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Old 22nd Mar 2023, 8:53 pm   #1
Draker4c
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Default Opinions on HH TPA 100D power amplifiers

I’m considering purchase of a pair of these for use as monoblocks for home listening I understand they are stable into low impedance loads . Could anyone give their opinion on sound quality and if they have any speaker protection circuitry? I understand they were used in broadcasting and studios back in the day. Would they be stable enough for Quad ESL63?
Many thanks Hugh
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Old 23rd Mar 2023, 3:36 am   #2
teetoon
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Default Re: Opinions on HH TPA 100D power amplifiers

Hi Hugh. I don't know if you've seen the thread I started back in 2011 ?

https://www.vintage-radio.net/forum/...ad.php?t=67605

There's a lot of info on the TPA series if you can read through a bit.

Generally, they are well made amps but the 100D is probably the worst sounding from a Hi Fi point of view. There is a bit of distortion that is only evident on sustained notes in the mid range ,to my ears. When compared with 50D's and 25D's, they dont exhibit this behaviour.
The main difference being the pre amp stage. In the 100D it's all discrete where as the 50 and 25's use a chip.
Wether the transistors in the 100D need to be closely matched I'm not sure. Certainly changing the pre transistors affects the output DC offset.
The manual states anything up to 100mv is ok.

I have wondered if maybe the 100D's sound better when driven hard ? They certainly sounded good on a friends disco set up.

There is absolutely no output protection on these amps. I once had a dummy load glowing when one of the small transistor legs was making a bad contact.

Remember that the model numbers refer to output into 15 ohms, so the 100D puts out 225 watts or more into 4 ohms.

If it was me, and I have not owned Quad 63's but back in the day I did have 2 pairs of 57's, I would not use the 100D's from the sound point of view but the 50D's certainly sound very nice as did the 25D's.

All of this said, I got a Quad 405 back in 2016 and I loved the sound of that and would say it was much nicer than the HH amps.

David.

Last edited by teetoon; 23rd Mar 2023 at 3:53 am.
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Old 23rd Mar 2023, 9:31 am   #3
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Default Re: Opinions on HH TPA 100D power amplifiers

Those HH mps date back to the early 70's and since then a number of things about how to design transistor amplifiers have been learned. Also, output transistors have got somewhat faster, leaving more margin in hand to allow feedbackk to be extended to be flat to the top of the audible range. They come after the old famous issues with bias runaway were solved, but before high frequency distortion and slew-rate limiting were properly attended to.

Respectable for their time, but in the decade after they were designed some actual progress was made. They were designed for industrial power levels and sacrificed some quality in that cause.

ESLs of all varieties are rather limited in the amount of power you can put into them before damage occurs. There are also transformers in the speakers to step up the voltage swing to that needed at the electrodes. So these speakers will benefit from neither the power nor the DC coupled output of these amps.

David
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Old 23rd Mar 2023, 9:52 am   #4
Craig Sawyers
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Default Re: Opinions on HH TPA 100D power amplifiers

The input spec of the ESL63 is 10V rms, 40V peak maximum signal input for undistorted output and 55V peak maximum.

No not a lot of power needed or desirable.

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Old 23rd Mar 2023, 12:14 pm   #5
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Default Re: Opinions on HH TPA 100D power amplifiers

To reiterate points already made: your ESLs are way too precious to be powered from this series of H+H amp.

In my humble opinion, the only H+H amps worth having are the MOSFET V series:

https://www.technicalaudio.com/pdf/H...00_amps_br.pdf

The V series are rugged and tend to go on forever (thermal runaway being eliminated). The spec is pretty decent as well. Doubt the modern H+H perform much better!

A friend of mine was telling me that some of the (earlier - not power amp) H+H designs use mains AC to illuminate the front panel...erm... If a customer brings one to him, he disconnects the illumination on reception and won't argue it with the client.
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Old 23rd Mar 2023, 1:00 pm   #6
Draker4c
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Default Re: Opinions on HH TPA 100D power amplifiers

Thanks to everyone for your excellent advice..I will steer clear! Hugh

Last edited by Draker4c; 23rd Mar 2023 at 1:06 pm. Reason: Typo
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Old 23rd Mar 2023, 2:49 pm   #7
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Default Re: Opinions on HH TPA 100D power amplifiers

Save them for a disco, I reckon.

Maybe that was what the BBC did with them? They could have been for the Radio 1 roadshow or Worker's playtime. Just because the beeb was somehow involved doesn't give everything uber-hifi status.

David
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Old 24th Mar 2023, 5:08 pm   #8
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Default Re: Opinions on HH TPA 100D power amplifiers

Back in the 1970's, the lack of DC protection on these amplifiers (as with many others of that era) meant good business for loudspeaker-reconing services...
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Old 25th Mar 2023, 11:08 am   #9
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Default Re: Opinions on HH TPA 100D power amplifiers

Hi,

Personally, I feel the current interest in these amplifiers stems to its similarity to the HH AM8/12, which were used to drive LS3/5a’s [as well as other speakers] in BBC studios, and because of this LS3/5a 'connection' they start to become a tad mythical.

AM8/12 has a discrete first stage/preamp, whereas the mid/late TPA used a 741. The AM8/12 has EQ for the LS3/5a.

As far as I know the BBC used the TPA as ‘workhorse’ monitor amplifiers.

Concur with Knobtwiddler regards the HH V Series… I used to do some part time Tech work in an HH dealer in Southend in the late 70's and early 80's and remember these arriving in the shop in late '79 or thereabouts.

Did some work on a Quad 405 last weekend and it renewed my appreciation for this amplifier.

Terry.
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Old 25th Mar 2023, 11:50 am   #10
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Default Re: Opinions on HH TPA 100D power amplifiers

Well mercy me These are back again I did repair my H+H amplifiers but I changed jobs at about this time and so did not get to listen to them on my system and I suppose they just got lost in time
Trevor
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