HH TPA series Power Amplifiers.

[teetoon]

Hi everyone, does anyone know where I could get a circuit diagram for the original HH TPA 100 professional power amplifier? Not to be confused with the TPA 100 D which is a completely different beast. I've already talked about this on the TUAC thread but don't want to Hi Jack so have started this one.
I have a collection of 12 TPA series including 3 TPA 100, 5 TPA 100 D, 2 TPA 50 D and 2 TPA 25 D.
I became a fan of these amps around 1975 when a local DJ brought a TPA 100 D in for repair at the shop that I worked in. It had a couple of blown 2N3773s and back then we only had 2N3055s in stock. Believe it or not, the amp was still used like this as there are 4 devices making up the output but it must have sounded bad!
Anyway, many years on I remained friends with said DJ and swapped a minidisc player for a pair of them. After changing the driver transistors and electrolytic capacitors, I was amazed by the sound and started looking on ebay to get some more.
Back to the topic, by mistake I bought 3 TPA 100 amps which turned out to be completely different. These have had a pre amp with tone controls fitted and I thought that the added panel on the front was covering the D of the model number. Lesson learned there, but I've tried to get info on these to no avail. Any ideas would be most welcome.

David.

[threeseven]

How does the TPA-100 differ from the 100D ? Asking because I have a couple of 100D's, both needing minor attention. Do you have a circuit for the 100D ?

[teetoon]

Hi threeseven, the TPA 100 is an earlier design that has a driver transformer and completely different circuit. The output devices are 2x 2N3773 and there are 2x 2N3441 on 4 seperate heat sinks. Where as the TPA 100 D is direct coupled and has 4x 2N3773 on 2 seperate heat sinks. The 100 board is completely different and has the driver transformer on it as well as a reed relay for audio muting during power up. Different pre stage aswell.
The 100 D is a really easy amp to work on. A circuit diagram is available from MAJ Electronics but I managed without one. The transistors on the board being 5x 2N3440, 2x 2N5415, 1x BC107B and1x BC177B. I just routinely change them all along with the small electrolytic caps. Unless there has been a burnout there's not much to go wrong.
What's the problem with your amps?

David.

[threeseven]

Hi David,
Interesting about the 100 !
One of mine has a blown switch suppressor cap, so not really an issue. The other is distorted. Haven't really investigated it but it could well be dodgy caps, at worst a faulty transistor or 2.
I like H&H though, no nonsense stuff for pro use.

[teetoon]

Hi again threeseven, those supressor caps are a common fault especially as they are up to 40 years old now and these amps were probably on for long periods. Re the distorted amp, have you checked the 6.3 amp fuses on the front panel. These will give distorted output if one of them has failed. Of course it could mean there's a shorted output transistor or even a leaky smoothing cap.
Look there first.

David.

[teetoon]

Hi everyone, I've tried to get some pictures of the TPA 100 amp. Not sure if it's right but here goes. Before anyone says it, I know the pre amp and tone controls are not original.

[robin0577]

Can't help you with service info I'm afraid, but I do have a number of TPA series amps corroding in a shed. If you want any for spares or to rebuild, PM me.

[Trevor]

H+H is this short for Harrison and Hill
Harrison went on to design a range of high performance amplifiers and did Hill go on to Hill amplification ?
As ever I am always interested in the history of our manufacturers
regards Trev

[kalee20]

I have come across a Hill power amplifier, well built and rugged, lots of power transistors in parallel (with emittes sharing resistors). The transistors were transformer driven here, too. So it is quite possible that the H+H and Hill had a common person.

[Valvepower]

Hi All,

Well you learn something new every day, and HH used a transformer driver stage!

From memory the 100D had a similar power amplifier circuit to that of early IC100S’s? This was before the IC input power amplifier circuit used in later amplifiers.

Guys, if after Trevor and anyone else there is a “transformer driver” TPA100 up for grabs I’ll be interested.

The other HH amps I remember are the S500D & IC100S. I used to help out in local music shop as a Tec, that was an HH dealer and I did see a quite a few HH amplifiers in my time.

The early MOSFET amplifiers (V800?) did sound rather nice.

I did meet Mike Harrison at a trade show in the 80’s, and did some work with one of the Ex HH sales guys who was also involved with the Rauch DVT amplifier.

Terry.

[threeseven]

Yes, I'd be up for a TPA-100 too.

[teetoon]

Hi everyone, I'm glad I mentioned it now. I've been a long time user of HH amps. The first one I bought was a VS Bassamp in 1976 for £134 from Bill Greenhalgh in Exeter. Then bought a MA 100 mixer amp, about £158 I think. When I started DJ'ing I used them as power amps before buying the S130 slaves. I upgraded to a couple of S500Ds and then a M900 on bass duty and V500 on mid tops. Ran these until the early 90s before going power mad with Amcron and then C Audio.

I had always thought that the TPA 100 Ds sounded better than the Musician series power amps, and I have confirmed this in later years. It's as though there is a low filter on the newer designs. Maybe as they were designed for musicians and not DJ's. The TPA's certainly go down low. The S500D's could fry voice coils quicker than you could blink if they went DC!

The IC 100 series were as Terry pointed out, very similar to the TPA 50 D. This model has a toroidal mains transformer too. Remember the model number refers to the output into 15 ohms so these amps always seem to have plenty in reserve. The TPA 100 D puts out 225 watts into 4 ohms.

David.

[Omegaman]

Hi Everyone,

I have circuits for pretty much all of the HH stuff, but unfortunately not the TPA's.
Never seen one with a transformer driver, though.

Regards

[Trevor]

I have received the tp100 power amplifier from teetoon and have sorted out the circuit in the main just need to sort the prorection circuit out
what a lump these are ! basically a small class a amplifier driving a pair of darlington connected output transistors I will post a diagram later on when i have sorted that out !
the build quality is quite good but the wiring is poor by modern standards very thin for the currents expected but I have seen the same in Quad /leak.rogers radford etc so pretty standard for the time
regards trev

[Valvepower]

Hi,

It will be very interesting to see the circuit for the TP100. The idea of Darlington output transistors being driven by a transformer sounds interesting. This would mean the transformer would have to provide less current for the output transistors, putting less current demand on the driver and transformer. I suppose careful attention would have paid to the thermal stability with the extra current gain in the output stage?

I found the following on a HH site which may be of general interest:

http://www.hhamplification.co.uk/gal...ery/hhpic1.jpg
http://www.hhamplification.co.uk/index.asp

Terry.

[Trevor]

Yes you are correct I have seen this done once before on an Iranian public address amplifier
The H+H does this and is simpler than the tuac
This brings me to the thermal stability issui this has always been a problem with transformer coupled amplifiers however if you adopt the amcron dc 300a appproach you can make a very usable amplifier use a low impedance driver and class b boosters
The transfer funtion is not perfect but to be honest you will not hear it and then the bias can be such that it can wander quite abit without audable effect
regards Trev

[dragonser]

Hi,
sorry if it has been mentioned elsewhere.
I think that Maj electronics may have some info available on the older HH amps ?
http://www.majelectronic.co.uk/

regards Peter B

[teetoon]

Hi everyone, Here's some pics of the TPA 50 D. The first 2 pics are a later one. The next 2 are a slightly older one with a few component changes and the layout on the board is slightly different. Last pic is a mid 70's TPA 100 D.
I've looked on the sites suggested many times but there's very little on the TPA series. The Majelectronic site is a good read though and his history of the HH amps is very informative. He mentions the early IC 100 amps having a similar power amp to the TPA 50 D.
Serial numbers on early amps were 4 digits, with the later amps having 5 digits according to the one's I have here.

David.

[Valvepower]

Hi,

Had a look at the photos and a few (hopefully correct) sparse memories came back to me about the power amplifiers used by HH.

In the later one the 741 was an integral part of the power amplifier circuit where the overall feedback was applied to the 741. In the slightly older one the power amplifier was a standard differential input power amplifier, and the 741 is voltage amplifier and buffer feeding the input of the power amplifier. I’ve also seen the 741 configured as filter for use with active speaker system (see below).

I have a pair of later TPA’s so I know the circuit fairly well, but as I don’t have slightly older ones I’m going more by memory and the photo with these. I'm keeping an eye open for a pair of these.

The basic power amplifiers were not dissimilar to the ones used in the instrument amplifiers.

I have seen the slightly older circuit used in an organ speaker cabinet, where the 741 was configured as an active filter to drive the HF and LF speakers. I can’t remember the make of organ speaker but from memory the amplifier used in the speaker could have been supplied by HH as an OEM assembly to the manufacturer of the speaker cabinet.

Crikey, I’m waffling on a bit.

Terry.

[teetoon]

Hi Terry, from the amps I've had, all the TPA 100 D's have a pair of 2N3440 transistors on the input. The 50 D's and 25 D's have a 741. I'm not that clued up about amp design but it would seem the 741 would have a lower distortion figure? I do wonder if the 2N3440's would have been selected components as in matched for performance. I say this after replacing them and noting different voltages around and a change in dc offset. HH specify + or - 100mv to be acceptable.

Now you mention it, a friend of mine told me of a large speaker cabinet he was shown with an HH amp in the back. I thought it to be something cobbled together but you learn something new every day.
Trev's mentioned a DC 300 A, now there's a story for another thread!

David.