Mods to preamp?

[brucew268]

“I’ve been thinking about my preamp lately” My wife hates to hear phrases like that because it usually means spending money… and time, when neither are in unlimited supply.

Yet I’ve read about upgrades, to caps and diodes on preamp power supplies, and to caps on the signal path, having sometimes significant results.

Current kit: Classe Audio 30 preamp and Classe Audio 70 amp (full balanced), Calyx 24/192 DAC fed by USB from a PC, MIT MH-750 speaker cables, Harmonic Technology IC’s. Good soundstage, good detail and space, good bass and sense of space. So nothing to winge about and fairly happy overall… and I can’t justify a new purchase. But there are reportedly much higher performing amplifier pairs out there. Could I move to a next level without serious dosh or new amplification?

It looks like stealth diodes are less than a pound each, so no worries there. They do look rather different than the stock, more like what I think may be opamps on my PCB. For caps: most of the exotic caps at hifi collective are much smaller values than the power supply caps, so I’m not really sure what my options are. It looks like I could get Nichicon FW for under £2 each, or Jensen Axial Electrolytics at maybe £6 each. Are there others I should consider, or maybe power supply caps are not where I want to focus?

The power supply has 8 diodes (1N4003) which might be replaced by fast stealth options, though I don’t see how to identify what replacement models would be best… and has 2 caps 16v 4700mF, and 4 caps 63v 1000mF, and then 2 Wima caps 63v 0.1mF.

The signal area is a bit more confusing. I try to read schematics about once every 10 years don’t claim to really understand too much about circuits except for the very basic function of resistors, capacitors, and the like. And when voltage and capacitance values differ in stock to purchase,I have no idea what is a good replacement value and what is not.

So the schematics say there should be 4 caps in the signal path, but two of them appear to be Wima 0.1mF (red) and two appear to be 47pF glass jobbies. And they don’t quite match the positions on the PCB, one 47pF is where the schematic says it should be and the other position on the PCB is empty but put instead at a position not identified on the schematic. Then there are 4 ‘decoupling’ caps, same Wima 0.1mF jobbies.

Thoughts, or who I should consult with?

(Wasn’t sure which forum this should go in. Feel free to move it if necessary.)

1006810069

[Reffc]

Whooaa there Bruce!

What is it you're hoping to change and what is it you think isn't right about the preamp as it stands? Without wishing to pour cold water over things, this fashion for changing capacitors will have absolutely no effect whatsoever in some circuits except to relieve you of your hard earned and should only be considered in those circumstances if the originals need changing.

You really need to know a little about the circuit before making decisions on what to change and why. Best advice would be to contact Classe, the manufacturers and ask them if doing as you suggest will yield the results you are trying to achieve. Classe are pretty decently designed and manufactured amps so you may end up disappointed that after spending so much on "upgrades" that it may result in no change or at least only subtle changes.

This comes back to the question "what is it you don't like about your current preamp and what is it you're trying to achieve?"

You need to be specific as throwing money on component upgrades can be very hit and miss otherwise. If the overall sound just isn't to your liking, is this the preamp or the power amp or even the speakers?

There are certain circumstances though where Cap upgrades can have significant improvement effects, particularly where the originals are clapped out and/or way out of tolerance, but it sounds unlikely that this could apply to yours as it would have used fairly modern and robust caps. Its a great preamp by all accounts. I'm struggling to see where you're going with this because by your own admission there's nothing really wrong with what you have. There's always "better" and if you start down that route, it usually gets expensive and is never ending. Perhaps you just need to listen to a few alternatives to either convince you that what you have is spot on for your needs, or that investing in a change would yield significant improvements. Perhaps try a passive preamp as well as in many cases this can open up the sound and result in less colouration (sometimes at the expense of gain/bass depending on the amp match and sources used).

[brucew268]

Fair question. In terms of my goals, to be honest:

I don’t really know completely.
I always read that if someone is going to improve the performance of a preamp, amp, or DAC, the first place to look is the power supply. And I’ve read several reports of upgraded power supplies and other components, either internally or externally with significant improvement on already excellent brands, whether Conrad Johnson, audio research, or others.
Usually I hear of added openness, ease, or naturalness to the sound, while also having increased depth and layers. I’ve read of CP-30/35 owners who speak of improvements when they went to a CP-50/60, etc. While I like the sound I’m getting, it would seem logical that some focus on the power supply might take what I like and go even further.

Do note that I was asking for the name of someone to consult with about this preamp, who might analyse where benefits might be obtained. I can query Classe, but my general experience is that manufacturers are very unhelpful when asked about mods to upgrade a box.

Thank you for your thoughts Paul. I do appreciate your input (and I did enjoy reading your amp bake-off.)

[Reffc]

It wouldn't hurt to try Classe Bruce as they might surprise you! Is it that you feel that improvements are necessary having heard the next models up, or just that if they are there to be had, why not have them? It could be worth finding out what the principle differences in the circuit are between the 30/35 and 50/60 as this might give some pointers as to whether it's all in the power supply or whether the circuit itself is different. If the former, then whilst it wouldn't hurt to have it professionally done (I would generally caution folk against messing with power supplies themselves unless they know what they're up to) you could find that it devalues the kit as you'd be taking it away from standard. There are exceptions to this where there are commercially recognised and available upgrades for specific items of kit. In your shoes, I'd try Classe and if they cant or won't supply the answer (or perhaps suggest you buy their latest and greatest) then I guess the sensible choices are 1) ask yourself if you think there's something missing and if not, keep what you have and enjoy it, or 2) look to try something different and audition as much as you possibly can. Don't rely on reviews for the answer. They're only one person's subjective opinion after all and usually in a system which won't bear much resemblance to your own.

[DSJR]

Just to add - PLEASE don't attack anything with a soldering iron until you've researched it VERY carefully :) Your gear will sharply devalue overnight if you do for a start.. Follow Paul's advice above :)

[brucew268]

...just that if they are there to be had, why not have them?

That would more describe it. I'll check with Classe, and will mind your advice.

[YNWaN]

I've done a lot of equipment modification and also heard a lot of modified gear. You won't significantly alter what you have now in the sense that it will sound like a different model. You may be able to modify specific aspects but for large scale differences you need to do more than exchange components.

To be honest, the components already used are pretty good Wima and Polystyrene capacitors (these are the glass ones you mention).

I should add that you also have to be a dab hand with a soldering iron and be prepared to completely dissemble the amps - removing the old components neatly is significantly more difficult than fitting the new ones.

If you really want to give it a go I would look toward the four bypass capacitors first.

I would also second the excellent advice given by the other AoS contributors above.

[Arkless Electronics]

Far too much emphasis is put on fairly foo aspects of power supplies! It's the regulation circuitry and grounding layout that's really important, not the rectifiers.... or even the transformer or smoothing caps in the case of pre amps.
You could usefully upgrade the OP27 op amps in the circuit to something better and more modern but if you don't have an oscilloscope leave them alone. There is a possibility of oscillation which if it goes undetected would probably take out your tweeters!

[brucew268]

Jez, when you say "It's the regulation circuitry and grounding layout that's really important," what do you mean in terms of grounding layout? What types of layouts tend to be the case, what is the negative aural result, and what would be a practical solution?

[Arkless Electronics]

Jez, when you say "It's the regulation circuitry and grounding layout that's really important," what do you mean in terms of grounding layout? What types of layouts tend to be the case, what is the negative aural result, and what would be a practical solution?

That would be an ecumenical matter!

I'm afraid it's far beyond the scope of an answer in a forum to explain the A - Z of grounding!! It's one of the more "black art" areas of design in some ways and would take the longest answer ever in the history of AOS.... There are thick electronics text books that cover JUST grounding and shielding!

[Mr Kipling]

That would be an ecumenical matter!

You watch Father Ted as well Jez?

That line is used in one episode when bishops pay a visit and Ted & Dougal train Father Jack to reply to any question with either of two responses, I think, and one of them being: " That would be an ecumenical matter."
What about those that take the view that high-feedback regulators "phase" the sound compared to say a simple pass transistor? Must admit I've never experimented myself and obviously you can comment better than I can.

[The Grand Wazoo]

You watch Father Ted as well Jez?

Funnily enough I was on You Tube yesterday, looking for a clip of the scene where Mrs Doyle is trying to give out sandwiches: Go on, go on, go on, ye will, ye will, ye will.......they're triangular!"

[Stratmangler]

Funnily enough I was on You Tube yesterday, looking for a clip of the scene where Mrs Doyle is trying to give out sandwiches: Go on, go on, go on, ye will, ye will, ye will.......they're triangular!"

What, this (http://theartofsound.net/forum/showthread.php?26466-Triangular-Sandwiches&p=458193#post458193) clip?

[Arkless Electronics]

You watch Father Ted as well Jez?

That line is used in one episode when bishops pay a visit and Ted & Dougal train Father Jack to reply to any question with either of two responses, I think, and one of them being: " That would be an ecumenical matter."
What about those that take the view that high-feedback regulators "phase" the sound compared to say a simple pass transistor? Must admit I've never experimented myself and obviously you can comment better than I can.

To be sure I'm a big fan... drink! feck! argh nuns!

That's a very interesting question which you have posed! Not too sure what you mean by "phase" the sound..... A series pass transistor can be used in either a high feedback regulator or a low feed back one.. or even a no feedback stabiliser (as opposed to a proper regulator). A shunt transistor can sink as well as source current which can be very advantageous in certain circumstances. Only really applicable though to pre amp supplies rather than power amps where the ability to sink current is actually far more important! A really good, fast, high feedback regulator can approach the ideal of a perfect voltage source far more than even a lead acid accumulator, and can have an internal source impedance equivalent to an inch of wire!
So long as loop stability is fairly optimum, thereby avoiding overshoot and ringing etc, I would say it is (generally) a good thing! A well executed regulator will give such a steady and low impedance voltage that even when the amp is in clipping no perturbance of the voltage will be apparent even with the scope on 1mV/Div!
A big electrolytic on the output of the regulator as the final pole in the response will tend to damp out any nasties... Too low an ESR in the output cap can actually cause problems as a high feedback regulator looks inductive as a source, due to the falling open loop gain, which can tend to produce a tuned circuit with the capacitor.... so some ESR is a good thing there...

As to subjective effects, well a good regulator can give superb results, but it is an area which is still more art than science in many ways. On occasions a seemingly superb regulator can kill the sound and this is one of those things where basically no one knows quite why! It's areas such as this that make audio electronic engineering so interesting and rewarding!

BTW your cakes are exceedingly good :D

[Arkless Electronics]

Well Mr Kipling it appears you have IT problems.... I received an email telling me you had replied and that it was your 5th attempt to post a reply.... but even that ended mid sentence after two lines....