The YARRA Preamplifier/HPA for Melbourne DB Group Buy

[xrk971]

You can use the RCA’s from Elecaudio or these that I have in my shop:

https://www.etsy.com/listing/1001951097/premium-rca-jacks-for-btsbyarra-pair

 

[Kokanee]

Thanks wcwc,

So are the 12HP059 rca connectors part of the whole rca unit or do they have to be ordered separately ?

I will check some of the links that people have posted for rca's and see what I can find.

 

[xrk971]

Those RCA’s need to be configured for 0deg mounting. By pulling out anchor pins from 90deg location to 0deg (end mounted) and bending legs of conductor pins straight.

 

[wcwc]

I ordered BNCs (dislike RCA connectors) to fit the pin profile on the PCB. You need connectors that have a PCB pin connection on the opposite end of the connector or 0 degree mounting. Also should allow for the connector to be supported by the back panel. They attach to the small switch board that came with your Yarra boards. They are not on the main PCB.

 

[Vunce]

This was my method for the I/O rear panel: Post# 773
https://www.diyaudio.com/community/...hpa-for-melbourne-db-group-buy.334457/page-39

 

[xrk971]

Manley RCA’s are the best in the business IMO.

 

[Kokanee]

Thanks everyone for their input. I saw the posts from Vunce about the Manleys, so will probably go with them.

One quick question concerning X125, X121, and X131, the headers under the pot pcb: Are they a straight header that is just soldered in bottom and top. If so, is their a part number for these to help me out.

Thanks

 

[Kokanee]

Got my header problem figured. I have a quick question about X123 and X133. Please see attached image.

JPS showed on one of his 3D sketches and looking at the schematic that pins 1&2 are joined together. JPS 3D shows a jumper type wire connection from the top. The connector I have in the image shows no such connection.

My question is can I solder the 2 pins together from the bottom of the pcb and accomplish the same result as having a jumper wire connection from the top of the connector. I think I can, but want to confirm.

Thanks for the help

 

[xrk971]

Yes, you can do this - it’s the connection to an optional headphone output. I think I simply put a 3 pin JST connector there and connected that to the headphone output jack.

 

[Kokanee]

Thanks X,

Just to confirm that the optional headphone output is X124 on the board.

 

[xrk971]

Yes, X124 is the headphone output.

 

[Kokanee]

Thanks X, I am going to use this as pre amp only, so I am going to solder X123 and X133 in place with no bridging of the pins. I will install X124 for possible future use. Please see attached pic as to how it will look.

Also, you can see that I have already soldered in the 4700uf caps for C126,128,136,138. After reading the posts that you had with thompsontechs concerning the time constant, would you leave the caps and the 47K resistor for R126,136 and live with the larger bleed time or should I consider reducing R126,136 to 1K ohm.

Thanks

 

[Kokanee]

Soldered X123 and 133 in place from underneath with a solder bridge on pins 1&2.

I have the C126 to C138 4700uf caps soldered in place back to back. I calculate the net resistance of 100K + 600 ohm to be 0.600K. My T= 0.7 x 0.6K x 2350 uf which equals about 1.0 sec, if my math is correct.

By using f=1/T, this gives a frequency 1.0Hz, so flat to around 10 Hz.

If this is all correct, can I change R126 and R136 to 600 ohm resistors and proceed with the build.

Not quite sure of all of this

 

[xrk971]

Sounds good.

 

[Kokanee]

Thanks X, any advantage to changing the caps to a lower value and calculating a different resistance value, or will it make no difference in the long run.

 

[xrk971]

If you won’t be using as a headphone amp,
I would go with smaller caps and assume your load is about 10k ohms. You might be able to use a smaller cap like Elna Silmic II.

 

[Kokanee]

Thanks for the reply. I soldered the 4700uf caps in a long time ago according to the BOM. I will be very careful when removing the 4 caps so as not to damage anything. I will see what caps I have in my inventory and plan the calculations based on the cap value I have and the assumed net resistance load of 10K. Thanks very much for the help.

 

[Kokanee]

Hi X, I think what I may do to exclude de-soldering the 4700 uf caps, is to make this Yarra board suitable for the HPA using the Melbourne DB. I will then use my other Yarra board for the Hakuin pre amp.

This way I can just adjust R126/R136 to recommended values, leave the 4700's in place and problem solved. I have not built any of the Melbourne DB yet, but have the components.

I think will solve a lot of my dilemma.

 

[Kokanee]

Hello X and others,

I need a little help in deciding whether to build the Yarra pre/HPA with capacitor coupling or DC coupling. I will be using it for preamp duties only, no HPA duties.

If I use capacitor coupling, the smallest capacitance value I can find is 100uf/250V/10mm lead space electrolytic caps for C126,C128,C136,C138. I am fine with this, if and only if, the 250V is OK to use.

Question: Can film caps be used instead of the electrolytics mentioned above.


If using DC coupling, does one just jumper C126, C128, C136, C138 and connect the Melb DB as per procedure?

Thanks for the help, I seem to be stumbling around trying to decide.

 

[Kokanee]

I have some Nichicon UFG 220uF / 100V for C126,C128,C136,C138. From post's I have read it is suggested to use a value of 1k2 for R126 and R136. If I use (100K x 1.2K / 100K + 1.2K) to get a net resistance of 1.18K, and then calculate the discharge time which is 0.7 x 1.18K x 111uF, I end up with a time 0.09 sec.

Does this seem plausible? I was thinking of using a 20K value for R126, R136 and end up with discharge time of about 1.5 sec. Am I calculating wrong? Thanks for the help.