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I have a stock DH200 power amplifier vintage 1980. I know there are companies which would rebuild my amp for a price, but I would much rather do it myself. I have been re-reading the Pooge Article in Audio Amateur. Since this article was originally written there has been quite an improvement in capacitors and there availability. In the article polystyrene and polypropylene caps are specified. Quite often they are used in parallel for bypassing.Can the number and type of capacitors be modified bringing the Pooged amp into the Twenty-first century?
Primarily I am concerned about the electrolytics in as the coupling capacitors. Do these caps have to be bypassed or can a metallized film cap be used in lieu of the eltrolytic and the bypass cap?
I would appreciate any additional insights you might have into this topology and or Walter G. Jung's email address.
Thanks in advance for your answers to this query.
Dave
I will keep you posted on my efforts to revamp my DH200. I was most concerned about the caps on the PC cards. I had forgotten about the ones in the power supply. I will replace those as well.I will try combinations of your various suggestions and I will let you know what I hear!
Again thanks for you input.
Dave
I have a DH500 that's gone through many modifications. It now has replacement circuit boards from Musical Concepts/Musical Design (www.musicaldesign.com). All in all, I have spent probably far too much time and money than the thing was worth. My suggestion is to stay with the more modest amounts of modification due to some issues:1. Its 15-20 years old and the electrolytics are near the end of their lifespan. The main power supply ones will cost some $$.
2. The MOSFets are of the type more likely to sound "hazy" according to Stan Warren.So, simple mods:
1. replace the input blocking capacitor with a piece of wire, DC coupling it.
2. Replace the electrolytic in the feedback network with a larger capacitance (deeper bass) and a better type (Black Gate).
3. Replace the onboard electrolytic power supply caps with larger valued low ESR types (ie Panasonic FA types from Digikey) and bypass with metalized Polypropelene film caps (.47uf to 2uf, 100v) that will fit well. An inexpensive one like Solen is fine.Stop.
Just these three things should result in much better sound quality and perhaps only $30 spent.
If you want to live a little dangerously, increase the bias current 20%. More dangerous is to eliminate the fuse protection of speaker and power supply rail fuses. Keep the 115v AC fuse.
This sounds like what i did ( so far ) to the DH-200 that i have torn apart and sitting under my puter desk as we speak. It's a project that got thrown to the side far too long ago !!! I would also add that changing the wire to something a little better will make a world of difference. The factory wire is tin plated copper and absolute junk.I would love to obtain a copy of the "pooge" article on this amp, just to see what they did. Is it available on line anywhere ? Sean
>
Since my original posting I have gone back and read all the Pooge articles and the subsequent letters. There doesn't seem to be any errors inthe DH200 Pooge article that were identified in subsequent letters. However there are some related articles (such as the Boak Regulator) which are relevant, but not actually necessary for the DH200 Pooge.Audio Amateur has pulled all of its articles together in a single publication. I have not seen the publication so I don't know what is included and what isn't.
Mark' comments are relevant. I got a message from one of the authors, Dick Marsh, and he suggested that I order information from multicap. His article at www.capacitor.com is worth reading. I will keep you posted on my progress, and I ask that you do the same.
Dave
One more mod I forgot is a bypass for the output devices. I can't remember if the supply for the front end was RC isolated from the main supply or if that was used in Musical Concepts mods and Adcom amps, but anyway bypass capacitors close to the loads are needed. So if there are seperate supplies, both need local electrolytic+film cap bypasses. Ironically, current Adcom amplifiers like the 5400 and 5802 are nice designs, but stupidly omit local bypasses. Measurements would not be better, but you'd think they would do it for the better sound, better reviews, and meager cost increase.The Pooge articles and the Jung/Marsh "Picking Capacitors" (Audio, 1980) were "cutting edge" in their day (actually a span of about 15 years), but components have gotten better and thinking has evolved. The DH200 was (I think) the first Pooge article and included rewiring with home made Litz wire. High purity copper was not as available then as now, so Litz was the thing at the time.
The capacitor article is now very dated and many of the Pooge articles are based on it. Low ESR, high frequency electrolytic, Black Gate, or polymer electrolytic capacitors did not exist back then. The article also focused on signal coupling capacitors where DF and DA are most important, whereas in power supplies low, linear resistance accross a wide frequency range are most important. Marsh's more recent papers at capacitors.com should be relyed on most.
I think Audio Electronics (formerly Audio Amateur) has a reprint collection of the Pooge articles. There is a clear evolution and the later ones put the early ones in perspective. Also important are the letters published in the magazine. Many of the construction articles contain errors that are addressed in letters over the next several issues. Refinements and other Pooge ideas are in those letters too. I hope the letters are in the reprints.
Thanks for the info and links. Does anyone already have the "pooge" book that compiles all of the articles ? Any good ??? Sean
>PS... Anyone else notice that they said "genetic gear" instead of "generic gear" on the website ??
A blast form the past! I did about as many mods to the DH200 as I have ever heard of. I cascoded the input stage(following Dick Marsh from AA). Then seperated the driver stage from the input stage. I added caps to both rails right at the output fets. Another pair of caps feed the seperated input stage. The star ground got very full. Later, I regulated the voltage to the input stage. Making a 60 volt regulator wasn't easy, and I blew up a few before I got it to work. I also put in an eight amp transformer, that didn't leave much room. I had to add in slow turn on because of the transformer. I matched all resistors and caps so each channel had the same values for a given component. So, R1 right was the same as R1 left. Caps were matched too (the small ones anyway.) I did the input jacks with something costly but I don't remember what. All the wiring was large, it seems to me I found a use for monster cable where it worked! What did I get out of all this? One damn good Hafler! Oh! I did rebias the thing too, but if I did it today I would NOT! Because the amplifier runs out to current to soon if you do. Its sound gets mushy. Besides it runs cooler with lower bias. I did four of these Dh200's and all worked well. BUT AGAIN, I replaced them all with modified Adcom 535'S. I had a tri-amp system then and the adcom's worked well in it. I still wonder if I could have done more to it. Like maybe, cascode the driver transistor too. Hmm. Good Luck and plaese keep me posted, bobwire
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