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H&H V200

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Randy Bohannon View Drop Down
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    Posted: 18 November 2022 at 2:11pm
Scored this one on ebay at last, after lusting after one for years.

Given the unknown history and knowing that it hadn't been used in a long time I opened it up before powering it on. First impressions are that they are very well built, the lashings around the wiring looms in particular for example, and mine was lucky enough to have an original pair of matching transformers installed



It needed a good clean out and I treated it to a full recap. There are actually very few capacitors in this amp, the originals being quality Phillips and Nichicon axial capacitors that most bore up quite well for being 40 years old in terms of measured leakage and ESR. The significant exceptions were the capacitors around the 15v Zeners that power and provide the reference for the peak detector circuit. I forgot to take a photo of the component side of the board before changing everything but the back of the board shows the amount of heat damage these two Zeners and their associated 680 Ohm (I think, the ink has long since burned off and I don't have a schematic for this model, only the larger V450) have done to the PCB...



The 6.8uF and 4.7uF caps were literally roasted brown... :D



The measured a mighty 100pF... :D

The chap who sold it said that both channels worked, though the input attenuator crackled on one channel and so I opened them up and.. by god this is quality for an audiophile amp, let alone a PA amp. It's a proper stepped attenuator and takes apart for cleaning beautifully. 

Before:








After:









Given how inordinately difficult these things are to take apart I thought I may as well take the bridging switch apart and clean it too, bad switch contacts have given me endless trouble on vintage equipment in the past. When they get like this Dexoit won't touch it, they need taking apart and cleaning with fine bronze wool.

Before:




After:



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Randy Bohannon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 18 November 2022 at 2:15pm
Put it back together and powered it up through a dim bulb tester and finding no shorts, plugged it in proper.

There is about 800mv of offset on one channel 25 on the other, one channel's MOSFETS gets warm and the other stay ice cold so this may need more investigation, does anyone know the bias figures for these amps?

Given the lack of source resistors, how does one bias an individual channel?
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Randy Bohannon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 18 November 2022 at 4:07pm
The offset and bias issues were both down to bad pots, both replaced with multiturn types. The offset settled down to +-0.5mV and I found the bias to measure 1.2V across the MOSFET pair gates as per this thread:

https://www.diyaudio.com/community/threads/looking-for-hh-electronics-schematics.286673/

The rather small and thin heatsink did feel a bit warm at this bias level so I adjusted it down to the 800mV level suggested in that thread and left it to stabilise. 

It did and I've just plugged it into the system to see how it sounds, I haven't had an amp with an input transformer before so am rather curious. :)
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kedwardsleisure View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 18 November 2022 at 5:40pm
technically you measure the bias at the output of the drivers rather than the output gates themselves
Kevin

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Randy Bohannon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 18 November 2022 at 10:44pm
Ooooooh, I see… 

So across R15/VR3 chain?

 Thank you for your help as always.


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kedwardsleisure View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 18 November 2022 at 11:21pm
you attach your meter across the 2 'G' terminals. There are normally solder pins on the pcb marked as such although I've also seen the wires soldered directly.
Kevin

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Randy Bohannon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 19 November 2022 at 7:14am
Got it, thanks.


Initial listening impressions are that it sounds very good in the treble and midrange, airier in the top end and more open in the mids that the Cloud VTX I A/B’ed it with.

The weakness is the bass, it seems thinner and less impactful than the cloud, much less so than the Crown K2. It also seems to distort more in the very low bass.

I’m not sure how much of this is design and how much of it is the input transformers and the main filter caps.

At 10,000uF per channel I would have expected the filter caps to be enough for an amp of this power level and so pulled them and measured them.

Despite looking a bit rough they measured ok on terms of capacitance and leakage, I’ve got a nice pair of 22,000uf 80v caps that fit the clamps nicely and so will install them to see if it makes any difference.

I would also like to bypass the transformers by way of experiment, did they make a special shorting plug for the sockets on these? 
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kedwardsleisure View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 19 November 2022 at 4:39pm
these are disco amps, if you want hifi performance I'd get a hifi
Kevin

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Randy Bohannon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 20 November 2022 at 7:16am
Actually I think these are better than a lot of hifi amps Kev… :D

I’ve got a fairly large collection of hifi gear and like it all from the valve gear, through the 70s receivers (my personal favourites) to modern gear and they all have their pace and are enjoyable to listen to.

I think the collecting bug has bitten with PA amps too unfortunately, I’m still on the look out for a nice Crest to compare to the rest. :)
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kedwardsleisure View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote kedwardsleisure Quote  Post ReplyReply Direct Link To This Post Posted: 20 November 2022 at 6:00pm
maybe a little vintage citronic PPX would float your boat, similar design to the H:H
Kevin

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Randy Bohannon View Drop Down
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Randy Bohannon Quote  Post ReplyReply Direct Link To This Post Posted: 20 November 2022 at 6:26pm
Thanks for the recommendation, I'll keep an eye out for one. Thumbs Up

A picture of the main capacitor next to it's successor,   despite being bulged like that measures at 12kuF against a rating of 10K.

The replacement is a 22,000uF 80v job but I think the bridge rectifier can handle the extra pulse current without an issue; if not I'll fit some speaker protection and a soft start and muting circuit at the same time.




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Post Options Post Options   Thanks (0) Thanks(0)   Quote shaun1264 Quote  Post ReplyReply Direct Link To This Post Posted: 20 November 2022 at 7:11pm
I uprated the filter caps in a JBL-Urei 6260 a while back from the original total  27,200uF 80v to 80,000uF 100v total.  For this I had to make leads to the caps and secure them under the main board.  I also uprated the bridge rectifier from the 25amp to 50amp and uprated the power switch.  

For all of these modifications I got an increase of power approx 20 watts more if I remember, bass was much improved , deep and well defined, clipping was much softer and actually slightly lower distortion .  

These amps have a huge transformer.  Built like a tank with Sanken output devices running at only a conservative amount,  low negative feedback design but low distortion from the output.  The bias is quite high around 480mV to reduce crossover distortion.
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