Modifying the Beresford TC-7510 DAC

[PJPro]

I've decided to take the plunge and have a go at modifying (modding) my Beresford DAC. There's a few threads out there that cover this......but I hope to produce a blow by blow guide for the electronics amateur (such as myself).

Inside the box

Beresford TC-7510 DAC Internals

This next bit is my interpretation of the internals and could be cobblers, so take it with a pinch of salt.

The board at the back is the DAC itself. On the very left are a couple of big capacitors which form part of the DC power input stage. Then there is the signal output stage which amplifies the analogue signal for the variable and fixed outputs. To the right of signal output stage are the actual DAC components.

The board at the front contains the bulk of the DC power input stage components (left), power switch, input selection, headphone amplifier and volume pot for controlling the headphone amp volume and the variable signal output.

Beresford TC-7510 DAC Output Stage

Beresford TC-7510 DAC Output Stage - closer

In the middle of the signal output stage you can see the surface mounted opamp (JRC4558) surrounded by surfaced mounted resistors and capacitors, radial electrolytic capacitors and, what look to me to be, a couple of ceramic capacitors (CC1 & CC2).

The Modifications

The first modifications (mods) I'm going to perform have the support of the designer. Stanley has produced a couple of .pdf files to document these mods and has discussed them on another forum. These mods are called Mod 21 and Mod 21 Pt 2. These mods focus on changes to the signal output stage.

However, if I do any other tweaks to the DAC, I'll use this thread to document them. Clearly, I'd be interested to read about the mods other people have performed and would encourage them to use this thread as well to keep them all in the same place.

Mod 21

Mod 21

Refering to the photo above, this mod removes the resistors at R11 and R14 and replaces them with a solder bridge and replaces the four identified electrolytic capacitors with 47uF / 16V rated versions.

The solder bridge is effectively free. I have ordered the four capacitors from Audio Upgrades and have gone for these.

4 x Rubycon ZA 16V 47uF. Cost = £7.60.

On the face of it this mod should be fairly easy to do and doesn't really give me any cause for concern.

The pdf by Stanley is available here.

Mod 21 Pt 2

Mod 21 Pt 2

Refering to the photo above, this mod replaces the JRC4558 opamp with a National Semiconductors LM4562MA opamp and replaces the decoupling capacitors at C5 and C6 with a couple of WIMA 220pF/100v polypropolene capacitors.

I have ordered the replacement opamp from Audio Upgrades which can be found here. I'll get the WIMA caps from Maplins which can be found here.

1 x LM4562MA Opamp. Cost = £5.49

2 x WIMA 220pF/100v. Cost = £0.30p

This mod is a different league to the first with the potential to brick the DAC. Removing the old opamp will be difficult enough. Soldering the new one in will be just as hard...maybe more so. I'm a bit worried about this one. Still, nothing ventured....

The pdf by Stanley is available here.

I'll update the thread as and when the components arrive and the work progresses. Now, where was I with that headphone amp thread....?

 

[daveh75]

PJPro:I've decided to take the plunge and have a go at modifying (modding) my Beresford DAC. There's a few threads out there that cover this......but I hope to produce a blow by blow guide for the electronics amateur (such as myself).

I'll update the thread as and when the components arrive and the work progresses. Now, where was I with that headphone amp thread....? Cool...will be keeping my on this thread and awaiting your impression's on the mod's!Keep up the good work

 

[idc]

This is so far over my head it is stratospheric, but again, great photos and very interesting.

 

[Anonymous]

Nice to see you getting the soldering iron out, think you will be pleased with the improvements.

However I would have gone for the Elna Silmic II (RFS Series) Electrolytic Capacitors instead of the Rubycon ZA's @£1.53 + vat each.
Here's a link
www.hificollective.co.uk/components/elna_capacitors.html

 

[PJPro]

trevor79:Nice to see you getting the soldering iron out, think you will be pleased with the improvements.
Trevor, have you done these mods already? If so, how did it go? Was it difficult?

trevor79:However I would have gone for the Elna Silmic II (RFS Series) Electrolytic Capacitors instead of the Rubycon ZA's @£1.53 + vat each.
Here's a link
www.hificollective.co.uk/components/elna_capacitors.html
Hhhmm. Perhaps I should have posted my intentions before buying the caps and requested advice on which to get. Oh well, I've ordered them now.

 

[TitusG]

Hi there

Just wondering what improvements these mods will make. Obviously for the better but do you have any idea how it will effect the sound? I should have paid more attention to my lecturer in college!

 

[Anonymous]

PJPro:trevor79:Nice to see you getting the soldering iron out, think you will be pleased with the improvements.
Trevor, have you done these mods already? If so, how did it go? Was it difficult?

trevor79:However I would have gone for the Elna Silmic II (RFS Series) Electrolytic Capacitors instead of the Rubycon ZA's @£1.53 + vat each.
Here's a link
www.hificollective.co.uk/components/elna_capacitors.html
Hhhmm. Perhaps I should have posted my intentions before buying the caps and requested advice on which to get. Oh well, I've ordered them now.

No I haven't modded one, but I do know my components. The mods are straight forward enough, a steady hand, cup of tea and a digestive!

My stuff is a little higher up the food chain so use more expensive components, ie Oscons for decoupling caps.

 

[PJPro]

The components have landed.

 

[PJPro]

TitusG:
Just wondering what improvements these mods will make. Obviously for the better but do you have any idea how it will effect the sound?
Take a look at this article by Tangent.

TitusG:I should have paid more attention to my lecturer in college!

I don't profess to have any great knowledge of electronics. I'm half competent at soldering and can follow instructions. However, I am learning....

 

[PJPro]

Thought I'd take a look at the replacement opamp.

LM4562MA

Errrr. It's a lot smaller than I was expecting. A lot, lot smaller! Doesn't bode well for the upgrade. My soldering iron tip will cover two legs at once!

 

[PJPro]

Hmmmmmm. Maybe it just looks smaller off the board?

 

[chebby]

Good luck PJ.

Boy, am I glad I got the TC-7520 with it's 2 handy DIP-8 sockets!

All I had to do was make sure the LM4562NA's were the right way round before I pushed them in. (And they are bigger than your SOIC versions.)

 

[PJPro]

I did a bit of preparation for these mods today by having another look at a couple of tutorials by Tangent. These were "Surface Mount Soldering Techniques" and "How to Desolder Electronic Parts". There are actually 15 tutorials in total from Tangent available here. All take the form of videos.

I also went out and bought a soldering iron from Maplins with a much finer tip. I got this one.....only to find out later from another of Tangent's tutorials that it might be a little under powered. Damn! Oh, well. I'll see how it goes.

12W Miniature Soldering Iron

 

[PJPro]

I do intend to complete the mods.......just been a little busy lately. Hopefully, I get round to it next weekend.

Watch this space!

 

[PJPro]

I've completed Mod 21 parts 1 and 2. I'll do the write up later this week. Sneak preview? Sweet!

 

[PJPro]

So the first step is to get the cover off the Beresford and investigate how to get access to the bottom of the DAC PCB. Four screws located underneath the Beresford secure the lid to base.

The lid off.

To gain access to the bottom of the DAC PCB, you need to take the screws out securing the sockets to the back of the Beresford. There's one each socket (except the DC power input).

Undoing the screws securing the sockets.

Finally, there's two screws securing the DAC PCB to the base. Undo these and put all the screws to one side....you don't want to lose one!

Undoing the screws securing the DAC PCB to the base.

You'll find that the DAC PCB won't actually just lift off as there's a big capacitor in the way. Gently ease the DAC PCB back so that the sockets clear their holes in the back and wiggle the PCB clear. The DAC PCB will still be connected to the power, switch and headphone amp PCB by the multi-wire connectors (grey things in the picture below).

The DAC PCB freed from the case.

OK. With the trusty NC10 to hand, to double check what I need to remove, we're ready to start!

Setup and ready to start.

I firstly removed the resistors at R11 and R14. To do this I used the oscillation method recommended by Tangent. You take the tip of your soldering iron and hold it on one end of the resistor for perhaps a second and then on the other end for a second and then back to the first.

The idea is that sufficient heat builds up so that the solder at both ends is molten and the resistor just falls off. This didn't quite work for me. I had to sort of clip the resistor with the tip of the iron as I switched back and forth between the ends and this helped to knock the resistor off...in fact it stuck to the tip of the iron.

The picture below shows where R11 and R14 were located (red rectangles).

R11 and R14 removed.

Now I need to remove the four electrolytic capacitors identifed in Stanley's picture. These are EC4, EC5, EC8 and EC9. From the underside, you need to find the pads where the capacitors are soldered on.

As these are electrolytic they have to be placed into the PCB a certain way round with regard to polarity. The convention is to make positive pads square (only when the component is sensitive to polarity), while other pads are round.

Knowing this helps identify the pads we are looking for. See the picture below, where the pads are identified using red rectangles.

EC4, EC5, EC8 and EC9 from underneath the PCB.

So, to extract the capacitor takes a little force. Tangent provides a video tutorial on now to do this. While you heat one of the pads with the soldering iron, gently lever the lead through the PCB by pushing against the capacitor body with your thumb. You might need to push quite hard.....just make sure you are pushing the right one!

You'll notice that the holes where the new capacitors need to pass through the PCB are blocked. We'll come to this later!

The electrolytic capacitors removed (from underneath the PCB).

That's the removal side of things for Mod 21. However, I'm going to press on with the part 2 removals.

The next things to remove are the decoupling capacitors at C5 and C6. These were surface mounted, so I used the oscillation technique and removed them without issue.

C5 and C6 removed.

Now I had to remove the opamp. Gulp! I tried using Tangent's technique but couldn't really get my soldering iron in there. So, I switched to the method advised by Stanley.

Take a sharp Stanley knife and cut the legs through on the opamp on one side. Stanley then recommends that you do the same on the other side but I found that by bending the opamp back and forth soon snapped the remaining legs.

Once the opamp body is separated from it's "feet" (which are still soldered to the PCB) you simply place your soldering iron on each of the remaining feet and sweep them towards where the opamp used to be with the tip of your iron.

Partially removed opamp.

All components removed.

Now everything has been removed, it's a matter of soldering on the replacement parts. That's for the next post.

 

[Anonymous]

Excellent!

Now clean up the holes before you think about inserting the new components.

It's easy then. ;-)

 

[PJPro]

Cleaning the holes was about the most difficult bit of the whole project (no pun intended). I don't own a desoldering vacuum gun thingy...or it would have been easy. Perhaps I'll invest in one?

 

[Anonymous]

Naw, just get a length of wire/paper clip etc heat it up and run it through the hole.

Also clean the board of flux (damp cloth), you don't want any arcing across when soldering the replacements in on the board.

 

[PJPro]

trevor79:Naw, just get a length of wire/paper clip etc heat it up and run it through the hole.
I didn't think of that! Thanks. I'll try it next time.

 

[PJPro]

Oopps. I've just bought one of these off ebay

Fluke 179

 

[PJPro]

trevor79:Also clean the board of flux (damp cloth), you don't want any arcing across when soldering the replacements in on the board.
I tend to use isopropyl alcohol to clean my boards.

Isopropyl Alcohol

 

[John Duncan]

Jeezy peeps. I would have a very expensive paperweight at the end of doing this...

 

[PJPro]

The first component I'm going to place on the board is the opamp. It's the smallest, most difficult and needs the most space to get in there. I used a pair of needle-nosed tweezers to pick the opamp up and position it on the board, making sure the feet of the opamp were over the soldering pads.

Note: you need to make sure that you get the opamp the right way around. In this instance, the round depression on the surface of the opamp needed to be in the top left hand corner.

Opamp in the tweezers. It's sooooo small!

I then held the opamp in place and applied the soldering iron tip to each of the feet in turn, pressing it down into the molten solder, until the opamp was soldered into place.

Opamp soldered in place.

To be honest, I didn't make the best job of this. I'm not convinced that the feet are as well soldered to the board as I'd have liked and it's more than a little skewiff! With a little more care and attention, I know I could have done better. My main concern here was laying on too much solder which would create a bridge that I couldn't remedy.

The next step to create the solder bridge across R11 and R14. I had a little trouble with R11 for some reason and couldn't get the bridge to form.....but I got there in the end.

Solder bridge across R11 and R14

Next up were the WIMA capacitors for C5 and C6. The slight problem here is that the ones which I removed were surface mounted whereas the replacements are through hole i.e. they have legs. To overcome this, I bent the legs to form little feet, giving me a little more lead to actually solder to the board.

WIMA capacitor modified for surface mounting (please excuse the rubbish photo).

I wanted to use the same method to solder the WIMAs to the board as I had used for the opamp. So, learning my lesson, I first placed small blobs of solder on the the pads to provide a little more into which to bed the WIMA feet.

Solder blobs on C5 and C6

Taking my miniture, needle-nosed pliers, I picked up each capacitor in turn, positioned it on the board and then pressed the feet down into the molten solder.

WIMA capacitors in place

All that remains is the electrolytic capacitors. The only complication here is to ensure that you get them into the board the right way round i.e. the positive lead to the positive pad. For this particular capacitor, the positive lead is the longer of the two. The negative lead is indicated by a pale stripe on the body. The positive pad is square. Push the leads through the board and bend them over to hold them in place.

Electrolytic capacitors on the board, ready for soldering

It's now a simple matter of soldering the capacitors in place by heating the pad and lead for a second or so with the iron and applying the solder to both.

Electrolytic capacitors soldered to the board.

I then trimmed off the excess lead using a pair of side cutters. The mods are complete.

The completed board.

I stuck the PCB back into the box and replaced all the screws. You can clearly see the WIMA caps in the top left hand side of the DAC.

Back in the box.

Finally, I needed to test the DAC to make sure all was well. No test voltages are provided...so I simply pressed on with actually using the DAC. To do this I fed the DAC a signal from my PC via optical cable. Rather than use my headphones, I plugged a pair of crappy active speakers into the headphone socket. If they got fried, it wouldn't matter.

First test: Expendable speakers.

All appeared to be well with this test. No clipping, no oscillation, no smoke! So I moved onto the final test, plugging my DIY Nova into the fixed line out and my Grado SR80s into the Nova.

Final test: full rig.

The first listen is more about detecting potential problems (which may be killing your headphones) rather than an enjoyable listen where you delight in the sonic improvements you've made. However, I am very pleased with the results. For me there seems to be more detail, increased separation between the instruments and more tightly controlled bass.

Ofcourse, my assessment could well be cobblers. I'm no golden ears and recognise that I may, subconsiously, be being a little less subjective than I would be if someone else had made the mods. Not only that, more than 24 hours have passed since I last heard my rig and I can't precisely remember what it used to sound like. Others may have that ability. I don't.

Should you bother with this upgrade? Well, it's fairly easy, doesn't cost much (if you have the tools) and takes a hour at most to complete. Yeah, I reckon it's worth it.

 

[Anonymous]

Excellent thread PJPro! Most people, including myself, wouldn't have the b...s!

Superb pictures and good narrative, I wish all instruction manuals were half this good!!

Let us know if its made a worthwhile difference in sound quality once you've enjoyed some well earned listening time!