Wow what a find I have a JLH cassette deck on the garage and his 80 watt unit I really liked his stuff
Do you have any info on the tuner you can post
Trev
Do you have any info on the tuner you can post
Trev
That’s a gorgeous amp! Very pretty, outside and inside too.
But I think funkuncut is right in wishing to preserve construction with minimal messy changes.
Best,
Steve
Just wanted to affirm your comments—- good observations. It would be interesting to know how much attenuation the volume control is introducing when positioned for a typical loud listening session.
But I think funkuncut is right in wishing to preserve construction with minimal messy changes.
Best,
Steve
Some years ago , I've found schematic , related to speaker impedance, kinda like negative output impedance for amplfier ,or current mode, can't remember now. There was a low (0,22 maybe) ohms shunt , some resistors , capacitors ,and fast opamp.Kinda of bridge ,combining positive and negative feedbacks. That was article ,published in one of popular radio magazine. Circuit's output was connected to amplifier input , so volume control must be no longer connected to amplifier itself.
So identically like in this amplifier, all opamp noise was audible always , independent of volume control position. I have heard a hiss , white noise , clearly ,and not only in silence. And offcourse i was disappointed and undone changes. Imagine , if that circuit would oscillate, you can easily blow speakers, and volume control won't help . In my opinion, silence must be present when you listen not loud . Hiss is thing from tape times. But everything is choice of user ,modify, improve something, or keep it conservated like just purchased and still in warranty.
So identically like in this amplifier, all opamp noise was audible always , independent of volume control position. I have heard a hiss , white noise , clearly ,and not only in silence. And offcourse i was disappointed and undone changes. Imagine , if that circuit would oscillate, you can easily blow speakers, and volume control won't help . In my opinion, silence must be present when you listen not loud . Hiss is thing from tape times. But everything is choice of user ,modify, improve something, or keep it conservated like just purchased and still in warranty.
I recall building the cassette deck cheaply (well I worked at PYE TV then... ), great sound, modded it to adjustable bias with a built in oscillator for calibration, and with coloured single LED vu meters, but the cassette mechanism was a bit clunky. Gave it away! Back in the day we were blessed with DIY design and construction availability.
I hope this isn't getting too far off topic. I'm going to listen to the amp a lot more before doing anything else to it - I think it wasn't designed for the level of input from cd, so it's actually quieter with MM input. I've tried it with a Shure M75 and a Goldring G800 (which always seems to have low output anyway) so far and it sounds really good, just not as pokey as with cd, but that is to be expected. The important thing is that it is now quiet (and I'm using it for reggae, jazz and rock anyhow...)
Interesting. My cassette recorder must have been a 'Series 1' as it had a slot loading mechanism.
I have the front loading cassette deck and that is full of 741 op amps
Getting back to your amp I would change out the 741's as a matter of course it will be much improved
Trev
Getting back to your amp I would change out the 741's as a matter of course it will be much improved
Trev
I replaced them with TL071s (see photo in post #16) It is now as quiet as I was expecting. Disabling the balance control already made a big difference, and I don't feel inclined to reinstate it just to see how much difference the new ICs make independently!
i was not sure if that was your actual amp ! But that's great you can now try some OP amp rolling ?
Trev
Trev
I have the full article for the front loader too. If anyone's interested I'll scan it and post it.
Here you go....
I'm happy to post you the paper copies if you pm me your address, and if you (or anyone else for that matter) would like the series 2 cassette deck, you're welcome to collect it from London or I can send it for postage cost. I haven't had it working, and I don't need another project at the moment, but it would be great to have it used and preserved.
I'm happy to post you the paper copies if you pm me your address, and if you (or anyone else for that matter) would like the series 2 cassette deck, you're welcome to collect it from London or I can send it for postage cost. I haven't had it working, and I don't need another project at the moment, but it would be great to have it used and preserved.
I built one of the casette decks some (many) years back and it was decent. Great electronics let down by an average mechanism and lack of Dolby or other noise reduction.
Tape head alignment was crucial and all the mechanisms needed it before you got the best from them. Also, the motor often needed to be turned on the mount to minimize noise pickup through the tape head.
Those things aside, the Hart kit was quality, easy to assemble and worth the not inconsiderable cost at the time.
Tape head alignment was crucial and all the mechanisms needed it before you got the best from them. Also, the motor often needed to be turned on the mount to minimize noise pickup through the tape head.
Those things aside, the Hart kit was quality, easy to assemble and worth the not inconsiderable cost at the time.
Certainly the amp, tuner and series 2 cassette I have all seem to be high quality electronics - the hardware such as faceplates, knobs etc. has a slightly British made-by-men-in-brown-coats-in-a-draughty-shed feel as opposed to Japanese made-by-robots-in-a-shiny-laboratory feel, but that is part of the charm too.
I'm just reviving this thread as I have re-instated the balance control part of the circuit and still find the hiss annoying. I do like the amplifier a lot, and am using it in a bedroom system where the hiss is too much , particularly at low levels or no signal state. Could anyone help with the implementation of the suggestion in post 18?
(Trev - I hope the tuner and cassette deck worked out ok!)
Great find! Well built and looks very nice.
Edit- try different ground points for balance control and see if that works.
Edit- try different ground points for balance control and see if that works.
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One of the (very many) things that I don't understand is why this balance control works the way it does - it boosts rather than cuts. I would have thought it more satisfactory to have the middle point not affecting levels, and then moving the focus by cutting one or other channel (as I think all my other amps/preamps do) I might just bypass R24 again and lose it, but is there a way of implementing it differently?
To confirm my understanding, you installed TL072 opamps with good improvement; hiss is acceptable with balance control disabled? But is excessive with control balance present at center position? The balance control was disabled by shorting R24 and its corresponding part in the other channel? Shorting R24 likely reduces hiss by at least 6dB.
I agree completely with @ximikas comments in post 18. You can aways "preview" the modification by cobbling a new volume control in front of the PA with existing volume at full volume; this will let you confirm acceptable hiss and adequate headroom of the tone/balance control stages before doing any major revision. We can coach if you want to pursue.
I agree completely with @ximikas comments in post 18. You can aways "preview" the modification by cobbling a new volume control in front of the PA with existing volume at full volume; this will let you confirm acceptable hiss and adequate headroom of the tone/balance control stages before doing any major revision. We can coach if you want to pursue.