Recapping PS in a Hafler DH-101

[gil1]

I have been recapping and replacing resistors with metal film on a DH-101 and the improvement has been great, a lot more more detail and some bass improvement.

I replaced the power supply caps from 1000uf 35v to 2200uf 50v, my question is...how much higher can I go without doing any damage and would it improve the bass a bit more? I would like to extend the bass up just a bit more.

I see there are upgrade kits on the market for these preamps with 4700uf caps for the PS.

Any input appreciated and thanks in advance.

[bosedtobosed]

i dont see the point of putting higher values in, why do you think it will improve the sound ?, plus it has +\- regulators after the main smoothing caps !, its only feeding the poweramp uamps

[carlmart]

bosedtobosed is quite probably right.

Throwing capacitors at a supply may improve things a little, but it all depends on where do you put them.

IMHO you should perhaps consider improving the supply as a whole thing, using better regulators that will probably make better use of better caps.

Even using chip regulators, like 3X7 types or their descendants, will improve on common 7xxx types, that it's probably what the DH-101 uses.

Upgrading the audio chips may also be considered. There was an article on The Audio Amateur on that: improving the DH-101. But I think they just replaced the passive parts and the chips.

[gil1]

You guys must excuse my ignorance and it is one of the reasons I post questions here. I usually follow tips from fellow members that have much more experience than I ever will and one of the tips I've gotten on how to extend the bass and overall sound improvement on this and other preamps is by beefing up the power supply especially by increasing the capacitor values, also replacing the regulators and even the transformer, some have told me to switch to fast Schottky diodes. So I am just taking it all in hoping to learn something from it.

Here is what I do know, I have two Hafler DH 101 preamps that I purchased at a good price, both sounded identical when I got them, one of them has gotten new metal film resistors, upgraded the PS capacitors, coupling capacitors and electrolytics, the difference between them now is like night and day, with the modded preamp having so much more detail, clarity and a bit more bass extension but would still like to get a bit more bass if its possible.

I appreciate all comments, thanks!

[bosedtobosed]

i would buy a better preamp,

[carlmart]

Originally posted by gil1 Here is what I do know, I have two Hafler DH 101 preamps that I purchased at a good price, both sounded identical when I got them, one of them has gotten new metal film resistors, upgraded the PS capacitors, coupling capacitors and electrolytics, the difference between them now is like night and day, with the modded preamp having so much more detail, clarity and a bit more bass extension but would still like to get a bit more bass if its possible. [/B]

If the input, feedback and output capacitors are large enough (use formula), then the bass extension might be related to the power amp and not the preamp.

In any case, I think it's time you should consider soldering IC sockets replacing the audio chips and start trying different DIP ICs and see what gets better. Treble and bass extension may not only increase but also improve in quality.

Oh, I don't remember if the DH101 has any filter stages. If it does then hardwire bypass them. That's very important.

What are the regulator chips?

[carlmart]

Originally posted by bosedtobosed
i would buy a better preamp,

If the volume/balance pots are good, there's not that much you may gain... as long as you improve on the parts.

If you keep your budget limited and don't go for too exotic parts, the investment should be much less considering the gains.

[gil1]

Thanks for the comments Carlmart, I dont think I have spent more than 15 dollars doing some of the recapping and replacing resistors for a preamp I got real cheap and the gains are already showing as I have mentioned before, I will check on the regulators and get back to you later on that.

This is all for fun, yes I can go purchase a new "better" preamp but then it would not be DIY!

Cheers

[carlmart]

Originally posted by gil1
[B]Thanks for the comments Carlmart, I dont think I have spent more than 15 dollars doing some of the recapping and replacing resistors for a preamp I got real cheap and the gains are already showing as I have mentioned before, I will check on the regulators and get back to you later on that.

In my list of priorities, now that you have replaced passive parts and the supply diodes, next I would pull out the audio chips (very carefully) and put IC sockets there (good quality types). There are several new types people are trying on this forum with excellent results, like the LM4562.

IMO then you will start listening to further improvements on the supply.

There three very important points that you have not mentioned that you did, like replacing the volume pot (what type is it?), bypassing equalizing stages and improving on the selection switches.

What power amplifier are you using following the preamp?

This is all for fun, yes I can go purchase a new "better" preamp but then it would not be DIY!

I certainly agree with that. The pleasure of listening to improvements resulting from our own work is certainly worth it.

[jackinnj]

Originally posted by carlmart


In my list of priorities, now that you have replaced passive parts and the supply diodes, next I would pull out the audio chips (very carefully) and put IC sockets there (good quality types). There are several new types people are trying on this forum with excellent results, like the LM4562.

The DH-101 uses discretes -- not IC's save for the voltage regulators:

http://www.hafler.com/techsupport/pd...preamp_man.pdf

I would replace the fixed voltage regulators with LM317/LM337 and bypass the adjust pin with a nice quality film cap -- if you can put a PEM on the power input this will help as well. There's a lot more junk on the power line these days than when the unit was released.

Replace C11 and C20 -- these are 10u/16V electrolytics -- you can use the WIMA 10u/16V film caps.