lpc1 bass response

Hi, finaly got my tsa1 amp working. but seems very low bass coming out of it, both channels. this amp looks like the origional .22 mfd caps (c113,133) were replaced with electrolytics. am not sure if that is causing this problem. would like to know if there is a modification that would increase bass as well. get two birds with one stone. the switch seems to work in changing the bass but not like i have seen another seeburg juke. thanks Mark

Is this a solid state or tube unit?
If solid state, the speaker coupling caps (if used) could be failing.
If tubes, the cathode bypass caps could be failing.
Both cause a loss of "punch".
I'd need a schematic to trace things out.

Ron may know more.

Mark,
Which amp--what "code" , is in that phono--
The LPC-1 was the first Seeburg (and any other brand) "transistorized" amps. Many "updates" were made in it over the year and 1/2 that it was produced. Also-which needles are installed ?--most "aftermarkets" lack bass response. Ron Rich

the amp is solid state tsa1 code d. i just got done recapping the electrolytics in it. the new needles are from turntable needles.com it is .7mil diamond. i slipped the origional needle back in and didn't notice a large diference. thanks Mark

here is a reprint of stuff I posted on another forum when this topic came about a month ago. Pick through it and see if any might be of help:

You are starting off with an obsolete pickup which has considerable
distortion and cantilever ringing. The cart only sounds decent when
strapped mono at the input. That having been said there are some simple
things that can noticeable improve the amp.



1)The first preamp transistors Q101 Left ch and Q109 right ch, are
unbypassed. My notes show that I add a cap across each emitter resistor
(R103-R107) A .15 =+5db at 14KHZ and I settled on a .22 which gives +6db@
8khz and rising above.



Further along in the circuit you might experiment with different
(larger) values of C156 and C158 in the volume control circuit. I didn't
bother because the first stage mods did what I needed.



Deeper bass can be had by increasing C104&108 to200mfd

" " C106-C126 to 2.2 mfd

" " C115-C135 to 4.7 mfd.

I recommend going one cap in each channel at a time to see if you get
excessive rumble, feedback or other issues -the changes radically
increase bass response.



I made changes to the biasing of the finals, but I don't know if those
would help or hurt in the amp you have due to different 'codes'.



On all of these older S-S amps I generally shorten AGC time constant by
reducing C145 from 100mfd to approx 47mfd. this helps even out levels
within a record. In hideaway use I experimented with values as low as
22mfd but this can cause audible pumping as peaks compress and release.
I am currently using 47mfd in these amps on location.

Those amps put out approx 13 watts rms both channels driven.

I have an LPC on-loc (not my choice) and use the Pickering conversion
stereo conversion cart with a modified TSA-7 amp. Beginning with the
pink amps (PFEAIU) they went to a 5 ohm load for the amps so using this
in an LPC results in lower output to the machine speakers, but I built
an simple emitter follower and feed a large house PA with that machine
so the internals aren't that important.
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For whatever reason when the TSA series came out, seeburg used the cart as part of the forward bias divider for the first stage and then cart impedance does matter.

For instance, if you use the later yellow needle cart (SS 160-up) on the early TSA series designed for T needle carts, the approx 460 ohm/ch plus higher output will overload and mis-bias the first stage. The result is muddy distortion -too much bass.

Its also important for the AGC system to be working properly. The diodes both in the rectifier and gain reduction bridges should be replaced with new silicon ones.

Another, unrelated issue with these early all-germanium amps is that germanium transistors suffer from gradually lowering impedance in their junctions, While the effects of this are particularly noticeable in circuits with a lot of feedback, even in circuits with coupling caps this can reduce bass and in-general cause the two channels of an amp to sound different.

This changing internal impedance also affects the output transistor in that they may idle hotter. I replace R127 & R160 which are 200ohm with 180 ohm. That improved the forward bias balance between the two halves, cools things down but doesn't cause crossover distortion.

The later amps designed to use the yellow needles (SS160-up) used silicon in their preamp-AGC and driver circuits and are stable over time.

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Normally there is a large increase in bass from the mid to last position on the bass switch. On these amps the bass boost in the volume control section is quite simple. Were the 0.22 and 0.15 caps on the volume control taps replaced in each channel? You should also measure to ground from each of these taps: Set bass to 'max' -that gets it's resistors out of the circuits and measure from each loudness tap to ground. These are the two taps off on their own -not the three together at the other end. The tap closest to the ground side of the control should be approx 7-8 k/ohm to ground and the other one should be approx 17K/ohm to ground.

These controls do changes a bit over time due in-part to deterioration from the DC inrush pulse that hits the carbon resistance element in the control. I have see radical changes in resistance and even open connections in these consumer-grade pots.

Rob/NYC