Refreshing Older Hafler Amp...

jakelm

Hello folks..

Starting a new project here.

I have a 20+ year old DH-200 Hafler amp, driving my 7b's. In another thread we were talking about AC/DC amps. Which brought up an idead for why my older amp just doesnt sound the same anymore.

Highs are getting crispy (harsh) and lows are not as definded as they used to be with this amp.

I have 2 sets of caps i am going to replace. And I wanted yo all's opinion on what to replace them with.

The first set is a pair of 10uF 16v electrolytic caps inline with the input.

The second are the huge 10,000uf 75v electrolytic.

PE is where I ussually buy parts, but they dont have anywhere close to the size I'm looking for. I might check Mouser.

Any ideas?...thoughts?

Thanks

Jake

jakelm

Anything else I might refresh on this amp , that might be in bad shape?

avguytx

Is that a scan of the service manual for it? I don't know much about Hafler servicing but wouldn't these benefit from checking DC offset and biasing? THAT can make a big difference in sound and performance not to mention excessive heat buildup. I know it did on some of my "vintage" gear.

mhardy6647

I'd probably replace all the electrolytics; certainly any in the signal path.

Good sources include www.digikey.com and www.mouser.com

If you cannot find the 10,000 uF @ 75 -- you can always parallel lower value electrolytics.

The other caps are probably decent enough -- the Haflers were good sounding amps. One would expect nothing less from the founder of Dynaco :-)

jakelm

avguytx wrote: »

Is that a scan of the service manual for it? I don't know much about Hafler servicing but wouldn't these benefit from checking DC offset and biasing? THAT can make a big difference in sound and performance not to mention excessive heat buildup. I know it did on some of my "vintage" gear.

Yes it is a scan of the service manual.

I'm not very experienced with refreshing amps, so i thought this would be a good amp to learn.

DC offset biasing? Can you explain alittle more? Or I can goolge if its too much to explain.

Jake

jakelm

mhardy6647 wrote: »

I'd probably replace all the electrolytics; certainly any in the signal path.

Good sources include www.digikey.com and www.mouser.com

If you cannot find the 10,000 uF @ 75 -- you can always parallel lower value electrolytics.

The other caps are probably decent enough -- the Haflers were good sounding amps. One would expect nothing less from the founder of Dynaco :-)

The amp was (and still is) an excellent amp for my vintage Polk 7b's. But I can start to hear the SQ going down hill. I would love to get this amp back to original specs and have it last another 20+ years.

And I love electronic projects..Nothing like the smell of burned solder in the morning.

But like I said, I am very inexperienced with refreshing amps. Any help you all could give would be great.

jakelm

Am I looking at the right caps here at mouser? To replace the large 10,000uf caps?

I certainly dont wan to buy the wrong thing..


http://www.mouser.com/search/Refine.aspx?Ne=1447464+254016+688315+688767+688737+2203862&N=1323038+4294826922+4294966396+4294948474+2203862+0&GetRecs=1&Msb=0&Mkw=capacitors&Ns=P_SField&Ntx=mode%20matchall&Ntk=Mouser_Wildcards&Ntt=*capacitors*

ohskigod

might want to give the guys at Musicalconcepts.com a holler for options. navigating there website is a bit of a chore, but look for there Hafler mods. they do them at the factory, or you can order the parts and do it yourself (sounds right up your alley)

you can email them with any questions and they will get back to you pretty quick.

having these guys do something to my Hafler DH500's in my 2 channel is on the future audio upgrades list, since there mods are generally well recieved from what I remember

jakelm

ohskigod wrote: »

might want to give the guys at Musicalconcepts.com a holler for options. navigating there website is a bit of a chore, but look for there Hafler mods. they do them at the factory, or you can order the parts and do it yourself (sounds right up your alley)

you can email them with any questions and they will get back to you pretty quick.

having these guys do something to my Hafler DH500's in my 2 channel is on the future audio upgrades list, since there mods are generally well recieved from what I remember

I would love to learn off of this amp and do it myself.

Thanks for the info.

heiney9

jakelm wrote: »

Hello folks..

Starting a new project here.

The first set is a pair of 10uF 16v electrolytic caps inline with the input.

The second are the huge 10,000uf 75v electrolytic.

PE is where I ussually buy parts, but they dont have anywhere close to the size I'm looking for. I might check Mouser.

Any ideas?...thoughts?

Thanks

Jake

The first set as we discussed are coupling caps.

The second set are PS bypass caps.

The coupling caps are more important to the sound because they are in the signal path so spend a little more money there than the PS bypass caps. I've heard many people have good luck with Panasonic or Mallory caps for the PS bypass caps. Just what I've heard over at WWW.DIYAUDIO.com I haven;t tried any of them personally.

Check out DIY audio as well there have been numerous threads on refreshing the Hafler DH 200 amps. And those guys are hard core and will be able to steer you in the right direction.

H9

heiney9

jakelm wrote: »

Yes it is a scan of the service manual.

I'm not very experienced with refreshing amps, so i thought this would be a good amp to learn.

DC offset biasing? Can you explain alittle more? Or I can goolge if its too much to explain.

Jake

DC offset shouldn't be a problem with capacitor coupled amps. One of the ideas to put a cap between input and output stages is to block any DC. If the caps are weak they could be passing DC but once they are replaced it's not an issue.

Being the novice you are I certainly wouldn't mess with biasing if you have no clue about what it is, how to measure and how to apply or subtract bias current. This is a great way to blow up the outputs by arbitrarily messing with the bias settings.

Bias
On tubes, bias is a small direct voltage applied to the grid to move the operating point of the device into a more linear range so as to reduce distortion.
On FETs, bias is a small direct voltage applied to the gate to move the operating point of the device into a more linear range so as to reduce distortion.
One bipolar transistors, bias is a small direct current applied to the base to move the operating point of the device into a more linear range so as to reduce distortion.
In magnetic tape recorders, bias is a very high frequency signal (often in the 100 kHz or higher range) mixed with the audio signal during recording. The purpose of bias is to reduce distortion by rapidly saturating the tape in both directions, minimizing the time spent in its non-linear magnetic hysteresis (see the WFTD Archives) curve. In more basic terms, bias makes it easier for the tape to respond to the audio signal in a linear fashion, and reduces distortion.

In all cases, the level of the bias must be carefully adjusted to achieve the best results. Too little bias increases distortion, too much reduces signal level and diminishes high frequencies

jakelm

Thanks for the info H9.

I undertsand the basics of biasing, but have nothing to measure it with, besides a Volt/ohm meter. I will certainly stay away.


Do yo think the PS 10,000uf caps should be replaced?

With the problems I am having in SQ (harsh highs and little low end), what should I look to refreshing? Anything else becides the input caps?

jakelm

I just emailed musicalconcepts.com. Hopefully they will throw back some good ideas into how to get this amp back to specs.

heiney9

jakelm wrote: »

I just emailed musicalconcepts.com. Hopefully they will throw back some good ideas into how to get this amp back to specs.

Seriously Jake check out www.diyaudio.com and do a Hafler search they are a popular subject over there for people wanting to do exactly what you are wanting to do. If for no other reason than to get some info.

heiney9

jakelm wrote: »

Thanks for the info H9.

I undertsand the basics of biasing, but have nothing to measure it with, besides a Volt/ohm meter. I will certainly stay away.


Do yo think the PS 10,000uf caps should be replaced?

With the problems I am having in SQ (harsh highs and little low end), what should I look to refreshing? Anything else becides the input caps?

As long as you are in there might as well replace them too. Getting it on a bench with someone knowledgeable will also give you some clues of other things that need attention.

Biasing is important as it can drift over time for several reasons. Many of the older amps had very poor biasing pots and get dirty, gummed up and sometimes are in different stages of failure. I don't have any specific knowledge about that being an issue in Hafler amps or not.

H9

jakelm

Just did the DIYaudio search H9 , thanks.

They do have a ton of stuff on modding the 500 and some on the 200.

Will take me days to read it all...good thing I dont have a life.

I dont know if this is a simple question or not, but, is there particular parts to look for in biasing? Is it as simple as "change this cap and you'll be back to spec"?

Biasing pots? located where? Is it something that can be just changed out, if matched?

jakelm

Oh ok..biasing pots are the little cubic looking boxes that a flat head screw driver can turn.

avguytx

I had thought about doing the work on my older Carver amps, too, as I am mechanically inclined. Then I decided to send them back and let people who do it for a living to take care of it for me! I'd rather not take the chance of "fudging" it up. But if you take it on yourself, do be careful!

heiney9

avguytx wrote: »

I had thought about doing the work on my older Carver amps, too, as I am mechanically inclined. Then I decided to send them back and let people who do it for a living to take care of it for me! I'd rather not take the chance of "fudging" it up. But if you take it on yourself, do be careful!

This is excellent advice unless you are really patient and into doing your own work and fixing your own mistakes . Also there is a minimum amount of equipment necessary to really do a proper job so if you don't have things like an osciliscope, variac, volt/ohm meter, soldering station, etc. it's very difficult to do a through job.

Swapping a few caps is probably managable but beyond that the skill needed increases exponentially (sp?).

Good luck

H9

heiney9

jakelm wrote: »

Is it as simple as "?

Nothing in electronics and repair is simple

jakelm

heiney9 wrote: »

Nothing in electronics and repair is simple

I know its not "simple", but those guys are speaking in a language only engineers could understand. They modding the intire board out. Changing cap values, voltage values, biasing. Way over my head.

But I'll keep reading.

heiney9

jakelm wrote: »

I know its not "simple", but those guys are speaking in a language only engineers could understand. They modding the intire board out. Changing cap values, voltage values, biasing. Way over my head.

But I'll keep reading.

For me I understand the conceptual parts and how the parts work together but I don't have the patience or ability to jump in there and start fixing and modding stuff. Like I said a schematic to me is like a foreign language in most cases. I took 4 years of electronics in HS and retained very little.

By the same token I look at and work with Plats of Survey, subdivision plats, assessors plats of land and metes and bounds legal descriptions for parcels of land all day long and I'm sure most would think it's a foreign language if they looked at it. So I suppose it's all relative.

H9

avguytx

Yes, h9...THAT would all be foreign to me!

jakelm

Well I can read a schem. And if I had the values of the parts, I am a great part changer. But as for "what values and brands work better where" I'm still learning.

With the symptons I am having with this amp , it is difficult to figure out what to repair or replace. I'm not looking to bridge the amp, or make it more powerful, I am also not looking to replace EVERYTHING on the board, just the problems.

But to find the problem, I need to learn how it all works.

But DIYaudio is like a 10 year old sitting in a senior college class and all the 10 year old wants to know is what is 2 plus 2.

It would be nice to have a friend sit next to me and go.."ok, you want higher gain?..change this and this..want to get the low end up again or the higher raspiness out..fix this"..instead I am subject to reading through thousands of words that are absolute greek to me.

I know what a capacitor is and does, I know that a resistor is and does, I can solder like a champ and i have a very steady hand. I was just hoping to take my very limited skills , a soldering gun and a multi meter, and do some repairs.

But it is not going as easy as I hoped....lol..

As much information as the internet has, it still isnt specific enough....lol

jakelm

It like asking.."how do I turn it on?"

reply.." well you need to find the part that is connected to a .0005uF capacitor that has 2 4ohm resistors in series with it with 3 5mm 22 gage wires running in parralell to it"

instead of..." you see that big red square thing on the front with the light next to it?...flip it up"


LOL

heiney9

Well until you have specific symptoms it's hard to trouble shoot. From what you've described so far I'd say the biggest improvement in sound will come from changing the aging caps and then taking it somehwhere or carefully learning how to set the bias properly.

Lean sounding amps that are a bit raspy usually are transformed with the above. I'm not sure what brand of cap to use in the signal path as there are so many.

H9

jakelm

H9.. I appreciate all the help you have given me and thanks for being patient with me and my questions.

I'll just take it one step at a time. Eventually replacing all the caps. Hopefully I can find the caps I need to refresh the amp.

jakelm

$199 for ONE 10,000uF BlackGate...wow that excpensive.

jakelm

Good read on setting bias,


http://www.tnt-audio.com/clinica/bias_e.html

heiney9

jakelm wrote: »

$199 for ONE 10,000uF BlackGate...wow that excpensive.

At one time I was going to change the PS caps in my Adcom and I would need (4) of these. I thought $800 was a bit much at the time .

jakelm

Especially when I can get one from mouser for $20.

http://www.mouser.com/search/refine.aspx?Ne%3D254016%252b1447464%26Ntt%3D7536DX103G075BC2A%26Ntk%3DMouser%5FWildcards%26N%3D1323038%26RefType%3DHome

Does the uF value of the caps matter or just the voltage?

The reason I asked is because I recieved an email back from musicalconcepts saying that he had the BlakeGates and the ones I should go with were 33uF 16v instead of the 10uF 16v, and for the larger PS caps 27,000 uF 80V instead of 10,000uF 75V

Those values are way different then the original values.