Pundit
Post by neilsan on Oct 6, 2018 20:17:42 GMT 12
Picked up 2 DH-200's off TMe. One nearly mint.Always wanted to get one to fiddle with.
Today I replaced the input rca's,the input cable,and fitted a decent input capacitor instead of the grotty electrolytic cap. Lot sweeter.warmer sound with the highs less edgy and bright.
Bass still not as tight as my 2150b ( a little boomy) but I'm planning to replace all electrolytics on the boards and increase the main caps to help with the bass. Not sure if I'll replace the resistors with metal film yet.Did that with my 2150b years ago and it made a difference then.
The rougher one....I've removed the headphone jack that had been fitted interrupting the speaker wires, but apart from that I might keep it as is so I can compare them in the future! Great fun.
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Post by michaelw on Oct 6, 2018 21:02:09 GMT 12
claasics.
power nosfets too like the perreaux
were they factory built or built from kits ?
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Pundit
Post by neilsan on Oct 6, 2018 21:30:18 GMT 12
Not sure how to tell Michael.
Serial numbers 200042 and 200044 from 2 different people.
Looks like the rough one has had 1 board repaired/replaced.Different mosfet numbers on that side too.
Used an Axon cap on the input and the amp sounds great.Might have to try the Axons in my 2150b too.
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Post by deano1974 on Oct 6, 2018 22:36:04 GMT 12
Hey Neilsan any chance of aome photos im curious
Manager & Product specialist at Rapallo AV & HI-FI
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Post by colinf on Oct 7, 2018 1:01:40 GMT 12
Classic amp. While you’re inside replacing parts, the negative feedback capacitor was critical for low distortion, C5 on the circuit diagram. It’s 470uF 6.3v and a Nichicon (ES series) Muse works well here. Make sure otherwise that the replacement is a non-polar type. The most critical resistors to change are R22, R23, R24 and R25. They are the negative feedback resistors.The rest can be left as normal. Also, if you can, measure the resistance of P1, the bias setting trim pot and replace it with either a new trim pot set at that value or a fixed resistor of that value. This is to maintain reliability as the old ones tend to become less stable over time. The main power caps can be upgraded as the originals would be quite old now and their ESR would be higher. Mosfets like their power supply caps to be in good condition. Also note that if you need spare mosfets and the originals aren’t available, the modern 2sk1058 and 2sj162 are the same mosfets but in a modern plastic case. 
AMR-iFi R&D
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Pundit
Post by neilsan on Oct 7, 2018 8:21:08 GMT 12
Thanks Colin.Appreciate that advice.Will do all that.
Scrawled on the transformer it says that bias was changed from 275ma to 425ma.Doesn't seem to get too hot at that.
Adjusted the 2150b up a bit as well all those years ago!
Dean,I'll give it a go.
Neil
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Pundit
Post by neilsan on Oct 8, 2018 11:17:01 GMT 12
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Post by deano1974 on Oct 9, 2018 6:40:29 GMT 12
Excellent they are beasts 😉
Manager & Product specialist at Rapallo AV & HI-FI
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Post by Owen Y on Oct 9, 2018 8:28:53 GMT 12
Film cap orientation - I have only one Axon cap left in my parts drawers (only a wee 1.5uF 250V one) & its outer foil end is at the 'A' end. If it's an input series coupling situation (as appears to be the case above) then connect outer foil end to source. If used for Gnding, connect outer foil to Gnd. ie outer-foil connected to lowest impedance. Usually (dramatically) better dynamics that way. If you don't have a scope, then check both ways by ear, the difference will likely not be small at the amp input. I don't think Axon/Solen outer-foil mark their caps.
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Pundit
Post by neilsan on Oct 9, 2018 10:13:24 GMT 12
Thanks Owen.I will try that.
Any suggestions of where to get about 18,000 micro Farad main caps from, or a decent make to look for,please.
Not too pricy!
Have worked out the electros I need from Parts Connexion,as per Colin's suggestion.
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Post by Owen Y on Oct 9, 2018 11:09:25 GMT 12
(Warning, IMVHO only below  ... ) For SS (low voltages), I tend to for Panasonic (technically excell manufacture) - A lot of audio enthusiasts talk about FC series but I have not tried them I have used Pana TSUP & TSHA in hi voltages in PSU situations but more recently I've become a fan of German F&T electros - they sound sharper & punchier (without sounding nasty) than the TSHA/TSUP (a bit un-dynamic in comparison). For regular PSU situations, the Panas are inexpensive. For the most critical PSU locations (eg last 'decoupling' cap at PSU connection to signal components), I would go for F&T from Hifi Collective, the GBP is still fairly good for us. For those big 18000uF PSU smoothing caps, you have 2 options (i) F&T do big value radial ones (ii) a lot of amp designers go for multiple paralleled smaller uF caps, which they say results in a faster responding PSU (but you have no space & if the fixing clamps can be costly). Be sure to get the right Voltage either way. It was/is also popular to bypass big electros with a smaller film cap - I've never liked the sound of doing this, but you can 'tune' an amp this way to taste - ie YMMV. For 'signal path' & more critical electros, I go for Elna Silmic these days (see also Hifi Collective) - beautiful tone, very natural. (Don't bother with Black Gates, ugh.) I have used also Nichicon Muse, as Colin mentioned, in the past. Bi-polar electros - I don't have a lot of experience - Black Gate N will give you hifi 'wow' factor, but to me they are way un-natural. And over-priced. Enough raving already 
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Post by Owen Y on Oct 9, 2018 11:22:05 GMT 12
I'd consider replacing the bridge rectifier with Schottky diodes or 'ultrafast/soft recovery' type - big difference to the sound of esp an old amp. You may have to mount 4 diodes on a tag-strip (as I did below) & you should check heat dissipation. 
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Post by Owen Y on Oct 9, 2018 11:24:33 GMT 12
Having said all that, don't go overboard cost-wise with an old amp (design)
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Post by Owen Y on Oct 9, 2018 11:28:38 GMT 12
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Pundit
Post by neilsan on Oct 9, 2018 12:12:36 GMT 12
Thanks for all that Owen.Bit to explore.
"Film cap orientation - I have only one Axon cap left in my parts drawers (only a wee 1.5uF 250V one) & its outer foil end is at the 'A' end."
Reversed one of the Axon caps like you said, and the bass is tighter now.Not as tight as my 2150b's but better than it was!
Am amazed at the sound I'm hearing from this amp actually.
Thanks again.
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Post by colinf on Oct 10, 2018 4:47:06 GMT 12
Actually, because the amp has a symmetrical input stage, unlike the Perreaux, the input cap (Axon) can be removed altogether and replaced with a short circuit. That then makes the amp direct coupled and eliminates another cap from the signal path. What preamp do you have? The negative feedback cap should be a non-polar type as this results in the lowest distortion in the bass. Polarised caps like the Silmic ii and Panasonic FC and FM are great sounding caps in polarised situations but as soon as the voltage is reversed across them, as it could be in the negative feedback on the Hafler, the dc resistance decreases and adds a rectifying effect at deep bass frequencies. A non-polar cap can be made up of two polarised caps by connecting them back to back in series with reversed polarity. Ie. (+ -) in series with (- +). That allows the use of Silmics in the feedback network. But it would be better to use a non-polar cap as it’s internal construction sees both sides of the aluminium foil oxidised instead of one side as in a polarised cap, and it’s ESR is lower and leads to lower distortion in the example Hafler circuit. Which caps did you decide on for the power supply caps? I remember Quad went through a stage where they were using cheaper Chinese caps in the 606 and 909 poweramps and it was found that replacing them with slit foil ones made the Quad circuit put out an order of magnitude lower distortion.
AMR-iFi R&D
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Pundit
Post by neilsan on Oct 10, 2018 8:17:15 GMT 12
The Nichicon Muse 470 mf cap at Parts Connexion is described as
470uF 16Vdc, ES Muse, Electrolytic Capacitor Bi-Polarized, +/-20% Tolerance, 12.5mmD x 25mmH
I assume that's non-polar Colin? I've dealt with Parts Connexion before.
My "passive" preamp is an LDR Clone Note.............http://www.buildanamp.com/
I haven't found any PS caps yet.Still looking!Aiming for round the 18,000 mF mark.
My 2150b has about 43,000 mF per side and the lights dim a bit on turn on! Don't think I need that much.
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Post by Owen Y on Oct 10, 2018 9:02:05 GMT 12
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Pundit
Post by neilsan on Oct 10, 2018 10:11:15 GMT 12
Thanks Owen. Need 75v up.
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Post by Owen Y on Oct 10, 2018 15:30:33 GMT 12
I see that they make also 80/100/160/250/350/400vdc in 18000uF.
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Post by colinf on Oct 10, 2018 19:05:47 GMT 12
From memory there is about 56v across each cap so you could get away with a 63v type. (If you could measure the actual voltage across them that would be helpful!) 80v ones would give a bit more leeway with power supply surges. Do you intend to use the same diameter caps as the originals, so that they fit right in? What diameter are they? Looking at the Hafler DH220 circuit it’s the same as the DH200 but they have removed the input capacitor and added a small dc offset network with a trimpot to adjust the input dc voltage to 0v. For if you remove the input cap on your DH200 and replace it with a short circuit: while you’re adjusting volume on your passive LDR volume control and you notice the woofer pumping in or out slightly as you do it, or some noise, you could either put the input cap back in or add in the dc offset trimpot from the DH220. It’s a small network consisting of 2 resistors, 2 diodes and a trimpot. The input stage power supply filter caps on the board are 100uf and you could use Silmic 100uf 100v cap to replace them.
AMR-iFi R&D
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Pundit
Post by neilsan on Oct 10, 2018 21:34:03 GMT 12
Thanks Colin. I'll download the 220 circuit and probably go for that.
The input main caps are 10,000 mf,so thought to help tighten up the bass I'd up them a bit.
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Pundit
Post by neilsan on Oct 10, 2018 21:35:30 GMT 12
Sorry thought you meant the main caps but rereading I see you mean the ones on the board.
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Post by Owen Y on Oct 11, 2018 8:38:21 GMT 12
The input main caps are 10,000 mf,so thought to help tighten up the bass I'd up them a bit. Actually, enlarging the capacitance tends to 'slow' the bass IME. OTOH is you make it too small, bass extension suffers. However, the opinion may be that these stock caps area rather small. Some folks like to consider the Resistance-Capacitance 'time-constant' of the PSU to ensure that the 'speed' of PSU is fast enough to respond to (transient) signals, balanced against sufficient PSU filter capacitance to ensure low enough LF extension. In any case, you'll find I think that modern caps tend to sound better anyway.
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Post by colinf on Oct 11, 2018 18:40:34 GMT 12
Bi-polar electrolytic caps are the same as non-polar. Just that the term bi-polar is usually used for electrolytic caps which can be used in either polarity direction in a circuit. Non-polar usually refers to caps that naturally have no polarity such as polypropylene film caps or ceramic caps. So sorry, I should really have put bipolar caps. To mean that both plates of the aluminium foil in the electrolytic cap have been oxidised to make it a non-polarised electrolytic cap. The signal encounters this construction in a bi-polar cap: cap lead - aluminium foil - oxide layer - electrolyte - oxide layer - aluminium foil - other cap lead. If instead two polarised caps are put back to back to make a non-polar cap, the signal encounters this: cap lead - aluminium foil - oxide layer - electrolyte - aluminium foil - other cap lead - next cap lead - aluminium foil - electrolyte - oxide layer - aluminium foil - final cap lead. So it’s better to use a bipolar cap than two polarised ones back to back as there are two fewer aluminium foils for the signal to pass through. And thus the ESR is lower in a bipolar cap. Congrats, you made it to the end of the paragraph!
AMR-iFi R&D
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Pundit
Post by neilsan on Oct 13, 2018 7:51:23 GMT 12
Thanks Colin.Don't know what happened to my last post.
Thought that was the case.
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Pundit
Post by neilsan on Jan 4, 2019 12:23:27 GMT 12
Film cap orientation - I have only one Axon cap left in my parts drawers (only a wee 1.5uF 250V one) & its outer foil end is at the 'A' end. If it's an input series coupling situation (as appears to be the case above) then connect outer foil end to source. If used for Gnding, connect outer foil to Gnd. ie outer-foil connected to lowest impedance. Usually (dramatically) better dynamics that way. If you don't have a scope, then check both ways by ear, the difference will likely not be small at the amp input. I don't think Axon/Solen outer-foil mark their caps. Seasons Greetings Owen. Called in and saw a retired tech friend today to check all the Axon caps I have.Turned out as you said, with the outer foil end at the "A" end.Thanks for that.He didn't know that as well. Have nearly finished replacing the caps and some resistors in one of the amps,so will post here when it's finished.
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Pundit
Post by neilsan on May 2, 2019 13:42:19 GMT 12
Well, finally got a chance to compare my untouched 200 with the one I've replaced all electro caps and a lot of resistors in.And the bias pots!
Very close in sound,maybe a tad more info coming through on the modded one.And it seemed a bit cleaner sound, but maybe that's me!
Very listenable anyhow.So will tackle the other one some day.
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Post by Owen Y on May 2, 2019 15:05:27 GMT 12
Give the big caps some running time. Often they take some music playing time to 'charge' and/or loosen up & 'breathe'.
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Pundit
Post by neilsan on May 2, 2019 21:29:29 GMT 12
Yeah,seems to be getting sweeter.
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