Recapping PS in a Hafler DH-101

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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 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.
 
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!
 
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?
 
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
 
gil1 said:
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.
 
Re: Re: Recapping PS in a Hafler DH-101

carlmart said:


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/pdf/DH-101_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.
 
Re: Re: Re: Recapping PS in a Hafler DH-101

jackinnj said:


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

http://www.hafler.com/techsupport/pdf/DH-101_preamp_man.pdf


Of course it does, considering when it was designed. I forgot about that.

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.

A series resistor, like 1ohm or so, on the V+ and V- lines before the regulator would help clean the junk too. Like 1000uF cap, 1 Ohm resistor, 1000uF cap. Of course 317/337 are the minimum to use.

Do not put a large cap at the regulators output: put one in parallel with the adjust pin to reduce noise, with diode protection (see National datasheet).

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

Are you sure they are 16v and not 160v?

IMHO the equalizing loop inside the line circuit should be eliminated. Simply unsolder R23, R24, R25 and C18.

You have replaced C12, haven't you? That should be polystyrene or silver mica at least.
 
I as well have been slowly upgrading a DH-101 based on member's suggestions - power supply caps, RCA connectors, power cord and plug, plus bypassed the equalization loops, and have noticed the improvements this makes.
This thread is the second or third thread I've read that suggests the replacement of existing resistors with metal film, but have not found specifically which resistors. Could anyone elaborate as to which resistor(s) replacement might provide the "best bang for the buck"?

gil1 - which did you replace?

Thanks to all - Dan
 
Originally posted by ddanbo This thread is the second or third thread I've read that suggests the replacement of existing resistors with metal film, but have not found specifically which resistors. Could anyone elaborate as to which resistor(s) replacement might provide the "best bang for the buck"?

Using Parts Connexion or Michael Percy as what you may find around easily.

As a rule I'd go for the most exotic ones in a phono preamp. Hafler only specified two 2% types, which if you need may replace for a Caddock or Shinkoh.

If you are not using that stage, then you can go for the best 1% types you can afford.

For exotics in that list you can still use Riken or Shinkoh. As you don't have that many resistors to change, if you can afford it go for them.

But I think the better deal are the PRPs, and if space allows go for .5W types. Holcos were the best deal, until they changed for steel terminals. If you can find them somewhere with copper terminals go for the H4 or H8 types.

Capacitors are the most critical, and any ceramic disc around should be exterminated. Replace them with polypropylenes or polystyrenes. Small ceramic values can be found in silver mica types.
 
Thanks for the great info!
Would you suggest replacing all the resistors on the DH-101 PC-4 board or would certain ones be considered more beneficial than others?
Phono section does not have high importance at the moment.

Thanks for the help - Dan
 

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ddanbo said:
Thanks for the great info!
Would you suggest replacing all the resistors on the DH-101 PC-4 board or would certain ones be considered more beneficial than others?
Phono section does not have high importance at the moment.

I'd replace all resistors & capacitors and eliminate the eq section.

And watch the volume/balance pots and the selection switch.
 
gil1 said:
LM317 and LM337 ...are they pin by pin replacements to the MC7818CT and MC7918CT found in the DH-101?


Yes and no. The Vin and Vout pins are in the same position in these 3-pin positive regulators (7818 and 317) and negative regulators (7918 and 337). But where the 7818 and 7918 have a ground pin, the 317 and 337 have an adjustable pin which has to put some resistance in-between when connecting to ground. A resistor will also have to be connected to the output pin. The ratio between those resistances is what will set the Vout.

You also can bypass this pin to ground to improve noise, as we recommended.

So in your case you will need some care and ingenuity to add these two resistors to both regulators. It's done on many DIY projects, so it can be done.

According to specs the LM are adjustable 1.5 amps while the MC series are fixed 1.0 amp.

Any of them should enough for you needs.
 
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