Modifying the Beresford TC-7510 DAC
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 (JRC455
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....?
This is so far over my head it is stratospheric, but again, great photos and very interesting.
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
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.
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!
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.
The components have landed.
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....
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!
Hmmmmmm. Maybe it just looks smaller off the board?
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.) 
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
I do intend to complete the mods.......just been a little busy lately. Hopefully, I get round to it next weekend.
Watch this space!
I've completed Mod 21 parts 1 and 2. I'll do the write up later this week. Sneak preview? Sweet!
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.
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