I'm a bit fuzzy on the timeline here.
you have a preamp that you updated 30 years ago and which presumably has worked/ sounded ok until...
you got a new deck and cartridge
and now there is no bass regardless which phono source you use? no other changes... but the bass went south?
I'd be suspicious of the many contacts in the preamp -- for the modular boards. I'd want to test continuity across these.
just tossing that out there.
you have a preamp that you updated 30 years ago and which presumably has worked/ sounded ok until...
you got a new deck and cartridge
and now there is no bass regardless which phono source you use? no other changes... but the bass went south?
I'd be suspicious of the many contacts in the preamp -- for the modular boards. I'd want to test continuity across these.
just tossing that out there.
As in no bass at all?
Its really difficult trying to imagine what you hear 🙂 and whether it is a subtle subjective thing or a real total loss of bass.
Could something like a missing ground at the input do this or more likely a phase reversal of the cartridge wires in one channel ?
Would it be worth not altering anything at this point and just reversing one speaker to make it out of phase and seeing if the phono stage now sounds better. Would that work if the inputs were out of phase and correct the error as a test?
Thank you! C305, C306 are now spot on at .33uF, but I've just realised that some halfwit didn't notice he'd been given .33uF instead of .033uF caps in the shop and soldered them where the .029uFs should be. I'll have to wait until after the weekend to get some more (of the right sort - maybe two .015uF in parallel....)
Sorry, I missed the previous two posts before replying. Timeline is that I updated it about 30 years ago - removed power supply so that it runs on 12v lead acid battery, followed the Russ Andrews recommendations for Disc Adapter board, Phono board and Amp boards. Didn't touch tone and filter board. A few years ago I updated the Tape Adapter board according to Dada recommendations to move the LF rolloff lower down. I mostly use it with CD or computer source through a DAC and all is well. I only noticed recently when comparing an LP to a CD that the bass was lacking, and by lacking I mean that I would have to turn the Bass control to maximum to get any meaningful output from the bass speakers. I use the 33 in a 4 way active system, and the bass section handles up to 270hz - with the other three channels turned off, not much is happening with an LP playing either with Garrard 301/Shure V15 III or Technics SL1200/Stanton 500. If I substitute a Kenwood C1, all is well in the bass department. If I understand correctly (and often I don't) all inputs are routed through the Tape Adapter board, so the problem is not there since CD and DAC are both sounding fine.
I've removed the mistakenly installed .33uF caps and will get the correct .029uF or .033uF after the weekend, when I shall also try the reverse polarity experiment. If I have time before that I'll check over the boards once again.
Many thanks indeed for help and suggestions - I do like the 33, and would be reluctant to give up completely!
I've removed the mistakenly installed .33uF caps and will get the correct .029uF or .033uF after the weekend, when I shall also try the reverse polarity experiment. If I have time before that I'll check over the boards once again.
Many thanks indeed for help and suggestions - I do like the 33, and would be reluctant to give up completely!
No. 0.022uF and .0068uF in parallel, as mentioned above. This value is critical to the whole enterprise. .0033uF is nowhere near adequate, for another example, although recent clone vendors don't seem to understand that.
You did mention some such value confusion in post #13, but you seem to have got your expected and actuals thoroughly mixed.
Thank you. I'll get a few capacitors as soon as I can, and try to get the value as close to 0.029uF as I can measure, although I don't know the accuracy of my DMM measurements. All the capacitors I have measured so far, even those within tolerance, have been low. Maybe my DMM reads low, or are capacitor values usually low? What would the exact effects be of slightly higher or lower values in the case of these two on the Disc Adapter board?
The confusion you are sowing here continues. How can a .33uF capacitor that is supposed to be .029uF be low?
Try to get 2% capacitors, and stick to the values in the service manual.
Try to get 2% capacitors, and stick to the values in the service manual.
Sorry to be sowing confusion! What I meant was that I have measured quite a few new capacitors, as well as old ones, both electrolytic and film types, 5% and 10%, and they have all been lower than their rated value. I don't know if this is common, but, since the tolerance is +/-, would it not be normal to find some which read higher? That is the reason for which I question the accuracy of my DMM. It is, however, all I have, so I shall try to get closer tolerances - I think that the shop I use has some 1% as well as 5% The original design used 10%, although I don't know if the production side tested and selected the better ones.
The tolerance of the caps will not make a dramatic change from your no bass to normal bass. If you are getting them from reputable suppliers then I would take it that they are in fact perfectly fine. Don't sweat the fine print 🙂 a fraction of a db here ore there is not going to sound any different for your issue.
Did you try reversing polarity on one channel as a quick test.
Failing all the above... if you have means of recording the line out of the preamp to a PC (Audacity again 🙂) we could have a listen to a short 30 second or so clip on phone vs line in. A 192kbs MP3 would be fine.
Did you try reversing polarity on one channel as a quick test.
Failing all the above... if you have means of recording the line out of the preamp to a PC (Audacity again 🙂) we could have a listen to a short 30 second or so clip on phone vs line in. A 192kbs MP3 would be fine.
That’s hardly necessary. There is an error of > 10x in the capacitor that determines T3. That is going to cause a -20dB error at 50Hz, by definition. This is a huge error.
Would the -20dB error be caused by the capacitor value being too low? What would happen if the value was higher than that specified? Forgive my lack of knowledge, I’m just trying to find out more.
It is caused by the capacitor value being > 10x too high. I already said that. 0.33uF that should be 0.029uF.
I can't get a handle on what is going on here. I also tried splitting one of the phono tracks into L and R and inverting one channel but that then sounds out of phase.
Quick plot of the first 5 seconds of the left channel from each to look at bass line amplitudes. Nothing jumps out somehow.
Maybe a dumb question 🙂 but do all records sound like this or just bass heavy ones. Could the vinyl be mastered with a cut in LF?
Quick plot of the first 5 seconds of the left channel from each to look at bass line amplitudes. Nothing jumps out somehow.
Maybe a dumb question 🙂 but do all records sound like this or just bass heavy ones. Could the vinyl be mastered with a cut in LF?
All records sound bass light - sadly I seem to have very few recordings both on LP and CD. I doubt if the Pink Floyd was mastered with LF cut, and it sounds good using the Kenwood preamp. Here are a couple more recordings....
Both the Pink Floyd and Santana recordings were made using a JVC L-E5 and not the Garrard 301/Shure V15III which is usually used with the Quad 33, but the differences between CD and Phono remain the same.
Yes up to a point. Obviously still different but the earlier tracks were much more bass heavy.
I can't really think of anything to suggest beyond saying its getting more to the point of needing diagnostics using a scope and a known good inverse RIAA sweep applied to the inputs. I think the Audacity one is probably fine but you can build inverse networks and then apply a constant amplitude frequency sweep to the network and feed the output of the network to the preamp.
Actually you can also apply line level music to them of course but a sweep would show any response irregularities.