and the dcg3?

Noob question, maybe asked before within the 468 pages :eek:

The output of the I-Select board is R+L+Ground (3 wires) while the inputs of the DCG3 are R+Ground and L+Ground (4 wires). What is the recommended way to interconnect these two boards? (double the ground signal coming from the i-select board? connect only one ground on the dcg3 side?)
 
Hi Salas,

I have made a start installing the resistors and I am about to put in a mouser order hopefully to get as many of the required items in one go. As Mouser gives so many options for everything could you please have a look and point me in the right direction if I am about to order anything incorrectly.Mon panier | Mouser France

Item 1, is for something else, please ignore.

Item 2, is for R9 as one is missing and I'd just like to check that this one is correct?

Item 3, I am building line-stage only 10R came with the kit should I put this 12R in to get a lower bias or is the 10R perfectly OK?

Item 4 is the DIP IC socket 8 pin for U1.

Item 5 TO220 silpads , The 6x plastic grommets I have not found them on Mouser. Are they for trapping the MOSFETs down? will a washer be ok?

Item 11, The info sheet says T350mA and in the kit the fuses are T400mA, I thought it a good idea to get some spares should I get the same as in the kit or get the 350mA?

If possible I would like to get a gain of 29db could you let me know which value for R6 would achieve this?


Also, I would like to get a volume pot and source selector, I realise that different volume pots have an effect on the final sound but I am unsure as to which one I should order, I don't mind how much it costs and would appreciate any advice on which one to get? and which source selector?
Also, is it advisable to have an extension rod on the volume pot in order to have the pot as close to the board as possible?

I am going to order the transformers from Canterbury Windings and would just like to check that the TM160A is correct?
Standard Range

Apologies for all the questions.

Thanks.
66deg AKA Simon.
 
Hi Salas,

I have made a start installing the resistors and I am about to put in a mouser order hopefully to get as many of the required items in one go. As Mouser gives so many options for everything could you please have a look and point me in the right direction if I am about to order anything incorrectly.Mon panier | Mouser France

Item 1, is for something else, please ignore.

Item 2, is for R9 as one is missing and I'd just like to check that this one is correct?

Item 3, I am building line-stage only 10R came with the kit should I put this 12R in to get a lower bias or is the 10R perfectly OK?

Item 4 is the DIP IC socket 8 pin for U1.

Item 5 TO220 silpads , The 6x plastic grommets I have not found them on Mouser. Are they for trapping the MOSFETs down? will a washer be ok?

Item 11, The info sheet says T350mA and in the kit the fuses are T400mA, I thought it a good idea to get some spares should I get the same as in the kit or get the 350mA?

If possible I would like to get a gain of 29db could you let me know which value for R6 would achieve this?


Also, I would like to get a volume pot and source selector, I realise that different volume pots have an effect on the final sound but I am unsure as to which one I should order, I don't mind how much it costs and would appreciate any advice on which one to get? and which source selector?
Also, is it advisable to have an extension rod on the volume pot in order to have the pot as close to the board as possible?

I am going to order the transformers from Canterbury Windings and would just like to check that the TM160A is correct?
Standard Range

Apologies for all the questions.

Thanks.
66deg AKA Simon.
Hi!i can advise you for the pot.put the best that you can buy.i have khozmo,20k,and in second built a tkd 20k.it should be 20k preferably,and series type.the tkd has a warmer sound,and khozmo has no sound of its own i think.you could also try gold point.very good results also,i have listened to it in another dcg3.for input selector i have used salas i select and is a perfect match.
 
I have been making a bit of progress today and have found some of the things I asked about above in the kit...ooops.
Please ignore item 4&5 as I have found them.
For U1 I have soldered in the DIP socket with the small notch to the top as it is drawn on the board. The AD823ANZ that slots into the socket could go either way around. I have seen a tiny notch in it and placed it in the same way as the socket (notch to the top) I'd just like to check that this is the correct way around?
Also the device above NEC EA2-12NJ could go either way around , as this would be difficult to de solder I thouht it best to check before its fixed if can it go either way around?


Thanks.
 
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@66deg

I have AD823 with notch in the middle plus a dot left of the notch next to pin one. And I have other year of production AD823 with middle notch only. Both are valid. You aligned the notch with the socket's notch as also printed on the board and that's alright.

In general examine other people's builds closely from photos they posted in this thread. There are very many of those.

Gain 29dB is a number found in described as sensitive power amps not in modern preamps. Are you sure you want that? Brings explosive volume and hiss increase in any normal system.
 
diyAudio Chief Moderator
Joined 2002
Paid Member
I am going to order the transformers from Canterbury Windings and would just like to check that the TM160A is correct?
Standard Range

Type: TM160A Continuous power rating: 50VA
Primary: 0-240V @ 50Hz
Electrostatic screen
Secondary: 18-0-18V @ 1.39A rms
GOSS band
Dimensions: approx 83x44mm
Mounting: mounting kit

That's a very good choice for the DCG3 transformers.
GOSS band keeps electromagnetic interference in check.
Few transformers offer such stray field shield as standard.
 
diyAudio Chief Moderator
Joined 2002
Paid Member
Hi Salas,
...

Item 5 TO220 silpads , The 6x plastic grommets I have not found them on Mouser. Are they for trapping the MOSFETs down? will a washer be ok?

Item 11, The info sheet says T350mA and in the kit the fuses are T400mA, I thought it a good idea to get some spares should I get the same as in the kit or get the 350mA?

For BOM little things read the manual's list many times. T350mA or T400mA isn't a big deal of a difference. Get the same as spares, no worries. For items which are coming from a mini-kit ask Tea for details. SilPads and nylon mounting grommets for the MOSFETS are essential. They must be isolated from their sinking both at the back and in the neck else kaboom! In the end you will check with the DMM's buzzer (continuity mode) that no MOSFET metal tab produces beeps when probing between it and the metal surface they are mounted on. Before powering up. If ts black anodized surface find a shiny spot to measure. You can also measure on the metal screws heads.
 
Its alive....

Another DCG3 is alive....
 

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diyAudio Chief Moderator
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The manual says that "all outputs should measure below +/-18V. Mine measures V->G= 17,4 V / G>V+=25,1V on one board and V+>G=17,2V / G>V-=25,1V on the other board. Any suggestions what I can have messed up...?

I am using two 18+18V transformers.

25.1V at a psu section output indicates a fault. Seems like the rectified dc level passes straight through. You could be having wrong or broken same position TO-92 small transistors in those two high output sections. Maybe PNP and NPN swapped over. Check the types and their places closely first.
 
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Hi Salas,

Thanks for all the info I'll send a PM to Tea regarding any questions about kit bits.
Could you tell me what gain in db for the following options in R6.
1K=?
499R=?
1.5K=?

Thanks for your help and advice.

As r_jik45 said Its already described as times gain in the manual

"4. Decide gain
The standard setting is 3x. That's a good figure for line and headphones. 2x to 4x is a recommended area of customization according to your needs. R6 sets the gain. 1K for 3x, 499R for 2x, 1.5K for 4x. Unity gain can't be set."

Converts to 4x=12dB 3x=9.54dB 2x=6dB